TECHNICAL FIELD

[0001] The present invention relates generally to cellular telecommunication systems, and more specifically to altering/modifying the operation of base transceiver stations (BTSs) used in cellular telecommunication systems.

BACKGROUND

[0002] One of the main challenges for the future of cellular telecommunication systems and networks is reducing power consumption. With increasing awareness of the potentially harmful effects on the environment caused by CO2 emissions, the depletion of non-renewable energy sources and other resources, etc, there is a growing consensus on the need to develop more energy-efficient telecommunication systems.

[0003] From the perspective of cellular network operators (i.e. companies that provide cellular telecommunication networks - in different countries these include the likes of Vodafone, China Mobile, Verizon, AT&T, T-mobile, Telstra, etc), reducing electrical energy consumption is not just a matter of being (or appearing to be) "green" and environmentally responsible; it is also very much a financially important issue. That is, it has a direct impact on profitability. This is because a significant proportion of the operational expenditure (OPEX) associated with operating a cellular telecommunication network relates to power/electricity costs (i.e. it goes to paying the electricity bill). This is illustrated in Figure 1 . More specifically, Figure 1 gives an indication of the percentage of total power consumption used by different components of (i.e. by the different categories of equipment used in) cellular telecommunications networks. As shown in Figure 1 , the component or category of equipment that uses the most power is the radio equipment/power amplifiers, and thus it would seem that a large potential for achieving savings in terms of power consumption may exist if these components (i.e. radio equipment) could be turned off when not needed, or if certain of them could be turned off when not needed. In other words, it is thought that if cellular telecommunication systems and networks could be made adaptable, and for example able to switch off elements of radio equipment and the like when demand is low, this could lead to cellular telecommunications networks that consume considerably less power.

[0004] However, whilst there would appear to be a need (or at least it would appear to be desirable/beneficial) to be able to make cellular telecommunication networks adaptable, and able to switch off elements of radio equipment and the like when demand is low, there are a number of impediments that have previously prevented this from being done.

[0005] A significant one of these impediments is that (prior to the present invention) it has been difficult or impossible for cellular telecommunication network operators to be able to turn individual radios of a given cellular network BTS on/off. And the reason for this is mainly because doing so has previously required access or permissions to manipulate or operate the underlying BTS operating systems and software. Importantly, these underlying BTS operating systems and software are generally provided and managed by the suppliers/manufacturers of the BTS radio equipment (e.g. the manufacturers of the actual transmitter/receiver hardware, etc), and moreover these suppliers/manufacturers of BTS radio equipment/hardware typically impose extremely tight security controls on the equipment operating systems and software, and on access thereto. As such, even cellular network operators (i.e. even the companies who provide cellular network services to customers and in whose BTSs the transmitter and receiver hardware, etc, is actually used) often do not have sufficient access or the ability to manipulate or operate the underlying BTS operating systems and software. This has (prior to the present invention) been a major obstacle to making cellular telecommunication networks adaptable, and in particular it has made it difficult or impossible (at least for cellular telecommunication network operators) to be able to switch off elements of radio equipment and the like when demand is low to save power.

[0006] A range of other methods for saving energy, particularly at wireless base transceiver stations, have been, or are being, trialed or used. One option that is sometimes used for achieving savings in terms of wireless BTS power consumption is to deploy/mount BTS radios at the top of the BTS tower/mast, near the BTS antennas, rather than e.g. at the base of the tower/mast which is further away from the antennas. The purpose of this is to achieve power savings by reducing the length of feeder cables extending between the BTS radios and the BTS antennas, thereby minimising feeder cable losses. Turning down the Tx (transmit) power on radios at low traffic times is also sometimes used to save energy. Other power savings have been sought simply by using more efficient radios and power supplies, and e.g. better controlling air conditioners and the like at the BTS. However, it is thought that it would be desirable if power savings could be achieved in addition to or beyond what is currently possible using these methods.

[0007] It is to be clearly understood that mere reference herein to any previous or existing devices, apparatus, products, systems, methods, practices, publications or to any other information, or to any problems or issues, does not constitute an acknowledgement or admission that any of those things, whether individually or in any combination, formed part of the common general knowledge of those skilled in the field, or that they are admissible prior art.

SUMMARY OF THE INVENTION

[0008] In one form, the invention relates generally to apparatus for use in a multi sector base station, wherein the base station includes a plurality of sector antennas and a base station radio for each sector antenna, and wherein the apparatus is operable:

^■ if the base station's traffic level is equal to or above a threshold level, to cause the base station to operate in a first configuration wherein:

o all base station radios are powered on, and

o downlink signals from a base station radio are conveyed to that radio's corresponding sector antenna, and

^■ if the base station's traffic level is below the threshold level, to cause the base station to operate in a second configuration wherein:

o at least one of the base station radios is powered off, and o for each sector antenna whose base station radio is powered off, downlink signals to said sector antenna are sent from a base station radio which is powered on.

[0009] In some embodiments:

in the first configuration:

o uplink signals received by a sector antenna may be conveyed to that antenna's corresponding base station radio, and

in the second configuration:

o uplink signals received by a sector antenna whose base station radio is powered off may be conveyed to a base station radio which is powered on.

[0010] Also, in some embodiments: ^■ in the second configuration:

o all but one of the base station radios may be powered off, o downlink signals to any sector antenna whose base station radio is powered off may be sent from the one base station radio which is powered on, and

o uplink signals received by a sector antenna whose base station radio is powered off may be conveyed to the one base station radio which is powered on.

[0011] In embodiments like those in the previous paragraph:

^■ in the first configuration:

o a different frequency may be used for uplink signals received, and downlink signals sent, by each sector antenna, and

^■ in the second configuration:

o the same frequency may be used for uplink signals received, and downlink signals sent, by all sector antennas.

[0012] Furthermore, in embodiments like those in the previous two paragraphs, each sector antenna may includes at least two antennas, namely a Main antenna and a Diversity antenna, and

^■ in the first configuration:

o each base station radio may send downlink signals to its corresponding Main and Diversity antennas, and

o uplink signals received by the Main and Diversity antennas associated with each base station radio may be conveyed to that base station radio, and

^■ in the second configuration:

o the one base station radio which is powered on may send downlink signals to all of the Main and Diversity antennas, and

o uplink signals received by all Main and Diversity antennas may be conveyed to the one base station radio which is powered on.

[0013] Suitably, separate apparatus may be provided for: ^■ converting the base station's mode of operation between the first configuration and the second configuration for the Main antennas, and

^■ converting the base station's mode of operation between the first configuration and the second configuration for the Diversity antennas.

[0014] In some embodiments, the apparatus may include a controller which is operable to interpret measurements of the base station's traffic level and to determine whether to convert the base station's mode of operation from the first configuration to the second configuration, or from the second configuration to the first configuration. The controller may also be operable:

^■ when converting the base station's mode of operation from the first configuration to the second configuration, to cause the relevant one or more base station radios to power off, and

^■ when converting the base station's mode of operation from the second configuration to the first configuration, to cause the relevant one or more base station radios to power on.

[0015] The apparatus may also incorporate one or more switches, and it may be that by switching the switch(es) appropriately the apparatus is operable convert the base station's mode of operation between the first configuration and the second configuration.

[0016] The apparatus may be functionally connected in between the sector antennas and their corresponding base station radios.

[0017] Each sector antenna may have an antenna feeder cable which connects the antenna to the apparatus, and each radio may have a radio feeder cable which connects the radio to the apparatus.

[0018] The apparatus may also include a first filter module for each of the respective antenna feeder cables, and the respective antenna feeder cables may connect the respective sector antennas to the respective first filter modules. Similarly, the apparatus may include a second filter module for each of the respective radio feeder cables, and the respective radio feeder cables may connect the respective base station radios to the respective second filter modules. Each of the first filter modules, and each of the second filter modules, may include a Tx filter and an Rx filter.

[0019] As mentioned above, the apparatus may incorporate one or more switches. The one or more switches may be connected functionally in between the first filter modules and the second filter modules, and the first filter modules and second filter modules may be operable to block passive intermodulation distortion (PIM) (in uplink and/or downlink signals) that may be created by the one or more switches or other components of the apparatus that are connected functionally between the first filter modules and the second filter modules.

[0020] The apparatus may further include an uplink splitter/combiner and a downlink splitter. The uplink splitter/combiner and the downlink splitter may be connected functionally in between the first filter modules and the second filter modules, and

■ in the second configuration:

o the downlink splitter may be operable to split a downlink signal produced by the one radio that is powered on, so that said signal is conveyed to all of the sector antennas, and

o the uplink splitter/combiner may be operable to (collect or) combine uplink signals received by the respective sector antennas such that a resultant/combined signal is conveyed from the uplink splitter/combiner to the one radio that is powered on.

[0021] The apparatus may be frequency band specific, and so for multiband base stations, a number of different or differently tuned apparatuses may be provided for use in the different frequency bands used by the base station.

[0022] In some embodiments, traffic levels at the base station may be continuously monitored. Traffic level monitoring may be performed by monitoring the downlink traffic on each sector.

[0023] In another form, the invention relates generally to a method for controlling the operating configuration of a multi sector base station, wherein the base station includes a plurality of sector antennas and a base station radio for each sector antenna, and wherein the method includes:

^■ measuring traffic levels in the base station;

^■ if the base station's traffic level is equal to or above a threshold level:

o causing the base station to operate in a first configuration wherein all base station radios are powered on and downlink signals from a base station radio are conveyed to that radio's corresponding sector antenna, and if the base station's traffic level is below the threshold level:

o causing the base station to operate in a second configuration wherein at least one of the base station radios is powered off, and for each sector antenna whose base station radio is powered off, downlink signals to said sector antenna are sent from a base station radio which is powered on.

[0024] In some embodiments of the method

in the second configuration:

all but one of the base station radios may be powered off, downlink signals to any sector antenna whose base station radio is powered off may be sent from the one base station radio which is powered on, and

uplink signals received by a sector antenna whose base station radio is powered off may be conveyed to the one base station radio which is powered on.

[0025] Also, in some embodiments the method may further comprise:

^■ in the first configuration:

o using a different frequency for uplink signals received, and downlink signals sent, by each sector antenna, and

^■ in the second configuration:

o using the same frequency for uplink signals received, and downlink signals sent, by all sector antennas.

[0026] The method may also involve continuously monitoring traffic levels at the base station, and/or performing traffic level monitoring by monitoring the downlink traffic on each sector.

[0027] In yet another form, the invention relates generally to apparatus for use in a multi sector base station, wherein the base station includes a plurality of sector antennas and a base station radio for each sector antenna, and wherein the apparatus is operable to cause the base station to operate in:

^■ a first configuration wherein downlink signals from each base station radio are conveyed to that radio's corresponding sector antenna, and

^■ a second configuration wherein downlink signals to at least one sector antenna are sent from a base station radio other than that antenna's corresponding base station radio.

[0028] In the form of the invention in the previous paragraph, in the second configuration, downlink signals to all sector antennas may be sent from one of the base station radios. The one base station radio that sends downlink signals to all sector antennas may be selectable from among all or some of the base station radios.

[0029] In the form of the invention in the previous two paragraphs, in both the first and the second configuration, uplink signals received by each sector antenna may be conveyed to that antenna's corresponding base station radio.

[0030] In a further form, the invention relates generally to a base station incorporating an apparatus as described above and/or as described in more detail below with reference to the Figures.

[0031] In yet another form, the invention relates generally to a base station when operated according to or using the method as described above.

[0032] And in yet a further form, the invention relates generally to installation (on or in a base station) of an apparatus of the kind described above and/or described in more detail below with reference to the Figures.

[0033] Any of the features described herein can be combined in any combination with any one or more of the other features described herein within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Preferred features, embodiments and variations of the invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the invention. The Detailed Description is not to be regarded as limiting the scope of the preceding Summary of the Invention in any way. The Detailed Description will make reference to a number of drawings as follows.

