Communication devices and communication methods

Abstract

A fourth communication device, e.g. an AP, is configured to communicate with a first communication device in coordination with a second communication device that is configured to communicate with a third communication device. The fourth communication device comprises circuitry configured to transmit a data unit to the first and the third communication device, the data unit being transmitted using different resource units to which different steering matrices have been applied, the different steering matrices being computed from different channel state information (CSI) sets; receive an interference feedback (IFB) response from the second and / or the third communication device, the IFB response including interference information indicating an interference level of the different resource units observed by the third communication device; evaluate the IFB response and optionally update the steering matrices and / or the allocation of steering matrices to resource units to be used for transmitting a subsequent data unit to the first communication device; and communicate with the first communication device using the optionally updated steering matrices in coordination with communication of the second communication device with the third communication device.

Description

Applicants: Sony Group Corporation 13.03.2025 1-7-1 Konan 4727P373WO - SK Minato-Ku Tokyo 108-0075 JAPAN Sony Europe B.V. The Heights, Brooklands Weybridge, Surrey KT130XW UNITED KINGDOM COMMUNICATION DEVICES AND COMMUNICATION METHODS BACKGROUND FIELD OF THE DISCLOSURE

[0001] The present disclosure relates to communication devices, in particular for use with coordi-nated beamforming. Further, the present invention relates to corresponding communica- tion methods. DESCRIPTION OF RELATED ART

[0002] Low latency and extremely high throughput are required for future wireless extended real-ity (XR) applications due to high definition video transmission for users’ movable positions at each time. For example, a Packet Error Rate of less than 0.1 % of and a data rate of200 Mbps may be desired for future XR applications, and data of one image may have to be sent within 16.6 msec at the latest if a Fps (frame per sec) of 60 Hz is assumed. Car- rier sense mechanism is adopted in WLAN as part of channel access, but is does not suf- ficiently ensure that each station (STA; herein generally called “communication device”) can transmit data whenever data traffic arrives at the STA. Furthermore, there are situa- tions in which a communication between a fourth communication device, e.g. an access point (AP), and an STA interferes low latency communication between two STAs, e.g., on a direct link such as a point-to-point (P2P) link.

[0003] The “background” description provided herein is for the purpose of generally presentingthe context of the disclosure. Work of the presently named inventor(s), to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admit- ted as prior art against the present disclosure. SUMMARY

[0004] It is an object to ensure low latency and / or extremely high throughput communication be-tween two communication devices and avoid or at least reduce interference of such a communication that may occur during parallel communication between a fourth communi- cation device and another communication device. It is a further object to provide devices, communication methods as well as a corresponding computer program and a non-transi- tory computer-readable recording medium for implementing the communication methods.

[0005] According to an aspect there is provided a fourth communication device configured tocommunicate with a first communication device in coordination with a second communica- tion device that is configured to communicate with a third communication device, the fourth communication device comprising circuitry configured to: - transmit a data unit to the first and the third communication device, the data unit being transmitted using different resource units to which different steering matrices have been applied, the different steering matrices being computed from different channel state information (CSI) sets;- receive an interference feedback (IFB) response from the second and / or the third communication device, the IFB response including interference information indicating an interference level of the different resource units observed by the third communication de- vice; - evaluate the IFB response and optionally update the steering matrices and / or the allocation of steering matrices to resource units to be used for transmitting a subsequent data unit to the first communication device; and - communicate with the first communication device using the optionally updated steering matrices in coordination with communication of the second communication device with the third communication device.

[0006] According to a further aspect there is provided a third communication device configured tocommunicate with a second communication device in coordination with a fourth communi- cation device that is configured to communicate with a first communication device, the third communication device comprising circuitry configured to: - receive a data unit from the second communication device and a fourth communi- cation device, the data unit at least from the fourth communication device being transmit- ted using different resource units to which different steering matrices have been applied; - receive an interference feedback (IFB) request from the second communication de- vice; - determine interference information indicating an interference level of the different resource units; - transmit an IFB response to the fourth communication device and / or the second communication device, the IFB response including the determined interference informa- tion; and - communicate with the second communication device in coordination with commu- nication of the fourth communication device with the first communication device.

[0007] According to a further aspect there is provided a second communication device configuredto communicate with a third communication device in coordination with a second commu- nication device that is configured to communicate with a third communication device, the second communication device comprising circuitry configured to:- transmit a data unit and an interference feedback (IFB) request to the third com- munication device; - receive an IFB response from the third communication device, the IFB response including interference information indicating an interference level of different resource units, used for transmitting a data unit from the fourth communication unit to the third com- munication unit and to which different steering matrices have been applied by the fourth communication device, and - transmit the received IFB response to the fourth communication device.

[0008] According to still further aspects a computer program comprising program means forcausing a computer to carry out the steps of the method disclosed herein, when said com- puter program is carried out on a computer, as well as a non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method disclosed herein to be performed are provided.

[0009] Embodiments are defined in the dependent claims. It shall be understood that the dis-closed communication methods, the disclosed computer program and the disclosed com- puter-readable recording medium have similar and / or identical further embodiments as the claimed communication devices and as defined in the dependent claims and / or disclosed herein. It is particularly noted that the embodiments relating to the fourth communication device shall be understood as embodiments of the second communication device, i.e., the second communication device may be configured in substantially the same manner as the fourth communication device and may carry out substantially the same operations as the fourth communication device.

[0010] One of the aspects of the disclosure is to make use of an interference feedback mecha-nism according to which interference feedback is transmitted from a participant (the “sec- ond communication device” or the “third communication device”) of the low latency and / or extremely high throughput communication to the fourth communication device, which may be configured to operate as an access point. The feedback response is transmitted in re- sponse to a data unit transmitted by the fourth communication device and carried on re- source units to which different steering matrices (or, more generally, “steering informa- tion”) have been applied. This data unit is transmitted by the fourth communication deviceand can be used by the third communication device for interference evaluation although the data content of the data unit is not necessarily directed to the third communication unit but may be directed to the communication device associated with the fourth communica- tion unit. The feedback response includes interference information indicating an interfer- ence level of the different resource units observed by the third communication device. This enables the fourth communication device to (optionally) update the steering matrices for use in the communication with its associated communication device (herein called “first communication device”) in such a way that interference of the communication between the participants (the second and third communication devices) of the low latency and / or ex- tremely high throughput communication is avoided or at least reduced.

