Communication devices and methods to perform conditional TXOP sharing

Abstract

A first communication device according to the present disclosure is configured to communicate with one or more third communication device and comprises circuitry configured to: obtain a transmission opportunity (TXOP); transmit an initial control frame to a second communication device, the initial control frame indicating that the obtained TXOP may be shared with the second communication device and including conditioning information prioritizing or restricting the use of the obtained TXOP to an operating mode and / or restricting frame exchanges of the second communication device during the obtained TXOP to one or more parameters; receive an initial control response frame from the second communication device, the initial control response an indication whether the second communication device can participate in the obtained TXOP; and allocate at least a part of the obtained TXOP to the second communication device allowing it to exchange one or more frames with one or more fourth communication devices taking account of the conditioning information.

Description

COMMUNICATION DEVICES AND METHODS TO PERFORM CONDITIONAL TXOP SHARINGBACKGROUNDFIELD OF THE DISCLOSURE

[0001] The present disclosure relates to first and second communication devices and methods for communicating with other (third and fourth, respectively) communication devices.DESCRIPTION OF RELATED ART

[0002] Coordinated Time Division Multiple Access (CTDMA) is a candidate technology for the next IEEE 802.11 amendment (802.11 bn). Essentially, the coordinated operation is introduced to allow an access point (AP), also referred to as sharing AP, to share a transmission opportunity (TXOP), which it obtained after contending to the medium, with anotherAP, also referred to as shared AP, which may subsequently perform a frame exchange with stations (STAs) within its basic service set (BSS). To make effective use of CTDMA in practical scenarios multiple challenges need to be addressed, in particular the way how to share a TXOP.

[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 admitted as prior art against the present disclosure.SUMMARY

[0004] It is an object to make effective use of CTDMA, in particular provide ways how to share a TXOP in the context of CTDMA. It is a further object to provide communication devices and corresponding methods as well as a corresponding computer program and a non- transitory computer-readable recording medium that stores therein a computer program product for implementing said methods.

[0005] According to an aspect there is provided a first communication device configured to communicate with one or more third communication device, the first communication device comprising circuitry configured to: obtain a transmission opportunity (TXOP); transmit an initial control frame to a second communication device, the initial control frame indicating that the obtained TXOP may be shared with the second communication device and including conditioning information prioritizing or restricting the use of the obtained TXOP to an operating mode and / or restricting frame exchanges of the second communication device during the obtained TXOP to one or more parameters; receive an initial control response frame from the second communication device, the initial control response an indication whether the second communication device can participate in the obtained TXOP; andallocate at least a part of the obtained TXOP to the second communication device allowing it to exchange one or more frames with one or more fourth communication devices taking account of the conditioning information.

[0006] According to a further aspect there is provided a second communication device configured to communicate with one or more fourth communication device, the second communication device comprising circuitry configured to: receive an initial control frame from a first communication device, the initial control frame indicating that a TXOP obtained by the first communication device may be shared with the second communication device, and including conditioning information prioritizing or restricting the use of the obtained TXOP to an operating mode and / or restricting frame exchanges of the second communication device during the obtained TXOP to one or more parameters; transmit an initial control response frame to the first communication device, the initial control response including an indication whether the second communication device can participate in the obtained TXOP; and receive an allocation of at least a part of the obtained TXOP from the first communication device allowing the second communication device to exchange one or more frames with one or more fourth communication devices taking account of the conditioning information.

[0007] 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 product, which, when executed by a processor, causes the method disclosed herein to be performed are provided.

[0008] Embodiments are defined in the dependent claims. It shall be understood that the disclosed methods, the disclosed computer program and the disclosed computer-readable recording medium have similar and / or identical further embodiments as the claimed devices and as defined in the dependent claims and / or disclosed herein.

[0009] One of the aspects of the disclosure is to make use of a concept exchanging an initial control frame and an initial control response including information regarding the sharing of an obtained TXOP and conditioning information that prioritizes or restricts the use of the obtained TXOP to an operating mode and / or restricts frame exchanges during the obtained TXOP to one or more parameters. Afterwards, the obtained TXOP may be shared, i.e. , at least part of the obtained TXOP may be allocated by a first communication device to a second communication device for communication with one or more fourth communication devices. Hereby, the conditioning information is observed by this communication / frame exchange of the second communication device. The sharing or use of an obtained TXOP is thus easily possible without much overhead and enables the effective use of the shared TXOP. This may particularly be used in a roaming scenario.

[0010] According to a further aspect there is provided a first communication device configured to communicate with one or more third communication device, the first communication device comprising circuitry configured to: obtain a transmission opportunity (TXOP); transmit an initial control frame to one or more second communication devices, the initial control frame indicating that at least a part of the obtained TXOP may be used by the second communication device to transmit one or more frames to one or more third and / or fourth communication devices and including conditioning information prioritizing or restricting frame transmissions of the second communication device during the obtained TXOP to one or more parameters; receive an initial control response frame from one or more of the second communication devices, the initial control response frame indicating whether the second communication device can participate in the obtained TXOP; and enable within at least a part of the obtained TXOP one or more of the second communication devices to transmit one or more frames to one or more third and / or fourth communication devices based on the conditioning information.

[0011] According to a further aspect there is provided a second communication device configured to communicate with one or more fourth communication device, the second communication device comprising circuitry configured to:receiving an initial control frame from a first communication device, the initial control frame indicating that a TXOP obtained by the first communication device may be used by the second communication device to transmit one or more frames to one or more third and / or fourth communication devices and including conditioning information prioritizing or restricting frame transmissions of the second communication device during the obtained TXOP to one or more parameters; transmitting an initial control response frame to the first communication device, the initial control response frame indicating whether the second communication device can participate in the obtained TXOP; and receiving an enablement within at least a part of the obtained TXOP from the first communication device allowing the second communication device to transmit one or more frames to one or more third and / or fourth communication devices based on the conditioning information.

[0012] These aspects preferably refer to a sounding scenario. In such a sounding scenario, the obtained TXOP may used by the second communication device to perform a frame exchange with one or more third communication devices, and the second communication device may be triggered to transmit a data unit for channel estimation by the one or more third communication devices. Thus, according to the present disclosure the conditional TXOP may condition the use of an obtained TXOP to some requirements fit for one or more of roaming, sounding and coordinated measurement in a multi-AP scenario.

[0013] The first communication device may operate as an AP in an embodiment, in particular as sharing AP. The second communication device may operate as an AP in an embodiment, in particular as shared AP. The third communication devices may operate as STAs, for instance in the BSS (also referred to as first BSS) of the sharing AP. The fourth communication devices may operate as STAs with which the shared AP performs frame exchange, for instance in the BSS (OBSS; also referred to as second BSS) of the shared AP.

