FIELD OF THE INVENTION

[0001] The invention relates generally to digital communication systems and in particular to spectrum sharing between a synchronous systems and bursty systems using IEEE 802.i l standard.

BACKGROUND OF THE INVENTION

[0002] The licensed spectrum below 6GHz became a very scarce resource. In addition, an overwhelming increase of the cellular capacity is predicted, especially due to the densification of the base stations. The solution to the capacity problem is using the shared spectrum, either license-exempt (LE) or lightly licensed, for providing cellular mobile or fixed services.

[0003] The shared spectrum is populated by access points and user devices implementing the IEEE 802.11 standard (collectively named stations - STA) and having specific rules for accessing a channel. However, such rules contradict the synchronous character of the systems using cellular standards.

[0004] In addition, some regulations enforce a behavior which is not suitable for the synchronous cellular standards, including conditional transmissions depending on the energy detection above a given threshold.

[0005] In order to overcome part of these problems, it has been proposed in the LTE community to use carrier aggregation by the UE (LTE User Equipment), such that always the operation on a licensed channel will be possible (see 3 GPP RP-131635) and will include the control signaling and user data. The un-licensed spectrum on the other hand, would be used only for best-effort downlink transmissions and eventual uplink transmissions. FIG.l summarizes this concept.

[0006] The discussions in the LTE community emphasized the problems of the above approach, the lack of predictability of the LTE system behavior being a strong barrier in the usage of the spectrum.

Furthermore, it should be noted that many smartphones already include an IEEE 802.11 -based wireless interface, so that the option for radio support of operation in shared bands is included therein. The work leading to this invention has received partial funding from the European Union Seventh Framework Programme (FP7/2007-2013) under Grant Agreement n° 318784.

SUMMARY OF THE DISCLOSURE

[0007] The disclosure may be summarized by referring to the appended claims.

[0008] It is an object of the present invention to enable reducing interference in a wireless communication network that is operative to serve both IEEE 802.11 standard compliant apparatus and non- IEEE 802.11 standard compliant devices.

[0009] Other objects of the present invention will become apparent as the description of the invention proceeds.

[0010] In accordance with a first embodiment of this invention there is provided a method for reducing interference induced by at least one wireless station operative in compliance with IEEE 802.11 standard and affecting at least one cellular entity operative in a cellular non-IEEE 802.11 compliant system, the at least one cellular entity being operative to enable transmission and reception of communications in a shared band wireless medium, wherein said method is characterized in that the at least one cellular entity is adapted to send at least one protecting message being in compliance with IEEE 802.11 standard, and to resend the at least one protecting message after at least one pre-defined time interval.

[0011] According to another embodiment, the at least one protecting message is a message defined by the IEEE standard 802.11 for reserving the shared band wireless medium and wherein the protecting message comprises a value set for a Network Address Vector (NAV) defining an interval of time during which IEEE 802.11 compliant devices listening on the wireless shared band medium, should defer from transmitting in the shared band wireless medium.

[0012] In a related embodiment, the at least one protecting message is a Clear to Send message.

[0013] By yet another embodiment, the at least one protecting message is transmitted along a frequency channel which is a primary channel for an IEEE 802.11 compliant wireless station.

[0014] In accordance with still another embodiment, the at least one protecting message is sent by an embedded STA (being a device that is compatible with relevant parts of IEEE 802.11 PHY and MAC sections). [0015] According to yet another embodiment, the embedded station is configured to switch between at least two frequency channels and to transmit the at least one protecting message on each channel at a different time.

[0016] In a related embodiment, the embedded station is associated with a different MAC address for each of the at least two frequency channels.

[0017] By another embodiment, at least one of the different MAC addresses is a unique MAC address only in a pre-defined geographical area.

[0018] According to another embodiment, at least one cellular entity present at the geographical vicinity of said embedded station is informed about at least one of the different MAC addresses associated with the embedded station.

[0019] In accordance with another embodiment, the non-IEEE 802.11 cellular entity is selected from a group that consists of: a base station, a relay and a cellular user device.

[0020] By still another embodiment, the at least one cellular entity is informed by another cellular entity that it has a capability to protect a channel against operation of another user device that complies with IEEE 802.11 standard.

[0021] In accordance with another embodiment, the duration of the pre-defined time intervals after which the protecting message is sent, is shorter than the duration of the interval of time defined by the NAV.

[0022] According to still another embodiment, the non-IEEE 802.11 cellular entity requires that another non-IEEE 802.11 cellular entity provides a protection for one or more specified channels against interferences caused by one or more operating IEEE 802.11 -compliant devices.

[0023] By yet another embodiment, the method provided further comprises a step of sending a request by the non-IEEE 802.11 cellular entity over a logical interface configured to enable inter-communications between base stations, that another non- IEEE 802.11 cellular entity provides protection for one or more specified channels against interferences caused by one or more operating IEEE 802.11 -compliant devices.

[0024] In a related embodiment, the logical interface is an LTE X2 interface.

[0025] According to another embodiment, a plurality of cellular user devices, presently operating within a specified geographical location, cooperate to provide protection against interferences caused by one or more IEEE 802.11 -compliant devices operating within said specified geographical area. [0026] In accordance with another embodiment, communications sent using the shared band wireless medium, comprise a subframe that includes the at least one protecting message and receive operation for radar detection.

[0027] By another embodiment of the present disclosure, information that relates to a subframe used for detecting a protected spectrum user is sent by the non-IEEE 802.11 compliant cellular entity to at least one other cellular entity.

[0028] According to a related embodiment, the protected spectrum user is a radar or a TV transmitter.