[0011] The foregoing paragraphs have been provided by way of general introduction and are notintended to limit the scope of the following claims. The described embodiments, together with further advantages, will be best understood by reference to the following detailed de- scription taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWING

[0012] A more complete appreciation of the disclosure and many of the attendant advantagesthereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: Fig. 1 shows a diagram of an exemplary system in which the present disclosure canbe applied. Fig. 2 shows a diagram of an exemplary use of Null Space Expansion in a systemshown in Fig.1. Fig. 3 shows a diagram illustrating the use of channel state information in exemplaryuse of Null Space Expansion in a system shown in Fig.2.Fig. 4 shows a diagram of an exemplary protocol of coordinated beamforming.Fig. 5 shows a diagram of the system shown in Fig. 1 in which different channels areindicated. Fig.6 shows a diagram illustrating an example of a frequency channel for a Non- P2P link and a P2P link. Fig.7 shows a diagram of an embodiment of a communication protocol according to the present disclosure. Fig.8 shows an embodiment of the format of a data unit transmitted in the concur- rent transmission according to the present disclosure. Fig.9 shows an exemplary embodiment of the preamble of the data unit illustrated in Fig.8.Fig. 10 shows another embodiment of the format of data unit according to the presentdisclosure.Fig. 11 shows an embodiment of an MPDU carried in the data unit illustrated in Figs.8 or 10.Fig. 12 an example of an acknowledgement frame according to the present disclo-sure.Fig. 13 shows an exemplary allocation of steering matrices according to the presentdisclosure.Fig. 14 shows a flowchart of an embodiment of a fourth communication method.Fig. 15 shows a flowchart of an embodiment of a third communication method.Fig. 16 shows a flowchart of an embodiment of a second communication method.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0013] Referring now to the drawings, wherein like reference numerals designate identical or cor-responding parts throughout the several views, Fig.1 shows a diagram of an exemplary system in which the present disclosure can be applied. In this example, high reliability and high data rate are both achieved in an XR application between STA2 and STA3. All STAs (generally also called communication devices) and the access point (AP; herein more generally also called “fourth communication device”) belong to the same basic service set (BSS). STA2 (e.g. a PC or console device; herein also called “second communication de- vice”) and STA3 (e.g. a head-mounted display; HMD; herein also called “third communica- tion device”) are connected with each other as a direct link (e.g. a Peer-to-Peer (P2P) link via a wireless connection) leveraging tunnel direct-link Setup (TDLS) as disclosed in the IEEE 802.11 standards. STA2 and STA3 can communicate with each other on a channel different from the primary channel of the BSS, but due to high throughput requirement for XR applications on the P2P link, it is hard to assign a wide bandwidth to the P2P link with- out overlapping with any other links making so that it may be inevitable for the AP not to interfere the P2P link. AP and STA1 (herein also called “first communication device”) can communicate with each other via a separate link, which may be a non-P2P link.

[0014] One of the technology areas to mitigate interference in scenarios of overlapping frequencychannels is beamforming. To yield better interference mitigation, channel state information (CSI) acquisition may be used at the beamfomer (e.g. the AP in Fig.1) through channel sounding with the unintended receiver (e.g. STA3 in Fig.1). However, the wireless chan- nel state changes over time to some extent and the sounding interval and interference mitigation level are in trade-off relationship. One of the reasons for the relationship is that steering matrices are just optimized to the CSI fed back to minimize interference, wherein the sounding interval should be shorter if the interference is required to be kept lower.

[0015] Generally, herein the term ‘basic service set (BSS)’ refers to a set of STAs that have suc-cessfully synchronized. The term ‘beamformee’ refers to an STA that receives a data unit, e.g., a physical layer (PHY) protocol data unit (PPDU), that has been transmitted using a beamforming steering matrix. The term ‘beamformer’ refers to an STA that transmits a data unit, e.g., a PPDCU, using a beamforming steering matrix.

[0016] The term ‘(channel) sounding’ refers to a technique that evaluates wireless channel. Typi-cally, the beamformer sends known sequences to the beamformee, which allows the beamformee to calculate channel state information (CSI), and the CSI is fed back to the beamformer. The term ‘(beamforming) steering matrix’ refers to a matrix determined using knowledge of the channel between a transmitter and an intended receiver that maps from space-time streams to transmit antennas with the goal of improving the signal power or signal-to-noise ratio (SNR) at the intended receiver and / or mitigating interference signal power at the unintended receiver. A steering matrix also refers a matrix for a subcarrier. If a signal is transmitted on multiple subcarriers, the transmitter should have steering matri- ces for the subcarriers. The term ‘CSI set’ refers to two or more CSIs, which indicated CSI observed / estimated at different times, or one CSI. The term ‘different steering matrices’ refers to steering matrices which may be computed from different CSI sets.

[0017] In an XR application, requirements of latency, reliability and throughput are hard to ensureat the same time through a proper selection of the sounding interval and the design of steering matrices design. To break the trade-off relationship, beamforming with channel prediction may be used. Null Space Expansion (NSE) has been paid attention as a simple beamforming algorithm to follow channel fluctuation.

[0018] In the following, let denote ^^^^^^ as the latest acquired CSI matrices and ^^^^^^ as the 2nd lat-est acquired CSI matrices. Both ^^^^^^and ^^^^^^are CSI matrices from the beamformer (e.g. AP in Fig.1) to the unintended receiver (e.g. STA3 in Fig.1). For a simple example (illus- trated in Fig.2) in NSE, the beamformer steers null to both ^^^^^^(denoted as ^^^^^^^^(^^^^) in Fig.2) and ^^^^^^(denoted as ^^^^^^^^(^^^^) in Fig.2) because each element of CSI matrices can be seen to change linearly, and thus the current CSI matrices^^^^(denoted as^^^^^^^^(^^)in Fig.2) can be also seen in the space which contains ^^^^^^and ^^^^^^. In other words, this al-gorithm expands the null space using several past CSIs to form a broad null at the cost of the beamformer’s spatial degree of freedom.

[0019] As described the above, NSE allows beamformers to steer null to several past CSIs withthe expectation that the null space would cover future / current CSI, but it still faces the is- sue of sounding interval optimization. This problem is illustrated in Fig.3, in which ^^^^is denoted as current CSI,is denoted as latest acquired CSI, ^^^^is denoted as second acquired latest CSI, and ^^^^ is denoted as third acquired latest CSI. Each ^^^^ (^^ = ^^~^^) isactually a complex vector, but it shall be assumed for simplification that each variant is a complex scalar number. In NSE, the beamformer acquires CSI ^^^^, ^^^^, and ^^^^, but the current CSI ^^^^is not acquired. The beamformee steers null with the expectation that CSI changes linearly from ^^^^and ^^^^and the current CSI is more likely to bebut if ^^^^ isunfortunately the peak of the line, the expected current CSI ^^(^^,^^)^^ is far from the actualcurrent CSI, and the null is steered in an improper direction (or space). It is worth to men- tion that if , which is the expected current CSI based on ^^^^ and ^^^^, is used for steer-ing null instead of, null would be steered in a rather proper direction (or space) be-cause ^^(^^,^^)^^ is closer to ^^^^ than ^^( ^^^^,^^)is.

[0020] One of multiple potential solutions is utilizing the spatial degree of freedom of the AP tosteer null (i.e., mitigate interference) to HMD while the AP sends data to STA1 and STA2 sends data to STA3 simultaneously, called coordinated beamforming (CBF). Generally, the AP derives steering matrix (more generally, steering information), which is orthogonal to channel between the AP and STA3 and uses the steering matrix to mitigate interfer- ence with STA3. Although CBF requires channel state information (CSI) and may require transmitters (e.g. AP and STA2 in Fig.1) to be synchronized with each other for better per- formance, it essentially enables simultaneous transmissions from the transmitters to differ- ent destinations on partially or fully overlapped channels while mitigating interference at unintended destinations. Concurrent sounding among transmitters is used for CBF to work with better performance. Although there are several different terms to indicate CBF, such as Coordinated Nulling, Joint Processing, etc., CBF herein shall be understood as a beamforming scheme where several transmitters steer null to unintended receivers for si- multaneous transmission yielding less interference at intended receivers.

