Access point and communication devices

Abstract

An access point configured to communicate with a first communication device and a second communication device, the access point comprising circuitry configured to: - transmit, in response to a coordinated beamforming (CBF) request, a CBF response to a second communication device that is configured to communicate with a third communication device; - receive a feedback response from the second communication device or the third communication device, the feedback response including postcoding information of the third communication device for communication with the second communication device and / or channel information of a channel between the access point and the third communication device; - determine second steering information based on the feedback response; and - communicate with the first communication device using the second steering information in coordination with communication of the second communication device with the third communication device.

Description

ACCESS POINT AND COMMUNICATION DEVICESBACKGROUNDFIELD OF THE DISCLOSURE

[0001] The present disclosure relates to an access point and to communication devices, in partic- ular for use with coordinated beamforming. Further, the present invention relates to corre- sponding communication 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. Carrier sense mechanism is adopted in WLAN as part of channel access,but is does not sufficiently ensure that each station (STA; herein generally called “commu- nication device”) can transmit data whenever data traffic arrives at the STA. Furthermore, there are situations in which a communication between 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 presenting the 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 an access point and another communication device. It is a further object to provide a corresponding method as well as a corresponding computer program and a non -transitory computer- readable recording medium that stores therein a computer program product for imple- menting said method.

[0005] According to an aspect there is provided an access point configured to communicate with a first communication device and a second communication device, the access point com- prising circuitry configured to: transmit, in response to a coordinated beamforming (CBF) request, a CBF re- sponse to a second communication device that is configured to communicate with a third communication device; receive a feedback response from the second communication device or the third communication device, the feedback response including postcoding information of the third communication device for communication with the second communication deviceand / or channel information of a channel between the access point and the third communi- cation device; determine second steering information based on the feedback response; and communicate with the first communication device using the second steering infor- mation in coordination with communication of the second communication device with the third communication device.

[0006] According to a further aspect there is provided a second communication device configured to communicate with a third communication device and an access point, the second com- munication device comprising circuitry configured to: transmit a coordinated beamforming (CBF) request to an access point that is con- figured to communicate with a first communication device and the second communication device receive, in response to the CBF request, a CBF response from the access point; and transmit a feedback request to the third communication device requesting it to transmit a feedback response to the access point, the feedback response including post- coding information of the third communication device for communication with the second communication device and / or channel information of a channel between the access point and the third communication device.

[0007] According to a further aspect there is provided a third communication device configured to communicate with a second communication device, the third communication device com- prising circuitry configured to: receive a training packet from an access point that is configured to communicate with a first communication device and the second communication device and / or a feed- back request from the second communication device to transmit a feedback response to the access point, the feedback response including postcoding information of the third communication device for communication with the second communication device; and transmit the feedback response to the access point in response to the feedback re- quest and / or training packet.

[0008] According to still further aspects corresponding methods, a computer program comprising program means for causing a computer to carry out the steps of the method disclosed herein, when said computer program is carried out on a computer, as well as a non-transi- tory computer-readable recording medium that stores therein a computer program prod- uct, which, when executed by a processor, causes the method disclosed herein to be per- formed are provided.

[0009] Embodiments are defined in the dependent claims. It shall be understood that the dis- closed methods, the disclosed computer program and the disclosed computer-readable recording medium have similar and / or identical further embodiments as the claimed de- vices and as defined in the dependent claims and / or disclosed herein.

[0010] One of the aspects of the disclosure is make use of a feedback response transmitted from a participant (herein called “third communication device”) of the low latency and / or ex- tremely high throughput communication to the access point. The feedback response in- cludes postcoding (or MIMO (Multi-Input-Multi-Output) equalizer) information, e.g., in the form of a postcoding matrix, which enables the access point to determine steering infor- mation, e.g., in the form of a steering matrix, for use in the communication with its commu- nication device (herein called “first communication device”) in such a way that interference of the communication between the participants (the second and third communication de- vices) of the low latency and / or extremely high throughput communication is avoided or at least reduced.

[0011] The foregoing paragraphs have been provided by way of general introduction and are not intended 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 advantages thereof will be readily obtained as the same becomes better understood by reference tothe 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 can be applied.Fig. 2 shows a diagram of the exemplary system shown in Fig. 1 , in which different channels are indicated.Fig. 3 shows an equation of the interference signal at the third communication device from the access point.Fig. 4 shows the equation of the interference signal at the third communication de- vice from the access point with partly different terminology than in Fig. 3.Fig. 5 shows a diagram of the exemplary system shown in Fig. 1 , into which exem- plary beams are indicated to illustrate an embodiment of the present disclo- sure.Fig. 6 shows a diagram of an embodiment of a communication scheme according to the present disclosure.Fig. 7 shows an example of a frequency channel allocation for two links.Fig. 8 shows a diagram of another embodiment of a communication scheme accord- ing to the present disclosure.Fig. 9 shows a diagram of still another embodiment of a communication scheme ac- cording to the present disclosure.Fig. 10 shows a flowchart of a communication method of an access point.Fig. 11 shows a flowchart of a communication method of a second communication de- vice.Fig. 12 shows a flowchart of a communication method of a third communication de- vice.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) 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) 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 forXR applications on the P2P link, it is hard to assign a wide bandwidth to the P2P link without overlapping with any other links. AP and STA1 (herein also called “first communication device”) can communi- cate with each other via a separate link, which may be a non-P2P link. The AP may be an interferer against STA2-STA3 link.

