Technical Field

The present invention relates to methods, apparatus and computer programs for controlling a communication device. The exemplary and non-limiting embodiments of this invention relate generally to wireless communication systems, methods, devices and computer programs, and specific embodiments relate to full duplex transmissions on unlicensed radio spectrum, for example using the IEEE 802.11 family of radio access technologies or cellular technologies that use a request to send/clear to send message exchange.

Background

Significant research has gone into efficiently utilising the licence exempt/unlicensed spectrum to offload traffic from cellular and thus help meet the increasing number of data-intensive uses that are hosted by (licensed) cellular radio systems such as for example 3G and 4G radio access technologies (RATs). Commonly the unlicensed radio spectrum is referred to as the Industrial, Scientific and Medical (ISM) band and/or television whitespaces (TV WS) or more generically the shared band(s), though these are not exhaustive.

The wireless local area network (WLAN) family of standards (commonly the RATs specified by IEEE 802.1 lb/g/n/ac/ah) typically use an access point (AP) which aids in coordinating access of the ISM band by individual users to minimise interference which is wasteful of the limited bandwidth. Different nations define the ISM band a bit differently, but for WLAN the 2.4GHz ISM band is generally divided into multiple overlapped channels. For example, in China and Europe (excluding Spain and France) the 2.4-2.4835GHz band is divided into 13 channels, each with a bandwidth of 22MHz, which support 3 orthogonal channels at the same time. There has been increased research recently into enhancing spectral efficiency by utilising full-duplex communication in wireless local area networks (WLAN). Full-duplex communication is based on the principle that radios can transmit and receive simultaneously on the same frequency band despite the inherent self- interference problem. The self-interference problem is mainly caused by a large imbalance between the radio device's own transmit signal power and that of the signal power it receives; typically its transmit power is a few orders of magnitude larger than the intended received signal strength which tends to severely degrade the intended received signal.

Relevant teachings in this regard can be seen at the following references:

• ACHIEVING SINGLE CHANNEL, FULL DUPLEX WIRELESS COMMUNICATION; by Jung II Choiy, Mayank Jainy, Kannan Srinivasany, Philip Levis, Sachin Katti [Proceedings of the 16th Annual International Conference on Mobile Computing and Networking (Mobicom 2010)].

• FULL-DUPLEX WIRELESS COMMUNICATIONS USING OFF-THE-SHELF RADIOS:

FEASIBILITY AND FIRST RESULTS; by Melissa Duarte and Ashutosh Sabharwal [Proceedings of the 44 ^th Annual Asilomar Conference on Signals, Systems, and Computers, 2010].

• EXPERIMENT-DRIVEN CHARACTERIZATION OF FULL-DUPLEX WIRELESS SYSTEMS; by Melissa Duarte, Chris Dick and Ashutosh Sabharwal [submitted to IEEE Transactions on Wireless Communications, July 2011].

• EMPOWERING FULL-DUPLEX WIRELESS COMMUNICATION BY EXPLOITING DIRECTIONAL DIVERSITY; by Evan Everett, Melissa Duarte, Chris Dick, and Ashutosh Sabharwal [accepted to the 45 ^th Annual Asilomar Conference on Signals, Systems, and Computers, 2010].

• PUSHING THE LIMITS OF FULL-DUPLEX: DESIGN AND REAL-TIME IMPLEMENTATION; by Achaleshwar Sahai, Gaurav Patel and Ashutosh Sabharwal [Rice University technical report TREE 1104]. • EFFICIENT AND FAIR MAC FOR WIRELESS NETWORKS WITH SELF- INTERFERENCE CANCELLATION; by N. Singh, D. Gunarwardena, A. Proutiere, B. Radunovic, H. V. Balan, and P. Key.

• UK Patent Application GB 1206574.4 filed on April 13, 2012.

• UK Patent Application GB1208098.2 filed on May 9, 2012.