[0035] Figure 1 - Graphical representation of the power consumption of different categories of radio access equipment used in cellular networks

[0036] Figure 2 - Illustration of the way using hexagons, rather than e.g. circles, to schematically represent the geographical area of coverage provided by cellular radio antennas allows representation of the collective/overall coverage area with no gaps

[0037] Figure 3 - Graphical representation of (i) an omnidirectional cell site (an "omni-site"), (ii) a one sector cell site (a "one-sector-site"), (iii) a two sector cell site (a "two-sector-site") and (iv) a three sector cell site (a "three-sector-site")

[0038] Figure 4 - Graphical representation of BTS locations, cell/sector boundaries and cell "radius" distances as used in most modern "three sectors per cell site" configurations

[0039] Figure 5 - Illustration of different "cell" definitions, and also of cell frequency allocations

[0040] Figure 6 - Illustration of a "3, 9" frequency re-use pattern in the "normal mode" (I), which becomes a "3, 3" frequency re-use pattern in the "switched mode" (II)

[0041] Figure 7 - Illustration of a "4, 12" frequency re-use pattern in the "normal mode" (I), which becomes a "4, 4" frequency re-use pattern in the "switched mode" (II)

[0042] Figure 8 - Illustration of a "7, 21 " frequency re-use pattern in the "normal mode" (I), which becomes a "7, 7" frequency re-use pattern in the "switched mode" (II)

[0043] Figure 9 - Photograph of a typical three sector base transceiver station (BTS) with the antenna mounted at the top of the mast etc

[0044] Figure 10 - Schematic representation of the radio and antenna equipment of a typical three sector base transceiver station (BTS)

[0045] Figure 1 1 - Schematic representation of the radio and antenna equipment of a typical three sector base transceiver station (BTS) fitted with Sector Switching Devices (SSD)

[0046] Figure 12 - Schematic representation of functional electronics used in the SSD in the "normal" mode

[0047] Figure 13 - Schematic representation of functional electronics used SSD in the "switched" mode.

[0048] Figure 14 - Antenna radiation patterns of a multi-sector site switched using the SSD [0049] Figure 15 - Schematic representation of functional electronics used in an alternative (second) SSD configuration

[0050] Figure 16 - Schematic representation of functional electronics used in an alternative (third) SSD configuration

[0051] Figure 17 - Schematic representation of functional electronics used in an alternative (fourth) SSD configuration

[0052] Figure 18 - Schematic representation of functional electronics used in an alternative (fifth) SSD configuration

[0053] Figure 19 - Block diagram of an alternative (sixth) and simple embodiment of the SSD, in which antennas from all three sectors are connected to BTS 1 (i.e. BTS Radio 1 ) when the SSD is in "Switched" mode, and BTS 2 and BTS 3 (i.e. BTS Radio 2 and BTS Radio 3) are placed into a shutdown state. This embodiment is compatible with both FDD and TDD systems

[0054] Figure 20 - Block diagram of another (seventh) alternative embodiment of the SSD, in which antennas from all three sectors can be connected to any one of BTS 1 (BTS Radio 1 ), BTS 2 (BTS Radio 2) and BTS 3 (BTS Radio 3) when SSD is in "Switched" mode, and the other 2 BTS Radios are placed into a shutdown state. This embodiment is compatible with both FDD and TDD systems

DETAILED DESCRIPTION

Concept, definition and nomenclature for cells, sectors, re-use patterns, etc, in cellular networks

[0055] Cellular telecommunication (sometimes called mobile telecommunication or mobile telephony) is a type of radio telecommunication in which a wireless connection is established or exists between a mobile phone handset of a "subscriber" (or "user") and one or more tower based transmitters. The mobile phone handset is sometimes referred to as a "user equipment" (or "UE"), and each tower incorporating radio transmitting and receiving equipment is typically referred to as a base transceiver station ("BTS") or simply a base station (BS) (or sometimes a "NodeB", "NB" or "eNB"). For the avoidance of doubt, these terms and abbreviations, namely base transceiver station, BTS, base station, BS, NodeB, NB and eNB, are all used herein to refer to the same thing, and they may therefore be considered synonymous, and they are used herein interchangeably.

[0056] Nowadays at least, a base transceiver station (BTS) usually has three antennas (or three antenna arrays), each of which provides 120 degrees of coverage around the base transceiver station tower. Thus, on a given BTS nowadays, the three antennas are usually positioned relative to one another to provide 3 x 120°= 360° of coverage around the tower. The span or area of coverage provided by a BTS can be referred to as a "cell". However, it is important to note that the term "cell" is sometimes also used in slightly different but related ways - i.e. it is sometimes given a related but somewhat different meaning/definition - and this can be a source of confusion. This issue is discussed further below.

[0057] As a user (i.e. someone who is talking or transmitting/receiving data on their mobile phone handset) moves from one cell or area of coverage to another, the mobile handset's communication connection is effectively passed from one local cell transmitter to another. For example, the connection may be passed from the BTS whose coverage area the user was initially/previously in to the BTS whose coverage area the user has moved into, or the connection might be passed from the coverage area provided by one transmitter to the coverage area provided by another transmitter even if both transmitters are actually physically mounted on the same BTS tower. This process of transferring the communication connection from one local transmitter to another, so as to provide the user as they move with uninterrupted service (i.e. uninterrupted voice or data communication capability) is often referred to as "handover". The methods and signalling protocols involved in facilitating handover can be quite complex but these need not be discussed any further for present purposes.

Cell/coverage area representation

[0058] In cellular telecommunication networks, the shape of the geographical area of coverage provided by a cellular radio antenna is, in reality, often complicated and/or varying, for example, due to geographical or landscape features that may cause the shape of the coverage area to differ from one location to another, even if the same antenna and transmitter/receiver equipment (and the same amount of power, etc) is used, or possibly due to environmental or other time-varying factors that may cause radio-transmission conditions (and hence the shape of the radio coverage area) to change as conditions change with time. In spite of this, for the purpose of representing the geographical area of coverage provided by cellular radio antennas (which as just mentioned can be complicated and/or varying shapes) it is traditional to use hexagons, and in particular (typically) regular hexagons.

[0059] Using hexagons to represent the shape of transmitter coverage areas helps to visualise a cellular network in terms of geographic layout, etc. However it should be borne in mind that (for reasons just explained) the hexagons used to represent the geographical areas of coverage provided by respective cellular radio antennas are really only an approximation of the actual shapes of the respective coverage areas. The reason why hexagons (and in particular regular hexagons) are used instead of, say, circles, to represent the shape of coverage areas is because, as illustrated in Figure 2, regular hexagons tessellate (i.e. they fit together in a repeating pattern without gaps) and therefore they can represent immediately adjacent coverage areas in two dimensions without any gaps in between. Hence, using hexagons allows the total area of radio coverage (i.e. as provided by multiple or all of the individual coverage areas collectively) to be represented without any gaps. In practice of course, cellular networks or systems sometimes do have gaps in coverage (i.e. particular geographic locations where limited or no coverage is provided), but nevertheless a hexagonal representation allows (at least for theoretical purposes) a neat and convenient visualisation.

Cell sites

[0060] In Figure 3, and in the various configurations/transmission schemes depicted therein, the black dot represents a "cell site". A cell site is the location where a base transceiver station's (BTS's) radio equipment, including its antennas, etc, is situated. For the purpose of visualisation, it may be convenient to consider a cell site (i.e. the black dots in the respective representations in Figure 3) to be the location of a BTS tower on which the BTS's antennas are mounted.

[0061] A "cell site" may be said to provide radio coverage to a "cell". Importantly, and for the avoidance of doubt, a cell site is always a location (or, in theoretical terms, it may be considered to be a point). In contrast, a cell which is serviced by a cell site (even where different definitions of the term "cell" are used) is always a geographical area.

[0062] As alluded to above, nowadays most cell sites have (or they provide) "sectors". Sectors are individual sub-areas of the total coverage are provided by a cell site. The division of the total area of coverage provided by a cell site into multiple distinct sub-areas or "sectors" is typically done to make the cell sites (and the cellular network as a whole) more efficient and to enable the cell sites (and the network) to accommodate greater volumes of "traffic" (i.e. a larger number of calls and/or a greater amount of data transfer in a given amount of time). Thus, as explained above, cell sites (and BTSs) nowadays often/usually have three antennas (thus three sectors per cell site), and where this is the case each antenna typically provides 120 degrees of coverage around the tower. Also, the three antennas of such a cell site (or BTS) are typically mounted/oriented such that, together, they provide 3 x 120°= 360° of coverage around the cell site (or around the BTS tower).

[0063] It was mentioned above that the area of coverage provided by a cell site or BTS may be referred to as a "cell". However, it was also mentioned that the term "cell" is sometimes given a related but differing definition/meaning, and that this can lead to confusion. This will now be explained in further detail.

[0064] In the configurations just mentioned, namely where each cell site (BTS) has three antennas each of which provides 120° of coverage such that together the cell site's (BTS's) antennas together provide 360° of coverage, each of the cell site's individual antennas often actually points and transmits into a different cell. Therefore, in these configurations, it is not the case that the cell site (BTS) is located in the centre of the cell, and it is not the case that the 360° of coverage provided by the cell site's three antennas together constitutes (or provides all the coverage for) a single cell. See the diagram marked "Wrong!" in Figure 5. On the contrary, in these configurations, each cell site (BTS) is located on the edge of a number of cells (in fact each cell site is located at the point of intersection between three different cells), and each of the cell site's antennas points and transmits into a different one of the respective cells. See the diagram marked "Right!" in Figure 5.

Types or categories of cells

[0065] Elaborating further on the discussion above, there are actually two different types or categories of cells. One of the categories of cell is often referred to as "omnidirectional", "omni cell", or simply "omni". The other category is often referred to as a "sector cell". These different categories are depicted and will be explained further below with reference to Figure 3. [0066] An omni cell is served by a BTS placed in its centre. Hence, the BTS's antenna system transmits in all directions (360°), possibly equally or approximately equally in all directions, and the said BTS's antenna system can be constituted by (or in other words it may make use of) a single omnidirectional antenna (i.e. an "omni- antenna") or an array of sector antennas. In other words, in the case of an omni cell, it actually is the case that the cell site (BTS) is located in the centre of the cell, and it is the case that the 360° of coverage provided by the cell site's omni-antenna or its array of sector antennas constitutes (and provides all the coverage for) a single cell. See the diagram (i) in Figure 3. (In other words, for an omni cell, the diagram marked "Wrong !" in Figure 5 should actually say "Right!".)

[0067] On the other hand, a "sector cell" is served by a BTS (a "sector site") located on the cell edge. A sector site BTS uses a sector antenna (or a sector antenna array), e.g. a 120° or 180° antenna (or a 120° or 180° antenna array), to serve one sector cell (sector). However, a sector site BTS may be provided with one, two or three such sector antennas (or sector antenna arrays), and each may be operable to service one sector cell (sector). Thus, a particular sector site BTS may service one, two or three sector cells (sectors), as illustrated in the diagrams (ii), (iii) and (iv) respectively in Figure 3.

[0068] Typically, "omni" configurations (provided using either an omnidirectional antenna or multiple appropriately oriented sector antennas) are used to gain coverage (or in other words because they are able to provide a greater area or range of coverage). On the other hand, as alluded to above, "sector cell" configurations are normally used to gain capacity (or in other words because they are able to handle a greater quantity of "traffic" - that is a higher volume of calls and/or data transmissions within a given period of time).

[0069] As an aside, one of the capabilities provided by embodiments of the present invention is the ability to change (or switch) a cell site's antenna configuration between multi-sectored and omni. For example, embodiments may enable a three-sector cell site to switch to operating as an omni cell, and it may do so by making all the cell site's antennas (i.e. the antennas for all three respective sectors) operate from a single radio (thus with all three sectors operating at the same frequency). Of course, it may also enable switching back so that the antennas for the (say) three respective sectors again operate using their own respective radios (and thus with the three sectors all operating at different frequencies, as normal). This will be discussed in further detail below. [0070] Returning to the present introductory discussion, it should next be noted that, in practice, each sector generally requires two (or more) Rx antennas and two (or more) Tx antennas. In this context, Rx stands for or means "receiver" or "receiving" or "receive", and Tx stands for or means "transmitter" or "transmitting" or "transmit". The reason why each sector requires at least two Rx antennas is to provide for Rx diversity, and similarly the reason why each sector requires at least two Tx antennas is to provide for Tx diversity.