[0014] A potential solution is utilizing the spatial domain of the AP to steer null (i.e., mitigate inter- ference) to HMD while the AP sends data to STA1 and STA2 sends data to STA3 simulta- neously, 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 interference with STA3. Although CBF re- quires channel state information (CSI) and may require transmitters (e.g. AP and STA2 in Fig.1 ) to be synchronized with each other for better performance, it essentially enables simultaneous transmissions from the transmitters to different destinations on partially orfully overlapped channels while mitigating interference at unintended destinations. Con- current sounding among transmitters is used for CBF to work with better performance. Alt- hough 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 simultaneous transmission yield- ing less interference at intended receivers.

[0015] Generally, the term ‘basic service set (BSS)’ refers to a set of STAs that have successfully synchronized. The terms ‘beamformee’ refers to an STA that receives a data unit, e.g., a physical layer (PHY) protocol data unit (PPDll), that has been transmitted using a beam- forming steering matrix. The terms ‘beamformer’ refers to an STA that transmits a data unit, e.g., a PPDCll, using a beamforming steering matrix. The terms ‘beamforming steer- ing matrix’ refers to a matrix determined using knowledge of the channel between a trans- mitter 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.

[0016] In the following explanations, the following conditions are assumed. The channel for the communication link between AP and STA1 may partially be overlapped with the channel for P2P link between STA2 and STA3. NPsP< N$nA3’ where NPsPis the number of spatial streams on the link between STA2 and STA3, and N$nA3is the number of receive anten- nas of STA3.

[0017] If STA2 has the capability or is assumed to perform interference suppression (in other words, steer null to AP transmitting signal to STA1), both NgPA1+ N^PA3>Nant and NSSA1+NssP>Nant3> where NgPA1is the number of spatial streams on the link between AP and STA1 , and NAPtis the number of transmit antennas of the AP. The equation NSSA1+NanA3>Nant means that the AP does not have enough transmit antennas to achieve transmission to STA1 while steering null to STA3 receiving Np$pspatial streams from STA2. The other equation NgPA1+ Np$p> N$nt3means that STA3 does not have enough receive antennas to receive a signal from STA2 while suppressing interferencefrom AP transmitting JV / p11spatial streams to STA1 . One of the examples to meet the above equations is that

[0018] If STA2 does not have capability or is not assumed to perform interference suppression the above condition can exclude NgPA1+ NP3P> N$nt3, and N$nt3NAPtshould be met. In this case,1, 2, 2) is one of the examples under this as- sumption.

[0019] In the above equations, N / $A1and NP3Pgenerally meet N / $A1< NAPtand NP3P< N$nt3’ respectively.

[0020] As a typical example for the discussion above, it may be assumed that the AP-STA1 link uses one spatial stream (SS), the STA2-STA3 link uses one SS, AP has two antennas and STA3 has two antennas. An Issue with CBF may be that the AP requires three anten- nas in this case, because one spatial degree of freedom (DoF) is allocated to the trans- mission to STA1 and the other two spatial DoFs are consumed to steer null to STA3. Intui- tively, ‘spatial DoF’ is the ‘number of AP’s antennas’ in this case. An issue with interfer- ence suppression (or Rx nulling) may be that STA3 requires three antennas in this case, because one spatial DoF is used to receive SS from STA2 and the other two spatial DoFs are consumed to steer null to AP. Intuitively, ‘spatial DoF’ is ‘number of STA3’s antennas’ in this case. If each device had more antennas, there would not be any issues, but in practice a small number of antennas generally provided or assumed.

[0021] In more general, upon the above-mentioned assumption, AP can use NAPtspatial DOFs at most but consumes Nsant2spatial degrees of freedom to steer null to STA3 with the conventional CBF. If NSSPAA+ N„PA3> NAPt, AP cannot prevent interfering STA3 when AP and STAs simultaneously transmit, or has to reduce at least NSS1to meet the condition NssjA1+ N„nA3< NAPt. To realize CBF under the condition NSSPAA+ N„PA3> NAPt, a BF al- gorithm and protocol improvement are required, for which several embodiments are pre- sented according to the present disclosure.

[0022] Fig. 2 shows a diagram of the exemplary system shown in Fig. 1 , in which different chan- nels are indicated. hAdenotes a channel of a link (also called first channel) from STA2 to STA3 (P2P link), h2denotes a channel of link (also called second channel) from AP to STA3 (interference link 1), and h3denotes a channel of link (also called third channel) from AP to STA1 (non-P2P link). Further, it shall be assumed that STA / c has N^tk(k = 1,2,3) antennas and AP has NA?t antennas.

[0023] In general operation, AP is aware of h2before steering null to STA3, but not aware of the postcoding matrix P (more generally, postcoding information) to be used at STA3 for the P2P link, because the postcoding matrix P is calculated based on at least hAas well as the number of spatial streams on the P2P link, which is typically determined by STA2. In this case, the steering matrix wAPof the AP may be calculated so that it is (nearly) orthog- onal to h2to ensure less interference at STA3. Equation (1) expresses a received signal as the j-th spatial stream ytat STA3 from STA2, where y^ is an intended signal from STA2, j / 1-1is an inter-spatial-stream interference from STA2, ytis an interference signal from AP for the i-th spatial stream from STA2 and wSTA2is steering matrix of STA2 for the P2P link. [X](a,b) indicates (a, h)-component of matrix X.