Figure 1 is reproduced from IEEE 802.1 lREVmbD12.0 and illustrates the current exchange when a source and destination utilise the carrier sense multiple access with collision avoidance (CSMA/CA) protocol for the distributed control function to access the unlicensed band channel during a contention window. Specifically, the source wishes to transmit to the destination and so listens to the channel for a distributed coordination function interframe space (DCF interframe space or DIFS). Assuming it hears no other station transmitting on the channel during the DIFS, the source entity then sends a request to send packet (RTS). The destination receives the RTS packet and waits a short interframe space (SIFS) to check that there are no other transmissions, and if the channel is still clear the destination sends a clear to send (CTS) packet. The source waits for another SIFS and if the channel remains clear it then sends its data. Upon reception of that data transmission, the destination entity awaits another SIFS and, assuming it receives and decodes the data correctly, the destination entity then sends its acknowledgement (ACK).

Another station (STA) is also shown at Figure 1 ; it may be waiting to send its own data transmission or not but it is used to show the purpose of the RTS-CTS exchange. Assume a first case in which this other station is spaced further from the source than from the destination such that it can hear source transmissions but not those of the destination. In this case, the other station hears the RTS and in response sets a network allocation vector (NAV-RTS) as shown, during which time the other station defers its own access of the unlicensed channel. It defers its access despite not hearing any CTS from the destination in reply to the RTS. In a second case, the other station is spaced further from the destination than from the source such that it can hear destination transmissions but not those from the source. In this second case, the other station hears the CTS and in response sets a network allocation vector (NAV-CTS) as shown, during which time the other station defers its own access of the channel. It defers its access despite not hearing any RTS from the source prior to the destination's CTS.

In this manner the RTS-CTS exchange solves the hidden node problem to help avoid collisions in the unlicensed band. But the length of the NAV is established for a given maximum length of the data transmission. If there is to be data also from the destination to the source it must go through an entirely new iteration with the data- sending destination then in the position of the source of Figure 1, which can only begin in a new contention window if there is no activity on the channel throughout the DIFS following the destination's ACK as shown. It is more efficient if both source and destination could engage in full duplex communications during the period the NAV protects the channel from collisions. But the channel is unlicensed spectrum and may not be always suitable for full duplex operations.

Summary

According to a first aspect of the present invention, there is provided a method for controlling a first communication device, the method comprising: sending to a second communication device a request to send message comprising an indication that data is intended to be sent in a full duplex mode; and in response to receiving in reply a clear to send message that indicates that the second communication device has data to send and is capable of the full duplex mode, sending a first data frame while receiving in the full duplex mode a second data frame from the second communication device.

According to a second aspect of the present invention, there is provided apparatus for controlling a first communication device, the apparatus comprising a processing system configured to control the first communication device to perform: sending to a second communication device a request to send message comprising an indication that data is intended to be sent in a full duplex mode; and in response to receiving in reply a clear to send message that indicates that the second communication device has data to send and is capable of the full duplex mode, sending a first data frame while receiving in the full duplex mode a second data frame from the second communication device.

According to a third aspect of the present invention, there is provided a computer program comprising a set of instructions which, when executed on a first communication device causes the first communication device to perform the steps of: sending to a second communication device a request to send message comprising an indication that data is intended to be sent in a full duplex mode; and in response to receiving in reply a clear to send message that indicates that the second communication device has data to send and is capable of the full duplex mode, sending a first data frame while receiving in the full duplex mode a second data frame from the second communication device.

According to a fourth aspect of the present invention, there is provided a method for controlling a second communication device, the method comprising: receiving from a first communication device a request to send message comprising an indication that data is intended to be sent in a full duplex mode; sending in reply a clear to send message that indicates that the second communication device has data to send and is capable of the full duplex mode; and sending a second data frame while receiving in the full duplex mode a first data frame from the first communication device.

According to a fifth aspect of the present invention, there is provided apparatus for controlling a second communication device, the apparatus comprising a processing system configured to control the second communication device to perform: sending, in reply to a request to send message that comprises an indication that data is intended to be sent in a full duplex mode received from a first communication device, a clear to send message that indicates that the second communication device has data to send and is capable of the full duplex mode; and sending a second data frame while receiving in the full duplex mode a first data frame from the first communication device.