[0014] 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 description taken in conjunction with the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWING

[0015] 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 to the following detailed description when considered in connection with the accompanying drawings, wherein:Fig. 1 shows a diagram illustrating the envisaged operation of a coordinated TXOP in the context of CTDMA.Fig. 2A a diagram illustrating a general roaming scenario.Fig. 2B shows a diagram of the basic architecture used for roaming and a link definition.Fig. 3 shows a diagram illustrating queue evolution at the source and target APs.Fig. 4 shows a diagram illustrating a first embodiment of the general use of a conditional coordinated TXOP according to the present disclosure.Fig. 5 shows a diagram illustrating a second embodiment of the use of a conditional coordinated TXOP according to the present disclosure in target AP assisted roaming.Fig. 6 shows a diagram illustrating control entity mediated information exchange according to an embodiment of the present disclosure.Fig. 7 shows a diagram illustrating a third embodiment of the use of a conditional coordinated TXOP according to the present disclosure for onboarding of a roaming station.Fig. 8 shows a diagram illustrating a fourth embodiment of the use of a conditional coordinated TXOP according to the present disclosure.Fig. 9 shows a diagram illustrating a fifth embodiment of the use of a conditional coordinated TXOP according to the present disclosure using prioritized transmission.Fig. 10 shows a diagram illustrating a fifth embodiment of the use of a conditional coordinated TXOP according to the present disclosure using assisted link measurement.Fig. 11 shows a diagram illustrating a seventh embodiment of the use of a conditional coordinated TXOP according to the present disclosure to enable roaming parameters collection from a target APFig. 12 shows a diagram illustrating an eighth embodiment of the use of a conditional coordinated TXOP according to the present disclosure to assist a target AP in a roaming scenario in respecting SOS agreements for traffics corresponding to the roaming STA.Fig. 13 shows a flowchart of a first communication method according to the present disclosure.Fig. 14 shows a flowchart of a second communication method according to the present disclosure.Fig. 15 shows a diagram illustrating a ninth embodiment of the use of a conditional coordinated TXOP according to the present disclosure for use in a sounding scenario.Fig. 16 shows a diagram illustrating further details of the ninth embodiment in the sounding scenario.Fig. 17 shows a diagram of an embodiment of a null data packet announcement frame that may be used for sounding.Fig. 18 shows a diagram of another embodiment of a second communication method according to the present disclosure during sounding.Fig. 19 shows a diagram illustrates different sounding examples.Fig. 20 shows a flowchart of another embodiment of a first communication method according to the present disclosure.Fig. 21 shows a flowchart of still another embodiment of a second communication method according to the present disclosure.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, Fig. 1 shows a diagram illustrating the envisaged operation of a coordinated TXOP in the context of CTDMA, which may be used for WLAN communication.

[0017] The schedule allocation frame 10 at the start of the TXOP addresses the sharing AP (herein also referred to as first communication device or AP1) to inform that the follow-up TXOP can be shared with another AP (further referred to as second communication device or AP2 or shared AP) and indicate the earliest time a transmission of the shared AP, may start within the obtained TXOP. A response 11 from the shared AP follows indicating that it can participate in the shared TXOP. The schedule allocation 10 and related response 11 is also present for both APs to prepare the current TXOP. Sequential data exchanges 12, 14 by the respective APs with corresponding STAs within their BSSs follows (the corresponding STAs being herein also referred to as one or more third communication device(s) associated the sharing AP and one or more fourth communication device(s) associated the shared AP). A shared AP allocation 13 is transmitted by the sharing AP toinform the shared AP that it may start frame exchange with its STA(s) and indicate further parameters to be used such as duration of the shared part of the TXOP for the AP2 allocation.

[0018] There are, however, a whole range of applications, besides the sequential data exchange of the respective APs with corresponding STAs within their BSSs, which could benefit from the coordinated AP transmission. Exemplary applications include roaming assistance, coordinated sounding, and coordinated scanning. For such applications the AP obtaining the TXOP has a precise incentive to share the TXOP and may recommend or restrict the use of the shared portion of the TXOP to the specific incentive. In the following this behavior and the idea of the present disclosure will be described in the context of roaming as one example of an application for which the present disclosure may be used.

[0019] Fig. 2A shows a diagram illustrating a general roaming scenario. Fig. 2B shows a diagram of the basic architecture used for roaming and a link definition. A STA, depicted as roaming STA (rSTA), is associated with a source AP (APS) on Linksand observes a better signal from a target AP (APt). Consequently, rSTA requests APSto perform roaming to APt(target AP), which includes: adding a new link (Linkt at APt), performing a transfer of basic information to speed up association (e.g., capabilities, security keys) and performing a transfer of information to enable smooth data session transitions with low to null data loss (i.e., transfer of context information including SNs, PNs, Block Ack Agreements, Stream Classification Service (SCS) Agreements).

[0020] The operation may be supported by the use of a control entity (CE), operating preferably at an upper MAC layer, which can be implemented in a centralized manner (one CE for several APs) or distributed (each AP affiliated with a CE) and which is performing a switching of the data path for traffic with rSTA from APSto APt.

[0021] Based on the capabilities of the devices, the operating channels at the APs and the mappings of the links at the AP MLDs (Multi-Link Devices), roaming operation may be single link (connectivity with only one link during roaming) or dual link (connectivity with two links during roaming) as follows:• Links= (APS, ch1), Linkt= (APt,ch1), rSTA is eMLSR (enhanced Multilink Single-Radio)- dual link;• Links=( APS, ch1), Linkt=( APt,ch1), rSTA is single link single radio - single link;• Links=( APS, ch1=Ps ow), Linkt=( APt, ch2=Pt ow), where ch1 and ch2 are defined as in Fig. 2B - dual link; and• Multi-link Links=( APS, ch1), LinktAPt,ch2), where ch1 and ch2 are different (single link in case of eMLSR STA or dual link in case of MLMR (Multi-Link Multi-Radio)).

[0022] Fig. 3 shows a diagram illustrating, on the right hand side an example of the evolution of the queues at the source and target APs and on the left side the impact on the DL and UL data sessions at the roaming STA. The following points in time are indicated in Fig. 3: At time 30 a roaming indication is received by the source AP or is issued at the source AP indicating that a roaming STA is ready to roam to a target AP and context information shall be transferred to the target AP. At time 31 the data path is switched (roaming activation indication is received) i.e., the target AP has an active data path for the traffic to the roaming STA and the source AP has an inactive data path for the traffic corresponding to the roaming STA. At time 32 there are incoming data units (DUs) for the rSTA at the target AP. At time 33 the last DU from the source AP is transmitted, or a timer is elapsed / a Link Disable / Enable notification is issued. In this context it shall be noted that roaming to a BSS substantially means the same as roaming to a communication device (in particular AP) of the BSS.