[0024] In a practical case, however, the number of implemented antennas is limited so that the above mechanism hardly works in some cases where NggA1+ N$nt3> Nant is met. It shall be assumed that h2is a Nas™3-by-A^ft(Nant3 Nant) matrix, and the rank of h2is Nant3- ln casethat AP tries to steer null to STA3, AP consumes N$nt3spatial degrees of freedom for nulling, and the AP can allocate at most NA£t- N$nt3spatial degrees of free- dom for transmission to STAs. In this case, the AP calculates wAPsuch that wAPis (al- most) orthogonal to h2as illustrated in Fig. 3 showing an equation of the interference sig- nal at the STA3 from the AP. If NA£t= N$nt3, the AP cannot allocate or calculate any vec- tors to the transmission to STA1.

[0025] If the AP is aware of Ph2, the AP possibly steers null to STA3 while transmitting data to STA1 simultaneously, even though NggA1+ N$nt3> Nantis met. In this case, the AP cal- culates wAPsuch that wAPis (almost) orthogonal to Ph2according to the present disclo- sure, instead of h2as described above. If the rank of Ph2, ranktPhz), is less than NA£t, the AP has to consume only rank^Ph^ spatial degrees of freedom, and can allocate or calculate at most NA£t- rank^Ph^ vector(s) for transmission to STA1 while AP steers null to STA3 which uses postcoding matrix P.

[0026] Regularly, P is calculated from a training field in each received signal from STA2. It is not guaranteed that it is always the same matrix because hAmay change to a certain extent. Furthermore, the size of P depends on the number of spatial streams on the P2P link. However, the AP can steer null to STA3 within a certain duration if the following conditions are met: i) Channels hAand h2can be seen static within the duration, which means that P can also be considered to be static, and ii) the number of spatial streams on the P2P link is fixed within the duration.

[0027] As mentioned above, Ph2(indicated as X in Fig. 4 showing the equation of the interfer- ence signal at the STA3 from the AP with partly different terminology than in Fig. 3) should be known by the AP. Furthermore, Ph2may be fed back to the AP. In the following, the feedback of Ph2in whichever format is called feedback response (it may be called feed- back information or Kernel Feedback as well).

[0028] In the following, an embodiment of a communication scheme or protocol for transmitting the feedback response (Kernel Feedback) is described. The communication link from the AP to STA3 shall be referred to as interference link 1 , and the communication link from STA2 to STA1 shall be referred to as interference link 2. It shall be assumed that each de- vice sometimes sends data to the destination on an interference link, and the signal on the interference link is not always treated as interference. In the following, the feedback re- sponse is considered only for interference link 1 .

[0029] As illustrated in Fig. 2, each of STA1 , STA2 (Console), and STA3 (HMD) is associated with AP. STA2 and STA3 establish the P2P link between them with support from the AP,for example based on TDLS. The capability of each device may be exchanged among the devices through establishing association and may include the capability of the feedback response. The method of P2P link establishment shall herein not be discussed in more detail.

[0030] Fig. 5 shows a diagram of the exemplary system shown in Fig. 1 , into which exemplary beams are indicated to illustrate an embodiment of the present disclosure. Fig. 6 shows a diagram of an embodiment of a communication scheme according to the present disclo- sure. Fig. 5 particularly indicates some of the essential steps of the communication scheme shown in Fig. 6, in particular steps 100, 200, 300 and 400. Part of the concept il- lustrated in Figs. 5 and 6 is that the AP sets a beam with knowledge of STA3’s receive (Rx) beam (or postcoding matrix). The AP may thus consume only one spatial DoF after it is aware of STA3’s Rx beam. Since the non-P2P link also requires a high data rate, STA2 and STA3 set Tx / Rx beam prior to the AP.

[0031] The P2P link can be valid until the time, which is indicated in the P2P link setup, or until the AP receives either from STA2 or STA3 an indication that the P2P link is terminated.

[0032] Initially (not shown), a capabilities exchange may be performed. STA3 may send to theAP the following indication:• ^ / s-m?nRxNu11' which is the minimum number of nulling to unintended / interference signal when STA3 receives a signal at the same time; and•Wss-MaxxNull> which is the maximum number of nulling to unintended / interference signal when STA3 receives a signal at the same time.This indication may be sent as a part of capabilities during association between AP and STA3.

[0033] In step 1 , a P2P link setup may be performed. As illustrated in Fig. 6, the P2P link be- tween STA2 and STA3 is established. Through the P2P link setup, AP, STA2 and STA3 negotiate, which frequency channel is allocated to the P2P link, and determine that a fre- quency channel for the P2P link is fully / partially overlapped with the frequency channel for the non-P2P link. STA2 may also establish a P2P link with STA1 in the same manner, butthe frequency channel between STA1 and STA2 shall include the frequency channel that is overlapped with both the non-P2P link and the P2P link. For example, if the primary channel P of the BSS and the secondary channel S1 of the BSS are allocated for the non- P2P link and the secondary channels S1 to S3 of the BSS are allocated for the P2P link between STA2 and ST A3, the channel frequency for the P2P link between STA1 and STA2 shall include the secondary channel S1.

[0034] Fig. 7 illustrates an example of a frequency channel allocation to both links. For the non- P2P link, P and S1 are allocated but S2 and S3 are not allocated (or not allocated some time). In another example, S1 to S3 may be allocated as channel candidates for the P2P link, but permission from the AP is needed before using S1 for the P2P link, for example due to prioritizing the non-P2P link on S1.

[0035] To differentiate P2P links, the P2P link between STA1 and STA2 is called ‘P2P link 12’, and P2P link between STA2 and STA3 is called ‘P2P link 23’ hereinafter. The P2P link 12 and interference link 2 are essentially the same, but the difference is whether the P2P link is established to send data or not.