[0029] According to another aspect of the invention there is provided a method for operating in a dual connectivity mode that comprises the steps of:

enabling a user device to communicate with a first base station and a second base station and to be served by the second base station in at least one frequency channel belonging to a shared band wireless medium;

at the second base station, initiating a search for a free channel in the shared band wireless medium and sending a request that only the first base station will serve the user device;

sending a message by the user device or by the second base station to the first base station, announcing that the user device should temporarily be served only by the first base station;

at the second base station, if a free channel in the shared band wireless medium is found, determining whether to utilize the free channel found;

sending a message by the user device or by the second base station to the first base station, announcing that the user device may be served by the second base station.

[0030] By still another aspect of the present invention there is provided a method for operating a cellular system in a shared band wireless medium where a user equipment (UE) is capable to operate simultaneously in a cellular mode on at least one channel and in a mode compatible with the IEEE 802.11 standard on at least one another channel, and aggregate data being exchanged in the cellular and the 802.11 modes on different channels.

[0031] According to a related embodiment, at least one of the at least one channel used in a cellular mode is comprised within at least one licensed band.

[0032] In accordance with another embodiment, the UE is configured to operate in a cellular mode that is compatible with the LTE standard. [0033] According to another embodiment, the second base station serving the UE is adapted to select an operating mode for the shared band wireless medium that is either compatible with the cellular standard or with the IEEE 802.11 standard, depending on the throughput which can be achieved in a channel by adopting one of the two modes.

[0034] By yet another aspect of the present invention, there is provided a cellular communication apparatus, comprising:

a radio interface, configured for communicating over a wireless network with at least one user equipment or with at least one base station in a shared band wireless medium;

a communication interface, adapted for exchanging messages;

at least one processor, adapted to:

implement a cellular protocol for communicating in the shared band wireless medium; and

generate at least one protecting message being in compliance with IEEE 802.11 standard and to enable resending the at least one protecting message after at least one pre-defined time interval; and

a transmitter configured to transmit protecting messages in the shared band wireless medium.

[0035] According to another embodiment of this aspect of the invention, at least two protecting messages have at least one overlapping interval.

[0036] In accordance with another embodiment, the cellular communication apparatus is adapted to operate as a base station or as a user equipment.

[0037] According to still another aspect of the present invention there is provided a cellular communication apparatus, comprising:

a radio interface, configured for communicating over a wireless network with at least one user equipment or with at least one base station in at least one shared band wireless medium and in at least one licensed band;

a communication interface, adapted for exchanging messages;

at least one processor, adapted to:

implement a protocol compatible with IEEE 802.11 in at least one channel in a shared band and a cellular protocol for communicating in at least one another channel in a licensed band wireless medium; and

aggregate data being exchanged in the cellular and the 802.11 modes on different channels. [0038] In accordance with another embodiment of this aspect, the cellular communication apparatus is adapted to operate as a base station or as a user equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The drawings do not represent an exhaustive representation.

[0040] For a more complete understanding of the present invention, reference is now made to the following detailed description taken in conjunction with the accompanying drawings wherein:

FIG. 1 - Represents a proposal of LTE operation in 5GHz using Carrier Aggregation; FIG. 2 - Represents the LTE TDD frame structure;

FIG. 3 - Represents an example of a flowchart for bursty LTE data transmission; FIG. 4 - Represents an example of sharing 160MHz between LTE and IEEE 802.11; FIG. 5 - Represents an example for the protection of 80MHz of spectrum using CTS; FIG. 6 - Represents an example of overlapping protection;

FIG. 7 - Represents an example for using a single STA for the protection of a block of 80MHz;

FIG. 8 - Represents an example for spectrum sharing in the time domain;

FIG. 9 - Represents an example of UE dual connectivity;

FIG. 10 - Represents the base station architecture; and

FIG. 11 - Represents an embodiment of the UE architecture.

DETAILED DESCRIPTION

[0041] Embodiments of the invention are described hereinafter in conjunction with the figures.

[0042] In this disclosure, the term "comprising" is intended to have an open-ended meaning so that when a first element is stated as comprising a second element, the first element may also include one or more other elements that are not necessarily identified or described herein, or recited in the claims.

[0043] In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It should be apparent, however, that the present invention may be practiced without these specific details.

[0044] Terminology used in the following description is similar to the terminologies used in connection with the 3GPP LTE and IEEE 802.11 technologies. However, it should be understood that this fact does not limit in any way the scope of the present invention to be used with these particular technologies, but rather any other applicable cellular technology that may be used while implementing the present invention, is encompassed by the present invention.

Overview of LTE frame structure

[0045] The LTE TDD (Time Division Duplex) frame structure and its possible configurations, as described in the LTE standard 3GPP TS 36.211 VI 1.4.0, are used in the following description. Frame structure type 2 is applicable to TDD.

[0046] The LTE TDD frame structure is illustrated in FIG. 2. The frame duration is 10ms and comprises ten subframes having 1ms duration each, where the subframes may be used for downlink, uplink or a combination thereof within a certain (special) subframe.

[0047] As it may be seen in the following Table 1, there is always a special subframe, designated "S" before switching from downlink subframes (designated by "D"), to uplink subframes (designated by "U").

