A METHOD OF ADJUSTING THE POSITION OF A PICOCELL BASE STATION, AND APPARATUS THEREFOR

Field of the Invention

The present invention relates to telecommunications, in particular to wireless telecommunications.

Description of the Related Art Wireless telecommunications systems are well-known. Many such systems are cellular, in that radio coverage is provided by a bundle of radio coverage areas known as cells. In each cell, a base station is located that provides the radio coverage. Traditional base stations provide coverage in relatively large geographic areas and the corresponding cells are often referred to as macrocells. It is possible to establish smaller sized cells within a macrocell. Cells that are smaller than macrocells are sometimes referred to as microcells, picocells, or femtocells, but we use the term picocells generically for cells that are smaller than macrocells. One way to establish a picocell is to provide a picocell base station that operates within a relatively limited range within the coverage area of a macrocell. One example of use of a picocell base station is to provide wireless communication coverage within a building.

Picocells can be deployed without detailed centralized cell-planning, for example by end-users or unskilled individuals installing picocell base stations in their offices and homes. In consequence, picocell base stations can often be placed at locations that are inappropriate. Locations are inappropriate if signals from such picocell base stations, in particular pilot signals, are detected by user terminals that are outside the building and are connected to the macrocell base station. An example of an inappropriate location is near a window and facing a busy road. A picocell base station in such a location causes interference to the macrocell base station. Also, undesirable handover attempts can be triggered, of that outside user terminal, from connection with the macrocell base station to connection with the picocell base station.

Picocell base stations are intended primarily for users belonging to a particular home or office. Handovers of radio connections of outside user terminals to the picocell base station are not desirable for several reasons. Firstly, handovers involve substantial resources in terms of signalling traffic. Secondly, in consequence, the process of handover to or from the picocell base station reduces the amount of data traffic that can be handled by the picocell base station at that time. This results in a reduction in quality of service to a home user.

The picocell base station is of a relatively low transmit power and hence each picocell is small compared to a macrocell. Accordingly, there can be a large number of picocells within an area roughly equivalent to the size of a macrocell. In consequence, a macrocell user moving along a road may frequently move in and out of range of picocell base stations, causing a rapid sequence of handover processes to and from picocells. As mentioned above, this is to the detriment of data handling performance of the picocells. Accordingly, there is a need to reduce handovers of radio connections of outside user terminals to and from picocells.

In cellular systems involving macrocells, good base station positions are determined by careful cell planning, and there is optimisation of the position by trained radio engineers. Specifically, the engineer monitors performance statistics of deployed base stations and make on-site adjustments in base station orientation and location accordingly.

Summary of the Invention

The reader is referred to the appended independent claims. Some preferred features are laid out in the dependent claims. The inventors realised that for base stations that are picocell base stations requiring optimisation by an engineer on site of location and orientation would be impractical, and is contrary to the autonomous and plug-and-play nature of some picocell base stations.

An example of the present invention is a method of adjusting the position of a picocell base station having at least one associated preferred user terminal. The method comprising the steps of the picocell base station: determining a rate of receipt of requests from user terminals for handover to the picocell base station; and dependent upon the rate of receipt exceeding a threshold, sending an indicator signal to a controller of the picocell base station indicating that the picocell base station should be repositioned.

Brief Description of the Drawings An embodiment of the present invention will now be described by way of example and with reference to the drawings, in which:

Figure 1 is a schematic diagram illustrating of a wireless communication network according to an embodiment of the invention,

Figure 2 is a diagram illustrating a picocell base station shown in Figure 1 located in a building,

Figure 3 is a diagram illustrating in more detail the picocell base station shown in Figures 1 and 2, and

Figure 4 is a flow chart illustrating operation of the picocell base station shown in Figure 3 in the network shown in Figure 1.

Detailed Description

As shown in Figure 1 , in a communication system 20, there is a base station 22 for wireless telecommunications. The base station has a radio coverage area 24 that is often referred to as a macrocell. The geographic extent of the macrocell 24 depends on the capabilities of the base station 22 and the surrounding geography. Within the macrocell 24, a picocell base station unit (PCBSU) 30 provides wireless communications within a picocell 32. The radio coverage area of the picocell 30 is much less than that of the macrocell 24. For example, the picocell 32 corresponds in size to a user's home.

Another PCBSU 34 provides wireless coverage within a picocell 36. A further picocell 38 provides wireless coverage within a picocell 40.

It is possible for a mobile terminal 44 within the macrocell 24 to communicate with the macrocell base station 22 in known manner. When the mobile terminal 44 enters into a picocell 32 for which the mobile terminal is authorised for communications within the picocell base station 30, it is desirable to handover the connection with the mobile terminal from the macrocell to the picocell. In the example shown in Figure 1, the user of mobile terminal 44 is a preferred user to use picocell 32. As shown in Figure 2, imagine that the picocell base station unit 30 is located inappropriately within a building 33 such as near a window 31, where the window is adjacent to a busy road. The picocell 32 then extends significantly beyond the building 33 through the window 31. In consequence, a user terminal 35 connected to the macrocell 24 but not being a user preferred for the picocell base station unit (PCBSU) 30, receives pilot signals from the PCBSU 30 and enters a process of handover to the PCBSU 30 by sending a handover request.