[0071] By way of further explanation "antenna diversity" (i.e. Rx diversity for Rx antennas and Tx diversity for Tx antennas) refers to a scheme that uses two or more antennas to improve the quality and reliability of a wireless link. Often, especially in urban environments, there is no clear line-of-sight between a transmitter and a receiver. Instead the transmitted signal is reflected along multiple paths before finally being received. Each of these bounces/reflections can introduce phase shifts, time delays, attenuations, distortions, etc, that can destructively interfere with one another at the aperture of the receiving antenna. Antenna diversity is used for mitigating these multipath problems. This is because, in basic terms, use of multiple antennas (i.e. the transmitting of the same signal by multiple antennas) offers a receiver several observations of the same signal. Each antenna will experience a different interference environment. Thus, for example, even if one antenna is experiencing a deep fade, it is possible that another will have a sufficient signal. Collectively such a system can provide a robust link. An antenna diversity scheme requires additional hardware and integration compared with single antenna systems. Also, with the multiple signals, there is a greater processing demand placed on the receiver, which can lead to tighter design requirements. Typically, however, signal reliability is paramount and using multiple antennas is an oft-used and effective way to decrease the number of drop-outs and lost connections, etc.

Cells vs sectors and cellular frequency re-use patterns

[0072] According to traditional definition, a cell site gives/provides radio coverage to a cell. And as mentioned above, the cell site is a location or a point, whereas the cell is a geographical area. Some have historically seen the "cell" as the single hexagon shown in the bottom right in Figure 5 - i.e. with the cell site in the centre and with the antenna coverage area, as represented by the surrounding hexagon, defining the "cell". Despite this being marked "Wrong!" in Figure 5, this interpretation actually holds true (i.e. it is correct) for omni-directional antenna systems - i.e. for omni cells. However, as directional antenna systems have been increasingly deployed, "cell sites" and "cells" have required clearer definition, in particular as more sectors (or cells) have become associated with a cell site.

[0073] Therefore, rather than referring to e.g. a "three-sectored cell," it is more appropriate (and more common) nowadays to refer to the three "cells" associated with a single cell site (or base transceiver station/BTS). And as it happens, each such "cell" is also a sector. In addition, rather than a given three "cells" (each of which is also a sector) being enclosed together in a single common hexagon, each cell is represented by its own hexagon. So, in effect, at least in "three sectors per cell-site" configurations nowadays, according to this definition, sectors and cells are the same (and the two words/terms mean the same thing).

[0074] In the diagram in the top left of Figure 5, three sectors (i.e. three "cells") that are all serviced by a common one of the cell sites are each labelled with a letter-number combination. The different letter-number combinations signify different signal frequencies used in that cell. In other words, in Figure 5, s1 , s2 and s3 each signify a different signal frequency used in the respective cell. Although the other cells in the diagram in the top left of Figure 5 are not labelled with s1 , s2 and s3, these same three signal frequencies are also used by the other cell sites pictured. Note, however, that no two immediately adjacent cells share a common signal frequency. This is to prevent cross-cell interference. The same principle applies in Figure 6, Figure 7 and Figure 8 discussed below.

[0075] Thus, as illustrated in Figure 5, in "three sectors per cell-site" configurations, each cell site uses three different signalling frequencies - one for each of the cells it services. In the particular configuration in Figure 5, there happens to be four different cell sites pictured, each of which has three different frequencies. The different frequencies allocated to the particular cells serviced by each respective cell site, and the way in which the different frequencies are arranged (i.e. the direction in which the different frequencies are "pointed", or in other words the particular cell to which a particular frequency is allocated, to avoid cross-cell interference), and the way in which this arrangement (or this frequency orientation) differs or is repeated between or across cell sites, defines a pattern that can be repeated to enable frequency re-use as the number of cell sites increases. Such a repeated arrangement of frequencies and cell sites is typically referred to as the "frequency re-use pattern" or "cell re-use pattern". Thus, the particular configuration in Figure 5 represents one possible frequency re-use pattern.

[0076] However, a range of other frequency re-use patterns can also be used. Examples of this are illustrated in Figure 6, Figure 7 and Figure 8. Each of these Figures actually includes two diagrams (labelled (I) and (II) in each case), and in all of these diagrams each small circular (red) dot represents a base transceiver station (BTS) - i.e. a cell site. In Figure 6, Figure 7 and Figure 8, the first diagram labelled (I) in each case relates to a "normal" BTS operating configuration (i.e. where the BTSs are not "switched" using the present invention/SSD). In contrast, in Figure 6, Figure 7 and Figure 8, the second diagram labelled (II) in each case relates to a "switched" BTS operating configuration (i.e. where the BTSs are "switched" using the present invention/SSD).

[0077] Referring to the first diagrams labelled (I) in each of Figure 6, Figure 7 and Figure 8, in these diagrams a single colour/shading appearing in three mutually adjacent cells indicates that those three cells share (i.e. they are all serviced by) a common BTS. However, it is very important to remember that in each of Figure 6, Figure 7 and Figure 8, the first diagram labelled (I) relates to a "normal" BTS operating configuration, and in a "normal" BTS operating configuration each one of the three cells serviced by a common BTS operates with a different signalling frequency vis-a-vis the other two cells serviced by that same BTS. The numbers that appear in each of the cells in each of the first diagrams (I) help to illustrate this last point. Thus, for example, for the particular BTS labelled "A" in diagram (I) of Figure 6, the numbers "1 ", "2" and "3" appearing in the adjacent cells serviced by this BTS indicate that the frequencies used in these cells are "frequency 1 ", "frequency 2" and "frequency 3", respectively, where each of these is of course a different frequency so that signal transmissions in one of these cells does not interfere with signal transmissions in either of the other two cells.

[0078] The different frequencies (i.e. like "frequency 1 ", "frequency 2" and "frequency 3" for the particular BTS "A" in diagram (I) of Figure 6, and likewise the different frequencies used in other cells) are often actually chosen specifically to help prevent or at least minimise inter-cell interference. A range of interference mitigation techniques and methodologies are actually often used for preventing or minimising inter-cell interference, and also for preventing or minimising intra-cell interference. (Intra-cell-interference may be said to be interference between two or more users or UEs who are located within the same cell and who are transmitting simultaneously (and because they are located within the same cell they will necessarily be transmitting simultaneously on the same general frequency). However, except to the limited extent that a few duplexing techniques and methodologies (which could be said to be somewhat related to intra-cell interference) are mentioned below (e.g. see the explanations of how embodiments of the present invention can operate in both "FDD" and "TDD" systems), further details or explanations of techniques and methodologies used for mitigating interference within and between cells in cellular telecommunications is outside the scope of the present disclosure (and in any case an understanding of this is not essential to understanding the present invention) and therefore will not be discussed.

[0079] Referring still to the first diagrams labelled (I) in each of Figure 6, Figure 7 and Figure 8, it is also important to note that, as between adjacent cells that are serviced by different BTSs, the frequency re-use pattern is such that there is also no adjacent cells serviced by different BTSs that operate using the same frequency. This again helps to prevent or at least minimise inter-cell interference as between adjacent cells serviced by different BTSs.

[0080] Turning now to Figure 6 specifically, as mentioned above the first diagram labelled (I) in Figure 6 relates to a "normal" BTS operating configuration. More specifically, this particular diagram illustrates a frequency re-use pattern that is commonly referred to as a "3, 9" pattern. As can be seen, there are three distinct cell site frequency arrangements (indicated by the colours green, yellow and blue, or at least by differing shading), and in this "normal" BTS operating configuration, each of these distinct cell site frequency arrangements has three frequencies, namely {1 ,2,3}, {4,5,6} and {7,8,9}, respectively. Accordingly, where a "3, 9" pattern is used, a total of 3 x 3 = 9 distinct frequencies are used - hence the name "3, 9". Incidentally though, when an embodiment of the present invention is used to switch the operating configuration of the BTS from the "normal" configuration to a "switched" configuration, the effect of this is to change the re-use pattern in Figure 6 to a "3, 3" pattern. This will be discussed further below with reference to the second diagram labelled (II) in Figure 6. [0081] Turning next to Figure 7, as mentioned above the first diagram labelled (I) in Figure 7 relates to a "normal" BTS operating configuration. More specifically, this particular diagram illustrates a frequency re-use pattern that is commonly referred to as a "4, 12" pattern. As can be seen, there are four distinct cell site frequency arrangements (indicated by the colours purple, yellow, blue and orange, or at least by differing shading), and in this "normal" BTS operating configuration, each of these distinct cell site frequency arrangements has three frequencies, namely {1 ,2,3}, {4,5,6}, {7,8,9} and {10, 1 1 , 12}, respectively. Accordingly, where a "4, 12" pattern is used, a total of 4 x 3 = 12 distinct frequencies are used - hence the name "4, 12". Incidentally though, when an embodiment of the present invention is used to switch the operating configuration of the BTS from the "normal" configuration to a "switched" configuration, the effect of this is to change the re-use pattern in Figure 7 to a "4, 4" pattern. This will be discussed further below with reference to the second diagram labelled (II) in Figure 7.

[0082] Turning now to Figure 8, as mentioned above the first diagram labelled (I) in Figure 8 relates to a "normal" BTS operating configuration. More specifically, this particular diagram illustrates a frequency re-use pattern that is commonly referred to as a "7, 21 " pattern. As can be seen, there are seven distinct cell site frequency arrangements (indicated by the colours green, yellow, blue, purple, pink, cyan and orange, or at least by differing shading), and in this "normal" BTS operating configuration, each of these distinct cell site frequency arrangements has three frequencies, namely {1 ,2,3}, {4,5,6}, {7,8,9}, {10, 1 1 , 12}, {13, 14, 15}, {16, 17, 18} and {19,20,21 }, respectively. Accordingly, where a "7, 21 " pattern is used, a total of 7 x 3 = 21 distinct frequencies are used - hence the name "7, 21 ". Incidentally though, when an embodiment of the present invention is used to switch the operating configuration of the BTS from the "normal" configuration to a "switched" configuration, the effect of this is to change the re-use pattern in Figure 8 to a "7, 7" pattern. This will be discussed further below with reference to the second diagram labelled (II) in Figure 8.

A typical three sector base transceiver station (BTS)

[0083] Figure 9 is a photograph of a typical three sector base transceiver station (BTS) 10. As shown in Figure 9, the BTS has a tower (or mast). The fact that the BTS mast in Figure 9 is painted with different coloured stripes may be for decorative or visibility purposes; however this has nothing to do with the present invention. Often the whole mast will be e.g. plain grey (or the colour of the concrete or steel from which the mast is made).

[0084] The BTS's antennas are mounted at the top of the mast. As the particular BTS depicted in Figure 9 is a three sector base transceiver station, there are accordingly three antennas (or three arrays of antennas) - one for each sector. In Figure 9, the antennas for Sector 1 , Sector 2 and Sector 3 are labelled as such. Note that, in Figure 9, whilst the antenna for each of Sectors 1 , 2 and 3 is labelled as an "antenna", and whilst each appears to be a single generally vertical elongate unit, in fact, each of these is actually an antenna housing. Each housing may contain only one antenna for the sector concerned, or (more typically) it may contain more than one antenna for the sector concerned. In the latter case, the housing would therefore contain an antenna "array" for that sector.

[0085] In fact, in Figure 9 and also Figure 10 and Figure 1 1 , it should be assumed that the antenna housings which are labelled as "Sector 1 antenna", "Sector 2 antenna" and "Sector 3 antenna" each actually contain two antennas within the one housing. The two antennas, in each case (i.e. the two antennas within each of these housings), may be assumed to have opposite polarization to each other. This may allow any polarization signal to be received by a sector antenna. The two oppositely polarised antennas will be referred to (as they normally are) as the "Main" antenna (or "Main" port) and the "Diversity" antenna (or "Diversity" port). For an explanation of the general concept of antenna diversity - see above.