Table 1 (36.211 Table 4.2-2): Uplink-downlink configurations

[0048] The special frame includes three fields: DwPTS, which is reserved for downlink transmissions, GP, which is reserved as a guard interval, and UpPTS which is reserved for uplink transmissions. GP is never used for data transmission, while UpPTS is not used for data transmission in certain typical implementations. The duration of these two fields depends on the UL-DL (uplink-downlink) configuration and the type of the cyclic prefix (normal or extended). However, their minimum accumulated duration is above 0.14ms, which presents a considerable number of opportunities for IEEE 802.11 -based devices to start their transmissions (based on energy detection) and interfere with the LTE upcoming up-link and downlink transmissions. In addition, there are many other similar opportunities for example, ABS (Almost Blank Subframe) subframes or other DL or UL subframes, which are not used for data transmissions. [0049] The ACK/NAK messages that comply with the LTE technology are defined in a synchronous mode, so that cancelling transmissions of DL or UL subframes would lead to an avalanche of re-transmissions, rendering the LTE operation impossible when the licensed spectrum is not used.

[0050] For TDD, the Primary Synchronization Signal ("PSS") is transmitted by the eNB (base station that operates in accordance with the LTE standards) within the third OFDM (Orthogonal Frequency Division Multiplex) symbol at slot 2 (subframe #1) and slot 12 (subframe #6), while the Secondary Synchronization Signal ("SSS") is transmitted within the last OFDM symbol of slot 1 (subframe #0) and slot 11 (subframe #5). These subframes are transmitted to ensure backward compatibility with the UE.

[0051] Together, the PSS and the SSS signals carry information that allows cell identification.

[0052] The Master Information Block transmitted at subframe 0 every 10ms includes the system DL bandwidth indicated by the number of the resource blocks (identical to the UL TDD bandwidth) and by the System Frame Number (SFN).

[0053] In systems that are compatible with the LTE standards, the operator is identified by the first field in the SIB1 (System Information Block Type 1) reserved for the primary PLMN (Public Land Mobile Network). The first transmission of the SystemlnformationBlockTypel is scheduled in subframe #5 of the radio frames for which the SFN (System Frame Number) mod 8 = 0, and repetitions are scheduled in subframe #5 of all other radio frames for which SFN mod 2 = 0 (as defined in 3GPP TS 36.331 Vl l .5.0 (2013-09)).

[0054] The physical cell identity is also included in SIB1 and may be read by a downlink receiver of another eNB or by a UE. The downlink receiver is in fact a UE used for the receiving operation and is typically embedded within the eNB.

[0055] Two or more eNBs may communicate with each other by using the logical X2 interface over the backhaul system or by over-the-air communication. An eNB may have its own identifier; the operated cell(s) may be identified by a physical identifier or by a global identifier.

[0056] In the proceeding description, any suitable identifier may be associated in conjunction with the term "eNB". In addition, the term "eNB" as used herein, should be understood to optionally encompass at least one relay, even if such a relay is not mentioned specifically. Mechanisms Relevant to IEEE 802.11 standard

[0057] The IEEE 802.11 transmissions are conditioned by virtual channel sense, based on NAV (Network Address Vector), and by the CCA (Clear Channel Assessment) based on the LBT (Listen Before Talk) mechanism, using the energy detection at the PHY (physical) level. The term "sense" as used herein, is used to denote a scenario where prior to transmitting, a node first listens to the shared medium (such as listening for wireless signals in a wireless network) to determine whether another node is transmitting or not.

[0058] NAV actually represents the duration for which the wireless medium is reserved for communication and is set, updated or reset by a number of control frames (in IEEE 802.11 , the term "frame" refers to "message") and management beacons using the "Duration" field, having in general 16 bits, each bit representing Ιμε. Thus, the wireless medium may be reserved by most of the control messages for a duration of maximum 2 ¹⁶ (approximately 65ms). Non-exhaustive examples of control frames that include the "Duration" field are RTS (Request to Send) and CTS (Clear to Send).

[0059] The wireless medium may be reserved while using the NAV by different mechanisms as DCF (Distributed Coordination Function), PCF (Point Coordination Function) and HCF (Hybrid Coordination Function).

[0060] Some of the protection mechanisms, which cause an STA (device compatible with relevant parts of IEEE 802.11 PHY and MAC sections) that is a potential interferer, to defer any transmission for a known period of time are described in IEEE 802.11 -2012 section 9.23.

[0061] The IEEE 802.11η and IEEE 802.1 lac amendments introduce a multi- carrier (multi-channel) concept, in which the beacon transmissions and the virtual channel sense take place only on the primary channel, while the CCA takes place on all channels. The AP (IEEE 802.11 Access Point) cannot transmit along any channel if it was assessed by the virtual carrier sense that the 20MHz channel used by the primary channel is not free.

[0062] The time during which a channel is used for transmission is un-predictable and may be highly independent of the flavors of IEEE 802.11, due to the aggregation of data units (A-MPDU) within a single transmission or due to the use of PCF or HCF. However, when the main target of the cell is Internet access and the backhaul or the remote servers are slow, there is a good chance for larger gaps to occur between transmissions.

[0063] In the present disclosure all control frames or management beacons which may be used for setting the NAV for a specified duration, are referred to as "protecting messages".

Regulatory Requirements

[0064] Even though many frequency bands may be shared, the major focus of the description provided hereinafter is placed on the 5GHz band, which is characterized by having a high spectrum portion allocated for shared usage.

[0065] IEEE 802.11 standard define channelization for different regulatory domains in its Annex E.

[0066] The European requirements set in ETSI EN 301 893 Vl.7.1 (2012-06) require that a cellular equipment will check the energy in the operating channel every 10ms and refrain from transmissions if the channel is found to be occupied.

[0067] FCC Part 15 regulations on UNII (Unlicensed National Information Infrastructure) do not impose any medium access etiquette, being more suitable for the LTE deployment.