[0021] An exemplary protocol of CBF is illustrated in Fig. 4, where AP1 and AP2 transmit a dataunit, e.g. a PPDU (PHY Protocol Data Unit), to STA1 and STA2, respectively, while steer- ing null to STA2 and STA1 respectively. AP1 and AP2 exchange frames to set the config- uration for CBF such as PPDU length, Guard Interval (GI) length, frequency channel, etc. Channel sounding may be included in this setup to allow APs to calculate steering matri- ces for CBF. After the CBF setup, a trigger may be sent from AP2 to AP1 to solicit concur- rent PPDU transmission. It may also be possible that AP1 sends a trigger to AP2. The trigger may also indicate parameters for concurrent PPDU transmission such as PPDU length, GI length, etc.

[0022] Although CBF is one of promising solutions to enable simultaneous transmission from dif-ferent transmitters, CSI feedback from each receiver to the transmitters has to be carried out beforehand so that each transmitter can steer the proper beam. CSI feedback reduc- tion is one of key components to mitigate overhead and / or improve system throughput, and Compressed Beamforming feedback was introduced in WLAN to reduce CSI feed- back size. In this scheme, if the beamformer (e.g. AP and console in Fig.1) will transmit, for example, two spatial streams using beamforming steering matrix, beamformee (e.g. STA1 and STA2 in Fig.1) transmits CSI parameters to the beamformer based on Givens Rotation beforehand, which essentially means two orthogonal vectors.

[0023] While each STA in the BSS usually communicates with the AP, communication betweennon-AP STAs, which is also called peer-to-peer (P2P) communication, can be set up with TDLS. In TDLS, STAs for P2P communication have to negotiate with the AP to allocate a frequency channel to the P2P link. The channel for the P2P link can be different from the primary channel of the BSS.

[0024] In general, MCS (Modulation and Coding Scheme) adaption, known as Link Adaptation,may be used to achieve high data rate and / or reliability besides SINR improvement. IEEE 802.11 defines a protocol for Link Adaptation, where the beamformer sends a MFB (MCS Feedback) Request and the beamformee sends a MFB in response to it. The way of de- termining optimal MCS is still dependent on the implementation, but the beamformee can refer to an SINR (Signal-to-Interference-and-Noise Ratio)-PER (Packet Error Rate) table to estimate MCS which can maximize the communication performance. Although LinkAdaptation is MCS optimization, it can be imagined that the transmit power and / or steer- ing matrices are alternative parameters to be optimized if MCS is fixed to meet a data rate requirement.

[0025] As described above, NSE would suffer from steering null to an improper direction (orspace) depending on sounding interval, and it needs to be refined to yield more robust (or broad) null to ensure the required communication quality on a P2P link. One of the rea- sons is that the optimal sounding interval depends on a change of the channel change from time to time. A communication protocol solving this problem does not exist and is dis- closed herein. In particular, to solve this problem, an interference feedback mechanism is disclosed which allows the beamformer to apply steering matrices, some of which are computed from CSI set while other steering matrices are computed from different CSI sets, over the bandwidth.

[0026] In the following, embodiments of the present disclosure will be described in detail. Initially,a system assumption and an exemplary BF algorithm for the use of NSE according to the present disclosure will be described. Fig.5 shows a diagram of the system shown in Fig.1 in which different channels are indicated.

[0027] As illustrated in Fig.5, each STA is associated with the AP in BSS. ^^^^(^^) denotes thechannel between AP and STA1, ^^^^(^^) denotes the channel from STA2 to STA3, and ^^^^^^^^(^^) denotes the channel from AP to STA3, where ^^ denotes time instance. STA2 and STA3 also establish a Peer-to-Peer (P2P) connection, wherein TDLS is one of multiple exemplary options to establish this connection. The link between AP and STA1 may be called ‘Non-P2P link’, the link between STA2 and STA3 may be called ‘P2P link’, and the link between AP and STA3 may be called ‘interference link’. To ensure high data on the P2P link, a wide bandwidth would be required as well as a high MCSs (Modulation and Coding Scheme), and some frequency channels would need to be shared with the Non- P2P link and the P2P link.

[0028] Fig.6 illustrates an example of a frequency channel for the Non-P2P link and the P2P link,where the primary channel P is allocated in the BSS and three secondary channels (S1-S3) are also allocated to the Non-P2P link and the P2P link, and the secondary channel S1 is allocated to both links.

[0029] As an example for illustration, it shall be assumed that the AP acquires two CSIs of the in-terference link with different time instance, ^^^^^^^^(^^2) and a CSI of the Non-P2P link ^^1(^^1), where ^^1is greater than ^^2. In NSE, AP calculates steering matrices to minimize in- terference to ^^^^^^^^(^^1) and ^^^^^^^^(^^2). One of the examples to calculate steering matrices ^^(^^1,^^2)in NSE from the CSIs is illustrated in equation (1), where ^^ is an arbitrary complex number, ^^^^^^(^^) is an eigenvector of matrix ^^, ^^^^is a Hermitian transpose matrix of ^^, ^^ is a noise power at each STA3’s antenna, and ^^ is an identity matrix:

[0030] For example, if the AP has four transmit antennas, STA2 has two receive antennas, andSTA3 has one receive antenna, the size of the above matrices / vectors are as follows: ^^1: 2-by-4 matrix,^^^^^^^^: 1-by-4 vector and^^^^^^^^: 2-by-4 matrix. It is also possible to define^^^^^^^^as derived from ^^-CSIs of interference links if the AP has sufficient spatial degree of free- dom and acquires / memorizes ^^-CSIs of the interference link. Equation (2) illustrates gen- eral forms of a way of calculation of steering matriceswhich are derived from

[0031] In the following, the protocol aspect is illustrated to allow beamformers to apply steeringmatrices , which are computed from different CSI sets for different groups ofsubcarriers. In particular, an exemplary protocol and frame format design are described.Fig.7 shows a diagram of an embodiment of a communication protocol 10 according to the present disclosure.

[0032] Although not illustrated in Fig. 7, STA3 may sometimes send data to the AP or vice versaon the interference link. In other words, signals on the interference link are not always treated as interference. Furthermore, although not illustrated in Fig.7, AP and STA2 may solicit STA3 feedback of interference level (interference feedback (IFB) in Fig.7) con- tained in an acknowledgement (Ack) frame. Ack frames can be partially identical to Ack frames and / or Block Ack frames standardized in IEEE 802.11 but may additionally contain IFB.