[0086] In any case, as shown in Figure 9, the three antennas (i.e. the three antenna arrays) each provide 120° of coverage, and the three antennas (arrays) namely for Sector 1 , Sector 2 and Sector 3 are positioned and oriented relative to one another (i.e. they are pointed) so as to create 120° x 3 = 360° of coverage about the mast.

[0087] As mentioned above, in Figure 9 (and this will generally be true for most BTS's) the antennas (or antenna arrays) for the respective sectors are mounted at the top of the mast. Also in Figure 9, the radios for the respective antennas are located at the base of the tower (in the case of Figure 9 they would actually be located in the small air conditioned building adjacent the base of the tower). However, the radios could alternatively be mounted (and in some cases they are nowadays) at the top of the mast/tower with or near the antennas. Or the radios could be mounted at some other place/height on the tower, or they could be located slightly away from the tower. For the avoidance of doubt, the mounting location of the radios is largely irrelevant to the operation of the present invention. That is to say, embodiments of the present invention may operate and may be used with different BTS configurations, e.g. regardless of whether the radios associated with the respective sector antenna arrays are located at the base of the mast, or the top, etc.

[0088] Usually (as in the Figures and explanations that follow) there is one radio connected to each sector antenna array. This is shown in Figure 10 which is a schematic representation of the radio and antenna equipment associated with a typical three sector cellular (BTS) like the one depicted in Figure 9. As shown in Figure 10, the radio connected to the Sector 1 antenna (array) is labelled as the Sector 1 BTS radio, the radio connected to the Sector 2 antenna (array) is labelled as the Sector 2 BTS radio and the radio connected to the Sector 3 antenna (array) is labelled as the Sector 3 BTS radio. Each of the BTS sector radios is connected to its corresponding sector antenna (array) by two coaxial feeder cables 40, one of which (40M) connects the radio to the sector antenna's Main port/antenna and the other which (40D) connects the radio to the sector antenna's Diversity port/antenna.

[0089] Note that, in Figure 10, the Sector 1 antenna, the Sector 2 antenna and the Sector 3 antenna are all shown side-by-side. However, this is simply for the purpose of schematic representation. In practice, these three antenna arrays would of course be mounted at the top of the BTS mast, and pointed/oriented at 120° to one another, as shown in Figure 9.

[0090] In typical/conventional three sector base transceiver stations (BTSs) 10 like the one depicted in Figure 9 and represented Figure 10, all three radios are normally powered on (and remain on) no matter what the traffic levels (i.e. all three radios operate regardless of how much traffic or data is being transmitted via the BTS). It is this aspect of the normal operation of a base transceiver station which is a focus of the present invention.

Description and explanation of embodiments of the invention: Sector Switching Device (SSD)

[0091] For the remainder of this description, in connection with different possible embodiments (see below), the apparatus (or the various apparatus collectively) by which the invention is implemented will referred to as a Sector Switching Device (SSD). However, different variations/embodiments of the SSD are referred to below, and they may be distinguished from one another according to the different reference numerals used.

What does the SSD do?

[0092] The SSD operates to reduce energy consumption in a cellular telecommunication base transceiver station (BTS) by

- shutting down parts of the base transceiver station equipment during low-traffic periods (i.e. when demands on the equipment are low and there is a need for only a small amount of data throughput via the BTS); and

- turning the said parts of the base transceiver station equipment back on during high-traffic (or higher-traffic) periods when demands on the equipment are higher and there is a need for a greater volume of data throughput via the BTS.

[0093] As will be evident, shutting down parts of the base transceiver station equipment during low-traffic periods will reduce the amount of power consumed by the base transceiver station during those periods, and this should thereby help to achieve an overall reduction in the amount of power consumed by the base transceiver station.

[0094] There are actually two aspects to the operation of the SSD. The first aspect relates to monitoring the level of traffic at the BTS site. The second aspect relates to actually shutting down, and turning on, the relevant portions of the base transceiver station equipment as required. These two aspects are related because the first aspect (monitoring the level of traffic at the BTS site) is performed specifically in order to determine when to shut down parts of the base transceiver station equipment and when to turn them back on again. For example, monitoring the level of traffic at the BTS site can enable parts of the base transceiver station equipment to be shut down when the amount of traffic (and hence the demands on the base transceiver station equipment) drops below a certain threshold level. And likewise it can enable the said parts of the base transceiver station equipment to be switched back on again when the amount of traffic (and the demands on the base transceiver station equipment) again equals or rises above the threshold level.

[0095] In relation to the first aspect of the SSD operation, namely monitoring the level of traffic at the BTS site, whilst this is essential to the proper functioning of the SSD (i.e. it is necessary in order to know when the SSD should be used to turn the base transceiver station equipment on and off) the actual way in which this traffic level monitoring is achieved (i.e. the way in which the level of traffic at the BTS site is monitored and measured) is not critical to the invention. One or more ways in which monitoring of the level of traffic at the BTS site may be achieved are discussed below. However, for the avoidance of doubt, monitoring of the level of traffic at the BTS site may be achieved in any suitable way without departing from the invention. Also, the way in which this information (i.e. the traffic level at the BTS site from time to time) is measured and/or quantified, and the way information or signals corresponding to measured or sampled traffic levels is generated and/or converted and then transmitted or provided to the SSD (i.e. for use in determining whether to switch off or turn on base transceiver station equipment) is also not critical. It is sufficient that the SSD can receive and use this information to determine when to turn the relevant base transceiver station equipment off and on. The present invention is therefore more focused on the way in which parts of the base transceiver station equipment can be turned on and off, as required, based on monitored traffic level information.

Where might the SSD be of benefit (or particular benefit)?

[0096] Strictly speaking, the SSD could potentially be used (and it may potentially provide benefit) in any base transceiver station. This is because most (if not all) base transceiver stations, regardless of their location, experience some variation of fluctuation in traffic levels. Such variations of fluctuations may arise, for example, at different times of day. For instance (and in urban/populated areas particularly), daylight hours might see a considerable amount of telephone call/data traffic at a base transceiver station, and this traffic volume might actually increase in the early-mid evening (i.e. early-mid evening may be a "peak" traffic time). However, the darkness/night-time hours from late evening through until dawn may often see considerably lower volumes of telephone call and data traffic. It may also be that there are differences in the amount of traffic passing through a base transceiver station as between week days vs weekends, or there may be higher levels of traffic on particular dates (e.g. festivals/holidays such as Christmas, Easter, etc). Naturally, traffic volumes, and also the size and/or significance of any variations of fluctuations in traffic volumes, will vary widely for base transceiver stations at different locations. [0097] Whilst the SSD could potentially be used (and it may potentially provide benefit) in any base transceiver station, it is also true that there may be some base transceiver stations which, often due to their specific location, may stand to benefit greatly from the SSD. This will generally be the case for base transceiver stations which experience very large or dramatic variations in traffic volume levels, or which only experience high traffic volumes at particular times. Take, for example, a base transceiver station located near a large sporting stadium. At times when there is no sporting or other event taking place at the stadium (and when the stadium is consequently empty) the base transceiver station may experience little or no traffic at all. This may actually be the majority of the time. On the other hand, at those particular times when a major sporting or other event is occurring at the stadium (often this may be only for an isolated period of several hours), there could potentially be many tens of thousands of people located inside the stadium (a relatively small geographic area), and consequently during such times, even if only a fraction of the people located in the stadium are attempting to make calls or transmit data, the result would nevertheless be an extremely large traffic volume experienced by the base transceiver station. Nevertheless, once the stadium event has concluded and the stadium has again emptied, the volume of traffic experienced by the base transceiver station may again drop to low or nil.

[0098] Similar situations to that described in the previous paragraph may exist for base transceiver stations at other locations as well. For example, a base transceiver station located alongside a major highway may experience very high call/data transmission volumes at the times of day corresponding to peak road traffic/congestion (i.e. during the morning and/or evening "rush hour" when a constant and large number of people are driving past the base transceiver station making calls or transmitting data); however at other times such as during the middle of the day and more so during the night (when there is much less road traffic on the highway and hence far fewer people driving past the base transceiver station making calls/transmissions) the base transceiver station may experience far lower call/data transmission volumes. Other base transceiver stations which might experience similar variations in traffic volumes include base transceiver stations located at or near universities, large educational institutions, conference centres, and the like, all of which may be heavily populated at some times of day but much less populated or empty at other times.

[0099] Clearly, in situations like those just described (which are merely illustrative examples), significant savings in terms of the amount of power used (consumed) by the base transceiver station may be achieved by shutting down parts of the base transceiver station equipment during the low-traffic (i.e. low demand) periods, and only turning the said parts of the base transceiver station equipment on during the high-traffic periods (i.e. only when required during periods of high demand).

[00100] Another possible situation where the SSD may be of significant benefit is in base transceiver stations that are solar powered. Typically, these are utilised in remote/rural areas where normal "grid" power is unavailable. However, any solar powered base transceiver station (regardless of location) could potentially benefit greatly from the SSD. This is because solar powered base transceiver stations generally have batteries. The batteries store the power which is generated from the sun (i.e. using photovoltaic panels, etc), but the base transceiver station is actually powered by energy drawn from batteries. Therefore, the ability of the SSD to shut down parts of the base transceiver station equipment during low-traffic (i.e. low demand) periods may clearly help to reduce the drain on, and hence reduce the depletion rate of, the batteries, and this may be particularly beneficial when there is low traffic (and hence when there is no need to be powering the base transceiver station to the level, or depleting the batteries at the rate, needed for satisfying high or peak demand), and it may also be beneficial during periods of reduced or no sun exposure (when the solar cells will generally be generating less or no power).

Description of the SSD

[00101] As has already been mentioned, Figure 10 contains a schematic representation of the radio and antenna equipment in a conventional three sector base transceiver station (BTS) 10. Figure 1 1 is actually similar to Figure 10 in that it too shows the radio and antenna equipment in a three sector base transceiver station 10; however Figure 1 1 also shows the SSDs (note that there are two SSDs) interposed between the sector antennas and their corresponding sector radios. The number and arrangement of the feeder cables 40M and 40D schematically represented is also different Figure 1 1 - this is in order accommodate the SSDs and their operation, as will become clearer from the discussion below.

[00102] Fundamentally, the function of the SSDs is to facilitate "switching" between two base transceiver station operating configurations. ^■ In one of these configurations, the "normal" configuration, the coaxial feeder lines (40M and 40D) connect the respective sector antenna arrays to their corresponding sector radios (i.e. just as normal, as shown in Figure 10). So, for example, in the "normal" configuration, two feeder cables, 40M and 40D, will connect the Main and Diversity ports of the Sector 1 antenna array to the respective Main and Diversity ports of the Sector 1 radio, and another two feeder cables, 40M and 40D, will connect the Main and Diversity ports of the Sector 2 antenna array to the respective Main and Diversity ports of the sector 2 radio, etc.

^■ However, in the other configuration, the "switched" configuration, the SSDs cause the feeder cables for all of the sector antenna arrays to connect to a single one of the BTS's sector radios. Thus, for example, in the "switched" configuration, the feeder cables 40M and 40D extending from the Main and Diversity ports on all three of the sector antenna arrays (i.e. all six of these cables) are instead switched/diverted (by the SSDs) such that they all connect to the Main and Diversity ports on a single one of the BTS sector radios (e.g. the Sector 1 BTS radio, although it could be any one of the three radios).

[00103] Note that the reason why two SSDs are required, and the reason why two are depicted in Figure 1 1 , is because one SSD 100M is required to perform switching for the cables 40M that normally connect the Main ports on the respective sector antenna arrays to the corresponding Main ports on the radios, and the other SSD 100D is required to perform switching for the cables 40D that normally connect Diversity ports on the respective sector antenna arrays to the corresponding Diversity ports on the radios. In other words, one SSD 100M switches the Main port signals, whereas the other SSD 100D switches the Diversity port signals.