[0068] The operation in shared bands is un-protected by regulations, so that a cellular system should be adapted to address a number of challenges:

A. To select one or more free channel(s);

B. To protect itself from IEEE 802.11 potential users of the channel;

C. For autonomous operation in a shared band or in dual-connectivity, it is preferred that the cellular system will share a channel with another synchronous system using a similar frame structure. This is natural for LTE deployments having a good channel reuse factor;

D. To continuously assess the channel status and its suitability for operation; and

E. To enable continuous radar detection in the relevant range of frequencies.

Protected Spectrum Users

[0069] For spectrum users who operate in frequency bands for which the regulations offer protection, for example radars in 5GHz or TV transmitters under 800 GHz, the eNB should be able to measure the received energy within short time intervals and to assess the presence of such protected spectrum users, based on their cognitive properties, such as pulse duration range and pulse repetition ratio.

[0070] The presence of protected spectrum users may also be assessed by using the position information and a database indicating the occupied channels at the base station location.

[0071] Detection of radars implies that the radio is in the receive mode, i.e. does not transmit any energy.

Detection of Free Channels

[0072] Instead of addressing the problems associated with the requirement of sharing a channel between two substantially different technologies like IEEE 802.11 and LTE, therefore the approach preferred herein is that a channel is normally used for technologies of the same type.

[0073] This approach leads to two aspects: one is related to the protection of a channel used by cellular technologies against IEEE 802.11 -based devices and the second one is related to the operation of the LTE systems so that two LTE quasi- collocated systems are able to share a channel.

[0074] The in-device collocation of LTE and IEEE 802.11 is not considered, as in a typical case only one technology will be selected by the user, by the device or by the operator for use in a specific unlicensed/shared band.

[0075] Detection of free channels is based on scanning the channels that are not currently used by protected users, measuring the energy sensed by the eNB and determining if the channel is used by cells using the same technology, by IEEE 802.11- compatible systems or by other systems.

[0076] In addition, the operating mode of systems that are compatible with an IEEE 802.11 standard, i.e. 802.11 a, 802.11 n, 802.11 ac, etc. as well as their occupied spectrum may also be assessed.

[0077] According to an embodiment of the disclosure, a database is provided that comprises for each base station or access point, in addition to its location information, used channels and operator identifier, also an indication of the type of technology used, so that the free channels and the technology used in occupied channels may be assessed by the position of the eNB. Furthermore, methods for assessing whether a channel is occupied by transmissions from cells utilizing LTE technology are also provided. Detection of Other Systems Implementing Similar Technologies

[0078] Once the LTE base station has selected a channel in which the protected spectrum users do not operate, the DL receiver should detect specific signals transmitted by other base stations and/or user terminals (UEs) which implement the same technology as the base station or different ones.

[0079] Signals that are specific to the LTE technology are the primary and secondary synchronization signals, transmitted by the base station twice in every frame of the six central resource blocks in the channel. These signals are used by a UE to detect the presence of an eNB, synchronize with it and derive the cell identity therefrom.

[0080] If the base station is adapted to determine only the cell identity, it is enough to detect only one occurrence of PSS or SSS. By detecting both occurrences, the full synchronization information may be obtained.

[0081] Other signals which may be used in this process are the DMRS of the DL transmissions.

[0082] When a UE transmits data, it can also transmit the demodulation reference signals (UL DMRS), defined in 3GPP TS 36.211. These signals which demonstrate good correlation properties, may be detected even when the surrounding interference is high and their detection indicates that a LTE-compatible UE is transmitting at the channel.

[0083] UE presence may also be assessed based on the Sounding Reference Signals (SRS). It is interesting to note that the uplink part of the special subframe (UpPTS) has a short duration, e.g. one or two OFDM symbols, and may be used for the transmission of uplink SRS, DMRS and random access preambles, which are also characteristic of the LTE technology.

[0084] SRS generation is based upon a sequence having the following parameters: the sequence group number, base sequence number, cyclic shift, and the like.

Identifying the Operator

[0085] A further optional step in the method provided by the present invention is the identification of the operator that provides wireless access to the eNBs and UEs using the given channel.

[0086] Optionally, the LTE-compatible downlink receiver included in the eNB may use the PSS and SSS for achieving synchronization with another eNB, and then decode SIB1 for obtaining the PLMN, being the operator's code, therefrom. If the operator's code is different from its own provisioned code, indicating that the other eNB belongs to a different operator, the eNB may search for another channel in order to detect a channel for which the operator's code of the other eNB is identical to that of its own operator, thereby ensuring the both eNBs are operated by the same operator.

[0087] It should be noted however, that the detection by the downlink receiver can be done only if the eNB transmitter is not saturating the eNB receiver. Such detection may be carried out before starting the operation, or during the operation either by refraining from transmitting during the specific OFDM symbols or by entering a short previously announced dormant mode. A shifted synchronization in time domain by two symbols can avoid the collisions but has the disadvantage of increased interference when the Tx of one eNB overlaps with an Rx of another eNB.

[0088] By one possible embodiment of the present invention, the SRS generation can be used eventually during the UpPTS, based on specific reserved parameters for coding the information transmitted by a UE. Such information may include the PLMN identifier and information that relates to capabilities of operating in unlicensed/shared bands. Using the UE transmissions for identifying the PLMN may be used also in case that the eNB serving the UE, is hidden.