[0036] After P2P link setup in step 1 , STA2 sends to AP a request for Coordinated Beamforming (CBF Req in Fig. 6) in step 2. The CBF request preferably includes one or more of the fol- lowing indications: i) A request to the AP to send a CBF response to STA2; and ii) the maximum number of spatial streams for the P2P link 23,'nupcoming CBF.

[0037] Further, the CBF request may include one or more of the following indications: iii) The total number of STA2’s spatial degree of freedom, which can be uti- lized in the upcoming CBF; iv) the allowable overlapped frequency channel between the non-P2P link and the P2P link 23 in the upcoming CBF; v) if traffic from STA2 to STA3 should be prioritized, preferred transmission time(s) / duration(s) for CBF and an identifier of CBF transmission; andvi) whether STA2 prefers channel sounding with STA3 on the P2P link 23 after the CBF response.

[0038] The CBF request of step 2 may also be interpreted by AP such that STA2 performs sounding with at least STA1 after the AP sends a CBF response to STA2 in response to the CBF request, or such indication may also be included in the CBF request.

[0039] After the AP received the CBF request from STA2 in step 2 (CBF res in Fig. 6), the AP sends a CBF response to STA2 in step 3. The CBF response preferably includes one or more of the following indications: i) Admission for CBF with STA2; ii) ^Vss-mFnA3 ;the minimum number of spatial degrees of freedom for nul- ling to STA3 from AP during CBF; and iii) The indication whether the transmission of a feedback response (Kernel feedback) is planned afterwards.The CBF response may also include an indication of the maximum number of spatial streams on non-P2P link(s), frequency channel for P2P link 12, and frequency channel for P2P link 23.

[0040] In some embodiments, the CBF request and CBF response may be exchanged as part of the P2P link setup in step 1 .

[0041] The AP may decide to obtain a feedback response from STA3 (i.e. , to perform Kernel feedback) if the number of spatial streams for transmission to STA1 from AP is greater than As7’-mmRxNu11, and then indicate that feedback response (Kernel Feedback) is planned afterwards.

[0042] If STA2 receives the CBF response in step 3, which indicates that feedback response from STA3 (Kernel feedback) is planned afterwards, STA2 may set up the P2P link 12 and perform channel sounding with STA1 on the P2P link 12 to enable steering null in step 400. If STA1 and STA2 do not need any frame exchange, for example STA2 does not have to steer null to STA1 in step 4, this P2P link setup (i.e., step 4) may be skipped.

[0043] After receiving the CBF response in step 3, STA2 conducts channel sounding with STA1 (steps 5, 6 and 7) and STA3 (step 100, including steps 101 , 102 and 103) to determine steering matrices for the P2P link 23. Channel sounding of STA2 with STA1 particularly aims at enabling STA2 to steer null to STA1 during CBF in step 400. This channel sound- ing and steering null to STA1 by STA2 are optional and may be skipped in some embodi- ments. Channel soundings of STA2 with each of STA1 and STA3 allows STA2 to calcu- late steering matrices (or set a beam) but may be skipped if each channel sounding is al- ready conducted before receiving the CBF response in step 4. If channel sounding with STA3 is not conducted beforehand, channel sounding with STA3 shall be conducted in step 100. Step 100 thus performs channel sounding between STA2 and STA3, in which STA2 sets the Tx beam (for steering matrices) to be used.

[0044] As illustrated in Fig. 6, in some embodiments, STA2 sends a Null Data Packet Announce- ment (NDPA) (steps 5 and 101) prior to sending a Null Data Packet (NDP; also called training packet or training data) (steps 6 and 102). NDPA and NDP can be designed and contain information as defined in the standard IEEE 802.11 , but NDPA (in step 101) may additionally include one or more of the following indications (FBCK request in the follow- ing): i) Sounding for feedback (Kernel feedback) is planned to take place after- wards; ii) The destination of the feedback (Kernel feedback), and / or the initiator of sounding for feedback (Kernel feedback); and iii) The number of spatial streams to be used on the P2P link 23 after the feedback (Kernel FBCK in Fig. 6).

[0045] After receiving NDP from STA2 (steps 6 and 102), STA1 and STA3 send CSI feedback (CSI FBCK) to STA2 in steps 6 and 103). The CSI feedback can be designed and contain information as defined in the standard IEEE 802.11 as Compressed Feedback.

[0046] In some embodiments, as illustrated in Fig. 6, the feedback request (Kernel Feedback re- quest, FBCK req in Fig. 6) may be included in or appended to a beamformed data unit, e.g. a PPDll (PHY Protocol Data Unit) or another NDP transmitted from STA2 to STA3 in a separate step 201 of step 200 instead of being included in the NDPA transmitted in step101. The feedback request is thus transmitted after the CSI feedback in step 103. In an optional step 202 ST A3 may transmit an acknowledgement (Ack) to STA2. Thus, in step 200 beamformed PPDll reception from STA2 is performed, in which the STA3 sets Rx beam (or postcoding matrices) to be used.

[0047] In the data unit transmission, STA2 may use (set) a steering matrix w2(i.e. , STA2 sets a beam), which is calculated from the CSI feedback from STA3 (transmitted in step 103), so that STA3 can calculate the postcoding matrix P for the P2P link 23 before STA 3 receives an NDP from AP (step 301), which enables STA3 to calculate the feedback response (Kernel feedback). If the beamformed data unit is not transmitted to STA3 during the time from P2P link setup for the P2P link 12 (step 4) to the NDP transmission from AP (step 301), STA3 may reuse the postcoding matrix which is already used in a previous commu- nication with STA2.