[0033] Initially, a P2P link setup 11 may be carried out. As illustrated in Fig.7, each of STA1,STA2 (Console), STA3 (HMD) is associated with the AP, and STA2 and STA3 establish a P2P link between them, potentially with support from the AP, for example based on TDLS. Although not illustrated in Fig.7, the capability of each device may be exchanged among the devices through establishing the association. The capability may also include the ca- pability to apply NSE for beamforming. Methods for P2P link establishment for P2P link setup 11 are generally known in IEEE 802.11 and shall not be discussed further here. The P2P link can be valid until the time indicated in the P2P link setup or until the AP receives an indication from either STA2 or STA3 that the P2P link is terminated.

[0034] Subsequently, a CBF setup 12 may be performed. AP and STA2 may exchange frames toset configurations for CBF in this step. According to Fig.7, CBF setup follows P2P link setup, but it is also possible in an embodiment that P2P link setup follows CBF setup. Channel soundings between AP and STA3 can be performed as part of the CBF setup and / or anywhere before CBF is performed. In the following, two or more channel sound- ings are assumed to be performed before CBF, which means that the AP obtains CSIs be- tween AP and STA3 at different times.

[0035] After P2P link setup 11 and CBF setup 12, STA2 can optionally send a trigger request 13to solicit the AP to send a trigger 14(e.g. a trigger frame) to STA2. The trigger 14 substan- tially indicates the destination to solicit to perform concurrent PPDU transmission. In an-other embodiment, STA2 may act as AP and STA2 can send a trigger to the AP. If the AP sends the trigger 14 as shown in Fig.7, the trigger may contain one or more of the follow- ing items of information: - an indication which resource unit (RU) and bandwidth are used for an Ack frame sent from at least STA3; - an indication that STA2 sends an Interference Feedback Request (IRQ) in subse- quent PPDU transmission to STA3, i.e., intended destination of the upcoming IRQ; and - an indication identical to what is indicated in a bandwidth (BW) subfield and an RU Allocation subfield in a HT Control field sent from STA2 to STA3, as explained below and illustrated in Fig.11.

[0036] An exemplary format of a data unit, in this example a PPDU 15 transmitted in the concur-rent transmission by the AP to STA1, is illustrated in Fig.8. The PPDU 15 contains a pre- amble, a STF (Short Training Field), an LTF (Long Training Field) and a data portion. In the STF, the LTF and the data portion, steering matrices are used, which are derived from different CSI sets, information comprising one or more CSIs. For example, as illustrated in Fig.8, steering matrices for subcarriers highlighted in white are ^^(^^1,^^2), steering matrices for subcarriers highlighted in black are, and steering matrices for subcarriers high- lighted in grey areare steering matrices derived from CSIs acquired at^^^^and ^^^^are steering matrices derived from CSI acquired at ^^^^.

[0037] One of the options to decide which steering matricesto apply to which subcarriersis that ^^(^^^^,, which is expected to yield better gain than any other^^^^), is allocatedas much as possible, while other steering matricesare allocated to one or two subcarriers within coherent bandwidth. In the exemplary steering matrices allocation illus- trated in Fig.13is expected as the best steering matrices at this point. In order to decide which are the best steering matrices, the steering matrices indicated in the IFB with the lowest interference level can be chosen.

[0038] STF is the training field to allow receivers to improve automatic gain control, which is alsoperformed with L-STF (Legacy STF) as described below. LTF is the training field to allowreceivers to at least estimate CSI from the transmitter to the receiver for decoding the data portion.

[0039] LTF can be designed to allow STA3 to estimate / calculate an intended signal level fromSTA2 and an interference signal from STA3. For example, LTF may comprise LTF sub- blocks, wherein each ^^-th LTF subblock at the ^^^^-th subcarrier may be expressed as in the following equations:Here, ^^^^^^(^^^^^^,^^^^―^^)^^^^is ^^-th LTF subblock at ^^^^-th subcarrier generated by AP, ^^^^^^(^^,^^ ^^^^^^―^^) ^^^^^^^^ is ^^-th LTF subblock at ^^-th subcarrier generated by STA2, ^^^^^^( ^^^ ^^ ^^^^) ^ is known symbol atcolumn element of ^^-by-^^ matrix ^^(^^), and

[0040] An exemplary embodiment of the preamble of the PPDU 15 is illustrated in Fig.9. It maycontain one or more of the following indications / fields: - L (Legacy)-STF: known sequence that allows receivers to perform PPDU detec- tion, coarse synchronization, AGC (Auto Gain Control) etc.; - L-LTF: known sequence that allows receivers to perform fine synchronization, CSI estimation to decode following fields; - L-SIG (Signal): indications of PPDU length; - RL-SIG: Repeated L-SIG to differentiate from other versions of PPDU; - U (Universal)-SIG: indications of version of the PPDU and parameters for decoding such as bandwidth, MCS, etc.; - SIG: additional indication of parameters for decoding the PPDU such as Guard In-terval size and LTF size applied in the appended portion; it may also contain destination specific information. For example, as illustrated in Fig.7, information specific to STA1 and information specific to STA3 are separately contained in this field.

[0041] L-STF, L-LTF, L-SIG and RL-SIG may optionally be identical to the same fields as definedin IEEE 802.11ax or IEEE 802.11be.

[0042] The SIG field may include one or more of the following indications as information specificto STA3: - Flag: indication that the following subfield contains ‘Number of Steering Matrices’ subfield and at least ‘RU Allocation for Steering Matrices #1’ subfield. - Number of Steering Matrices: number of CSI sets which are used to calculate steering matrices applied in the PPDU. For example, if three different steering matricesare applied as illustrated in Fig.8, this subfield indicates three.The indicated value is equal to number of RU Allocation for Steering Matrices #^^ sub- fields, where k is an arbitrary integer number. For ease of implementation to fix the length of the SIG field, ‘Number of Steering Matrices’ subfield is not required, while the number of ‘RU Allocation for Steering Matrices’ subfields should be a fixed number, for example four. In this case, if the number of different steering matrices is less than four, the excess number of ‘RU Allocation for Steering Matrices’ are reserved. - RU Allocation for Steering Matrices #^^: indication to which subcarriers steering matrices derived from the same CSI set are applied in the subsequent part, e.g. STF, LTF and data portion. For example, RU Allocation for Steering Matrices #1 indicates subcarri- ers where is used. It is generally not essential which steering matrix is applied to which subcarrier, but the fact that a different steering matrix is applied should be indi- cated.

[0043] Fig.10 illustrates another embodiment of format of a PPDU 15 according to the presentdisclosure, where another LTF (tail PPDU as explained below) is appended to the PPDU. In STF, the first LTF and data portion, one steering matrix, for exampleis applied, but in the tail PPDU several steering matrices can be applied, which are also different from the steering matrices applied in the first LTF and data portion. The field indicating in-formation of the tail LTF can also be appended to the PPDU, e.g. as SIG2 illustrated in Fig.10. It indicates the same information as in the ’Number of Steering Matrices’ subfield and ‘RU Allocation for Steering Matrices #^^’ mentioned above. In this embodiment, the SIG field does not have to include those subfields, but may include the following indication as part of information for all intended destinations: length of SIG2 field and the tail LTF. The SIG2 field may also contain an indication that the indications in SIG2 field are specific to STA3. If the steering matrices are applied as illustrated in Fig.10, the ‘Number of Steer- ing Matrices’ subfield indicates two because two steering matricesareused in the tail LTF.