According to a sixth aspect of the present invention, there is provided a computer program comprising a set of instructions, which, when executed on a second communication device causes the second communication device to perform the steps of: sending, in reply to a request to send message that comprises an indication that data is intended to be sent in a full duplex mode received from a first communication device, a clear to send message that indicates that the second communication device has data to send and is capable of the full duplex mode; and sending a second data frame while receiving in the full duplex mode a first data frame from the first communication device.

The processing systems described above may comprise at least one memory including computer program code and at least one processor.

There may be provided a computer readable memory tangibly storing a set of instructions as described above.

Further features and advantages of the invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only, which is made with reference to the accompanying drawings.

Brief Description of the Drawings

Figure 1 shows a prior art timing diagram showing time intervals and messages for a conventional WLAN source to access a WLAN channel and is background for how this conventional procedure may be adapted according to these teachings for full duplex operations;. Figure 2 shows an example of a timing diagram similar to Figure 1 but adapted according to a first embodiment of these teachings such that neither the full duplex data transmissions nor the full duplex ACKs need to be aligned;

Figure 3 shows an example of a timing diagram similar to Figure 1 but adapted according to a second embodiment of these teachings in which timing of the full duplex data transmissions is such that they are aligned;

Figure 4 shows an example of a timing diagram similar to Figure 1 but adapted according to a third embodiment of these teachings in which timing of the full duplex ACKs is such that they are aligned;

Figure 5 shows an example of a timing diagram similar to Figure 1 but adapted according to a fourth embodiment of these teachings such that the second station STA2 sends its ACK of the STA1 data immediately after STA2 completes sending its own data transmission;

Figures 6A-B each show logic flow diagrams that illustrates from the perspective of the different devices (STA1 and STA2) shown in Figures 2-5 the operation of a method, and a result of execution of computer program instructions embodied on a computer readable memory, in accordance with certain exemplary embodiments of these teachings; and.

Figure 7 shows a non-limiting example of a simplified block diagram of two devices in wireless communication with one another and are exemplary electronic devices suitable for use in practising some example embodiments of these teachings.

Detailed Description

While the specific examples presented below are in the context of the unlicensed band and the IEEE 802.11 wireless local access network (WLAN) radio access technology (RAT), these are not limiting to the broader teachings of the invention which may be applied with similar advantages using other RATs apart from WLAN and the IEEE 802.11 family of standards. In RATs developed for accessing unlicensed frequency bands there is typically some exchange similar to the RTS-CTS detailed for Figure 1 to avoid collisions with a hidden node. Other non-WLAN systems may use a different name for this exchange, and/or for their channel access procedures. Any of these may be functionally similar to those detailed below for WLAN systems, and such different terminology does not remove implementations in other RATs from falling within the teachings herein. Additionally examples of methods according to the present invention can be applied for radio techniques such as LTE-based D2D (device to device) or LTE-based local area solution which may utilise random access mechanisms for exchanging data and control messages. Potentially the LTE D2D may be deployed to the unlicensed band, to licensed cellular band or as a part of a communication system designed for Public Safety operation. Similar RTS/CTS exchanges may be adopted for the above mentioned LTE based systems as well as in LTE-Advanced radio access technologies.

According to exemplary embodiments of these teachings, the RTS-CTS exchange is used to evaluate the radio link for suitability of full duplex operation of the data transmission that follows. In the four different example embodiments below, new RTS and CTS frames are defined for this purpose. Figures 2 to 5 illustrate single packet transmissions by each of the two stations STA1 and STA2, but these can be readily extended to multiple packet transmissions. Also a single packet transmission may multiplex several packets into one packet transmission opportunity.

One protocol for such multi-packet transmissions in the IEEE 802.11 framework that might be used alongside these teachings is enhanced distributed channel access (EDCA). Under EDCA there is a bias toward sending higher priority traffic due to the different wait times as compared to those of Figure 1. Specifically, there is an arbitration interframe space (AIFS) for packets with different access categories. As currently defined, AIFS[Access Category] = AIFSN[AC] x aSlotTime + aSIFSTime; and so for a given category the AIFS can be shorter than a DIFS but not shorter than a SIFS, while another category may have its AIFS shorter than a SIFS. Additionally, under EDCA the station gets contention-free access for the duration of a transmission opportunity (TXOP) for transmitting its data, in multiple frames if it prefers.