[0048] After the sounding / feedback (steps 100 and 200) is finalized AP sends NDPA (step 301) and NDP (step 302) to STA3 for channel sounding of interference link 1. STA2 (or STA3) may optionally send a frame (called sounding request from STA3 in step 8 in Fig. 6) that is implicitly or explicitly soliciting AP for the NDPA / NDP transmission, i.e., informs the AP that STA3 is ready for step 300. This sounding request in step 8 may be designed and contain information identical to a CF (Contention-Free) End frame defined in the standard IEEE 802.11 to indicate that STA2’s TXOP (Transmission Opportunity) is terminated.

[0049] If STA2 transmits to AP the sounding request in step 8 soliciting AP for channel sounding of interference link 1, this sounding request may also include an estimated interference level at STA1 in the upcoming CBF. The estimated interference level can be derived from the CSI feedback from STA1 to STA2 (step 7) and the CSI feedback from STA3 to STA2 (step 103), for example, by use of the following equation:h12is the CSI indicated in the CSI feedback from STA1 to STA2, w2is the first Eigenvec- tor of h^2h12, p is an expected transmission power of STA2 for the P2P link 23 duringrow and j-th column element of Y1.

[0050] The NDPA of step 301 may be designed and contain information as defined in the stand- ard IEEE 802.11 , and it may also include an indication to solicit the intended receiver(s) for a feedback response (Kernel feedback).

[0051] After receiving the NDPA and NDP, STA3 transmits the feedback response (Kernel feed- back) to AP in step 303. Thus, in step 300 the transmission of the feedback response is initiated and performed, in which STA3 informs the AP of Ph2(=X).

[0052] After receiving the feedback response, the AP calculates steering matrices based on the feedback response and transmits a trigger to STA2 to perform CBF (step 401). The time / duration may be determined based on the scheduling information received within the CBF request. Afterwards, the AP and STA2 may perform CBF and concurrently transmit data, e.g., in the form of PPDlls (steps 402, 403). Thus, in step 400 simultaneous trans- missions of AP and STA2 are enabled since the AP sets its Tx beam (or steering matri- ces) so that it yields less interference with STA3’s Rx beam. The AP can calculate steer- ing matrices wAPas shown in the following equation:where k is real number for power coefficient and e is one of eigen vectors of Z with the most eigen valuewhere Hi is a channel matrix of the channel between the AP and STA1 , H3is matrix indi- cated in the feedback response (Kernel feedback), N is the Noise-to-Signal Ratio, and I is an identity matrix.

[0053] Fig. 8 shows a diagram of another embodiment of a communication scheme according to the present disclosure. In this embodiment, NDPA may be transmitted from AP or concur- rently from both AP (step 301) and STA2 (steps 5 and 101), as illustrated in Fig. 8. In this case, NDPs may be concurrently transmitted from both AP (step 302) and STA2 to STA1 (step 6) and STA3 (step 102), and feedback may also be concurrently or non-concurrently transmitted from STA1 to AP (step?) and STA2 (step 7) and from STA3 to AP (step 303) and STA2 (step 103).

[0054] Although not shown in Fig. 8, an indication may be transmitted such that the NDPA(s) and the subsequent NDPs are aiming for a feedback response (Kernel feedback) for the inter- ference link. This indication may include an information which receivers are planned to send a feedback response (Kernel feedback) to which transmitter(s). This indication may be included in NDPA(s) or transmitted before the NDPA(s). The indication can be inter- preted by intended receivers (STA3 in Fig. 8) such that STA3 is solicited for a feedback response after receiving a data frame from STA2 after the FBCK (step 103).

[0055] Fig. 9 shows a diagram of still another embodiment of a communication scheme accord- ing to the present disclosure. In this embodiment, NDPA (step 301), NDP (step 302) and the feedback response (Kernel feedback) (step 303) may follow the CBF response. In this case, Ph2indicated in the feedback response (Kernel Feedback) can be derived under ei- ther one of the following assumptions: i) STA3 uses predetermined postcoding matrices (P), such as DFT (Dis- crete Fourier Transform) matrices, in receiving the PPDll transmitted with upcoming CBF; or ii) STA3 uses the same postcoding matrices (P) in receiving the PPDll transmitted with upcoming CBF.A trigger 404 is transmitted from STA2 in step 404 to trigger the concurrent PPDll trans- missions by AP and STA2 in the CBF (steps 402, 403).

[0056] Fig. 10 shows a flowchart of a communication method 500 that may be carried out by an AP. In a first step 501, the AP transmits, in response to a coordinated beamforming (CBF) request, a CBF response to a second communication device that is configured tocommunicate with a third communication device. In a second step 502, the AP receives a feedback response from the second communication device or the third communication de- vice, the feedback response including postcoding information of the third communication device for communication with the second communication device and / or channel infor- mation of a channel between the access point and the third communication device. In a third step 503, teh AP determines second steering information, e.g. a second steering ma- trix, based on the feedback response. In a fourth step, the AP communicates with the first communication device using the second steering information in coordination with commu- nication of the second communication device with the third communication device.

[0057] Fig. 11 shows a flowchart of a communication method 600 that may be carried out by a second communication device, e.g. STA2. In a first step 601 , STA2 transmits CBF request to an AP that is configured to communicate with a first communication device and the sec- ond communication device. In a second step 602, STA2 receives, in response to the CBF request, a CBF response from the AP. In a third step 603, STA2 transmits a feedback re- quest to the third communication device requesting it to transmit a feedback response to the access point, the feedback response including postcoding information of the third communication device for communication with the second communication device and / or channel information of a channel between the AP and the third communication device.