[0023] A roaming indication indicates to a source AP that context transfer and data path switch can be performed. This should occur once the rSTA has finished flushing its MPDUs towards the source AP or has notified the source AP to discard and perform Roaming Link Activation. A roaming link activation (RAI) indicates that a new link is available for UL transmission, and DL data may start being transmitted from the target AP.

[0024] At the time when a non-AP STA sends a roaming indication that UL traffic has been sent and context can be exchanged, APSmay still have DUs for the respective STA from various access categories (AC) in its queues. These are marked as S_VI’ and S_BE’ in Fig. 3 (corresponding to an inactive link) and represent DUs from video and best effort categoryrespectively. Once the context is transferred and the data path is switched, these Dlls correspond to an inactive data link, i.e. , the data link of the source AP for traffic to the roaming STA becomes inactive. As time evolves, new Dlls are coming in the queue of the target AP, depicted in Fig. 3 with S_VO* and S_VI* (i.e., corresponding to voice and video access categories of an active data path). However, APtmay be blocked from starting the transmission of the new Dlls, because of remaining buffered data units at the source AP, which prevent APSfrom transmitting a link disable / new link enable indication. This is mainly an issue in the single link roaming. Also in the single link roaming context, the remaining Dlls at the APSfor rSTA prevent rSTA from starting an uplink transmission to the target AP.

[0025] If APtstarts transmission of a traffic with the same priority of that of buffered Dlls at APS, the new packets will come with a packet number (PN) which is larger than the one with which the buffered Dlls would be sent. If APSstill sends those Dlls after APt, a STA following the baseline replay counter rules will have to discard these Dlls. If APSand APtare using the same channel, they may end up contending for traffic to the same STA or APtmay win contention before APS, if it is contending for a higher priority AC.

[0026] Stream Classification Service (SCS) agreements between an AP and its associated STA are established to indicate that the particular traffic flows for which they are established have some defined parameters, e.g., transmission bounds which should be respected. When a roaming procedure is performed, SCS agreements may be transferred from the source AP to the target AP, however respecting transmission time bounds may be difficult and may benefit from source AP assisting for a predefined interval after the context transfer.

[0027] Coordinated transmissions in roaming context can achieve one or more of reduced suspension time of the UL and LIL / DL and reduced data loss during roaming and may ensure that existing SCS requirements are met particularly in point of scheduled traffic, latency and reliability requirements. However, this may only be effective if the cTXOP is shared for the respective tasks.

[0028] Fig. 4 shows a diagram illustrating a first embodiment of the general use of a conditional coordinated TXOP according to the present disclosure. Initial control frames (ICF) 40 and initial control response frames (ICR) 41 , which - contrary to the schedule allocation 10 and response frames 11 shown in Fig. 1 - restrict the sharing operation to a specific operating mode (also understood as a restriction to a specific goal) and / or the frame exchanges to respect one or more specific parameters. The further steps 42 to 44 substantially correspond to steps 12 to 14 shown in Fig. 1. The sharing AP is further referred to as AP1 and the shared AP as AP2.

[0029] The ICF 40, which is sent first after obtaining the TXOP, is designed to indicate that the TXOP may be shared and to contain a field referred as Information Collection and Conditional Sharing Indication or ICCSj 40a including conditioning information restricting the use of the obtained TXOP (also referred as conditional TXOP or cTXOP or shared TXOP) to an operating mode and / or restricting frame exchanges of the second communication device during the obtained TXOP to one or more parameters. The conditioning information may serve the purpose of information collection and conditional sharing and may have two parts: a first part contains a request for schedule relevant information (RSI) for the particular cTXOP and a second part (also referred to as conditional cTXOP indication (CCTI)) that indicates parameters based on which a set of conditions that should be respected during the sharing transmission within the cTXOP can be determined at the shared AP AP2.

[0030] The CCTI included in the ICCSj 40a may include one or more of the following pieces of information:• indication that the TXOP may be shared for a particular operating mode, e.g., a sounding, measurement or roaming mode and / or only frames corresponding to the / a particular task may be transmitted by the shared AP within the allocated part of the obtained TXOP (e.g., in case of sounding: NDP (null data packet) type frames, feedback frames, and / or acknowledgements);• indication of an operating mode of the particular TXOP, based on which a set of conditions are defined in the standard (e.g., roaming mode, sounding mode);• indication of a set of parameters which restrict the type of traffic transmitted by the shared AP within the allocated part of the obtained TXOP (e.g., in case of roaming: only traffic from specific TIDs, only traffic to specific stations (will be explained in more detail below);• indication of a subset of channels which should be used during the shared TXOP by AP2 (e.g., the shared AP can only use the indicated subset of channels for PPDlls containing data traffic);• indication of a set of STAs which should be addressed by the shared AP (e.g., edge STAs, STAs within coverage area which were identified as interferes to neighboring APs or potential roaming STAs to candidate neighboring APs; roaming STAs, in case of roaming; a set of STAs with periodic traffic requirements and whose transmission schedules overlap with the ones for which the sharing AP has obtained the TXOP; a set of STAs with periodic traffic requirements and overlapped transmission schedules, for which a sounding should be performed, in view of a concurrent transmission in coordinated beamforming (CBF) / coordinated spatial reuse (CSR);• indication of a set of PHY parameters that should be used (e.g. in the case of sounding: number of supported estimation sequences for channel estimation, number of dimensions to be sounded, and / or feedback type); and• indication of whether the shared transmission should be for uplink data traffic or downlink data traffic or can be left at the decision of the sharing AP.

[0031] The RSI included in the ICCSj 40a may include one or more of the following pieces of information:• size of data units corresponding to an indicated TID or to a particular STA;• size of data units corresponding to flows associated with a data path which is no longer active e.g., in case of roaming• size of data units destined to a STA for which the roaming procedure is ongoing (a link switch indication notifying the source AP of the channel deterioration and intention to roam has been sent by the rSTA to AP1 , however a roaming activation has not yet been transmitted or the context has not yet been transferred);• sounding related parameters, in particular number of sounding dimensions, type of estimation sequences, feedback format or number of fourth communication devices to be sounded;• planned duration of a transmission for the data units, whose size is indicated or a part of the data units, whose size is indicated, and a transmission should be accommodated in the obtained TXOP);• planned duration of a transmission respecting the condition set; and• duration needed to prepare a transmission respecting the allowed parameters within the cTXOP.