Figures 2 to 5 are each similar to Figure 1 but show only the RTS-CTS handshake and a bi-directional full duplex data exchange with associated ACKs. Other SIFS which are not shown, the DIFS and the NAVs shown in Figure 1 are substantially similar when applied to Figures 2 to 5 unless stipulated otherwise in Figures 2 to 5. That Figures 2to 5 have two stations STA1 and STA2 in place of the Figure 1 source and destination is of no account; two STAs provide more clarity than describing a destination as sending data in a full duplex mode and so in practice an access point AP may be in the position of either STA shown at Figures 2 to 5.

The example of Figure 2 is described first and afterwards the examples of Figures 3 to 5 are described to the extent that they depart from the example of Figure 2. Notably different from Figure 1 is the RTS frame and the CTS frame, which in Figures 2 to 5 are denoted as RTS-FD 202 and CTS-FD 206 to make the distinction (FD=full duplex). The RTS-FD message 202 includes a full duplex indication 202A at the start (though in other embodiments this indication may be signalled at any position in the frame) and a self-channel estimation 202C at the end of the conventional RTS 202B message. In this conventional portion 202B, the STA1 indicates the estimated duration of the data transmission 208 it expects to send. Sent by STA1 in Figure 2, the full-duplex indication 202A in the RTS-FD 202 is used to query STA2 in terms of data availability (whether STA2 even has data to send to STA1) and also about its full-duplex transceiver capability (whether STA2 is full- duplex capable on this channel).

STA2 waits a SIFS 204 (or possibly an AIFS in other embodiments) and, if the channel remains clear, it replies to the RTS-FD 202 with a CTS-FD 206, if in fact it is full duplex capable and has data to send to STA1. The CTS-FD message 206 includes a full duplex indication 206A at the start and also a self-channel estimation 206C at the end of the conventional CTS 206B message. The full-duplex indication 206A in the CTS-FD 206 indicates that the STA2 full duplex capability and its need for full duplex transmission between the RTS-FD transmitter at the STAl and the CTS-FD transmitting STA2. The CTS-FD 206 also has a self-channel estimation 206C at the end of this message 206.

In the Figure 2 example, STA2 will include the following in the CTS-FD message 206. If STA2 does not have data to send to the RTS-FD 202 transmitter (STAl), it will indicate that in the FD indication field 206A of the CTS-FD 206. This informs the sender of the RTS-FD (STAl) that it does not need to activate its receiver during its own transmission of data at 208. If instead STA2 does have data to send, it estimates the duration of that expected transmission 210 by combining the duration information from the conventional portion 202B of the RTS-FD frame 202 and sets this value to the CTS-FD duration field in the conventional portion 206B of the CTS-FD message 206.

In an embodiment, the duration field values in the RTS-FD 202 and in the CTS-FD 206 include the duration of the respective self-channel estimation 202C, 206C. This allows the STAl to begin sending its data frame 208 one SIFS following the end of the self-estimation 206C of the CTS-FD frame 206 that was sent by STA2. In the case of an EDCA TXOP, the duration of the TXOP window can also be used to update this duration information.

In one exemplary embodiment, in addition to the self-channel estimation 202C, 206C by the STAl and STA2 as shown in Figure 2, STAl can perform a signal to noise and interference ratio (SINR) estimation from the RTS-FD 202 it receives and similarly STAl can do the same from the CTS-FD 206 that it receives. Based on the self-channel estimation 202C, 206C and the SINR estimation, the STAs can more precisely evaluate the full duplex possibility between them on the wireless link. If the conditions for the full duplex transmission are fulfilled for STA1, it indicates the FD enablement in the physical layer convergence protocol (PLCP) header 208A which is appended by STA1 prior to its data transmission 208. STA1 also updates in the PLCP header 208A the frame duration value according to the information in the RTS-FD frame 202 and the CTS-FD frame 206, including the required time for the ACK transmissions 212, 214. As will be seen, the different examples of Figures 2 to 4 have different timings for these ACKs. Depending on the protocol, the ACKs may be transmitted in half duplex manner, and in this case the various duration fields should correctly reflect the relevant timing.