[0044] Fig.11 illustrates an embodiment of an MPDU (MAC Protocol Data unit) carried in thePPDU, wherein the MPDU described here is carried in the PPDU 16 transmitted from STA2 to STA3. In other words, the MPDU illustrated in Fig.11, especially indications in the HT (High Throughput) Control field, are intended to inform STA3.The MPDU contains a Frame Control field, a Duration / ID field, a DA (Destination Address) field, a SA (Source Address) field, a BSSID field, and an FCS (Frame Check Sequence), which may be identi- cal to the definitions of these field in IEEE 802.11. The MPDU may further contain a HT (High Throughput) Control field, which indicates information about the solicited feedback.

[0045] The HT Control field may contain one or more of the following subfields, wherein ‘destina-tion’ hereby means STA3 in this example: - IRQ (IFB Request): indication to solicit destination(s) to send feedback; - RU (Resource Unit) Allocation: indication of RU where Ack frame is sent from the destination; - BW: indication of bandwidth where Ack frame is sent from the destination; and - IFB Flag: indication that HT Control field contains indication for IFB to differentiate other usage way of HT Control. The IRQ may also include an indication of the destination of the feedback.

[0046] The HT Control field, which is defined in IEEE 802.11, has limited bit length. It shall explic-itly indicate that the HT Control field contains information for which usage. Subfields for MCS Feedback defined in IEEE 802.11 can be reused for the IFB Request, but areneeded to be interpreted that the subfields are indications for the IFB Request, not for MCS Feedback. To differentiate from another usage way of the HT control such as MCS Feedback, an IFB Flag may be included that indicates that the information in the HT Con- trol is for the IFB Request. For instance, the last bit in the HT Control field may be set to zero, at least for the MCS feedback.

[0047] The indications illustrated above as part of the HT Control field may be contained in an-other field / element. In this case, the IFB Flag may indicate where the field / element is in the PPDU 15.

[0048] After receiving the PPDUs 15 and 16, STA3 evaluates the quality of the steering matriceswith the information carried in the PPDU 16, e.g., with the information contained in the SIG field in the preamble of the PPDU 16. In this context it should be noted that the con- tent of the PPDU 15 (e.g. the MPDU carried in the PPDU 15) is for STA1 (as illustrated in Fig.7 by the arrow from the AP to STA1) and the content of the PPDU 16 is for STA3 (as illustrated in Fig.7 by the arrow from the STA2 to STA3). However, the preambles of both PPDUs 15 and 16 can be observed by STA3 to estimate the interference level. The qual- ity may e.g. be SIR (Signal-to-Interference Ratio), SINR (Signal-to-Interference-and-Noise Ratio) or an average of the received signal level. In an example, the ‘Number of Steering Matrices’ subfield indicates that the transmitted PPDU contains three ‘RU Allocation for Steering Matrices #^^’ subfields, ‘RU Allocation for Steering Matrices #^^’ subfield indicates subcarrier group ^^^^ where ^^ = ^^,^^,^^.are applied to ^^^^, ^^^^ and^^^^respectively, but STA3 does not know which steering matrices are applied to which subcarrier group but is informed that different steering matrices are applied to different subcarrier groups.

[0049] In an embodiment, STA3 can calculate / estimate the quality of the steering matrices in thefollowing way, wherein it shall be assumed as an example that ^^^^^^(^^,^^^^^^^^^^) are received ^^-thLTF subblocks at the ^^^^-th subcarrier. ^^^^^^( ^^^ ^^ ^, ^^ ^^^^)is the received signal of the LTF subblockfrom both STA2 and AP. For example, STA2 calculates SIR, as steering matrices quality, for subcarrier group ^^^^as expressed in the below equation:|^^^^|2|^^^^|2, where

[0050] is an average received intended signal level on subcarrier group ^^^^, and |^^^^|^^is an average received unintended signal (or interference) level on subcarrier group^^^^. When calculating SIR in the above example way, STA3 shall be informed of at least the values of ^^, ^^, ^^, which are indicated in the SIG field.

[0051] After evaluation of the quality, STA3 sends IFB as part of Ack frame 17. Fig. 12 illustratesan example of an Ack frame which may contain one or more of the following fields: - Address 1: MAC Address of destination; and - HT Control: information regarding IFB.

[0052] The HT Control field may contain one or more of the following subfields:- Unsolicited MBF: Indication whether the frame is solicited by AP or STA2; - Number of Steering Matrices Indices: Indication of number of ‘Steering Matrices Index #^^’ subfield; - Steering Matrices Index #^^: Indication of subcarrier groups where same CSI set are used for Steering Matrices applied in the latest PPDU from AP; this subfield may indicate the same value in ‘RU Allocation for Steering Matrices #^^’ in the latest re- ceived PPDU from AP; - Interference Level #^^: Indication of (average) interference level at sub- carrier groups indicated in ‘Steering Matrices Index #^^’ subfield; and - IFB Flag: Indication that HT Control field contains an indication for IFB such as ‘Steering Matrices Index #^^’ subfield to differentiate from other usage way of HT Control.

[0053] The indications, which are illustrated above as part of HT Control field, can be containedin another field / element. In this case, the IFB Flag indicates where the field / element is in the Ack frame 17.

[0054] In another embodiment, STA3 may send IFB without being solicited from either AP orSTA2. In this case, ‘Unsolicited IFB’ subfield may indicate that the IFB is not solicited.

[0055] After receiving IFB, the AP can change (update) the subcarrier allocation of steering matri-ces in the next PPDU(s) to be transmitted. In particular, this update of steering matrices essentially means that the AP changes how many subcarriers are allocated to which steering matrices. In some situations, e.g., if the channel is completely or substantially sta- ble and / or if the interference may be neglected as it is too low, the same subcarrier alloca- tion can be maintained and needs not to be changed / updated. The change / update of the subcarrier allocation is thus an option and is only optionally made.

[0056] As illustrated in Fig.7, an Ack frame 18 is transmitted from STA1 after the Ack frame 17.The Ack frame 18 can also be sent before the Ack frame 17 or concurrently with the Ack frame 18. In the case where the Ack frames 17 and 18 are sent concurrently, the fre- quency channels for the Ack frames can be different, and the channel / bandwidth indicated in the trigger frame 14 is allocated to the frequency channel for the Ack frame 17, while the frequency channel for the Ack frame 18 is set to a different channel / bandwidth such as the primary channel of the BSS. Although not illustrated in Fig.7, the trigger frame can be sent to solicit concurrent Ack frame transmission. Furthermore, if the destination of the Ack frame 17 is set to only STA2, STA2 can send AP indications indicated in the HT Con- trol field in the Ack frame 17, after STA2 receives the Ack frame 17 from STA3.