[0032] The cTXOP response 41 includes a field ICCSr41a that includes at least an indication whether shared AP can participate in the cTXOP. In an embodiment it may include one or more of the following pieces of information:• a response to the CCTI representing an indication of whether the shared AP can respect the indicated parameters and is willing to participate in the shared TXOP or not. In the latter case and in one embodiment, a cTXOP response 41 may not be sent at all.• a response to the RSI including the requested information.More detailed examples of the content of these fields and their usage are further explained below in the context of roaming.

[0033] Fig. 5 shows a diagram illustrating a second embodiment of the use of a conditional coordinated TXOP according to the present disclosure in target AP assisted roaming. In this embodiment, the target AP, after receiving a roaming notification for the roaming STA, contends for the channel and obtains a TXOP which it shares with the source AP with which the roaming STA (rSTA) is associated. Thus in this embodiment, the target AP shall be understood as the sharing AP, and the source AP as the shared AP. The roaming notification can be e.g., a roaming activation notification, which has been received from the CE, indicating that the data path has been switched or a link switch notification, which has been received from the rSTA. The obtained TXOP is shared with the source AP to enablea DL transmission from the source AP to the rSTA and thus accelerate the DL transmission of the remaining Dlls towards the rSTA.

[0034] In the following figures referred to the roaming scenario, the following nomenclature is used: The target AP APtis the sharing AP and is referred to as AP1 (first communication device). The source AP APSis the shared AP and is referred to as AP2 (second communication device). The roaming station rSTA is - before roaming - associated with the BSS of AP2 and referred to as fourth communication device and - after roaming - associated with the BSS of AP1 and may then be referred to as third communication device.

[0035] In other words, in a roaming scenario the rSTA may use a portion of the shared TXOP for data exchange with AP2 and a portion of the shared TXOP for data exchange with AP1. However, this may not always be the case. In the general layout shown in Fig. 4, the STAs which use the portion of the TXOP corresponding to the sharing AP do not necessarily need to be with the rSTA. The TXOP is shared for the same STA, i.e. , rSTA in blocks 42 and 44, only in the particular cases illustrated in Figs. 7 and 8. Also in these cases, there may be also other STAs with which the AP1 exchanges traffic within its part of the TXOP, besides the rSTA. Similarly, for the cases illustrated in Figs. 11 and 12, the frame exchange in the first part can be with rSTA or with any other STA within the BSS.

[0036] The operation illustrated in Fig. 5 is partly the same as the operation shown in Fig. 4 and the same reference numbers are partly used. However, specific requirements on the indication and request fields in the IGF are different. In the most general form, the TXOP may have been obtained by AP1 to serve any of the STAs within its BSS. The TXOP sharing with the restrictions as described may be applied to one or more TXOPs obtained by AP1 within a predefined interval, corresponding to the maximum time that the source AP (AP2) can continue transmitting buffered Dlls to the rSTA. The frame exchange depicted in block 46 has to respect the conditions derived based on the conditional TXOP parameters indicated e.g. in the IGF in block 40a. The AP2 allocation block 43 has a similar function as in Fig. 4, i.e., announce the start of the shared portion of the TXOP which AP2 can use under the indicated conditions. Parameters of the AP2 allocation block can be set based on information within the ICR response frame, in particular block 41a.

[0037] The CCTI part included in the ICCSj 40a may include one or more of the following indications:• AP2 (the source AP) should transmit at least one MPDll towards the rSTA, within the shared part of the obtained TXOP.• AP2 transmits traffic only from one or more particular TID(s) - e.g., TID(s) for which traffic corresponding to rSTA has already started to be queued at AP1 (the target AP) or TID(s) corresponding to buffered Dlls at AP2 for rSTAs.• An indication of a “roaming” mode, indicating that at least a part of the shared portion of the TXOP should be used by the shared AP to transmit control and / or data messages to a roaming STA. is the indication may be implicitly interpreted by AP2 as: AP2 can only use the shared portion of the TXOP if its transmission includes at least one MPDll towards a roaming STA for which a roaming procedure is ongoing, or at least one MPDll towards a roaming STA for which it does not have an active data path anymore to the DS (distribution system) or at least one MPDU from an AC corresponding to TID(s) for which buffered data units exist at the source AP, for which there is no longer an active data path connection.• AP2 transmits a Link Disable indication towards rSTA, indicating the termination of the buffered traffic.

[0038] The RSI part included in the ICCSj 40a may include one or more of the following pieces of information:• request for information about the size of buffered data units for rSTA;• request for estimated duration of transmission of buffered data units towards rSTA:• estimate of the start time when the sharing AP could start the transmission satisfying the conditions within the CTTI;• estimate of the required duration of the transmission of the sharing AP, satisfying the conditions within the CTTI; and• Estimate of the required duration of the transmission of the sharing AP, satisfying the conditions within the CTTI and which is smaller than an indicated duration corresponding to the allowed duration of an AP2 allocation within the obtained TXOP.

[0039] The cTXOP response 41, in particular the field ICCSr41a, may include one or more of the following pieces of information as part of an RSI response:• information about the size of buffered units for rSTA;• estimated duration of transmission of data units towards rSTA;• estimated duration of the transmission of AP1 with the constraints indicated in CTTI; and• whether the device is ready for a transmission satisfying the conditions of the conditional shared TXOP or earliest time a transmission towards rSTA, satisfying the indicated conditions, can be performed.

[0040] The duration of the transmission of the sharing AP within the cTXOP should be smaller than a duration information derived based on the total duration of the TXOP or a duration explicitly indicated by the sharing AP. Thus, in case the transmission of the data units towards rSTA requires a longer transmission time than the allowed cTXOP duration, AP2 may indicate an indication of remaining Dlls for rSTA and / or an indication of an estimated duration for the transmission of the remaining Dlls after the cTXOP.

[0041] The information about the buffered Dlls at the source AP, which are intended for rSTA, may be different than the one which was available at the time of the context transfer. The target AP may determine this information from frame exchanges between the source AP and rSTA, however this would require explicit signaling from the source AP to the target AP within TXOPs obtained by the source AP to rSTA and the target AP constantly monitoring those TXOPs, which may be inefficient.