[00104] In terms of the physical location of the SSDs, similar to the BTS radios, the Main and Diversity SSDs can be located at the top of the base transceiver station tower (and they may be if this is where the radios are located), or alternatively they may be located at the base of the tower (if that is where the radios are), etc. The SSDs also need not necessarily be located in the same place as the radios. However, regardless of the physical location of the SSDs, SSD switching is synchronised as between the Main port SSD and the Diversity port SSD such that both Main and Diversity switch at the same time. What is meant by "switching" is, of course, switching between the two BTS operating configurations mentioned above. This will be discussed further below. Detailed operation of the SSD in one embodiment

[00105] Figure 12 and Figure 13 contain a schematic representation of the functional electronics and components used inside an SSD 100 in accordance with one embodiment of the invention. Note that Figure 12 illustrates the SSD 100 in the "normal" mode, whereas Figure 13 illustrates the SSD 100 and the "switched" mode. The only difference between the two figures is therefore the position of the various switches.

[00106] It is important to note from the outset that Figure 12 and Figure 13 show the functional electronics for only one of the two SSDs required by a given BTS - i.e. they show functional electronics for only one of the SSDs in Figure 1 1 . The SSD 100 in Figure 12 and Figure 13 could therefore by either the "Main" SSD 100M, or the "Diversity" SSD 100D, in Figure 1 1 .

[00107] Figure 12 and Figure 13 also depicts the SSD controller 90. The SSD controller 90, whilst depicted schematically as a separate, larger box, may actually be integrated in or as part of the base transceiver station (BTS) controller (shown inside the SSD controller box 90). Communications between SSD 100 and the SSD controller 90, and also DC power for the SSD 100, can be carried via the feeder cables 40. In any case, the SSD controller (wherever it happens to be located and/or however it happens to be configured/implemented) is effectively the control centre for the SSD 100. The controller 90 interprets measurements of BTS traffic levels and it determines when to initiate a "switching" instruction. As discussed previously, the controller 90 may be configured to "switch" the BTS from the "normal" mode to the "switched" mode when the traffic level (i.e. the amount of traffic/data passing through the BTS) drops below a certain threshold level. Conversely, the controller 90 may "switch" the BTS from the "switched" mode back to the "normal" mode when the traffic level equals or exceeds the threshold level.

[00108] In practice, prior to performing a switching instruction, the controller 90 would send signals to the relevant base transceiver station radios to turn off before then signalling the SSD to switch from one configuration to the other.

[00109] The SSD controller 90 may communicate with the SSD 100 using any form or type of communication protocol. For the avoidance of doubt, no limitation whatsoever exists on the communication method or protocol used, or on the way in which the SSD controller 90 and the SSD 100 exchange information. However, it is thought that one option that may be suitable for facilitating communication may be AISG.

[00110] The Antenna Interface Standards Group, sometimes referred to using the acronym AISG, is actually a non-profit international consortium formed by collaboration between communication infrastructure manufacturers and network operators with the purpose of maintaining and developing a standard for digital remote control and monitoring of antenna line devices in the wireless industry. Thus, the AISG is a standard-setting organisation (SSO). However, in the industry, the term AISG is often also used to refer, not to the organisation, but to the particular devices, protocols, etc, that have been developed and standardised by the organisation. Therefore, it is often actually the case that the term AISG refers to the standardised communication devices, protocols, etc, and that is how this term will be used herein.

[00111] AISG is based on a RS485 communication bus, which is a multi-device bus. ALDs (Antenna Line Devices) such as CNI (Control Network Interface), TMAs (Tower Mounted Amplifiers), ACU (Antenna Control Unit), RRH (Remote Radio Heads) and Antenna Remote Electrical Tilt (RET) control devices may be used and may be connected in star or daisy chain using AISG.

[00112] As mentioned above, the SSD controller 90 interprets measurements of traffic levels and determines when to initiate a "switching" instruction. In addition, the SSD controller 90 is also responsible for actually turning the relevant BTS radios off and on. The SSD controller 90 may communicate with the respective BTS radios using a data connection such as, for example, LAN or USB, although as above no limitation whatsoever exists on the communication method or protocol used, or on the way in which the SSD controller and the BTS radios exchange information.

[00113] Turning next to the functional electronic parts and components of the SSD, this will be described initially with reference to Figure 12 (although the parts and components depicted in Figure 13 are the same).

[00114] As can be seen in Figure 12, each of the antennas (which could all be Main antennas or Diversity antennas) has a feeder cable 40 which extends from the antenna into the SSD 100. Each of the feeder cables 40 connects to a respective filter module 1 10. More specifically, the feeder cable which extends from Antenna 1 connects to a filter module 11 the feeder cable which extends from Antenna 2 connects to a filter module 1 10 ₂ and the feeder cable which extends from Antenna 3 connects to a filter module 1 10 ₃ . Each of the respective filter modules 110 contains a Tx filter and an Rx filter. Therefore, the filter module 1 10-1 associated with Antenna 1 contains a Tx filter 1 10-i _j x and an Rx filter 1 10 _Rx , the filter module 1 10 ₂ associated with Antenna 2 contains a Tx filter 1 10 ₂ j _x and an Rx filter 1 10 ₂ ,R _x , etc.

[00115] Each of the respective BTS radios also has a feeder cable 40 which extends from the radio into the SSD 100. Each of these feeder cables 40 connects to a respective filter module 170. More specifically, the feeder cable which extends from the BTS Radio 1 connects to a filter module 170^ the feeder cable which extends from the BTS Radio 2 connects to a filter module 170 ₂ and the feeder cable which extends from the BTS Radio 3 connects to a filter module 170 ₃ . Each of the respective filter modules 170, again, contains a Tx filter and an Rx filter. Therefore, the filter module 170i associated with the BTS Radio 1 contains a Tx filter 170-i _jx and an Rx filter 170-i _,Rx , the filter module 170 ₂ associated with the BTS Radio 2 contains a Tx filter 170 _2jx and an Rx filter 170 _2,Rx , etc.

[00116] The purpose of the respective filter modules 1 10 (associated with the respective antennas) and of the respective filter modules 170 (associated with the radios) is to block any passive intermodulation distortion (PIM), in both the Tx and Rx signals, that may be created by the other components in the SSD 100 such as the switches, three-way splitters, etc, discussed below. In other words, the switches, splitters, etc, are located between the filter modules 110 and the filter modules 170 such that any PIM they may produced does not pass through the filter modules and out of the SSD 100.

[00117] The actual filter components used for the filter modules 1 10 and 170 and their constituent Tx and Rx filters etc - that is the make, model, technical specification, etc, for these - is not critical. In any case, the selection of appropriate filter components to achieve the purpose and function just described should be within the capability and experience of a person skilled in this area.

[00118] As just alluded to, the SSD 100 also incorporates a number of switches 104 and 105. It is by "switching" these switches appropriately that the SSD 100 switches between the "normal" mode and the "switched" mode. This is discussed further below. Again, the actual switches (or switching components) used for the switches 104 and 105 is not critical, and the selection of appropriate components to achieve the function (described below) should be within the capability of a person skilled in this area.

[00119] The SSD 100 also incorporates a three-way Tx splitter 120 and a three-way Rx splitter (or combiner) 130. The Tx splitter 120 operates in the "switched" mode to split the Tx signal from the single radio (BTS Radio 1 in the example of Figure 12 and Figure 13) so that that Tx signal is conveyed to and transmitted by all three of the antennas (Antenna 1 , Antenna 2 and Antenna 3). The Rx splitter (combiner) 130 operates, again in the "switched" mode, to effectively "collect" or "combine" the Rx signals received by the three respective antennas (Antenna 1 , Antenna 2 and Antenna 3) so that they can be conveyed to the single radio (BTS Radio 1 in this example). The "switched" mode will be discussed further below. Again though, the actual splitter components used for the splitters 120 and 130 are not critical, and the selection of appropriate components to achieve the required function for these should be within the capability of a person skilled in this area.

[00120] The SSD 100 further incorporates a low noise amplifier (LNA) 160 on the uplink path from each of the antennas. Note that the term "uplink" refers to signals transmitted by (i.e. sent from) a user equipment (e.g. from a mobile phone handsets or the like) to a BTS. In contrast, signals sent in the opposite direction, namely from the BTS to an individual user equipment (or to multiple user equipments in a broadcast manner), are referred to as "downlink".

[00121] As has been mentioned, the SSD separates the uplink and downlink signals using a duplexer filter. Furthermore, the SSD operates to switch them (i.e. the SSD switches the uplink and downlink signals) separately. More specifically, the downlink signals are switched by the switches 104, whereas the uplink signals are switched by the switches 105. See below. The switches are controlled by a control board 109 within the SSD 100. The SSD control board 109 communicates with the SSD controller 90.

[00122] In order for the LNA 160-1 associated with Antenna 1 to be on the uplink path from that antenna, LNA 160 _! is located immediately after the Rx filter 1 10 _Rx in the uplink direction. Similarly, in order for the LNA 160 ₂ associated with Antenna 2 to be on the uplink path from that antenna, LNA I6O ₂ is located immediately after the Rx filter 1 0 ₂ ,Rx in the uplink direction, etc. The purpose of the LNAs is to compensate for the insertion loss of the SSD in the uplink band. Once again, the actual low noise amplifier componentry used (make, model, technical specification, etc, of any components) is not critical.

Explanation of SSD operation: normal mode

[00123] In both BTS operating modes - i.e. regardless of whether the BTS is operating in the "normal" mode or whether it has been switched by the SSD 100 to operate in the "switched" mode - traffic levels at the BTS are continuously monitored. In the particular example depicted in Figure 12 and Figure 13, the traffic level monitoring is actually achieved by monitoring the downlink traffic on each sector (i.e. for each sector antenna) using couplers and detectors 1 12, 1 14 and 1 16. However, as has been mentioned, the actual way in which traffic level monitoring is achieved (i.e. the way in which the level of traffic at the BTS site is monitored and measured) is not critical to the invention.

[00124] If the BTS is already operating in the "normal" mode and the traffic level detected on the three sectors is (or remains) above a predetermined threshold level, the SSD controller 90 simply decides to continue operating the BTS in the "normal" mode (i.e. in the "normal'Yhigh-energy state).

[00125] On the other hand, if the BTS is initially operating in the "switched" (low energy) mode, and if the traffic level detected on all three sectors then increases above the predetermined threshold level, the SSD controller 90 will decide to switch from the "switched" (low-energy) mode to the "normal" (higher-energy) mode. If/when this occurs, the SSD controller 90 sends a turn-on data signal to BTS Radio 2 and BTS Radio 3 to start up (recall that BTS Radio 1 is already on in the "switched'Vlow-energy mode). The SSD controller 90 then switches the sector 1 , 2 and 3 antennas to BTS Radio 1 , BTS Radio 2 and BTS Radio 3, respectively, thus placing the BTS in the "normal" (high-energy) operating state.

[00126] It is mentioned above that the SSD 100 incorporates a number of switches 104 and 105, and that the switches 104 switch the downlink signals whereas the switches 105 switch the uplink signals. Thus, it is by "switching" these switches 104 and 105 appropriately that the SSD 100 switches between the "normal" mode and the "switched" mode. In fact, the way in which the switches 104 and 105 operate to "switch" the BTS from operating in the "normal" mode to operating in the "switched" mode, and vice versa, can be understood by comparing Figure 12 with Figure 13. This is because Figure 12 depicts the SSD with all of the switches 104 and 105 shown in the position they adopt when in the "normal" (high-energy) mode. In contrast, Figure 13 depicts the SSD 100 with all of the switches 104 and 105 instead shown in the position they adopt when in the "switched" (low-energy) mode.

[00127] The actual signal transmissions/flows that occur within the SSD 100 when the SSD (and hence the BTS) is operating in the "normal" mode will now be discussed.

[00128] When an uplink signal is received by Antenna 1 , this signal initially travels from Antenna 1 , along the feeder cable 40 to the filter module 1 10i . Being an uplink signal (and hence an Rx signal from the BTS's point of view), this signal then passes through the Rx filter 1 10 _Rx and then through the LNA 160-1 (where it is amplified) before reaching a first switch 105. Because this first-reached switch 105 is (in the "normal" mode) in the position shown in Figure 12, the signal consequently flows therefrom directly to a second such switch 105, and because this second-reached switch 105 is (again in the "normal" mode) in the position shown in Figure 12, the signal consequently flows therefrom into the Rx filter 170 _Rx of the filter module 170 _! . From there, the signal continues on directly (via the feeder cable 40) to the BTS Radio 1 .