[0057] Subsequently, a trigger request 19, a trigger 20, a PPDU 21 and a PPDU + IFB request22 may be transmitted in the same manner as explained above for the same elements 13 to 16. These operations represent a next transmission of the AP, which includes that the AP uses the optionally updated steering matrices in its communication with STA1 (by transmitting the PPDU 21) in coordination with communication of STA2 with STA3 (by transmitting PPDU 22). Thus, in the exemplary protocol illustrated in Fig.7, the transmis-sions of elements 13 to 16 are the initial steps (representing a first transmission operation) to gathering IFB, and after Ack 17 and 18, the AP can update the steering matrices based on the IFB. The transmissions of elements 19 to 22 thus represent a second transmission operation, which is triggered from STA2 by the trigger request 19. These second transmis- sions of elements 19 to 22 may only happen after Ack 17 and 18 if STA2 has data traffic to transmit to STA3.

[0058] It shall be noted that in another embodiment the AP may transmit an IFB request to STA3in addition to or instead of the transmission of the IFB request 16 and / or 22 by STA2 to STA3.

[0059] Before describing an example of the allocation of steering matrices to subcarriers, it shallbe assumed in an exemplary embodiment that STA3 informs the AP thatyields the least interference level,yields the second least interference level, andyield the worst interference level.means a steering matrix which is calculated from CSIs acquired at the time of ^^^^and ^^^^at AP.

[0060] First, AP checks whether each fed back steering matrices yields less than an acceptableinterference level on P2P link. The acceptable interference level can be informed by STA2 and / or STA3, or it can be calculated based on the required SINR or MCS which may be informed by STA2 and / or STA3. The acceptable interference level, the required SINR, and / or the required MCS may, e.g., be informed to AP in the P2P link setup 11 and / or CBF setup 12.

[0061] If there are any steering matrices which are indicated, in interference feedback, to yield aninterference level larger than the acceptable interference, AP does not allocate any sub- carriers for the steering matrices. For example, if interference levels ofare less than the acceptable interference level, butis not, the AP usesand(which may also be considered as an update of steering matrices) for the next transmission in CBF,. Moreover, if the remaining steering matrices are less than two, the AP can perform channel sounding with STA3.

[0062] After determining which steering matrices are used in the next transmission of elements19 to 22 (in particular of elements 21 and 22), AP allocates as many as possible subcarri- ers to the steering matrix which yields less interference, while one subcarrier per coherent bandwidth is allocated to other steering matrices. For example, as mentioned above, one subcarrier per coherent bandwidth of ^^^^^^^^is allocated for ^^(^^1), and the remaining subcar- riers are allocated to ^^(^^1,^^3). The coherent bandwidth means a bandwidth within which ^^^^^^^^can be seen to have high correlation (or close complex channel gain), and the coher- ent bandwidth can be computed by the AP with at least the latest channel sounding feed- back.

[0063] The AP can determine the criteria of ‘high correlation’ based on the acceptable interfer-ence level as shown ^^^^in the following equation. ^^^^ = aug max ^^(^^) ≤ ^^, 0 ≤ ^^ ≤ Δ^^,Δ^^In the equation, ^^^^^^^^(^^^^,^^^^) is CSI on ^^^^-th subcarrier at STA3’s ^^^^-th receive antenna, ^^^^is number of STA3’s receive antennas,^^is a normalization factor,^^^^^^^^,^^^^^^is the mini- mum / maximum subcarrier frequency in the bandwidth, and ^^ is the threshold for determin- ing coherency.

[0064] Fig.14 shows a flowchart of an embodiment of a fourth communication method 100. Thismethod may be carried out by the fourth communication device, e.g. the AP, that is config- ured to communicate with STA1 in coordination with STA2 that is configured to communi- cate with STA3. In a first step of the communication method 100, the AP transmits a data unit to the STA1 and STA3, the data unit being transmitted using different resource unitsto which different steering matrices have been applied, the different steering matrices be- ing computed from different channel state information (CSI) sets. In a second step 102, the AP receives an IFB response from STA2 and / or STA3, the IFB response including in- terference information indicating an interference level of the different resource units ob- served by the third communication device. In a third step 103, the AP evaluates the IFB response and optionally update the steering matrices and / or the allocation of steering ma- trices to resource units to be used for transmitting a subsequent data unit to STA1. In a fourth step 104, the AP communicates with STA1 using the optionally updated steering matrices in coordination with communication of STA2 with STA3.

[0065] Fig.15 shows a flowchart of an embodiment of a third communication method 200. Thismethod may be carried out by STA3. In a first step 201 of the communication method 200, STA3 receives a data unit from STA2 and the AP, the data unit at least from the AP being transmitted using different resource units to which different steering matrices have been applied. In a second step 202, STA3 receives an interference feedback (IFB) request from STA2. In a third step 203, STA3 determines interference information indicating an interfer- ence level of the different resource units. In a fourth step 204, STA3 transmits an IFB re- sponse to the AP and / or STA2, the IFB response including the determined interference in- formation. In a fifth step 205, STA3 communicates with STA2 in coordination with commu- nication of the AP with STA1.

[0066] Fig.16 shows a flowchart of an embodiment of a second communication method 300.This method may be carried out by STA2. In a first step 301 of the communication method 300, STA2 transmits a data unit and an interference feedback (IFB) request to STA3. In a second step 302, STA2 receives an IFB response from STA3, the IFB response including interference information indicating an interference level of different resource units, used for transmitting a data unit from the AP to STA3 and to which different steering matrices have been applied by the AP. In a third step 303, STA2 transmits the received IFB re- sponse to the AP.

[0067] Thus, the foregoing discussion discloses and describes merely exemplary embodimentsof the present disclosure. As will be understood by those skilled in the art, the present dis- closure may be embodied in other specific forms without departing from the spirit or es-sential characteristics thereof. Accordingly, the disclosure of the present disclosure is in- tended to be illustrative, but not limiting of the scope of the disclosure, as well as other claims. The disclosure, including any readily discernible variants of the teachings herein, defines, in part, the scope of the foregoing claim terminology such that no inventive sub- ject matter is dedicated to the public.

[0068] In the claims, the word "comprising" does not exclude other elements or steps, and the in-definite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain mea- sures are recited in mutually different dependent claims does not indicate that a combina- tion of these measures cannot be used to advantage.

[0069] In so far as embodiments of the disclosure have been described as being implemented, atleast in part, by software-controlled data processing apparatus, it will be appreciated that a non-transitory machine-readable medium carrying such software, such as an optical disk, a magnetic disk, semiconductor memory or the like, is also considered to represent an embodiment of the present disclosure. Further, such a software may also be distrib- uted in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0070] The elements of the disclosed devices, apparatus and systems may be implemented bycorresponding hardware and / or software elements, for instance appropriated circuits. A circuit is a structural assemblage of electronic components including conventional circuit elements, integrated circuits including application specific integrated circuits, standard in- tegrated circuits, application specific standard products, and field programmable gate ar- rays. Further a circuit includes central processing units, graphics processing units, and mi- croprocessors which are programmed or configured according to software code. A circuit does not include pure software, although a circuit includes the above-described hardware executing software.