[0058] Fig. 12 shows a flowchart of a communication method 700 that may be carried out by a third communication device, e.g. STA3. In a first step 701 , STA3 receives a training packet from an AP that is configured to communicate with a first communication device and the second communication device and / or a feedback request from the second com- munication device to transmit a feedback response to the AP, the feedback response in- cluding postcoding information of the third communication device for communication with the second communication device. In a second step 702, STA3 transmits the feedback re- sponse to the access point in response to the feedback request and / or one or more train- ing packets.

[0059] The device may be implemented by respective units or circuitry, e.g. a processor, pro- cessing circuitry, a computer, dedicated hardware, etc., that carries out the functions of the device. Alternatively, a common unit or circuitry, e.g. a common processor orcomputer, may implement the various functions of the device, or separate units or ele- ments may be used that together represent the circuitry.

[0060] Thus, the foregoing discussion discloses and describes merely exemplary embodiments of 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.

[0061] 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 measures are recited in mutually different dependent claims does not indicate that a com- bination of these measures cannot be used to advantage.

[0062] In so far as embodiments of the disclosure have been described as being implemented, at least 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.

[0063] The elements of the disclosed devices, apparatus and systems may be implemented by corresponding hardware and / or software elements, for instance appropriate circuits or cir- cuitry. A circuit is a structural assemblage of electronic components including conventional circuit elements, integrated circuits including application specific integrated circuits, stand- ard integrated circuits, application specific standard products, and field programmable gate arrays. Further, a circuit includes central processing units, graphics processing units,and microprocessors 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. A circuit or circuitry may be implemented by a single device or unit or multiple devices or units, or chipset(s), or processor(s).