[0042] One or more of the parameters in the conditional sharing indication (= OCTI) may be set based on signaling exchange, e.g. via the control entity affiliated with the source AP and target AP. Fig. 6 shows a diagram illustrating control entity mediated information exchange according to an embodiment of the present disclosure. After a successful transmission of part or all buffered Dlls from a particular TID within a TXOP, prior to the shared TXOP of the target AP, the source AP may transmit an indication via the CE towards the target AP, to signal that new traffic from the particular TID can be transmitted. Based onthis information, if the source AP starts a shared TXOP to enable the transmission of the remaining outstanding data units, the target AP sets within the sharing conditions TID priorities and optionally allocation durations corresponding to the information exchanged over the CE. In particular, in Fig. 6, the following steps are depicted. In step 50, the source AP transfers context information to the target AP and optionally informs of remaining buffered Dlls and corresponding traffic indicators. In step 51 the Data path is switched from the source AP to the target AP via the Control Entity. In step 52, the source AP obtains a TXOP which it uses to transmit remaining data units to the rSTA. This can be an ordinary TXOP, i.e., not a shared TXOP. Upon a successful transmission of all or some of the buffered DUs from a particular TID, the source AP informs the target AP of the updated remaining size of DUs or corresponding duration to transmit these DUs. This information is further used by the target AP when obtaining a TXOP, which it shares with the source AP, as shown in the block 55. In the example in Fig. 6 and block 55, the target AP, which is also the sharing AP, conditions the source AP to transmit traffic corresponding to a TID for which there are remaining DUs or sets the allocation duration for the AP2 according to the duration of transmitting the traffic corresponding to rSTA and TIDi or selects the frame exchanges in block 56 to correspond to a TID set which does not include the TIDi, for which there exist remaining DUs at the source AP. Step 56 corresponds to the frame exchange within the part of the TXOP allocated to the sharing AP and steps 57 and 57 correspond to the frame exchange within the part of the TXOP allocated to the shared AP.

[0043] Fig. 7 shows a diagram illustrating a third embodiment of the use of a conditional coordinated TXOP according to the present disclosure for onboarding of the rSTA. The target AP obtained the TXOP for onboarding the rSTA, e.g., for performing a sounding procedure 47 in order to optimize PHY parameters to be used within the follow up transmissions between the target AP and rSTA, for obtaining information about the amount of data to be transmitted by the rSTA e.g., by means of a buffer status 48 (buffer status report BSR of UL traffic from rSTA) or information about the channel quality information CQI (e.g., RSSI, channel state information, beamforming feedback), if a sounding procedure was indicated within 47, and for accommodating UL transmissions, particularly in case an SCS agreement with schedule information has been established and transferred.

[0044] Similar to the second embodiment illustrated in Fig. 6, the target AP is the sharing AP (AP1). In this case, a further indication LS (link switch) towards rSTA to switch to monitoring the links from the two APs or switch to the link corresponding to AP1 may be transmitted to the rSTA, for instance as part of an initial frame within the frame exchange 47 between AP2 and rSTA or within the allocation frame 43. Sufficient padding may be included to allow the rSTA to restart monitoring both links or at least the link from AP2 after the transmission from AP1 is finished.

[0045] Fig. 8 shows a diagram illustrating a fourth embodiment of the use of a conditional coordinated TXOP according to the present disclosure, in which the target AP transmits traffic corresponding to one or more TIDs within a TID set that is non-overlapping with a set of TIDs of the traffic to be sent by the source AP. In this case the target AP (AP1) obtains the TXOP for Dlls that should be transmitted to rSTA. These Dlls contain traffic from one or more TIDs within the TID Set 1. If the CE has already changed the data path of the traffic exchanged with rSTA to the target AP, the target AP may have started receiving Dlls for rSTA. In this case, AP1 may first check the status of the transmission of the Dlls corresponding to the particular TID for the rSTA (explicitly if the information is not available from previous control message exchanges with AP1 or the CE). If AP1 cannot wait for a transmission of buffered Dlls of the respective TIDs from AP2, it should inform AP2 to discard the respective MPDlls. AP1 may allow AP2 to use a part of the TXOP to transmit traffic corresponding to one or more TIDs within a TID Set 2, which is non-overlapping to TID Set 1, as shown in the frame exchange 61.

[0046] In this case, the CCTI may contain one or more of the following pieces of information:• intended rSTA and TIDs which are intended for transmission;• indication whether the AP2 should discard the buffered Dlls corresponding to the rSTA and one or more TIDs within a TID Set (AP1 cannot accommodate the traffic from the particular TIDs anymore) or may inform about the status e.g., size of buffered Dlls from the particular TIDs or estimated duration of a transmission of the traffic corresponding to the particular TIDs (if AP1 may still attempt to accommodate the respective MPDlls); and• indication of a first set of TIDs for which the transmission is intended for rSTA and a second set of TIDs, which indicate the TIDs of the traffic that AP2 may transmit to rSTA within the shared part of the TXOP.

[0047] If AP1 may accommodate the transmission of the one or more MPDlls, from TID Set 2, the RSI may further request one or more of the following pieces of information:• indication of whether Dlls for the intended TID(s) are buffered and transmission can be performed within the current TXOP (or within an indicated interval e.g., within SIFS), which may include a request for the estimated duration of the transmission of the respective buffered Dlls;• indication of whether Dlls are buffered for the intended rSTA from different Tl Ds and can be transmitted within the current TXOP (or within an indicated interval), which may include a request for the estimated duration of the transmission of the respective buffered Dlls.

[0048] Fig. 9 shows a diagram illustrating a fifth embodiment of the use of a conditional coordinated TXOP according to the present disclosure using prioritized transmission. AP1 may prioritize the transmission of AP2 for frame exchanges sent within a roaming procedure or exchanged with a roaming STA, as shown in Fig. 9, i.e. , frame exchange 62 between AP2 and rSTA is performed earlier than frame exchange 63 between AP1 and rSTA. AP1 allocation 45 is an indication to the one or more STAs within the BSS(AP1) that a DL transmission addressed to them will follow. This frame can be implemented as a simple RTS or MU RTS.

[0049] The prioritized transmission of AP2 has been so far can be motivated by various factors such as: i) AP1 has an intended transmission to a roaming STA from a particular TID, however it can delay the transmission within the TXOP if a transmission fromthe source AP of traffic with the same TID and for the rSTA is ready to be transmitted. ii) AP1 wants to accelerate the roaming procedure, enabling AP2 to send or finish the transmission of buffered Dlls such that the latter can disable the link to the rSTA. iii) AP2 is ready for the transmission of the buffered Dlls towards the rSTA.Prerequisites are, however, that a roaming procedure has been at least initiated (e.g., the roaming activation notification that the data path has been switched to AP1 , the rSTA has transmitted a link switch notification). This operation can also be supported by a control message exchange between the source and the target APs via the CEs to ensure that AP2 has the transmission ready at the start of the TXOP and AP1 has the required information for the allocation within the TXOP. This information can be obtained as shown in Fig. 6.