[00129] Much the same applies to uplink signals received by Antenna 2 and Antenna 3. Thus, when an uplink signal is received by Antenna 2 or 3, this signal initially travels from Antenna 2 or 3, along the relevant feeder cable 40, to the filter module 1 10 ₂ or H O3. Being an uplink signal (and hence Rx from the BTS's point of view), the said signal then passes through the relevant Rx filter 1 10 _{2 Rx} or 1 10 _3iRx and then through the corresponding LNA 160 ₂ or 160 ₃ (where it is amplified) before reaching a switch 105. Because the said switch 105 is (in the "normal" mode) in the position shown in Figure 12, the signal consequently flows therefrom directly to into the Rx filter 170 _{2 Rx} or 170 _{3 Rx} of the filter module 170 ₂ or 170 ₃ . From there, the signal continues on directly (via the feeder cable 40) to the BTS Radio 2 or 3.

[00130] In relation to the downlink, when a downlink signal is generated by BTS Radio 1 , this signal initially travels from Radio 1 , along the feeder cable 40 to the filter module 170-1. Being a downlink signal (and hence a Tx signal from the BTS's point of view), this signal then passes through the Tx filter 170i _Tx and then directly to a first- reached switch 104. Because this first-reached switch 104 is (in the "normal" mode) in the position shown in Figure 12, the signal consequently flows therefrom directly to a second such switch 104, and because this second -reached switch 104 is (again in the "normal" mode) in the position shown in Figure 12, the signal consequently flows therefrom through the detector and coupler 1 12 and into the Tx filter 1 10ij _x of the filter module ^ ^ 0^ . From there, the signal continues on directly (via the feeder cable 40) to be transmitted by Antenna 1 to UE(s) serviced by Antenna 1 .

[00131] Much the same applies to downlink signals generated by BTS Radios 2 and 3. When a downlink signal is generated by BTS Radio 2 or BTS Radio 3, this signal initially travels from Radio 2 or 3, along the relevant feeder cable 40 to the corresponding filter module 170 ₂ or 170 ₃ . Being a downlink signal (and hence Tx from the BTS's point of view), the said signal then passes through the Tx filter 170 _2jx or 170 _3jx and then directly to a switch 104. Because the switch 104 is (in the "normal" mode) in the position shown in Figure 12, the signal consequently flows therefrom through the detector and coupler 1 14 or 1 16 and into the Tx filter 1 10 _2jx or 1 10 _3jx of the filter module 1 10 ₂ or 1 10 ₃ . From there, the signal continues on directly (via the feeder cable 40) to be transmitted by the relevant Antenna 2 or 3.

Explanation of SSD operation: switched mode

[00132] As mentioned above, in both BTS operating modes, and hence this includes when the BTS has been switched by the SSD 100 to operate (and when it is operating) in the "switched" mode, traffic levels at the BTS are continuously monitored. More specifically, traffic levels are continuously monitored on all three sectors. In the particular example depicted in Figure 12 and Figure 13, the traffic level monitoring is actually achieved using couplers to sample the downlink signal of the BTS. More specifically, for each sector, a coupler is used to sample the transmitted signals and a detector is used to convert the RF signal into an equivalent DC voltage that is converted into a digital value for measurement. However, as has been mentioned, the actual way in which traffic level monitoring is achieved (i.e. the way in which the level of traffic at the BTS site is monitored and measured) is not critical to the invention.

[00133] If the BTS is already operating in the "switched" mode and the traffic level detected on the three sectors is (or remains) below a predetermined threshold level, the SSD controller 90 simply decides to continue operating the BTS in the "switched" mode (i.e. in the low-energy state).

[00134] On the other hand, if the BTS is initially operating in the "normal" (high energy) mode, and if the traffic level detected on all three sectors then decreases/falls below the predetermined threshold level, the SSD controller 90 will decide to switch from the "normal" (high-energy) mode to the "switched" (low-energy) mode. If/when this occurs, the SSD controller 90 sends a turn-off/shutdown data signal to BTS Radio 2 and BTS Radio 3 (recall that BTS Radio 1 remains on in the "switched'Vlow-energy mode). The SSD controller 90 then switches the sector 1 , 2 and 3 antennas all to BTS Radio 1 , thus placing the BTS in the "switched" (low-energy or energy saving) operating state in which one of three radios (BTS Radio 1 ) is left on, but the other two are turned off, thereby potentially leading to an energy consumption reduction of about two thirds or 66%.

[00135] Recall also from above that the SSD 100 switches between the "normal" mode and the "switched" mode by "switching" the switches 104 and 105 appropriately.

[00136] The actual signal transmissions/flows that occur within the SSD 100 when the SSD (and hence the BTS) is operating in the "switched" mode, as depicted in Figure 13, will now be discussed.

[00137] In the "switched" mode, when an uplink signal is received by Antenna 1 , this signal initially travels from Antenna 1 , along the feeder cable 40 to the filter module 1 10i . Being an uplink signal (and hence an Rx signal from the BTS's point of view), this signal then passes through the Rx filter 1 10 _iRx and then through the LNA 160-1 (where it is amplified) before reaching a first switch 105. Because this first-reached switch 105 is (in the "switched" mode) in the position shown in Figure 13, the signal consequently flows therefrom into the three-way Rx combiner 130. At the three-way Rx combiner 130 the signal is collected or combined with the uplink signals received by Antenna 2 and Antenna 3, and the resultant/combined signal is then conveyed from the three-way Rx combiner 130 to a second switch 105. Next, because this second-reached switch 105 is (again in the "switched" mode) in the position shown in Figure 13, the resultant/combined signal flows into the Rx filter 170I ,R _x of the filter module 170-i. From there, the resultant/combined signal continues on directly (via the feeder cable 40) to the BTS Radio 1 .

[00138] Still referring to the "switched" mode, when an uplink signal is received by Antenna 2 or Antenna 3, the said signal initially travels from Antenna 2 or Antenna 3, along the relevant feeder cable 40 to the relevant corresponding filter module H O ₂ or H O ₃ . And, once again, being an uplink signal (and hence Rx from the BTS's point of view), the said signal then passes through the relevant Rx filter 1 10 ₂ , _R x or 1 10 _3! R _x and then through the relevant LNA 160 ₂ or 160 ₃ (where it is amplified) before reaching a first switch 105. Because, in each case, this first-reached switch 105 is (in the "switched" mode) in the position shown in Figure 13, the signal (which it should be recalled was originally received by Antenna 2 or Antenna 3) consequently then flows from the first- reached switch 105 into the three-way Rx combiner 130 where it is collected or combined with the uplink signals received by the other of Antenna 3 or Antenna 2 and Antenna 1 . The resultant/combined signal is then conveyed from the three-way Rx combiner 130 to the second switch 105, and as above, because this second-reached switch 1 05 is (in the "switched" mode) in the position shown in Figure 13, the resultant/combined signal flows into the Rx filter 170 _iRx of the filter module '\ 70- _\ . From there, the resultant/combined signal continues on directly (via the feeder cable 40) to the BTS Radio 1 .

[00139] In relation to the downlink, in the "switched" mode, when a downlink signal is generated by BTS Radio 1 (and it should be recalled that BTS Radio 1 is the only one of the three radios which is operating or even turned on in the "switched" mode), this signal initially travels from Radio 1 , along the feeder cable 40 to the filter module 170i . Being a downlink signal (and hence a Tx signal from the BTS's point of view), this signal then passes through the Tx filter 170 _Τ χ and then directly to a first-reached switch 1 04. Because this first-reached switch 104 is (in the "switched" mode) in the position shown in Figure 13, the signal consequently flows from the first-reached switch 1 04 into the three-way Tx splitter 120. At the three-way Tx splitter 120, the signal (which was originally generated by BTS Radio 1 ) is split (or duplicated) into three equal but separate/distinct signals (or signal copies), one each destined for Antenna 1 , Antenna 2 and Antenna 3. Each of these separate signals is therefore conveyed from the three- way Tx splitter 120 to a respective one of the second -reached switches 104. Because each of these second-reached switches 1 04 is (in the "switched" mode) in the position shown in Figure 13, the respective signals therefore continue through these respective second-reached switches 104, then through the relevant detector and coupler 1 12, 1 14 and 1 16, and into the relevant Tx filter 1 10-i _Tx , 1 10 ₂ ,τ _χ and 1 1 0 _{3 T} x of the corresponding filter modules 1 10i , 1 10 ₂ and H O ₃ . And from there, the signals continue on directly (via the relevant feeder cables 40) to be transmitted by the relevant Antennas 1 , 2 and 3 to user equipments serviced by the BTS.

[00140] It should be noted that, in the "switched" mode, any downlink signal produced by the BTS is produced solely by BTS Radio 1 . Therefore, even though such a downlink signal (in the "switched" mode) becomes transmitted by all three of the antennas (Antenna 1 , 2 and 3), nevertheless the signal (which is transmitted by all three antennas) is necessarily at a single frequency. Accordingly, in the "switched" mode, any downlink signal produced by the BTS is transmitted by all three antennas on the same frequency.

[00141] The practical effect of this will now be explained with reference to Figure 6, Figure 7 and Figure 8. The first diagram (I) in each of these Figures was described above in the context of (i.e. for the situation where) all of the depicted BTSs (which are represented by the small circular (red) dots) are operating in the "normal" mode. In contrast, the second diagram (II) in each of these Figures relates to the situation where all of the depicted BTSs are operating in the "switched" mode. As described above, in the "switched" mode, any downlink signal produced by a BTS is transmitted by all three antennas of that BTS on the same frequency. Accordingly, in the "switched" mode, the same frequency is necessarily used in all three cells serviced by the BTS (for both downlink and uplink).

[00142] Therefore, turning to diagram (II) in Figure 6, this diagram illustrates that if all BTSs are operating in a "switched" BTS operating configuration, there are again three distinct cell site frequency arrangements (again indicated by the colours green, yellow and blue, or at least by different shading), however each of these now (i.e. in the "switched" mode) uses only a single (i.e. the same) frequency. In diagram (II) in Figure 6, the cell sites (BTS) that transmit using frequencies {1 ,2,3} for their respective cells when in the normal mode are shown instead using frequency {1 } only for all three cells when in the "switched" mode (however the choice of frequency {1} is arbitrary, and it could be that frequency {2} only, or {3} only, is chosen for use by these BTSs in the "switched" mode, although this may also depend on the SSD design and configuration). Similarly, the cell sites (BTS) that transmit using frequencies {4,5,6} for their respective cells when in the normal mode are shown instead using frequency {4} only for all three cells in the "switched" mode (however the choice of frequency {4} is again arbitrary, and it could be that frequency {5} only, or {6} only, is chosen, although this may also depend on the SSD design and configuration). And again, the cell sites (BTS) that transmit using frequencies {7,8,9} for their respective cells when in the normal mode are shown instead using frequency {7} only for all three cells in the "switched" mode. Accordingly, if all BTSs are operating in a "switched" BTS operating configuration, a total of 3 x 1 = 3 distinct frequencies are used - hence this may be referred to as a "3, 3" pattern. [00143] Referring to diagram (II) in Figure 7, this diagram illustrates that if all BTSs are operating in a "switched" BTS operating configuration, there are again four distinct cell site frequency arrangements (again indicated by the colours purple, yellow, blue and orange), or at least by different shading), however each of these now (i.e. in the "switched" mode) uses only a single (i.e. the same) frequency. In diagram (II) in Figure 7, the cell sites (BTS) that transmit using frequencies {1 ,2,3} for their respective cells when in the normal mode are shown instead using frequency {1 } only for all three cells in the "switched" mode (however the choice of frequency {1 } is arbitrary, and it could be that frequency {2} only, or {3} only, is chosen for use by these BTSs in the "switched" mode, although this may also depend on the SSD design and configuration). Similarly, the cell sites (BTS) that transmit using frequencies {4,5,6} for their respective cells when in the normal mode are shown instead using frequency {4} only for all three cells in the "switched" mode (however the choice of frequency {4} is again arbitrary, and it could be that frequency {5} only, or {6} only, is chosen, although this may also depend on the SSD design and configuration). And it is the same for the cell sites (BTS) that transmit using frequencies {7,8,9} and {10,1 1 , 12} in the normal mode - these are shown using frequency {7} only and {10} only. Accordingly, if all BTSs are operating in a "switched" BTS operating configuration, a total of 4 x 1 = 4 distinct frequencies are used - hence this may be referred to as a "4, 4" pattern.