[0064] It follows a list of further embodiments of the disclosed subject matter:1 . Access point configured to communicate with a first communication device and a second communication device, the access point comprising circuitry configured to: transmit, in response to a coordinated beamforming (CBF) request, a CBF re- sponse to a second communication device that is configured to communicate with a third communication device; receive a feedback response from the second communication device or the third communication device, the feedback response including postcoding information of the third communication device for communication with the second communication device and / or channel information of a channel between the access point and the third communi- cation device; determine second steering information based on the feedback response; and communicate with the first communication device using the second steering infor- mation in coordination with communication of the second communication device with the third communication device.2. Access point according to embodiment 1 , wherein the feedback response, received from the second communication device or the third communication device, includes a channel matrix of a channel between the access point and the third communication device and / or information of a product of a postcoding matrix and a channel matrix between the access point and the third communication de- vice.3. Access point according to embodiment 1 or 2, wherein the CBF response includes information regarding a number or minimum number of spatial degrees of freedom for steering null to the third communication device during coordinated beamforming.4. Access point according to any one of the preceding embodiments, wherein the CBF response includes: information whether the feedback response is desired to be received from the third communication device, and / or an indication that a feedback request or a training packet is transmitted to the third communication device from the access point.5. Access point according to embodiment 4, wherein the feedback request is transmitted jointly with second communication device.6. Access point according to any one of the preceding embodiments, wherein the circuitry is configured to transmit a training packet and optionally a training packet announcement to the third communication device triggering the third communica- tion device to transmit the feedback response.7. Access point according to any one of the preceding embodiments, wherein the circuitry is configured to determine a second steering matrix representing the second steering information such that the product of a postcoding matrix representing the postcoding information, a channel matrix representing the channel information and the second steering matrix is substantially zero.8. Access point according to any one of the preceding embodiments, wherein the circuitry is configured to communicate with the first communication device in coordination with communication of the second communication device with the third com- munication device.9. Access point according to any one of the preceding embodiments, where in the circuitry is configured to transmit the feedback request to the third communication device after transmitting, in response to the CBF request from the second communication device, a CBF response to the second communication device.10. Second communication device configured to communicate with a third communica- tion device and an access point, the second communication device comprising circuitry configured to: transmit a coordinated beamforming (CBF) request to an access point that is con- figured to communicate with a first communication device and the second communication device receive, in response to the CBF request, a CBF response from the access point; and transmit a feedback request to the third communication device requesting it to transmit a feedback response to the access point, the feedback response including post- coding information of the third communication device for communication with the second communication device and / or channel information of a channel between the access point and the third communication device.11. Second communication device according to embodiment 10, wherein the circuitry is configured to transmit the feedback request to the third communi- cation device requesting it to transmit a feedback response to the access point in re- sponse to a training packet received from the access point.12. Second communication device according to embodiment 10 or 11 , wherein the circuitry is configured to communicate with the third communication device via a direct link and / or to transmit the channel information of a channel between the access point and the third communication device via the direct link.13. Second communication device according to any one of embodiments 10 to 12, wherein the circuitry is configured to transmit the feedback request as part of a data unit or appended to a data unit transmitted to the third communication device.14. Second communication device according to any one of embodiments 10 to 13, wherein the circuitry is configured to determine first steering information, in particular a first steering matrix, based on first channel information of a channel between the second communication device and the third communication device; andtransmit the transmit the feedback request using the first steering information as separate information or included in or appended to a data unit.15. Second communication device according to any one of embodiments 10 to 14, wherein the circuitry is configured to communicate, after transmitting the feedback request and in response to a trigger from the access point, with the third communication device in coordination with the communication of the access point with the first communication de- vice.16. Second communication device according to any one of embodiments 10 to 15, wherein the circuitry is configured to transmit, before transmitting the feedback request to the third communication device, a training packet and optionally a training packet an- nouncement to the third communication device triggering the third communication device to transmit first channel information of a channel between the second communication de- vice and the third communication device.17. Second communication device according to any one of embodiments 10 to 16, wherein the circuitry is configured to include into the training packet announcement one or more of: information that sounding for generating the feedback response is planned; the destination of the feedback response; and the number of spatial streams to be used for the communication between the sec- ond communication device and the third communication device on the direct link during coordinated beamforming.18. Second communication device according to any one of embodiments 10 to 17, wherein the circuitry is configured to transmit, after receiving the CBF request, a training packet and optionally a training packet announcement to the first communication device triggering the first communication device to transmit fourth channel information of a channel between the second communi- cation device and the first communication device; and determine a fourth steering matrix based on the fourth channel information for steering null to the first communication device during coordinated beamforming.19. Second communication device according to embodiment 17 and 18, wherein the circuitry is configured to transmit the training packets and optionally training packet announcements to the first communication device and the third communication de- vice simultaneously and optionally simultaneously to a transmission of a training packet and optionally a training packet announcement from the access point to the third commu- nication device.20. Second communication device according to any one of embodiments 10 to 19, wherein the circuitry is configured to transmit, after transmitting the feedback request, a sounding request to the access point informing the access point that the third communica- tion device is ready for generating the feedback response.21 . Third communication device configured to communicate with a second communi- cation device, the third communication device comprising circuitry configured to: receive a training packet from an access point that is configured to communicate with a first communication device and the second communication device and / or a feed- back request from the second communication device to transmit a feedback response to the access point, the feedback response including postcoding information of the third communication device for communication with the second communication device; and transmit the feedback response to the access point in response to the feedback re- quest and / or training packet.22. Third communication device according to embodiment 21 , wherein the circuitry is configured to communicate with the second communication device via a direct link and / or wherein the feedback response includes the postcoding information of the third communication device for communication with the second communication de- vice via the direct link.23. Third communication device according to embodiment 21 or 22, wherein the circuitry is configured to determine the postcoding information based on one or more data units received from the second communication device.24. Third communication device according to any one of embodiments 21 to 23, wherein the circuitry is configured to include in the feedback response second channel in- formation of a channel between the access point and the third communication device.25. Third communication device according to any one of embodiments 21 to 24, wherein the circuitry is configured to include in the feedback response a postcoding ma- trix, representing the postcoding information, of the third communication device for com- munication with the second communication device and a channel matrix, representing the channel information, of a channel between the access point and the third communication device.26. Third communication device according to any one of embodiments 21 to 25, wherein the circuitry is configured to transmit, before receiving the feedback request, first channel information of a channel between the second communication device and the third communication device to the second communication device.27. Third communication device according to any one of embodiments 21 to 26, wherein the circuitry is configured to communicate, after transmitting the feedback re- sponse and in response to a trigger from the access point, with the second communica- tion device in coordination with the communication of the access point with the first com- munication device.28. Communication method of an access point configured to communicate with a first communication device and a second communication device, the access point comprising circuitry configured to: transmit, in response to a coordinated beamforming (CBF) request, a CBF re- sponse to a second communication device that is configured to communicate with a third communication device; receive a feedback response from the second communication device or the third communication device, the feedback response including postcoding information of the third communication device for communication with the second communication device and / or channel information of a channel between the access point and the third communi- cation device;determine second steering information based on the feedback response; and communicate with the first communication device using the second steering infor- mation in coordination with communication of the second communication device with the third communication device.29. Communication method of a second communication device configured to com- municate with a third communication device and an access point, the second communica- tion device comprising circuitry configured to: transmit a coordinated beamforming (CBF) request to an access point that is con- figured to communicate with a first communication device and the second communication device receive, in response to the CBF request, a CBF response from the access point; and transmit a feedback request to the third communication device requesting it to transmit a feedback response to the access point, the feedback response including post- coding information of the third communication device for communication with the second communication device and / or channel information of a channel between the access point and the third communication device.30. Communication method of a third communication device configured to communi- cate with a second communication device, the third communication device comprising cir- cuitry configured to: receive a training packet from an access point that is configured to communicate with a first communication device and the second communication device and / or a feed- back request from the second communication device to transmit a feedback response to the access point, the feedback response including postcoding information of the third communication device for communication with the second communication device; and transmit the feedback response to the access point in response to the feedback re- quest and / or one or more training packets.31 . 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 28, 29 or 30 to be performed.32. A computer program comprising program code means for causing a computer to perform the steps of said method according to embodiment 28, 29 or 30 when said com- puter program is carried out on a computer.

Claims

CLAIMS1. Access point configured to communicate with a first communication device and a second communication device, the access point comprising circuitry configured to: transmit, in response to a coordinated beamforming (CBF) request, a CBF re- sponse to a second communication device that is configured to communicate with a third communication device; receive a feedback response from the second communication device or the third communication device, the feedback response including postcoding information of the third communication device for communication with the second communication device and / or channel information of a channel between the access point and the third communi- cation device; determine second steering information based on the feedback response; and communicate with the first communication device using the second steering infor- mation in coordination with communication of the second communication device with the third communication device.

2. Access point according to claim 1 , wherein the feedback response, received from the second communication device or the third communication device, includes a channel matrix of a channel between the access point and the third communication device and / or information of a product of a postcoding matrix and a channel matrix between the access point and the third communication de- vice.

3. Access point according to claim 1 , wherein the CBF response includes: information regarding a number or minimum number of spatial degrees of freedom for steering null to the third communication device during coordinated beamforming; and / or information whether the feedback response is desired to be received from the third communication device; and / or an indication that a feedback request or a training packet is transmitted to the third communication device from the access point.