[0050] Fig. 10 shows a diagram illustrating a sixth embodiment of the use of a conditional coordinated TXOP according to the present disclosure using assisted link measurement. A target AP assisted roaming application is illustrated for the case in which the rSTA has moved away from the source AP and is still capable of receiving the source AP transmission, but the source AP cannot receive the UL transmission from the rSTA anymore. The roaming notification is a link switch indication that was addressed to a Control Entity and processed at the lower layers by the target AP.

[0051] As part of ICF / ICR exchange (40, 41) and / or AP2 Alloc / ICR exchange (43, 65), the rSTA may be additionally requested to respond in order to inform the target AP that it is ready to receive a transmission from the source AP. The response may be performed on a different set of resource units (Rus) or a different set of subchannels as the ones used for the transmission of the ICR of the AP2, such that AP1 can correctly determine the response from rSTA. The frame exchange between AP2 and rSTA can be performed with robust MCSs and avoiding a request for BAck, as this frame cannot be directly received by theAP2. Once the AP2 finishes the planned transmission, it sends a Link Disable to the rSTA to send all valid Dlls to the upper layers and switch the link to the target AP. Alternatively, at the end of the frame exchange 62 from AP2 to rSTA, the rSTA may send a BAck to the AP1 , which forwards its content, e.g. via a CE, to the AP2. In this case a further transmission from AP2 to rSTA can be performed if there are remaining buffered Dlls at the source AP. The ICRs 63, 64 used by the rSTA may be simplified versions of the ICRs 41 , 65 used by the shared AP, i.e. , with reserved bits corresponding to the ICCSrfields.

[0052] Prerequisite is that an association has previously been performed (capabilities of the rSTA and APtare mutually known). In this case APtforwards to the CE a notification, corresponding to the link switch indication, which initiates the context transfer. APtobtains a TXOP, becoming the sharing AP, i.e., AP1 , and it shares the TXOP with the source AP, which becomes the shared AP, i.e. AP2, for the latter to perform DL transmission of the remaining packets. The operation is similar to the one illustrated in Fig. 5, however in this case AP1 should ensure that rSTA is aware of the respective transmission from AP2, for instance by performing a control message exchange on Links with rSTA, which indicates that a DL transmission from AP1 will follow and inquires whether rSTA can receive this transmission (e.g., the channel is clear).

[0053] Fig. 11 illustrates a seventh embodiment of the cTXOP in which the source AP obtains a TXOP and shares part of it with one or more potential target APs in order to collect information to be used within a further roaming procedure. If the source AP has received from the rSTA an indication that there is a significant degradation in its signal (e.g. reduced RSSI), it may trigger one or more potential target APs to send measurement signals that allow a faster collection of potential roaming APs. Such an operation enables faster roaming without the need for a STA to constantly monitor beacons transmission from the neighboring APs. If there is already a target AP as main candidate for the roaming (e.g., rSTA has collected measurement information from beacons), or even if the roaming procedure has already started (in the sense of exchange of control messages for link enablement and activation), a measurement or sounding phase performed by the target AP to better select PHY parameters can improve the smooth transition. In this case, after obtaining a TXOP, the source AP becomes the sharing AP, i.e. AP1 , and shares the obtained TXOP with the target AP, i.e. AP2, as depicted in Fig. 11.

[0054] ICCSj 40a indicates the target AP or potential target APs for the respective STAs which should send one or more measurement frames 70. In case of more target APs, a potential schedule of the transmissions within the cTXOP should be included. Furthermore, ICCSj 40a may indicate the type of channel measurement that should be performed (e.g., to gather RSSI information if multiple target APs or, in the case of one specific target AP: RSSI and / or CQI, BF feedback, link parameters).

[0055] Fig. 12 shows a diagram illustrating an eighth embodiment of the use of a conditional coordinated TXOP according to the present disclosure in which an obtained TXOP is shared to assist a target AP in respecting SCS agreements, which were initially established between a source AP and a rSTA and were transferred to the target AP as part of a roaming process, i.e., the target AP should ensure that the streams corresponding to the agreement respect the QoS conditions, e.g., delivery within time constraints.. Since the source AP has information about established SCS agreements for a particular rSTA, it may be required to assist the target AP in respecting these. For example if a periodic DL traffic with TIDi is supposed to be transmitted within an interval [t^n • tc axL if the source AP obtains a TXOP, thus becoming the sharing AP (AP1), it should enable the target AP (AP2) to schedule the new packets within an interval which respect the time constraints. If it still has buffered data units for the particular stream. Further, it should transmit those within the first part of the obtained TXOP.

[0056] If an uplink traffic from rSTA should be transmitted within an intervalAP1 may share the TXOP and allocate time within the TXOP for AP2 to respect the UL respective limits. Within the ICCSj 40a, AP1 may indicate that the transmission of AP2 within the shared TXOP can only be for the UL traffic of rSTA and / or for a specific SCS flow.

[0057] The ICCSj 40a should specifically include in this case the transmission boundaries of the interval in which the respective transmission should be performed in DL of AP2 or the transmission boundaries in which AP2 should trigger the transmission of rSTA, within cTXOP. Additionally, an indication of an identifier of the SCS flow can be present based on which the target AP can determine QoS parameters of interest e.g., time constraints, in case this information has already been exchanged via the CE as part or follow up of acontext transfer. Within Fig. 12, D represents a duration until a transmission of the stream corresponding to the SCS may be started. AP1 should ensure that this term is such that the time constraints of the stream can be satisfied. The frame exchange, depicted in 71 depends on the direction of the traffic for which the SCS agreement was established e.g. if AP1 assists in respecting an SCS for an UL traffic of rSTA then it requests AP2 to trigger the transmission of rSTA within the respective interval and conditions the sharing of the obtained TXOP to frames corresponding to the respective SCS agreement. A similar behavior can be envisioned for SCS of DL traffics in which case the frame exchange in 71 is for frames from AP2 to the rSTA.

[0058] Fig. 13 shows a flowchart of a first communication method 100 that may be performed by a sharing AP (the first communication device). In a first step 101, a transmission opportunity (TXOP) is obtained. In a second step 102, an initial control frame is transmitted to a second communication device, the initial control frame indicating that the obtained TXOP may be shared with the second communication device and including conditioning information prioritizing or restricting the use of the obtained TXOP to an operating mode and / or restricting frame exchanges of the second communication device during the obtained TXOP to one or more parameters. In a third step 103, an initial control response frame is received from the second communication device, the initial control response including an indication whether the second communication device can participate in the obtained TXOP. In a fourth step 104, at least a part of the obtained TXOP is allocated to the second communication device allowing it to exchange one or more frames with one or more fourth communication devices taking account of the conditioning information.