Protection of Operation in Shared Bands

[0089] The protection of a "victim" cellular system should be from the following potential aggressors:

1. Devices and APs using the IEEE 802.11 technology;

2. Devices and base stations using the same cellular technology and served by the same operator as the "victim" system;

3. Devices and base stations using the same cellular technology as the "victim" system while the victim system and the interfering entity are served by a different operator;

4. Devices and APs using a different technology.

[0090] The protection against IEEE 802.11 -based devices and APs utilizes techniques that are associated with the virtual channel sense. In order to achieve this goal, according to an embodiment of the present invention, each eNB and'UE operating in a shared band embeds an IEEE 802.11 STA (i.e. the relevant PHY and MAC functionality) for transmitting medium reservation messages in accordance with the IEEE 802.i l standard. [0091] For IEEE 802.11 APs based on IEEE 802.1 In or IEEE 802.11 ac, the virtual channel sense takes place only on a primary channel; if this channel is found to be busy, all other used channels will be considered busy as well. Therefore, according to this embodiment, it is preferred to send the medium reservation messages on the primary channel in case of IEEE 802.1 In or IEEE 802.1 lac system.

[0092] There is no virtual coexistence in case that an IEEE 802.11a device is operative at a channel used by IEEE 802.11η or IEEE 802.11 ac system as secondary channel, because in secondary channels, neither IEEE 802.1 In based devices nor IEEE 802.1 lac-based devices will apply virtual carrier sensing.

[0093] Normally, the coexistence based on CCA (energy detection) is not useful, as there is no guarantee that the eNB or UE will transmit continuously during the entire intended time and the detection threshold is a rather high power level. Non-continuous transmission happens frequently due to the high granularity of the data fragmentation relative to the subframe duration, the silent intervals for radar detection (if relevant) and the Tx/Rx GAP intervals.

[0094] According to another embodiment of the present invention, the method provided further comprises a step of enforcing protection by CCA if dummy data is transmitted (e.g. to fill all the subframes and symbols used by the eNB or the UE), while incurring the penalty of increased power consumption.

[0095] As a general principle used in the following description, at least the eNB includes an embedded IEEE 802.11 STA which is compatible with the IEEE 802.11 protocol PHY and MAC functionality needed for transmitting protection messages, i.e. control frames and management beacons.

Protection in Cases of Event-Driven Carrier Aggregation

[0096] FIG. 3 demonstrates the steps taken by an eNB prior to starting a downlink transmission in shared spectrum using the CA approach.

[0097] Prior to beginning a DL transmission, the eNB controller orders the embedded STA within eNB to acquire the medium using a control or management message providing protection.

[0098] The embedded eNB controller may also request (by using a message transmitted over the Uu interface, possibly sent within the licensed spectrum to the target UE(s)) to seize the shared medium for a given duration of time. The term "Uu" refers to the radio interface between eNB and UE. In turn, the UE controller requests the embedded IEEE 802.11 STA to carry out this task. Upon seizing the medium, the local IEEE 802.11 STA informs the eNB controller that the medium has been seized while the remote IEEE 802.11 STA informs the UE controller of its own medium seizure. In response, the UE controller communicates the event over Uu interface, preferably in the licensed spectrum, to the eNB. When the medium is seized by both entities (i.e. at the eNB location and at the UE location), the eNB sends at least several subframes that may comprise synchronization signals. A short CSI (Channel State Information) assessment may be carried out by the UE and the CSI feedback may be received by the eNB through the PUCCH (Physical Uplink Control Channel), preferably in a licensed band.

[0099] A somewhat similar process takes place if the transmission is initiated by the UE. According to this option, the UE requests (possibly while using the licensed spectrum or the shared spectrum) a wireless medium protection, at the eNB location. Only when the wireless medium is acquired by a successful transmission of a protection message at the eNB and the event has been reported back to UE, the UE will transmit data. The UE may also protect the medium at its location, with an IEEE 802.11 protection message, if it has the required capabilities to do so.

[00100] As may be noted from the above description, an asynchronous LTE transmission will consume a lot of time due to the required interactions, which in turn may result as being spectrally inefficient.

[00101] In order that a cellular entity will transmit, the embedded station should preferably provide continuous protection by following a process such as the one discussed below.

Continuous Protection

[00102] When applying the continuous protection process, the channel(s) are protected continuously from IEEE 802.11 aggressors.

[00103] This protection process should be carried out, as a minimum requirement, at the eNB location. However, in order to avoid cases wherein an aggressor device does not hear the protection messages sent by eNB, the UE may carry out its own local protection.

[00104] The first goal set for the protection mechanism at a given location is the protection of intervals during which no transmissions are made, or the transmissions' energy is too weak when integrated over the channel. These intervals are the receive subframes or transmit subframes with no data transmitted within all the symbols or within all the resource elements. A preferred way to protect these intervals is by applying virtual protection. The virtual protection may be achieved by sending IEEE 802.11 protecting messages while using the IEEE 802.11 PHYs, which are used in that band or in adjacent channels.

[00105] Preferably, the basic mode for sending protecting messages is that of IEEE 802.1 la, as IEEE 802.1 In and IEEE 802.1 lac are compatible therewith.

[00106] Given that all the devices that are compatible with the IEEE 802.11 a, IEEE 802.1 In and IEEE 802.1 In standards use a 20MHz channel (named primary channel) for the virtual channel occupancy detection, the protecting messages may be transmitted separately by the embedded STA on each of these channels, as shown in FIGs. 4 and 5, where for each frequency channel, one STA has been assigned for sending for example a CTS message to itself or to eNB, at both eNB and UE locations.

[00107] FIG. 4 depicts also a case where a 160MHz IEEE 802.1 lac system tries to operate in an 80MHz band (channels 52, 56, 60, 64), firstly used by an LTE system, while the primary IEEE 802.1 lac channel is neither one of the channels used by the LTE system, for example channel 44. In this case, it may be required that the embedded STA will send protecting messages along the primary channel utilized by the IEEE 802.11 ac system in the adjacent 80MHz frequency block (channel 44), not actually used by the LTE system.