[0071] It follows a list of further embodiments of the disclosed subject matter:1. Fourth communication device configured to communicate with a first communica-tion device in coordination with a second communication device that is configured to com- municate with a third communication device, the fourth communication device comprising circuitry configured to: - transmit a data unit to the first and the third communication device, the data unit being transmitted using different resource units to which different steering matrices have been applied, the different steering matrices being computed from different channel state information (CSI) sets; - receive an interference feedback (IFB) response from the second and / or the third communication device, the IFB response including interference information indicating an interference level of the different resource units observed by the third communication de- vice; - evaluate the IFB response and optionally update the steering matrices and / or the allocation of steering matrices to resource units to be used for transmitting a subsequent data unit to the first communication device; and - communicate with the first communication device using the optionally updated steering matrices in coordination with communication of the second communication device with the third communication device. 2. Fourth communication device according to any preceding embodiment, wherein the circuitry is configured to obtain a CSI at one or more different points in time and wherein a CSI set comprises the CSI obtained at one point in time or at two or more different points in time. 3. Fourth communication device according to any preceding embodiment, wherein the circuitry is configured to include into the data unit or transmit along with the data unit steering matrix information indicating one or more of: - an indication that information regarding steering matrices is included, - the number of steering matrices,- the allocation of resource units to the different steering matrices, and- which channel state information (CSI) sets have been used for computing the re- spective steering matrices.4. Fourth communication device according to any preceding embodiment, wherein the circuitry is configured to include the steering matrix information into a pream- ble or a postamble or a separate field of the data unit, in particular into a signaling field or a training field of a preamble or a postamble of the data unit. 5. Fourth communication device according to any preceding embodiment, wherein the circuitry is configured to apply the same steering matrix for one or more re- source units. 6. Fourth communication device according to any preceding embodiment, wherein the circuitry is configured to transmit a trigger to at least the second communica- tion device to inform about the desired concurrent communication of the fourth communi- cation device to the first communication device in coordination with communication of the second communication device with the third communication device. 7. Fourth communication device according to any preceding embodiment, wherein the circuitry is configured to evaluate the IFB response and optionally update the steering matrices and / or the allocation of steering matrices to resource units by allocating at least one subcarrier within a coherent bandwidth to steering matrices that satisfy an in- terference quality criterion and / or by not allocating any subcarriers within a coherent band- width to steering matrices that do not satisfy the interference quality criterion. 8. Fourth communication device according to embodiment 7, wherein the circuitry is configured to determine if a steering matrix satisfies the interfer- ence quality criterion based on a predetermined interference quality criterion and / or based a communicated interference quality criterion obtained from the second and / or third com- munication device and / or based on interference-related information, in particular signal-to- interference-plus-noise ratio (SINR) and / or modulation coding scheme (MCS), obtained from the second and / or third communication device. 9. Fourth communication device according to any preceding embodiment, wherein the fourth communication device is configured to operate as access point.10. Fourth communication device according to any preceding embodiment, wherein the circuitry is configured to transmit an interference feedback (IFB) request to the third communication device. 11. Third communication device configured to communicate with a second communi- cation device in coordination with a fourth communication device that is configured to communicate with a first communication device, the third communication device compris- ing circuitry configured to: - receive a data unit from the second communication device and a fourth communi- cation device, the data unit at least from the fourth communication device being transmit- ted using different resource units to which different steering matrices have been applied; - receive an interference feedback (IFB) request from the second communication de- vice; - determine interference information indicating an interference level of the different resource units; - transmit an IFB response to the fourth communication device and / or the second communication device, the IFB response including the determined interference informa- tion; and - communicate with the second communication device in coordination with commu- nication of the fourth communication device with the first communication device. 12. Third communication device according to embodiment 11, wherein the circuitry is configured to include into the IFB response information indicating one or more of: - an indication that interference information regarding steering matrices is included, - the number of steering matrix indices, and- the interference level per steering matrix index.13. Third communication device according to embodiment 11 or 12, wherein the circuitry is configured to include the IFB response into a field of an IFB frame transmitted to the fourth communication device, in particular into a control field of the IFB frame.14. Third communication device according to embodiment 11, 12 or 13, wherein the circuitry is configured to transmit an interference quality criterion and / or inter- ference-related information, in particular signal-to-interference-plus-noise ratio (SINR) and / or modulation coding scheme (MCS) to the fourth communication device and / or the second communication device.15. Second communication device configured to communicate with a third communica-tion device in coordination with a fourth communication device that is configured to com- municate with a first communication device, the second communication device comprising circuitry configured to: - transmit a data unit and an interference feedback (IFB) request to the third com- munication device; - receive an IFB response from the third communication device, the IFB response including interference information indicating an interference level of different resource units, used for transmitting a data unit from the fourth communication unit to the third com- munication unit and to which different steering matrices have been applied by the fourth communication device, and - transmit the received IFB response to the fourth communication device. 16. Second communication device according to embodiment 15, wherein the circuitry is configured to request the fourth communication device to transmit a trigger for a data unit transmission in coordination with the second communication device. 17. Communication method of a fourth communication device configured to communi- cate with a first communication device in coordination with a second communication de- vice that is configured to communicate with a third communication device, the communi- cation method comprising: - transmitting a data unit to the first and the third communication device, the data unit being transmitted using different resource units to which different steering matrices have been applied, the different steering matrices being computed from different channel state information (CSI) sets;- receiving an IFB response from the second and / or the third communication device, the IFB response including interference information indicating an interference level of the different resource units observed by the third communication device; - evaluating the IFB response and optionally update the steering matrices and / or the allocation of steering matrices to resource units to be used for transmitting a subsequent data unit to the first communication device; and - communicating with the first communication device using the optionally updated steering matrices in coordination with communication of the second communication device with the third communication device. 18. Communication method of a third communication device configured to communi- cate with a second communication device in coordination with a fourth communication de- vice that is configured to communicate with a first communication device, the communica- tion method comprising: - receiving a data unit from the second communication device and a fourth commu- nication device, the data unit at least from the fourth communication device being trans- mitted using different resource units to which different steering matrices have been ap- plied; - receiving an interference feedback (IFB) request from the second communication device; - determining interference information indicating an interference level of the different resource units; - transmitting an IFB response to the fourth communication device and / or the sec- ond communication device, the IFB response including the determined interference infor- mation; and - communicating with the second communication device in coordination with com- munication of the fourth communication device with the first communication device. 19. Communication method of a second communication device configured to commu- nicate with a third communication device in coordination with a fourth communication de- vice that is configured to communicate with a first communication device, the communica- tion method comprising:- transmitting a data unit and an interference feedback (IFB) request to the third communication device; - receiving an IFB response from the third communication device, the IFB response including interference information indicating an interference level of different resource units, used for transmitting a data unit from the fourth communication unit to the third com- munication unit and to which different steering matrices have been applied by the fourth communication device, and - transmitting the received IFB response to the fourth communication device.20. A non-transitory computer-readable recording medium that stores therein a com-puter program product, which, when executed by a processor, causes the method accord- ing to embodiment 17, 18 or 19 to be performed. 21. A computer program comprising program code means for causing a computer to perform the steps of said method according to embodiment 17, 18 or 19 when said com- puter pro-gram is carried out on a computer.