[00144] Referring to diagram (II) in Figure 8, this diagram illustrates that if all BTSs are operating in a "switched" BTS operating configuration, there are again seven distinct cell site frequency arrangements (again indicated by the colours green, yellow, blue, purple, pink, cyan and orange, or at least by different shading), however each of these now (i.e. in the "switched" mode) uses only a single (i.e. the same) frequency. In diagram (II) in Figure 8, the cell sites (BTS) that transmit using frequencies {1 ,2,3} for their respective cells when in the normal mode are shown instead using frequency {1 } only for all three cells in the "switched" mode (however the choice of frequency {1 } is arbitrary, and it could be that frequency {2} only, or {3} only, is chosen for use by these BTSs in the "switched" mode, although this may also depend on the SSD design and configuration). Similarly, the cell sites (BTS) that transmit using frequencies {4,5,6} for their respective cells when in the normal mode are shown instead using frequency {4} only for all three cells in the "switched" mode (however the choice of frequency {4} is again arbitrary, and it could be that frequency {5} only, or {6} only, is chosen, although this may also depend on the SSD design and configuration). And it is the same for the cell sites (BTS) that transmit using frequencies {7,8,9}, {10, 1 1 , 12}, {13, 14,15}, {16, 17, 18} and {19,20,21 } in the normal mode - these are shown using frequency {7} only, {10} only, {13} only, {16} only and {19} only. Accordingly, if all BTSs are operating in a "switched" BTS operating configuration, a total of 7 x 1 - 7 distinct frequencies are used - hence this may be referred to as a "7, 7" pattern.

[00145] Thus, as mentioned in passing above, one of the important capabilities provided by embodiments of the present invention is the ability to switch a cell site's mode of operation between multi-sectored and omni. It is perhaps worth noting that the idea of configuring a multi -sectored BTS for omnidirectional operation - at least in the downlink direction - has been proposed previously. For instance, a patent application by Ericsson (US20140248906, "Methods and Arrangements for Positioning in Wireless Communications Systems") describes a three sector BTS in which the downlink signals from the transmitter in BTS Radio 1 are broadcast from all three sector antennas simultaneously, thereby creating a quasi-omnidirectional radiation pattern. Note, however, that the reasons for doing this in the Ericsson patent application are different and unrelated to reasons for doing so in the context of the present invention. Also, in this Ericsson patent application, uplink signals from Antennas 1 , 2 and 3 are still conveyed to the receivers in BTS Radios 1 , 2 and 3, respectively, i.e. in the conventional fashion for a sectorised cell site. In any case, an important (and arguably fundamental) difference between the system in the above Ericsson patent application and the present invention is that the Ericsson system is a fixed and permanent installation that cannot dynamically switch from an omnidirectional to a sectorised mode of transmission. In complete contrast, the present invention can enable dynamic switching between omnidirectional and sectorised modes of operation (and back again) as the need arises. Moreover, in embodiments of the present invention, the switching process can be made completely automatic if desired, without requiring any changes to the BTS hardware or software.

Antenna patterns of a multi-sector site switched using the SSD

[00146] Figure 14 illustrates antenna radiation patterns of a multi-sector site switched using the SSD. As explained above, the BTS's existing antennas are used in both normal mode and switched mode. In Figure 14, the radiation patterns for normal mode are coloured, and when SSD switches the antennas to single radio the pattern effectively is the black pattern. It can be seen that, in the "switched" mode (when the antennas are fed with the same frequency signal from a single BTS radio), the resulting antenna radiation pattern tends toward an omnidirectional pattern.

Other possible implementations/embodiments of the SSD

[00147] Figure 15 contains a schematic representation of the functional electronics and components used inside an SSD 200 in accordance with a second possible embodiment of the invention.

[00148] It is important to note again that Figure 15 (like Figure 12 and Figure 13) shows the functional electronics for only one of the two SSDs required by a given BTS - i.e. it show functional electronics for only one of the SSDs in Figure 1 1 . The SSD 200 in Figure 15 could therefore be either the "Main" SSD 200M or the "Diversity" SSD 200D.

[00149] The embodiment of the SSD 200 depicted in Figure 15 will not be described in the same detail as the SSD 100 above, because those skilled in this area should be able to readily interpret Figure 15, and understand the operation of the SSD 200, based on the explanations given above with reference to Figure 12 and Figure 13.

[00150] Nevertheless, as those skilled in the art will readily appreciate from Figure 15, the embodiment of the SSD 200 differs from the embodiment of the SSD 100 in that the SSD 200 is only operable to switch the transmitter (not the receiver) to a single BTS radio. In other words, with the SSD 200 in Figure 15, even when the SSD switches the BTS to operate in the "switched" mode, uplink signals received by all three of the antennas (Antenna 1 , Antenna 2 and Antenna 3) are still conveyed directly to their respective BTS radios (BTS Radio 1 , BTS Radio 2 and BTS Radio 3), and not all to a single radio as is the case for SSD 100 in the "switched" mode.

[00151] With the SSD 200 depicted in Figure 15, any of the BTS radios (BTS Radio 1 , 2 or 3) can be selected/used as the transmission (Tx) source.

[00152] Figure 16 contains a schematic representation of the functional electronics and components used inside an SSD variant 300.

[00153] It is important to note yet again that Figure 16 shows the functional electronics for only one of the two SSDs required by a given BTS - i.e. it show functional electronics for only one of the SSDs in Figure 1 1 . The SSD 300 in Figure 16 could therefore be either the "Main" SSD 300M or the "Diversity" SSD 300D. [00154] The SSD variant 300 depicted in Figure 16 will not be described in detail, because those skilled in this area should be able to readily interpret Figure 16, and understand the operation of the SSD 300, based on the explanations given above.

[00155] As those skilled in the art will readily recognise from Figure 16, the SSD variant 300 differs from the embodiments of the SSD 100 and 200 in that the SSD 300 is not actually switchable at all. Instead, the SSD 300 could be installed as a retrofit to cause an existing multi (three) sector BTS to be (always) driven by a single BTS radio (Radio 1 in this example, although it could be any of the three radios). This could potentially prove useful if there is a need, for example, for greater range but low capacity in a particular location, and to therefore change the operation of the existing multi (three) sector BTS at that location to effectively operate in an "omni" fashion (which, as explained above, can be better for achieving greater range if with somewhat reduced capacity).

[00156] Figure 17 contains a schematic representation of the functional electronics and components used inside an SSD 400 in accordance with a fourth possible embodiment of the invention.

[00157] It is important to note again that Figure 17 shows the functional electronics for only one of the two SSDs required by a given BTS - i.e. it show functional electronics for only one of the SSDs in Figure 1 1 . The SSD 400 could therefore be either the "Main" SSD 400M or the "Diversity" SSD 400D.

[00158] The embodiment of the SSD 400 depicted in Figure 17 will not be described in detail, because those skilled in this area should be able to readily interpret Figure 17, and understand the operation of the SSD 400, based on the explanations given above.

[00159] Nevertheless, as those skilled in the art will readily appreciate from Figure 17, the embodiment of the SSD 400 differs from the embodiment of the SSD 100, and it is similar to the embodiment of the SSD 200, in that the SSD 400 is only operable to switch the transmitter (not the receiver) to a single BTS radio. In other words, with the SSD 400 in Figure 17, even when the SSD switches the BTS to operate in the "switched" mode, uplink signals received by all three of the antennas (Antenna 1 , Antenna 2 and Antenna 3) are still conveyed directly to their respective BTS radios (BTS Radio 1 , BTS Radio 2 and BTS Radio 3), and not all to a single radio as is the case for SSD 100 in the "switched" mode. [00160] However, the SSD 400 depicted in Figure 17 differs from the SSD 200 depicted in Figure 15 in that, in the SSD 400, only the BTS radio 1 can be used as the transmission (Tx) source.

[00161] Figure 18 contains a schematic representation of the functional electronics and components used inside an SSD 500 in accordance with a fifth possible embodiment of the invention. It is important to note again that Figure 18 shows the functional electronics for only one of the two SSDs required by a given BTS.

[00162] The embodiment of the SSD 500 will not be described in detail, because those skilled in this area should be able to readily interpret Figure 18, and understand the operation of the SSD 500, based on the explanations given above.

[00163] The SSD 500 in Figure 18 has frequency conversion mixers associated with the BTS Radio 2 and the BTS Radio 3 to allow for possible frequency shifting.

FDD vs TDD systems

[00164] It was mentioned above that a range of interference mitigation techniques and methodologies are often used for preventing or minimising inter-cell interference, and also for preventing or minimising intra-cell interference. However, it was also stated above that further details or explanations of these techniques and methodologies for mitigating interference within and between cells is outside the scope of the present disclosure.

[00165] Something that will be briefly discussed, however, is the issue of duplexing. To understand what duplexing is (in the context of cellular telecommunications at least) it should first be noted that it is essential, in any cellular communications system , for downlink and uplink transmissions to be able to occur simultaneously. This is essential, for example, because it enables spoken conversations to be made, with either end being able to talk and listen as required. Likewise, in relation to data transmission and exchange, it is often necessary to be able to undertake virtually simultaneous or completely simultaneous communications in both directions.

[00166] In order for a cellular telecommunications system (or indeed any radio communications system) to be able to communicate in both directions it is necessary to have what is termed a duplex scheme. There are several methods that can be adopted. For applications involving cellular telecommunications, where it is required that the base transceiver station (BTS) and also the user (UE) are able to operate (i.e. to transmit and receive) simultaneously, two schemes are commonly used: one is commonly known as "frequency division duplexing" ("FDD"), and the other is commonly known as "time division duplexing" ("TDD").

[00167] In a FDD system (i.e. a system in which frequency division duplexing is used), two distinct channels (i.e. two distinct frequency bands) are used, specifically one for uplink and the other for downlink. In other words, in FDD systems, the uplink and downlink channels are assigned to different frequency bands respectively. Each band is isolated from the other by means of (possibly amongst other things) duplexing filters in the front end of the base transceiver station.

[00168] In contrast, in a TDD system (i.e. in a system in which time division duplexing is used), only a single channel (i.e. only a single frequency band) is used, but distinct timeslots are allocated for transmission and reception. In other words, in TDD systems, a single frequency channel is used to transmit signals in both downlink and uplink directions, and this is made possible by assigning separate (possibly albeit not necessarily alternating) timeslots to transmit and receive operations. Filters may not be strictly necessary in TDD systems, except perhaps as a way of preventing out-of-band interference from external signal sources from entering the system and desensitising the base station receiver.

Compatibility of the SSD with FDD and TDD systems

[00169] The various embodiments of the SSD that are discussed above and shown in: Figure 12 and Figure 13; Figure 15; Figure 16; Figure 17; and Figure 18, are actually suitable for use in FDD systems only.

[00170] This is made evident from the duplexing filters at the SSD input and output ports in these embodiments, which act to separate the uplink and downlink signals from each other as they pass through the SSD. This enables the low-power uplink signals to be boosted in the low-noise amplifier, which helps to preserve the noise figure of the base station's receiver. It also prevents any passive intermodulation (PIM) generated by the high-power downlink signals as they pass through the SSD's switch network from entering the base station's receiver and creating a blocking or desensitisation problem.

[00171] However, the present invention is by no means restricted to embodiment or implementation only in FDD systems. Indeed, the invention (and embodiments thereof) can also be made to work (and may be implemented) in TDD systems. An SSD 600 in accordance with one such embodiment, which is a simple and relatively general embodiment, and which is suitable for implementation in a TDD system, is depicted in Figure 19.