As shown in Figure 3, each picocell base station unit, PCBSU, 30 includes a memory 46 in which is stored a list 48 of "preferred" user terminals. The PCBSU 30 includes a counter 50 of handover requests received by the PCBSU 30 from other user terminals, which we can call "non-preferred" users, over a predetermined period. The PCBSU 30 also includes a reposition decision stage 52, connected to both a reposition indicator 54 and a power control stage 56. The reposition decision stage 52 is also connected to the memory 46.

Operation

As shown in Figure 4, the list 48 of preferred user terminals is created (step a) by the owner of the PCBSU 30 during setup. The preferred user terminals are those of the usual users of the PCBSU, for example family members of a PCBSU bought for home use, or office workers of a PCBSU bought for office use.

Handover requests from preferred user terminals are acted upon by the PCBSU 30 without, of course, being counted by counter 50. Handover requests from other user terminals are counted (step b) in the counter 50, and in this embodiment, those requests are acted upon to effect handovers. After counting for a predetermined period, the count is evaluated in the reposition decision stage by being compared (step c) to a predetermined threshold.

If the threshold is not exceeded, then (step d) the counter is reset and counting of handover requests from non-preferred user terminals is restarted.

Indicating that PCBSU should be repositioned

As also shown in Figure 4, on the other hand, if the threshold is exceeded, then the reposition indicator 54 is instructed by the reposition decision stage 52 to inform (step e) the owner of the picocell base station unit (PCBSU) 30 that the PCBSU is not placed in an acceptable position so should be repositioned (for example by relocation and reorientation). In this example, the owner is so informed by the reposition indicator 54 sending a Short Message Service (SMS) message to the PCBSU owner's user terminal, such as his/her mobile terminal.

Reducing Transmit Power

As shown in Figure 4, the next step is to reduce (step f) transmit power. Specifically, the PCBSU 30 reduces the power of its pilot channel so as to reduce chances of the PCBSU being detected by non-preferred users who might be, for example, in a street near to the building. The PCBSU 30 also lowers the transmit power of all other channels so as to seek to reduce its interference to macrocell user terminals. hi this example, the degree of transmit power lowering to be applied is preset in the PCBSU 30. The degree of lowering was selected during manufacture, for example dependent upon the preference of the anticipated network operator, hi this example, preference is given to the interests of the preferred users by the degree of

lowering having been selected to be moderate. Accordingly, the power levels are lowered only to an extent that quality of service to preferred user terminals is not degraded despite interference to non-preferred (macrocell) users remaining.

In an otherwise similar example (not shown), preference is given to the interests of non-preferred (macrocell) user terminals by the degree of lowering being selected to be severe. Accordingly, power levels are reduced severely so as to severely reduce interference to non-preferred user terminals despite the reduction in quality of service to preferred user terminals. In another, otherwise similar, embodiment (not shown), the PCBSU can instead stop transmitting altogether. This option may be preferred where network operators would wish to give precedence to the macrocell network performance over that of the PCBSU. This would also serve as an incentive for users to reposition their PCBSU quickly. hi another, otherwise similar, example (not shown), which type of degree of lowering to apply, namely moderate or severe, is selected automatically; for example severe lowering is selected upon the PCBSU being persistently determined as being in an inappropriate position.

Moving PCBSU and resetting

Returning to the example shown in Figure 4, the picocell base station unit (PCBSU) 30 is switched off, and repositioned (step g) by the owner by being moved to another location and/or into another orientation (for example in azimuth), within the building. Once the PCBSU 30 has been moved, it is switched on again, causing the counter 50 of handover requests from non-preferred user terminals to be re-zeroed (step h) then the process of counting (step b) requests for handovers from non- preferred user terminals starts again.

Some more alternative examples hi an otherwise similar embodiment (not shown) to that shown in Figure 4, only handover requests from preferred user terminals result in handover. Handover requests from non-preferred user terminals are recorded and in response to each

handover request, the handover process is initiated. However authorisation of a non- preferred user terminal to handover is denied, so handover is not completed.

In some embodiments, rather than, or in addition to, the owner of the PCBSU being informed to move the PCBSU by SMS message to his/her user terminal, a visual prompt is provided, such as a status light on the PCBSU outer casing. In some embodiments, a less discrete means of indication is provided, such as a loudspeaker giving audible "beep" tones. Such less discrete indicators are particularly useful as a second stage of indication upon finding that more discrete indicators (e.g. SMS message, visual status light) have not caused the owner to reposition the PCBSU within a predetermined time period.

In some embodiments, rather than noting PCBSU switch-on as a trigger to reset the counter of handover requests from non-preferred user terminals, the PCBSU detects that the PCBSU has been moved by identifying a significant change in a received signal, such as power level. In some embodiments, instead of resetting the counter to a zero count upon the

PCBSU being moved, a running average is kept of the number of handover requests from non-preferred user terminals within a limited time window, for example, in the last so-many minutes. Accordingly, only recent occurrences of handover requests from non-preferred users are considered. In some embodiments, the time window size can be varied.

In some embodiments, a picocell base station unit (PCBSU) owner is provided with information as to possible degradation of quality of service being experienced. This can be an incentive for the owner to move the PCBSU.

General

The present invention may be embodied in other specific forms without departing from its essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing

description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.