If the full duplex link evaluation was negative, such as from the STAl 's self estimation 202C or from its SINR check of the CTS-FD frame 206 it received from STA2, then STA1 can prevent the full duplex transmission from STA2 by indicating that in the PLCP header 208A. But even if STA1 indicates in the PLCP header 208A that the full duplex transmission is allowed, STA2 can choose not to transmit in full duplex mode if the determination of STA2 from its self estimation 206C is that the link does not support it. In this case the STA1 would have its receiver active and prepared for full duplex operation when it sends its data 208, but so long as STA1 does not detect any transmission for it from STA2 within some specified time it can close out its receiver for the remaining duration of its transmission 208. Such a specified time may be for example the synchronisation sequence of STA2.

To sufficiently attenuate a self-channel interference signal at the receiver, a periodic self-channel sounding is often required. These teachings incorporate such a self-channel sounding mechanism into the RTS-FD frame 202 and into the CTS-FD frame 206. Interference on the channel may for example be estimated from the pilot sequence which is placed at the end 202C, 206C of those frames 202, 206 by the device that transmits that same pilot sequence. Alternatively these pilot sequences may be within the body 202B, 206B, but Figure 2 shows them as distinct for clarity of explanation. In one example embodiment (shown in Figure 3 as 218A-B) the STA may send, prior to the RTS-FD transmission, a so called null data packet (NDP) sounding packet which has no specific timing relation to the RTS-FD transmission. This NDP is used in 802.1 1 to send a channel sounding to the intended destination address. In case of full duplex transmission, such an NDP message can be used for self- interference measurement, e.g. by setting the destination address to be the transmitter address and adding a self-channel estimation field to the message. Potentially a new NDP type for the full duplexing purpose may be specified to differentiate it from the conventional NDP format. Alternatively such self-channel estimation could be made with a CTS-to-Self (in which the destination address is the transmitter address) message with a self-channel estimation field added as described above. Reference numbers 218A and 218B at Figure 3 represent either the self addressed NDP or the CTS-to-self message that in these embodiments are sent by STA1 and STA2 respectively, and used by those same stations for assessment of the channel for full duplex mode operations. By utilising the above methods for self-channel estimation, the transmitter of the pilot sequences or NDP could potentially omit the self-channel estimation part 202C from the RTS(-FD) message 202 or additionally or alternatively omit the self-channel estimation part 206C from the CTS(-FD) message 206.

By assigning the self-channel sounding pilots to the end of the frame or inside the frame body after synchronisation and PLCP header, self-interference estimation can be guaranteed to be interference-free from the transmission of other stations that are in communication range. Additionally, having periodic self-interference channel sounding associated with the RTS-FD frame 202 and the CTS-FD frame 206 frame formats enables the STAs to use full-duplex transmission in more dynamic channel conditions than is assumed possible in certain of the full-duplex references mentioned in the background section above.

It is known in general to perform self-interference signal attenuation separately in both analog and digital processing domains (see references cited in the background section). Analog domain processing typically does not impose any specific constraints for pilot signals. However, for digital domain processing it is preferable to have self-channel sounding pilots which are flat in the frequency domain and orthogonal in the code-domain. The frequency- flat property enables the channel to be estimated in the frequency domain with different self-channel estimation strategies. Similarly, orthogonality in the code domain makes it simpler to separate the self-interference channels for the case of multi-antenna transmission. All of these techniques can be used by the STAs for the channel self-estimation using the pilot sequences at 202C and 206C.