[00108] The protecting messages are transmitted according to an embodiment of the invention in an overlapping mode, such that each protection message is transmitted before the protection duration of the previous transmitted message has been expired. This procedure is demonstrated in FIG. 6.

[00109] In the example demonstrated in FIG. 6, two LTE frames are presented, including 40 subframes / frame. A subframe is assigned in each frame for the transmission of a protection message in a given channel. The repetition period for the transmission of the protection message in each channel is one full frame (40 subframes), while the protection duration set by NAV is longer, thus creating an overlapping protection interval.

[00110] In other words, the interval extending between transmissions of the protection IEEE 802.11 frames (for example CTS) by the embedded STA along a given 20MHz frequency channel, is lower than the setting of the "duration" field of these messages. The effect of such message will be to set the NAV of the surrounding eNBs to a duration value which is higher than the repetition period of the protection messages.

[00111] The same embedded STA may be used in a time/frequency multiplex mode, as shown in FIG. 7, for an example where the protection target is a chunk of 80MHz. The same embedded STA can switch between frequency channels and transmit on each channel at a different time.

[00112] In order to avoid the reciprocal interference between the transmit LTE operation and the embedded STA transmissions; it is preferred to separate these two transmissions from each other in the time domain.

Different Channel Widths of the LTE and IEEE 802.11 Systems

[00113] Protection should preferably be carried out separately for each one of the potential interfering IEEE 802.11 compatible systems. If there are possible different channel widths for the primary channel, as in the case of the IEEE 802.11a standard which can operate with 5, 10, 20 MHz channels, the channel size of the protecting messages should also be one (or more) of 5, 10, 20 MHz, in order to correspond to the respective channel size.

[00114] The decision on the channel widths used for protection can be made either separately by the eNB and UE or by a mutual coordination.

[00115] In both cases, the required messages will be transmitted over the LTE Uu or Un (in LTE, the term "Un" refers to the interface between the donor eNB and a relay) interfaces, and the information fields in these messages may include the UE or eNB or cell identifier, which channels are being occupied by transmissions of systems that are compatible with IEEE standard(s), and/or the channels to be protected.

Overlapping Protection Areas

[00116] According to yet another embodiment of the present invention, in case those UEs that are operative within a cell area do not have the protection capability of an embedded STA, the eNB may request, through a message conveyed over the Uu or Un interface, another UE to send the protecting messages also in the channels used by the un-protected UEs.

[00117] One way of carrying out the latter embodiment is to include in the UE capability list, a field adapted to provide "protection capability" information. This field will be of help in differentiating between the two UE types. [00118] Furthermore, in order to carry out the above embodiment, preferably, one should be able to convey a message over the Uu/Un interface, informing the UE about additional channel(s) that needs to be protected.

Discontinuous Tx/Rx

[00119] When a UE enters sleep mode, the embedded STA may be requested by the UE to cease the protection operation, e.g. in order to reduce the power consumption of the STA.

[00120] However, the STA should become operational before the moment when the UE starts to operate in order to ensure that protection is maintained throughout the UE operating period.

Assignment of MAC Address

[00121] The system operation should preferably be consistent with the legacy operation of IEEE 802.11 -based systems, otherwise it might be ignored by real IEEE 802.11 compatible systems. A point of concern is the duplication of MAC addresses due to overlapping transmissions by the same embedded STA.

[00122] In order to avoid the above problem, different MAC addresses should be used for overlapping transmissions on a single channel and also for transmissions on different channels.

[00123] In the example demonstrated in FIG. 7 eight different MAC addresses may be required per eNB or per UE. These MAC addresses may not be globally unique, and it should suffice if they are unique within a given geographical area. They may be provisioned for the eNB own use and/or for the UEs arriving to that geographical area.

[00124] Another possibility is pre-allocation of a number of possible MAC addresses, which together form a pool of MAC addresses. Each eNB informs the neighboring eNBs over the X2 interface which addresses, out of the address' pool, it has already consumed (e.g. while sending a message that comprises the base station own identification and the associated Ethernet addresses for the embedded STA).

[00125] The distribution of MAC addresses to UEs may take place over the Uu (UE- eNB) interface or over Un (relay - UE interface).

[00126] Preferably, when the UE changes the serving eNB(s) it informs the new serving eNB which are the STA addresses that have already been assigned to it. If the new serving eNB assesses that the MAC addresses are already in use within its neighborhood, it will provide the UE (over the Uu Un interface) a set of new MAC addresses.

Combining Protection and Radar Detection Within the Same Subframe

[00127] The duration of a protection signal, based on the lowest IEEE 802.1 la data rate of 6 Mb/s (48 coded bits per symbol) is given by the PHY overhead (13 symbols) and the length of the RTS or CTS fields, that correspond to 4 symbols (20 bytes maximum). This total of 17 symbols requires, for 20MHz channel spacing, a transmission time of 55 μβ, while for a 5MHz channel spacing the transmission time will be 220μ8, which is less than the time period associated with of an LTE slot (500μ≤). The remaining time in a 1ms subframe may be used for radar detection.

Coordination of Silent or Protection Intervals

[00128] The silent intervals are mainly used for radar detection and should preferably be inserted to enable this functionality within those frequency channels where radar detection is required by regulations. These intervals may also be useful for performing CCA prior to sending protection messages.

[00129] Each system will assign repetitive silent intervals having a frequency and duration that depend on the radar cognitive parameters, such as duration of the pulse and its repetition rate, allowed delay of detection and acceptable probability of detection.