[00172] In the SSD 600 in Figure 19, when the SSD is in the "Switched" mode, the antennas for all three sectors are connected to BTS Radio 1 , and BTS Radio 2 and BTS Radio 3 are placed into a shutdown state. The sequence of steps that is followed in switching between the "Normal" mode and the "Switched" mode in the SSD 600 in Figure 19 is also identical to the SSD in (for example) the embodiment 100 described above. The chief difference between the SSD 600 in Figure 19 and (as an example) the SSD in the embodiment 100 described above is that the SSD 600 in Figure 19 is a wideband device in which the downlink & uplink signals follow a common path between the input & output ports of the SSD. In other words, unlike the SSD 100 in which separate transmission paths are provided within the SSD (between the BTS radio(s) and the respective antennas) for downlink signals (which are Tx from the BTS's point of view) and uplink signals (which are Rx from the BTS's point of view), in contrast the SSD 600 does not have (between the radio(s) and its respective antennas) separate transmission paths for downlink and uplink signals - i.e. within the SSD 600, uplink and downlink signals passing between the radio(s) and the antennas follow a common (i.e. uplink and downlink signals both follow the same) transmission path through the SSD 600. As a result of this, the SSD 600 in Figure 19 is compatible with both FDD and TDD BTSs.

[00173] An alternative SSD embodiment 700, which is also compatible with both FDD and TDD systems, is shown in Figure 20. The SSD 700 in Figure 20 differs from the SSD 600 in Figure 19 in that the antennas from all three sectors can be connected to any one of BTS Radio 1 , BTS Radio 2 and BTS Radio 3 when the SSD 700 is in "Switched" mode, and the other two BTSs are placed into a shutdown state. The configuration of the SSD 700 in Figure 20 provides the following potential benefits (possibly amongst others):

^■ When switching between the "Normal" and "Switched" modes of operation, the SSD 700 can alternate (or allow alternation) between BTS Radio 1 , BTS Radio 2 and BTS Radio 3 from day to day (or from time to time), thereby potentially allowing wear and tear to be shared (or spread approximately evenly, etc) among multiple or all BTS Radios.

^■ It may allow the network operator to reduce the risk of inter-cell interference in the network by ensuring that neighbouring BTSs with the same frequency allocations (which can potentially occur in some frequency re-use patterns) do not all switch to the exact same frequency channel when their SSDs are in "Switched" mode.

Additional points relating to embodiments of the SSD

[00174] In most embodiments, the components which make up the SSD and which provide its functionality will normally be housed/mounted within an enclosure or housing and typically the enclosure or housing will have (at least, or amongst other things) six coaxial connectors and a one AISG connector. The AISG connector may be used to connect multiple SSDs installed on the mast of (or at some other location on or near) a BTS.

[00175] In some if not most or all embodiments, SSDs will be band specific. Each band may therefore have a different frequency SSD, with the frequency of the SSD being determined/characterised by the filters used within the SSD. Multiband base transceiver stations (BTSs) would therefore use SSDs of different frequencies to cater for the bands at that site. Typical frequency bands on which Mobile communications operate include 700MHz, 850MHz, 900MHz, 1800MHz, 1900MHz, 2100MHz, 2300MHz, 2600MHz.

[00176] An SSD may also be capable of passing any AISG signals and also DC to each of an antenna's remote electrical tilt receivers. AISG is a protocol specifically used to communicate with antennas. AISG signals may thus be passed through the SSD so that the antenna can also receive the AISG signals.

[00177] Another point to note is that, in telecommunications networks like the ones schematically depicted in Figure 6 to Figure 8 for example and others, namely networks in which multiple sectorised BTSs are provided which provide telecommunication service coverage to adjacent (and adjoining) geographic areas, it may be that all of the BTSs are provided with SSDs. However, this may not always be necessary or required, and it may be that only some (or a selected one or more) of the BTSs are provided with SSDs. For example, it may be that only the one or more BTSs in the network that happen to be located physically/geographically near, say, a sporting stadium or the like (and which is/are consequently likely to experience major fluctuations in traffic volumes) may be provided with SSDs. Furthermore, regardless of whether all of the BTSs in the network, or only one or some of them, are provided with SSDs, it also may not always be necessary or required for every SSD in the network to be in the same mode (i.e. the "normal" mode or the "switched" mode) at the same time. On the contrary, the various different SSDs associated with the different BTSs in the network may often switch back and forth between the "normal" mode and "switched" mode at different times, potentially independently of one another and without regard to the state of the SSDs in adjacent or neighbouring BTSs.

[00178] It should be noted, however, that in some networks - especially those that use a "3, 9" frequency re-use pattern - the choice of which one of the BTS Radios an SSD uses when it causes the BTS to operate in "Switched" mode may require some network-level planning in order to reduce the risk or potential inter-cell interference. More specifically, SSDs in respective adjacent BTSs that use the same three frequencies should be configured such that each BTS uses a different BTS Radio (and hence a different frequency) when in "Switched" mode vis-a-vis the surrounding/adjacent BTSs that have the same frequency allocation. Thus, for example, BTSs in a network that all use the frequencies {1 ,2,3} when in the "Normal" mode should not necessarily all switch to BTS Radio 1 (and its corresponding frequency {1 }) when in "Switched" mode, especially if they all switch to the "switched" mode at the same time. Instead, some BTSs should switch to BTS Radio 1 , others to BTS Radio 2, and the rest to BTS Radio 3. The choice of which specific BTS Radio a BTS should use when in the "switched" mode depends on which configuration minimises the potential for inter-cell interference with other cells.

Possible integration of SSD Technology with or into Tower Mounted Amplifiers (TMAs)

[00179] Another way in which the present invention might be embodied (for example with componentry suitable for providing functionality equivalent to the SSD in one or more of the embodiments discussed above) is by combining this with, or incorporating it (or its functionality) into a Tower Mounted Amplifier (TMA).

[00180] TMAs are bidirectional devices that are frequently employed in cellular BTSs to improve the noise figure of the BTS receiver. TMAs can also be useful in preventing external out-of-band interference signals from entering the system via the antenna and desensitising the BTS receiver. TMAs are designed to be inserted into the RF path between the BTS radio and the corresponding antenna, usually as close to the antenna as possible, and they are available for both FDD and TDD systems.

[00181] Those skilled in the art (or at least those familiar with the construction, componentry and operation of TMAs) may recognise that the embodiments of the SSD discussed above with particular reference to: Figure 12 and Figure 13; Figure 15; Figure 16; Figure 17; and Figure 18, have numerous architectural features in common with an FDD TMA. For example, the SSDs in these embodiments have a duplexing filter at the BTS Radio and Antenna ports, and a low-noise amplifier in the uplink path. The SSDs in these embodiments also have control modules equipped with AISG modems to allow the BTS to communicate with the SSD and instruct it to change its operating mode if necessary. These are all features that are also commonly found in FDD TMAs, which suggests that it may well be possible for a suitably modified SSD to act as an outright replacement or substitute for a conventional FDD TMA.

[00182] Similarly, it may be possible in principle for a suitably modified TDD- compatible SSD to provide the same functionality as a TDD TMA (in addition to its core SSD functions), thereby eliminating the need for a separate TDD TMA to be installed at that site.

MIMO Systems

[00183] The present invention, or embodiments thereof, may also be adapted for use in so-called MIMO systems. MIMO, which stands for "multiple-input, multiple output", is a method for multiplying the capacity of a radio link by using multiple transmit and receive antennas to exploit multipath propagation. The use of multiple antennas in (or for the purpose of implementing) a MIMO system, whilst somewhat related to the use of multiple antennas for the purpose of achieving antenna diversity (discussed above), is perhaps best thought of as notionally separate from (and not be confused with) the use of multiple antennas for achieving antenna diversity.

[00184] A MIMO scheme typically employs multiple antennae at the transmitter (e.g. multiple antennas may be provided for a single BTS sector) and also at the receiver (e.g. the user's mobile handset may also have multiple antennas) to enhance the data capacity achievable between the transmitter and the receiver.

[00185] By way of example, a 2x2 "single user MIMO" (SU-MIMO) configuration contains two antennae at the transmitter (e.g. two antennas are provided for the single BTS sector that is serving a particular user) and two antennae at a single receiver (e.g. two antennas at a single user's mobile handset). Likewise, a 4x4 SU-MIMO configuration contains four antennae at the transmitter and four antennae at the single receiver that is in communication with the transmitter. There is no need for the transmitter and receiver to employ the same number of antennae. Typically, a BTS in a wireless communication system will be equipped with more antennae in comparison with a UE, owing to differences in power, cost and size limitations. It should also be noted that so called "multi-user MIMO" (MU-MIMO) is often employed, and this involves a single BTS which is able to perform MIMO communication with multiple users (e.g. multiple user mobile handsets) at once.

[00186] In view of the foregoing, those skilled in the art will appreciate that, if the present invention, or any embodiment thereof, is to be adapted for use in a MIMO systems, a larger number of (for example) SSD units may be required in comparison with situations where the present invention (or an embodiment thereof) is implemented in a non-MIMO system. This is due simply to the larger number of antennas involved.

Other Applications

[00187] The present invention, and embodiments thereof, and the technology of the SSD discussed above, may also be adapted to suit (or for use in) other applications such as, for example, public Wi-Fi hotspot systems, or in fact any multiple radio communication system that experiences traffic fluctuations over time.

Benefits and advantages of the SSD

[00188] As explained in the Background section above, a major impediment that has previously prevented cellular telecommunication networks from being made adaptable, and more specifically which has prevented network operators from being able to switch off elements of radio equipment and the like when demand is low, is that doing so (at least without the present invention) has required access or permissions to manipulate or operate underlying operating systems and software of the BTS radio equipment/hardware. However, the suppliers/manufacturers of this BTS radio equipment/hardware typically impose extremely tight security controls on the equipment operating systems and software, and on access thereto. As such, even cellular network operators often do not have sufficient access or the ability to manipulate or operate the underlying BTS operating systems and software. This has (prior to the present invention) made it difficult or impossible for cellular telecommunication network operators to be able to switch off elements of radio equipment and the like to save power when demand is low.

[00189] Embodiments of the present invention overcome this problem because, in basic terms, the SSDs provide a hardware solution that enables the same outcome to be achieved (i.e. turning off individual radios at a BTS to save power during low-traffic periods) but without needing access to or the ability to control the underlying operating system/software of BTS equipment/hardware.

[00190] The SSDs are also retrofittable to existing BTSs with only minimal alteration to the existing BTS hardware, software, systems and infrastructure. Thus, in short, another major benefit of the SSDs is that they can be installed on any existing base transceiver station.

[00191] In some embodiments, an SSD may also be fully autonomous - that is, able to perform and "act upon" its own measurements of local traffic levels. An autonomous SSD may therefore not require network statistics or the like in order to determine when to "switch", etc. The significance of this should not be underestimated, particularly in the context of practical implementation and deployment of SSDs within existing cellular telecommunication network infrastructure, because the fact that an SSD is autonomous (and not reliant on information exchange from other network components, etc) may help to minimise disruption or the need for change to other parts of cellular network infrastructure during implementation.

[00192] SSDs in various embodiments may also be able to adapt to any size and type of base transceiver station - including by using multiple SSDs. Tower top or tower base transceiver stations can be accommodated. SSDs may also be scalable to suit any number of sectors. Usually there will be three sectors, but sometimes up to six sectored sites are used. In any case, SSD embodiments may be implemented regardless of the number of sectors per site.

[00193] SSDs may be switched automatically (as discussed in detail above), or alternatively manually, between the "normal" and "switched'Venergy saving states. The switching thresholds and preferred functions can be tailored on a per site basis, according to the particular requirements, conditions, etc, at a particular site. [00194] And of course, most importantly, the SSDs allow BTS radios to be turned off when appropriate in order to save power.

[00195] In the present specification and claims (if any), the word 'comprising' and its derivatives including 'comprises' and 'comprise' include each of the stated integers but does not exclude the inclusion of one or more further integers.

[00196] Reference throughout this specification to One embodiment' or 'an embodiment' means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases 'in one embodiment' or 'in an embodiment' in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations.

[00197] In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims (if any) appropriately interpreted by those skilled in the art.