Also shown at Figure 2 is a full duplex header 208B, shown for clarity of this description as being distinct from the PLCP header 208A. In one embodiment this header 208B carries information about timing that differs from conventional WLAN practice, and is useful for informing third parties such as the hidden node ("other" in Figure 1) of when the current exchange between STA1 and STA2 will end. As specifically shown at Figure 2, the data frame 208 from STA1 and the data frame 210 from STA2 have different lengths, and so in Figure 2 at least their respective ACKs 214, 212 may finish at different times. Or the earlier ACK1 transmission 212 may include an updated duration of the transmission so as to protect the reception by STA2 of the later ACK2 transmission 214. Additionally, in case of a fragmented protocol data unit (PDU) transmission, the ACK2 may have an updated duration due to the transmission of the next fragment of the data packet. The duration difference between ACK2 and ACK1 is interpreted as an extension to the DIFS period 216, depicted as FD-DIFS 206-FD at Figure 2. For the case where multiple data transmissions follow one after the other according to an EDCA TXOP, the FD-DIFS 216-FD should be chosen so that both transmissions are synchronised to end by the end of the TXOP as in normal EDCA TXOP operation. Any of those non-conventional timings can be indicated in the PDLP header 208B so that any third parties/hidden nodes can know the timing when they may again contend for the unlicensed band channel. In one non-limiting example, the timing relations between the transmission of the data frame 208 from STA1 and the data frame 210 from STA2 can be specified as follows:

The full duplex transmission of STA2 shall begin N symbols after the transmission of the PLCP header 208B for the data frame 208 from STA1. The value for N is selected to be sufficiently large so as to enable decoding of the control part for that data transmission 208 from STA1 (where N is a positive integer).

With respect to the Figure 2 timing relations between the data frames 208, 210 and their respective ACKs 214, 212, this allows the STA2 to transmit its ACK1 212 to the STA1 after a SIFS1 period following the data frame 208 being ACK'd, while also allowing the STA1 to respond with its own ACK2 214 after a SIFS2 period following the data frame 210 that is being ACK'd. The transmission time mismatch between these two ACKs 214, 212 and the following DIFS period 216 is accounted for with the flexible-length FD-DIFS period 216-FD.

Figure 3 shows a timing diagram similar to that of Figure 2 but showing a second embodiment in which the lengths of the data transmissions 208, 210 from STA1 and STA2 are matched. Specifically, the transmission length of the data frame 210 from STA2 is adjusted to end at the same time as the data frame 208 from STA1. Both ST As can send their ACK 214, 212 at the same time (one SIFS after the data frame 208, 210 being ACK'd), and the next contention window can begin one DIFS after the full duplex ACKs. In this case, STA2 uses the duration indication given by STA1 in the body 202B of the RTS-FD message 202 as a constraint on how much data it can send in its data frame 210.

Figure 4 shows a timing diagram similar to that of Figure 2 but showing a third embodiment in which the feedback transmissions 214, 212 for the respective data frames 208, 210 are matched in time and fully duplexed. In this case, a FD-SIFS period 204-FD is imposed following whichever of the data frames ends first, which in the example of Figure 4 is frame 208. The value for the FD SIFS period 204-FD is derived from the transmission time length difference of these two data frames 208, 201, including headers and the difference in the transmission start times. This embodiment enables the ACKs 214, 212 to be transmitted at the same time and also for there to be a normal DIFS period after the ACKs until the next contention period begins.

Figure 5 shows a timing diagram similar to that of Figure 2 but showing a fourth embodiment in which the STA2 can reply immediately with its ACK 212 of the data frame 208 it received once it completes sending its own data frame 210, providing a minimum threshold time Tp has passed from the end of the data frame 208 being ACK'd. This minimum threshold time ensures sufficient processing time to decode the data frame 208 being ACK'd, and can for example be specified to be some value of K microseconds. The same minimum threshold time TP is also imposed for the ACK 214 sent by STA1 for the data frame 210 it received. Since in the Figure 5 embodiment the ACKs 214, 212 are not aligned in time, a normal DIFS period 216 is imposed following the later-sent ACK 214 and an extended DIFS-FD period 216-FD is imposed following the earlier-sent ACK 212 before the next contention window can begin.

Different embodiments of these teachings provide the technical effects of avoiding the hidden terminal/hidden node problem while also providing ACK protection. They also enable sufficient measurements to be made for the communicating devices to check whether the full duplex communication is feasible on the current radio link between them. And advantageously from a control overhead perspective these embodiments require no pre-configuration of the link or any a priori knowledge for using full duplex on the unlicensed band.