[00130] Reducing the inter-cell interference by the coordination of the silent intervals in which the radar detection will take place, may contribute to obtaining a more reliable detection.

[00131] The network-wide reservation of silent subframes, which can form a repetitive pattern, may be achieved through provisioning either by a central entity or by a distributed inter-eNB communication over the X2 interface. In both cases it is required that the silent subframes are identified.

[00132] In a case of a distributed communication, the eNB, when installed in an area, may seek for its neighboring eNBs and request their settings of the silent intervals. Based on these settings, the new eNB will program its own silent intervals in an identical mode.

[00133] In both cases, the synchronized time interval for both transmissions of the protection signal and radar detection can be bundled together and fit either into one of the subframes #1 or #2 which are common to all LTE TDD configurations or in one of subframes #7-9 which are common to 10ms Tx/Rx periodicity.

Collocation of eNBs

[00134] In case of eNBs collocation, the interference levels may be too high when the same frequency channel is used for both eNBs. The way to separate the interference is by channel separation or by time separation. For example, in case where a common frequency block is used, a negotiation process for determining the channels to be used by each eNB, should take place.

[00135] The negotiation process can take place over the X2 inter-base station interface and could be conducted as follows:

eNB A starts the negotiation process, by announcing its preferred frequency channel (each possible channel has an assigned number) and the numbers of the other possible channels to be used;

eNB B announces the number of a picked channel from the pool of remaining channels and informs if it needs more channels for its operation; eNB A picks, if needed, another channel and announces its number to eNB B;

The process continues until either there are no more channels to be picked or both eNBs' needs are satisfied.

[00136] When the frequency separation cannot resolve the inter-system interference generated by eNBs collocation, time separation should be applied. As a general rule, the subframes carrying the synchronization and control information should be kept operational for each eNB. This can be achieved by shifting the frame start and blanking (making silent) the subframes of the other system, which occur at the same time.

[00137] The example demonstrated in FIG.8 uses TDD configuration no. 3 for each eNB. Unfortunately, there are four such subframes in each TDD system. When there is a high number of subframes to be kept, a restriction on the available number of subframes for uplink transmissions is introduced.

[00138] This problem may be resolved if, in configurations using a 10ms switching- point periodicity, the number of relevant subframes will be reduced to two, as in the case of FDD (Frequency Division Duplex) frame type 1.

[00139] In addition, in some of the blanked subframes one system works in the downlink mode while the other one in the uplink mode. [00140] In the example of FIG. 8 subframes #0, #1, #5 and #6 were kept for DL transmissions, leaving only one subframe (#4) for uplink transmissions; the frame start of the second system was shifted by three subframes. In each system, subframes DO, D5, D6 and the special subframe SI are used. Subframes DO, D5 should preferably be always transmitted. More uplink subframes may be used if subframe D6 is not transmitted, as the synchronization can be done by using cells in the licensed spectrum. Subframe SI may also not be used for transmission.

Carrier Aggregation (CA)

[00141] In case that carrier aggregation is done as shown in FIG.l, the synchronization of the UE with the eNB can be done by using the licensed spectrum, hence there would be no essential need to transmit PSS and/or SSS and/or MIB and/or SIB1 in the un-licensed spectrum.

[00142] However, for this case also, there should be selected a free channel or a channel which can be shared with the cellular technology of interest.

[00143] As a minimal requirement, only the downlink traffic on the PDSCH (Physical Downlink Shared Channel) is transmitted along the shared spectrum.

[00144] For successful reception, the used channel should be protected at both the eNB and the UE locations. Protecting the channel at both the eNB and the UE locations is required for bidirectional use of the shared channel for both data and control transmissions in both directions.

[00145] In fact, CA can take place between cells on different used channels in the same shared band, in the same way in which is done for licensed bands. At the UE location, the primary and secondary channels assigned to a specific UE using the cellular technology, should be protected.

[00146] In case that the CA is done over two different shared spectrum bands, it would be required that the embedded STA is able to switch between the bands in order to protect each channel. In order to support such an operation, the information about the UE capability, should indicate the shared bands which are supported by the embedded STA.

Dual Connectivity

[00147] The UE operation in dual connectivity mode is shown in FIG. 9. In a typical situation, the UE should be connected to the MeNB (Master eNB), operating in licensed spectrum and will actually be served by a SeNB (Secondary eNB) operating at a shared spectrum. Nevertheless, the MeNB could also operate at the shared spectrum.

[00148] As this mode of operation is more demanding, the channel selection can include a step of evaluating the actual errors occurred when transmitting test data in both directions. This step may include the use of protection mechanisms, and use for the evaluation the actual error rate, time for transmission, user throughput, and the like.

[00149] In case that high interference is found at the SeNB using the shared spectrum, it is possible to hand-over the UE entire operation, from the SeNB to the MeNB, for the interval of time required to search for a new free channel.

[00150] In this case, a message should be sent by the UE to the MeNB informing the latter that due to the fact that the SeNB is busy searching for another operational channel, the UE requests a temporarily hand-over. Once the SeNB has resumed the operation, the UE will inform the MeNB that the normal operation can be resumed.

[00151] In another variant, in case of a channel search, the SeNB sends a message to the MeNB either through a UE using dual connectivity or directly over the X2 interface, announcing interruption of service and requesting handover of the served UEs to the MeNB. When the service becomes possible once again, the SeNB will inform the MeNB about this change and the UEs will be handed-over by the MeNB to the SeNB, while implementing a traffic forwarding mechanism.

Dual LTE and IEEE 802.11 Operation

[00152] There are a number of variants of the system presented herein, which may operate as a dual IEEE 802.11 -LTE system:

[00153] Variant 1 : A UE operates at a given time either in LTE or in IEEE 802.11 modes; in this case the UE shall indicate to the serving eNB its capability to support the IEEE 802.11 mode.