[0059] Fig. 14 shows a flowchart of a second communication method 200 that may be performed by a shared AP (the second communication device). In a first step 201, an initial control frame is received from the first communication device, the initial control frame indicating that a TXOP obtained by the first communication device may be shared with the second communication device , and including conditioning information prioritizing or restricting the use of the obtained TXOP to an operating mode and / or restricting frame exchanges of the second communication device during the obtained TXOP to one or more parameters. In a second step 202, an initial control response frame is transmitted to the first communication device, the initial control response including an indication whether the secondcommunication device can participate in the obtained TXOP. In a third step 203, an allocation of at least a part of the obtained TXOP is received from the first communication device allowing it to exchange one or more frames with one or more fourth communication devices taking account of the conditioning information .

[0060] Fig. 15 shows a diagram illustrating a ninth embodiment of the use of a conditional coordinated TXOP according to the present disclosure for use in a sounding scenario. Fig. 15 particularly shows a scheme of a coordinated sounding for coordinated beamforming (CBF) / coordinated spatial reuse (CSR).

[0061] In Fig. 15, (third communication devices) are associated with AP1 and may respond to the IGF 40, whereas ST ® (fourth communication devices) are associated with AP2. AP1 and AP2 may perform coordinated transmissions such as CSR or CBF. The ICF 40 indicates within the ICCSj 40a that the following TXOP is for sounding and only APs which can participate in a coordinated transmission can transmit. It further indicates that within at least part of the TXOP, the shared APs can or should transmit packets to allow channel estimation at the STAs associated with AP1 . It may optionally indicate that the TXOP contains a second part. Within the second part of the TXOP, AP2 enables a group of STAs, which are associated with itself and which can participate in the coordinated scheme, to estimate channels from the AP1 and / or AP2 and to transmit feedback.

[0062] Within a first part T1 of the TXOP, the APs transmit estimation sequences to and receive feedback from the STAs associated with the sharing AP. Within a second part T2 of the TXOP the APs transmit estimation sequences to the STAs associated with a shared AP, indicated by the sharing AP. The respective shared AP can be announced in the depicted AP2 allocation frame 81 , or it can be implicitly determined as the first AP, which was addressed to transmit an NDP within the first sounding sequence 80.

[0063] In Fig. 15, STA^, associated with AP1 , may respond to the ICF 40 by transmitting ICRs 83, whereas STA^, associated with AP2, will respond within a second sounding sequence 82, if applicable.

[0064] To make the implementation easier and avoid requiring the shared APs to know all the capabilities of the sounded STAs, AP1 indicates a configuration which is supported by all the STAs involved in the following sounding phase, preferably within the ICF 40. This should be respected or used as basis for the transmission of the NDP. For example, the ICF 40 may indicate the number of sounded dimensions supported by all the sounded STAs. The number of estimation sequences that will be used by AP2 should not exceed this number, in the first sounding sequence 80, particularly in case of sequential sounding.

[0065] Furthermore, the AP2 may train a particular configuration or a particular group of STAs. For example, a beamforming configuration has been decided in a previous training, and AP2 would only collect measurements with respect to that configuration. Thus, the number of sounding dimensions that are used by the AP2 in the NDPs can be further adjusted as long as the indication within the ICF 40 is not exceeded. Furthermore, the AP2 may also need the feedback (the ICRs 41) received from the STAs associated with AP1. Therefore, AP2 may indicate parameters related to the feedback type, format and size that it expects to receive, in particular the number of columns of the feedback matrices, indicating number of streams or umber of nulling directions, and partial bandwidth for which it expects to receive the feedback. These parameters are adjusted with respect to the ones indicated in the ICF 40, i.e., the partial bandwidth and number of streams or nulling directions should not exceed the bandwidth and capabilities, respectively, as indicated in ICF 40. Furthermore, these parameters may be indicated within the ICRs 41.

[0066] Fig. 16 shows a diagram illustrating further details of the ninth embodiment in the sounding scenario. In particular, a sounding sequence for the sharing AP (AP1), corresponding to the first sounding block 80 in Fig. 15, is depicted in Fig. 16 together with the ICF 40 and ICR 41 frames based on which the TXOP was obtained. The obtained TXOP should be understood as a series of transmissions which can be performed without requiring the involved STAs to contend for channel access. However, the duration information of the obtained TXOP does not need to indicate from the beginning the complete duration of the TXOP. For example, the duration information indicated within the ICF can be set to only cover the duration of the ICF- ICR exchange and necessary SIFSs. Subsequently, a second duration information is included in the first NDP-A frame of the Sounding Sequence Sharing AP, indicating the duration of this respective sequence plus a SIFS and finally athird duration indication in signaled in the fourth control frame 81, based on indication in the ICR frame from the shared AP and indicating the duration of the sounding sequence of the shared AP.

[0067] In practice, it can happen that only this first sounding block 80 is performed in one TXOP. For instance, if AP1 can apply CBF or CSR while AP2 cannot, AP2 may transmit PPDlls corresponding to one or more beamforming configurations it may use and only AP1 may collect the feedback. Another case in which the TXOP may comprise only of the first sounding block 80 is if multiple APs are part of the sounding procedure, in which case the view of AP1 and of the rest of the APs can be different, i.e., AP1 trains for AP2, but an allocation for AP2 would involve AP2 obtaining feedback for interference from another AP which is not relevant to AP1. In this case, additional sounding blocks within the flow.

[0068] As shown in Fig. 16, the first sounding block 80 may comprise two sounding phases 90, 92 and two feedback phases 91 , 93, following a respective sounding phase. In the first sounding phase 90, AP1 transmits an NDP-A (NDP announcement) frame and an NDP frame to the associated stations, STA^. In the first feedback phase 91, AP1 transmits a BFRP (Beamforming Report Poll) frame to the associated stations, STA^, who respond by reports to AP1. In the second sounding phase 92, AP1 transmits a modified NDP-A frame 94 (also referred to as second control frame) to the associated stations, STA^ and to AP2, . so that AP2 is able to know the capabilities of these sounded STAs to be sounded, e.g. sounding dimension, since AP2 should respect these capabilities. AP2 transmits an NDP frame towithin SIFS of receinving the modified NDP-A frame. In the second feedback phase 93, AP1 transmits a BFRP frame to the associated stations, STA^, who respond by reports to AP2. By use of the initial ICR 41 , AP2 can indicate the desired feedback configuration for use in the NDP-A in the second sounding phase 92.

[0069] A scheme for coordinated measurement for STAs associated with AP1 is similar to the one in Fig. 16, with the exception that, since the feedback is relatively easy to compute and has a low dimension, the feedback phases 91 may be skipped and a feedbackcorresponding to the channels from both AP1 and AP2 to the ,can be collected by AP1 in response to one BFRP frame.