Figures 6Aand 6B each show logic flow diagrams which summarise some example embodiments of the invention. Figure 6A illustrates certain embodiments of these teachings from the perspective of the device which sends the RTS-FD frame 202, while Figure 6B illustrates similarly from the perspective of the device which sends in reply the CTS-FD frame 206. Any of the apparatus implementing any of Figures 6A and 6B may be implemented by the entire device/system (STA1, STA2, a non-STA AP, or a STA-AP for example), or by one or more components thereof, such as a modem, chipset, or the like. Each of Figures 6A and 6B may be considered to illustrate examples of the operation of a method for operating a device, and a result of execution of a computer program tangibly stored in a computer readable memory, and a specific manner in which components of an electronic device are configured to cause that electronic device to operate.

Such blocks and the functions they represent are non-limiting examples, and may be practised in various components such as integrated circuit chips and modules, and the exemplary embodiments of this invention may be realised in an apparatus that is embodied as an integrated circuit. The integrated circuit, or circuits, may comprise circuitry (as well as possibly firmware) for embodying at least one or more of a data processor or data processors, a digital signal processor or processors, baseband circuitry and radio frequency circuitry that are configurable so as to operate in accordance with the exemplary embodiments of this invention.

Such circuit/circuitry embodiments include any of the following: (a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and (b) combinations of circuits and software (and/or firmware), such as: (i) a combination of processor(s) or (ii) portions of processor(s)/software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone/UE, to perform the various functions summarised at Figure 3) and (c) circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present. This definition of "circuitry" applies to all uses of this term in this specification, including in any claims. As a further example, as used in this specification, the term "circuitry" would also cover an implementation of merely a processor (or multiple processors) or portion of a processor and its (or their) accompanying software and/or firmware. The term "circuitry" also covers, for example, a baseband integrated circuit or application specific integrated circuit for a mobile phone/user equipment/STA or a similar integrated circuit in a network access node/AP or other network device.

First consider Figure 6A which is from the perspective of the device that sends the RTS-FD message 202, termed for clarity a first communication device. This RTS message is sent to some second device and includes an indication that data is intended to be sent in a full duplex mode. At block 604, after sending the RTS frame, the first device receives in reply a CTS message 206 that indicates that the second device has data to send and is capable of the full duplex mode, and in response to receiving that CTS message the first device sends a first data frame while receiving in the full duplex mode a second data frame from the second device.

Further portions of Figure 6 A summarise some but not all of the above exemplary embodiments. Block 606 stipulates that the first data frame comprises a header that confirms the full duplex mode for the first and second data frames. This is further detailed at block 608, where both the RTS message and the CTS message further indicate a frame duration value, and the header of the first data frame comprises an updated frame duration value. For any of the embodiments summarised at Figure 6A, block 610 details that the first device assesses suitability of the full duplex mode by measuring the pilot sequence it sends to itself, either prior to the RTS message (for example, in a self addressed NDP or a CTS-to-self message separate from and prior to the RTS-CTS exchange) or the pilot is within the RTS message itself. Or in another embodiment, the first device can assess this suitability from a NDP it sends, such as for example prior to the RTS message. And in summary of the embodiment shown at Figure 2, block 612 shows that the first device sets a start time for a next contention window to begin one normal DIFS following a latest one of the ACKs to the first and second data frames. In this embodiment, each of the ACKs is spaced one normal SIFS from an end of the first or second data frame to which they correspond. Figure 6B is from the perspective of the device that sends the CTS-FD frame 206 in reply to receiving the RTS-FD frame 202. For convenience consider this the second communication device. At block 652 it receives from a first device a RTS message comprising an indication that data is intended to be sent in a full duplex mode. At block 654 it sends in reply a CTS message that indicates that the second device has data to send and is capable of operating in the full duplex mode. Then at block 656 the second device sends a second data frame while receiving in the full duplex mode a first data frame from the first device.