[00154] Variant 2: A UE makes aggregation of data exchanged in the LTE and the IEEE 802.11 modes on different channels, which may be located at the same or different bands. In this case, the UE should indicate to the eNB its capability of operating simultaneously in both modes.

[00155] Variant 3: A eNB operates in a shared band either in LTE or IEEE 802.11 mode, depending on the throughput which may be achieved in a channel(s) in each one of these modes; [00156] Variant 4: A eNB operates in a shared band in both LTE and IEEE 802.11 modes; in this case, the eNB should indicate to the UE having suitable capabilities, the selected channels for operation, the operational mode of each channel and the assigned primary and secondary channels for LTE mode.

[00157] The eNB or the UE may internally coordinate the switching of the embedded STA in order to support both modes of operation, e.g. protection in the LTE mode and communication in the IEEE 802.11 mode.

Interference From Transmitters Using Different Technologies

[00158] If the LTE system is interfered by other transmissions, it may try to cause those interfering transmitters to abandon the operation in the channel being interfered by executing continuous transmissions, using even dummy data for a limited period of time. Such transmissions should be announced to the neighboring eNBs which may be also affected, over the X2 interface.

[00159] Preferably, the radar detection, if required, should not be interrupted by the transmission of dummy data, i.e. silent intervals should still be inserted.

Base Station Implementation

[00160] A modified TDD base station radio architecture is illustrated in FIG. 10. In this figure, the base station modules include a Network Interface - 1001, providing the data connection and a Base Station Control Block 1002, including the LTE Control Plane and the Layer 2/Layer 3 processing of the LTE User Plane. For signal processing in accordance with the LTE technology signal processing block 1003 is used, while for signal processing using IEEE 802.11 technology signal processing block 1004 is used. The signal processing block 1004 can be used for protection only or for both protection and user connection using the IEEE 802.11 technology. Both signal processing blocks, receive and transmit the baseband signals from/to multiplexer 1010 which, under the eNB control, further connects them to radios 1006 and 1007, where one is operative at the shared Band 1 and the other is operative at another Band 2, which can be FDD or TDD, shared or licensed. The antennas 1005 connect the radios to the wireless medium. The eNB control block 1002 has also the function of routing the user data and the control plane data to the appropriate signal processing unit. [00161] A Memory block 1008, containing RAM and non- volatile memory (FLASH or ROM), is used by the eNB Control Unit 1002, and depending on the actual eNB implementation, may be used also by the Network Interface 1001.

[00162] A possible embodiment of the present invention is the use of an incumbent TDD or FDD base station as Master eNB and the described base station, operating within the shared spectrum, as Secondary eNB.

[00163] The IEEE 802.11 signal processing block may also be used for regular IEEE 802.11 operation.

UE implementation

[00164] FIG. 11 presents the resulting UE architecture. The central radio control, including the functions related to the Layer 2/Layer 2 User Plane and Control Plane as described in 3QPP TS 36.300 and radio activities, is located within a central processing unit 1102, which may also perform other high-layer user services, including running applications.

[00165] The user interfaces, such as the display, speaker, and microphone, are located within the user interface block 1101.

[00166] A memory block 1108, containing RAM and non- volatile memory (FLASH or ROM) is used by the central processing unit 1102, and depending on the actual UE implementation, may also be used by the user interfaces 1101.

[00167] For signal processing according to LTE technology the signal processing block 1103 is used, while for signal processing using the IEEE 802.11 technology, signal processing block 1104 is used. The signal processing block 1104 can be used for protection purposes only or for both protection and user connection using IEEE 802.11 technology. Both signal processing blocks, receive and transmit the baseband signals to multiplexer 1110, which, under the control of the central processing unit, connects them to the radios 1106 and 1107, one of which is operative at the shared Band 1 and the other operative at another Band 2, which can be FDD or TDD, shared or licensed.

[00168] Antennas 1105 connect the radios to the wireless medium. The central processing unit 1102 has also the function of routing the user data and control plane to the appropriate signal processing unit.

[00169] The IEEE 802.11 signal processing block may also be used for regular IEEE 802.11 operation. [00170] The present invention has been described using detailed descriptions of embodiments thereof that are provided by way of example and are not intended to limit the scope of the invention in any way. The described embodiments comprise different features, not all of which are required in all embodiments of the invention. Some embodiments of the present invention utilize only some of the features or possible combinations of the features. Variations of embodiments of the present invention that are described and embodiments of the present invention comprising different combinations of features noted in the described embodiments will be clear to persons of the art.

[00171] For example, the description of the hereinabove embodiments refers to LTE as an example of an applicable cellular technology. However, the same procedures mutatis mutandis may be applicable to other cellular technologies included in IMT- 2000 or IMT.Advanced or any evolution thereof.

[00172] The shared spectrum was exemplified for the case of 5GHz. However, it should be understood that the present invention also encompasses operation in other license-exempt or light licensed bands.

[00173] The protection was described hereinbefore against IEEE 802.11 interferers, but it should be understood by those skilled in the art that same mechanisms may be applied against other technologies operating in license-exempt or light licensed bands.

[00174] Although the description provided herein refers to the use of base stations, it should be understood that other central or distributed wireless transmission entities, such as access points, Node B, relays, etc., may also be used in a similar fashion to that of the present disclosure.

[00175] The examples provided demonstrate certain ways of carrying out the invention. It is to be understood that this invention is not intended to be limited to the examples disclosed herein and the scope of the invention is limited only by the following claims.