4. Access point according to claim 1 , wherein the circuitry is configured to transmit a training packet and optionally a training packet announcement to the third communication device triggering the third communica- tion device to transmit the feedback response.

5. Access point according to claim 1 , where in the circuitry is configured to transmit the feedback request to the third communi- cation device after transmitting, in response to the CBF request from the second commu- nication device, a CBF response to the second communication device.

6. Second communication device configured to communicate with a third communica- tion device and an access point, the second communication device comprising circuitry configured to: transmit a coordinated beamforming (CBF) request to an access point that is con- figured to communicate with a first communication device and the second communication device; receive, in response to the CBF request, a CBF response from the access point; and transmit a feedback request to the third communication device requesting it to transmit a feedback response to the access point, the feedback response including post- coding information of the third communication device for communication with the second communication device and / or channel information of a channel between the access point and the third communication device.

7. Second communication device according to claim 6, where in the circuitry is configured to transmit: the feedback request to the third communication device requesting it to transmit a feedback response to the access point in response to training packets received from the access point; and / or the training packets and optionally training packet announcements to the first com- munication device and the third communication device simultaneously and optionallysimultaneously to a transmission of a training packet and optionally a training packet an- nouncement from the access point to the third communication device; and / or, after transmitting the feedback request, a sounding request to the access point in- forming the access point that the third communication device is ready for generating the feedback response.

8. Second communication device according to claim 6, wherein the circuitry is configured to communicate with the third communication device via a direct link and / or to trans- mit the channel information of a channel between the access point and the third communi- cation device via the direct link; and / or communicate, after transmitting the feedback request and in response to a trigger from the access point, with the third communication device in coordination with the com- munication of the access point with the first communication device.

9. Second communication device according to claim 6, wherein the circuitry is configured to determine first steering information, in particular a first steering matrix, based on first channel information of a channel between the second communication device and the third communication device; and transmit the transmit the feedback request using the first steering information as separate information or included in or appended to a data unit.

10. Second communication device according to claim 16, wherein the circuitry is configured to transmit, before transmitting the feedback request to the third communication device, a training packet and optionally a training packet an- nouncement to the third communication device triggering the third communication device to transmit first channel information of a channel between the second communication de- vice and the third communication device.

11. Second communication device according to claim 10, wherein the circuitry is configured to include into the training packet announcement one or more of:information that sounding for generating the feedback response is planned; the destination of the feedback response; and the number of spatial streams to be used for the communication between the sec- ond communication device and the third communication device on the direct link during coordinated beamforming.

12. Second communication device according to claim 6, wherein the circuitry is configured to transmit, after receiving the CBF request, a training packet and optionally a training packet announcement to the first communication device triggering the first communication device to transmit fourth channel information of a channel between the second communi- cation device and the first communication device; and determine a fourth steering matrix based on the fourth channel information for steering null to the first communication device during coordinated beamforming.

13. Third communication device configured to communicate with a second communi- cation device, the third communication device comprising circuitry configured to: receive a training packet from an access point that is configured to communicate with a first communication device and the second communication device and / or a feed- back request from the second communication device to transmit a feedback response to the access point, the feedback response including postcoding information of the third communication device for communication with the second communication device; and transmit the feedback response to the access point in response to the feedback re- quest and / or training packet.

14. Third communication device according to claim 13, wherein the circuitry is configured to communicate with the second communication device via a direct link and / or wherein the feedback response includes the postcoding information of the third communication device for communication with the second communication de- vice via the direct link.

15. Third communication device according to claim 13, wherein the circuitry is configured to include in the feedback response:second channel information of a channel between the access point and the third communication device, and / or a postcoding matrix, representing the postcoding information, of the third commu- nication device for communication with the second communication device and a channel matrix, representing the channel information, of a channel between the access point and the third communication device.

16. Third communication device according to claim 13, wherein the circuitry is configured to transmit, before receiving the feedback request, first channel information of a channel between the second communication device and the third communication device to the second communication device.

17. Communication method of an access point configured to communicate with a first communication device and a second communication device, the access point comprising circuitry configured to: transmit, in response to a coordinated beamforming (CBF) request, a CBF re- sponse to a second communication device that is configured to communicate with a third communication device; receive a feedback response from the second communication device or the third communication device, the feedback response including postcoding information of the third communication device for communication with the second communication device and / or channel information of a channel between the access point and the third communi- cation device; determine second steering information based on the feedback response; and communicate with the first communication device using the second steering infor- mation in coordination with communication of the second communication device with the third communication device.

18. Communication method of a second communication device configured to com- municate with a third communication device and an access point, the second communica- tion device comprising circuitry configured to:transmit a coordinated beamforming (CBF) request to an access point that is con- figured to communicate with a first communication device and the second communication device receive, in response to the CBF request, a CBF response from the access point; and transmit a feedback request to the third communication device requesting it to transmit a feedback response to the access point, the feedback response including post- coding information of the third communication device for communication with the second communication device and / or channel information of a channel between the access point and the third communication device.

19. Communication method of a third communication device configured to communi- cate with a second communication device, the third communication device comprising cir- cuitry configured to: receive a training packet from an access point that is configured to communicate with a first communication device and the second communication device and / or a feed- back request from the second communication device to transmit a feedback response to the access point, the feedback response including postcoding information of the third communication device for communication with the second communication device; and transmit the feedback response to the access point in response to the feedback re- quest and / or one or more training packets.

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