Further portions of Figure 6B summarise some but not all of the above exemplary embodiments. At block 658 the sending of the second data frame (sent in block 656) is conditional on but not required by the first data frame comprising a header that confirms the full duplex mode for the first and second data frames. In block 660 is the embodiment in which the second device assesses suitability of the full duplex mode by measuring the pilot sequence it sends to itself, either prior to the CTS message (for example, in a CTS-to-self message separate from and prior to the RTS-CTS exchange) or the pilot is within the CTS message itself. Or in another embodiment the second device can perform this assessment using a NDP it sends itself. Block 662 summarises the different embodiments for timing. In the second embodiment detailed above with respect to Figure 3, the second device constrains the second data frame to terminate at the same time as the first data frame. In the third embodiment detailed above with respect to Figure 4, the second device sends an ACK to the first data frame one SIFS after an end of the second data frame. And finally in the fourth embodiment detailed above with respect to Figure 5, the second device sends an ACK to the first data frame immediately following an end of the second data frame, conditional on a minimum processing time TP having elapsed.

Reference is now made to Figure 7 for illustrating a simplified block diagram of various electronic devices and apparatus that are suitable for use in practising some example embodiments of this invention. In Figure 7 there are only STA1 /first device 10 and STA2/second device 20, but either or both may further have a connection to a cellular wireless network through a cellular network access node such as a NodeB or eNodeB or other type of base station which can further provide connectivity with a broader network (e.g. another cellular network and/or a publicly switched telephone network PSTN and/or a data communications network/Internet).

The first device 10 includes processing means such as at least one data processor (DP) 10A, storing means such as at least one computer-readable memory (MEM) 10B storing at least one computer program (PROG) IOC, and communicating means such as a transmitter TX 10D and a receiver RX 10E for bidirectional wireless communications with the second device 20 via one or more antennas 10F. Also stored in the MEM 10B at reference number 10G is the first device's rules for using the RTS/CTS exchange to enable full duplex communications in an IEEE 802.11 radio access technology, or other RAT, on the unlicensed band as is detailed further above.

The second device 20 also includes processing means such as at least one data processor (DP) 20A, storing means such as at least one computer-readable memory (MEM) 20B storing at least one computer program (PROG) 20C, and communicating means such as a transmitter TX 20D and a receiver RX 20E for bidirectional wireless communications with the first device 10 via one or more antennas 20F. The second device 20 may also have software at 20G for using the RTS/CTS exchange to enable full duplex communications as noted immediately above.

While not particularly illustrated for the first device 10 or for the second device 20, those devices are also assumed to include as part of their wireless communicating means a modem which may be inbuilt on an RF front end chip within those devices 10, 20 and which also carries the TX 10D/20D and the RX 10E/20E.

At least one of the PROGs lOC/lOG in the first device 10 is assumed to include program instructions that, when executed by the associated DP 10A, enable the device to operate in accordance with the exemplary embodiments of this invention, as detailed above particularly with respect to Figure 6A. The second device 20 also has software 20C/20G stored in its MEM 20B to implement certain aspects of these teachings as detailed above particularly with respect to Figure 6B. In this regard, the exemplary embodiments of this invention may be implemented at least in part by computer software 10G, 20G stored on the MEM 10B, 20B which is executable by the DP 10A of the first device 10 and/or by the DP 20A of the second device 20, or by hardware, or by a combination of tangibly stored software and hardware (and tangibly stored firmware). Electronic devices implementing these aspects of the invention may not be the entire first and second devices 10, 20, but exemplary embodiments may be implemented by one or more components of same such as the above described tangibly stored software, hardware, firmware and DP, modem, system on a chip SOC or an application specific integrated circuit ASIC.

In general, the various embodiments of either device 10, 20 can include, but are not limited to personal portable digital devices having wireless communication capabilities or more generally communication devices, including but not limited to user equipments and terminals, multi-band cellular telephones with WLAN, LTE and/or LTE-A (or other cellular) capabilities, navigation devices, laptop/palmtop/tablet computers, digital cameras and Internet appliances, as well as machine-to -machine devices which operate without direct user action.

Various embodiments of the computer readable MEMs 10B, 20B include any data storage technology type which is suitable to the local technical environment, including but not limited to semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory, removable memory, disc memory, flash memory, DRAM, SRAM, EEPROM and the like. Various embodiments of the DPs 10A, 20A include but are not limited to general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), and multi-core processors. The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.