Claims

CLAIMS1. Fourth communication device configured to communicate with a first communica-tion device in coordination with a second communication device that is configured to com- municate with a third communication device, the fourth communication device comprising circuitry configured to: - transmit a data unit to the first and the third communication device, the data unit being transmitted using different resource units to which different steering matrices have been applied, the different steering matrices being computed from different channel state information (CSI) sets; - receive an interference feedback (IFB) response from the second and / or the third communication device, the IFB response including interference information indicating an interference level of the different resource units observed by the third communication de- vice; - evaluate the IFB response and optionally update the steering matrices and / or the allocation of steering matrices to resource units to be used for transmitting a subsequent data unit to the first communication device; and - communicate with the first communication device using the optionally updated steering matrices in coordination with communication of the second communication device with the third communication device.

2. Fourth communication device according to claim1, wherein the circuitry is configured to obtain a CSI at one or more different points in time and wherein a CSI set comprises the CSI obtained at one point in time or at two or more different points in time.

3. Fourth communication device according to claim 1, wherein the circuitry is configured to include into the data unit or transmit along with the data unit steering matrix information indicating one or more of: - an indication that information regarding steering matrices is included, - the number of steering matrices,- the allocation of resource units to the different steering matrices, and- which channel state information (CSI) sets have been used for computing the re- spective steering matrices.

4. Fourth communication device according to claim 1, wherein the circuitry is configured to include the steering matrix information into a pream- ble or a postamble or a separate field of the data unit, in particular into a signaling field or a training field of a preamble or a postamble of the data unit.

5. Fourth communication device according to claim 1, wherein the circuitry is configured to apply the same steering matrix for one or more re- source units.

6. Fourth communication device according to claim 1, wherein the circuitry is configured to transmit a trigger to at least the second communica- tion device to inform about the desired concurrent communication of the fourth communi- cation device to the first communication device in coordination with communication of the second communication device with the third communication device.

7. Fourth communication device according to claim 1, wherein the circuitry is configured to evaluate the IFB response and optionally update the steering matrices and / or the allocation of steering matrices to resource units by allocating at least one subcarrier within a coherent bandwidth to steering matrices that satisfy an in- terference quality criterion and / or by not allocating any subcarriers within a coherent band- width to steering matrices that do not satisfy the interference quality criterion.

8. Fourth communication device according to claim 7, wherein the circuitry is configured to determine if a steering matrix satisfies the interfer- ence quality criterion based on a predetermined interference quality criterion and / or based a communicated interference quality criterion obtained from the second and / or third com- munication device and / or based on interference-related information, in particular signal-to- interference-plus-noise ratio (SINR) and / or modulation coding scheme (MCS), obtained from the second and / or third communication device.

9. Fourth communication device according to claim 1, wherein the fourth communication device is configured to operate as access point.

10. Fourth communication device according to claim 1, wherein the circuitry is configured to transmit an interference feedback (IFB) request to the third communication device.

11. Third communication device configured to communicate with a second communi- cation device in coordination with a fourth communication device that is configured to communicate with a first communication device, the third communication device compris- ing circuitry configured to: - receive a data unit from the second communication device and a fourth communi- cation device, the data unit at least from the fourth communication device being transmit- ted using different resource units to which different steering matrices have been applied; - receive an interference feedback (IFB) request from the second communication de- vice; - determine interference information indicating an interference level of the different resource units; - transmit an IFB response to the fourth communication device and / or the second communication device, the IFB response including the determined interference informa- tion; and - communicate with the second communication device in coordination with commu- nication of the fourth communication device with the first communication device.

12. Third communication device according to claim 11, wherein the circuitry is configured to include into the IFB response information indicating one or more of: - an indication that interference information regarding steering matrices is included, - the number of steering matrix indices, and- the interference level per steering matrix index.

13. Third communication device according to claim 11,wherein the circuitry is configured to include the IFB response into a field of an IFB frame transmitted to the fourth communication device, in particular into a control field of the IFB frame.

14. Third communication device according to claim 11, wherein the circuitry is configured to transmit an interference quality criterion and / or inter- ference-related information, in particular signal-to-interference-plus-noise ratio (SINR) and / or modulation coding scheme (MCS) to the fourth communication device and / or the second communication device.

15. Second communication device configured to communicate with a third communica-tion device in coordination with a fourth communication device that is configured to com- municate with a first communication device, the second communication device comprising circuitry configured to: - transmit a data unit and an interference feedback (IFB) request to the third com- munication device; - receive an IFB response from the third communication device, the IFB response including interference information indicating an interference level of different resource units, used for transmitting a data unit from the fourth communication unit to the third com- munication unit and to which different steering matrices have been applied by the fourth communication device, and - transmit the received IFB response to the fourth communication device.

16. Second communication device according to claim 15, wherein the circuitry is config- ured to request the fourth communication device to transmit a trigger for a data unit trans- mission in coordination with the second communication device.

17. Communication method of a fourth communication device configured to communi- cate with a first communication device in coordination with a second communication de- vice that is configured to communicate with a third communication device, the communi- cation method comprising: - transmitting a data unit to the first and the third communication device, the data unit being transmitted using different resource units to which different steering matriceshave been applied, the different steering matrices being computed from different channel state information (CSI) sets; - receiving an IFB response from the second and / or the third communication device, the IFB response including interference information indicating an interference level of the different resource units observed by the third communication device; - evaluating the IFB response and optionally update the steering matrices and / or the allocation of steering matrices to resource units to be used for transmitting a subsequent data unit to the first communication device; and - communicating with the first communication device using the optionally updated steering matrices in coordination with communication of the second communication device with the third communication device.

18. Communication method of a third communication device configured to communi- cate with a second communication device in coordination with a fourth communication de- vice that is configured to communicate with a first communication device, the communica- tion method comprising: - receiving a data unit from the second communication device and a fourth commu- nication device, the data unit at least from the fourth communication device being trans- mitted using different resource units to which different steering matrices have been ap- plied; - receiving an interference feedback (IFB) request from the second communication device; - determining interference information indicating an interference level of the different resource units; - transmitting an IFB response to the fourth communication device and / or the sec- ond communication device, the IFB response including the determined interference infor- mation; and - communicating with the second communication device in coordination with com- munication of the fourth communication device with the first communication device.

19. Communication method of a second communication device configured to commu- nicate with a third communication device in coordination with a fourth communication de-vice that is configured to communicate with a first communication device, the communica- tion method comprising: - transmitting a data unit and an interference feedback (IFB) request to the third communication device; - receiving an IFB response from the third communication device, the IFB response including interference information indicating an interference level of different resource units, used for transmitting a data unit from the fourth communication unit to the third com- munication unit and to which different steering matrices have been applied by the fourth communication device, and - transmitting the received IFB response to the fourth communication device.

20. A non-transitory computer-readable recording medium that stores therein a com-puter program product, which, when executed by a processor, causes the method accord- ing to claim 17, 18 or 19 to be performed.

Images