[0070] For coordinated measurements, the scheme again needs a coordinated use of the TXOP in the sense that the AP2 sends some frame during the TXOP obtained by another AP, but it is not performing a real frame exchange with the non-AP STAs. It is unlikely that a continuation with an AP2 allocation, as in Fig. 15, would occur, but the measurement phase would rather comprise the first sounding block.

[0071] A variant for the sounding sequence for STAs associated with AP1 is to transmit the NDPs jointly by AP1 and shared APs in each of the sounding phases. For this scheme a continuation with an AP2 allocation block 81 as shown in Fig. 15 is likely because both APs need feedback from both STAs associated with themselves as well as non-associ- ated STAs. Furthermore, for this case, there are only two APs that participate in the coordinated sounding at a time.

[0072] In another embodiment, particularly if CBF is to be applied, the feedback of the channels from AP2 tois important to AP2 and should be received by AP2. However, if the feedback is to be sent simultaneously by all or a part of the STAs, STA^, need to respect several transmission parameters such that the receiving AP can correctly decode all the transmissions. Essentially, the STAs should adapt their transmission powers, carrier frequency offsets and their transmission start times such that they are within required boundaries at the AP2.

[0073] The precorrection is usually performed based on parameters of the trigger frame that is immediately preceding the transmission of the trigger-based PPDlls from the non-APs. However, since in this case it is AP1 triggering the transmission, the processing should be adapted. Several options are including i) an indication of an adjusted expected reception level of the response frame from the addressed STA to the intended receiver, ii) an indication of parameters based on which the addressed STAs should compute pathloss information during a sounding phase and iii) AP1 triggering AP2 to send a sync PPDll, similarto an NDP after the BFRP, based on which the STAs can adjust their transmission parameters. This process would imply some changes in the non-AP STA procedures.

[0074] To enable and set up the following sounding phase, AP1 indicates to AP2 that it may transmit one or more frames during the obtained TXOP, conditioned by conditioning information in the ICF. AP1 thus enables AP2 to transmit one or more frames to the STAs associated with AP1 and / or STAs associated with AP2 during the obtained TXOP based on indicated parameters.

[0075] The conditioning information filters who can participate and which parameters to use. The conditioning information may thus include one or more of the following:- AP coordination identifier that identifies one or more APs which can share time / spatial resources at a particular time so that only an AP which is part of this can respond;Coordination Group Identifier that identifies a group of APs and non-AP STAs associated with the respective APs, which have been chosen to be trained together during a previous training round or negotiation period; a polled AP should respond with an ICR only if it needs to train one or more fourth communication devices (STAJassociated with AP2), which are part of the group; sounding scheduling interval identifier representing an interval within which one or more APs can cooperate to identify coordinated transmission schemes and train channel parameters; coordinated transmission schedule interval representing an interval within which one or more APs can coordinate their transmissions based on previously negotiated arrangements, e.g. during a negotiation phase the APs have mutually informed each other of periodic traffic patterns which occur at similar times and may require coordinated transmissions; coordination type; if a coordination type for a particular set of STAs and APs has been already chosen, the sounding can be limited to gathering channel information relevant for the respective scheme, e.g., CSR with TPC (transmitter power control), CSR without TPC, CBF full (indicates a CBF scheme in which all participating APs can mitigate interference), CBF partial (indicates a CBF scheme in which onlyone or some of the APs can mitigate the interference, if a coordination type has not yet been determined, the feedback rounds can be organized to allow the APs to gain this information, e.g., a SNR based down-selection of STAs sending full CSI to a cooperating AP; andPHY parameters representing a set of PHY parameters defining requirements of a transmission during the TXOP and / or of the respective coordination scheme for which the sounding within the TXOP occurs.

[0076] The IGF may optionally include one or more of the following indications in addition (among the APs which can participate, this determines how the transmission within the TXOP will be performed, informs what can be performed and requests information on what is required by the polled AP): indication that within a second part of the TXOP, the AP2 may enable AP1 to transmit one or more NDP frames to STA^; it should be interpreted by the AP2 as an inquiry on whether the latter needs to use part of the TXOP for enabling STA® to estimate the channels from the AP1 ; indication that within a second part of the TXOP, the AP2 should enable AP1 to receive feedback of channel information from AP1 to STA® , with a format based on predefined parameters or parameters indicated within the IGF, or feedback corresponding to a previous training session with an identifier indicated within the IGF (missing feedback segments of a previous training); indication that a second part of the TXOP can be used by the AP2 to exchange sounding frames with STA^2

[0077] Some of these information elements listed above can be implicit, if a coordination type within the IGF is defined. For instance, for GSR without TPC or CBF partial, AP1 does not need feedback from the STA^ or AP2 does not feedback from theAll the information elements listed above can be implicit if a coordination type has already been chosen and only two APs can participate (e.g. for CBF for joint sounding). In practice, it may be useful to allow sounding for multiple APs / configurations if possible, because during the coordinated transmission it can happen that one of the APs is not ready with the transmission (e.g., traffic for the respective STAs has not yet arrived) or channel conditions do notallow it to participate in the coordinated transmission scheme. If multiple APs can perform sounding, only parts of the sounding blocks may be performed, as shown below with reference to Fig. 17.

[0078] In the following, further details regarding the “enabling” mentioned above will be explained. AP1 enables AP2 to transmit one or more frames to theby transmitting a second control frame. This control frame is the NDP-A block 94 in Fig. 16. This control frame includes a user field identifying the respective AP and a set of PHY parameters to be used in the transmission of the one or more frames by AP2, where the parameters have been chosen based on capabilities of theand information within the ICF and / or ICR, as will be explained below in more detail. Hence, this operation refers to the sounding sequence of AP1.

[0079] To determine the set of parameters within the control frame 94, AP1 should first indicate a first set of PHY parameters within the ICF and determine corresponding PHY parameters from the ICR received from the AP2.

[0080] The PHY parameters indicated within the ICF depend on the capabilities of the STA^ to be sounded within the respective TXOP. The PHY parameters within ICF may include one or more of the following: number of spatial streams which the AP1 plans to use in the transmission of the one or more sounding frames to the STA*1^ maximum number of spatial streams that can be sounded by AP2; bandwidth with which the sounding frames (NDP) will be sent; bandwidth for which the feedback from theto the AP1 should be sent; maximum number of streams for which thecan provide feedback;LTF type, Gl type, number of subcarriers to be grouped within the feedback, and codebook size.Some of the parameters can be predefined or indicated within an initial negotiation phase (e.g., LTF and Gl type, codebook, number of grouped subcarriers Ng). Others are more dynamic and depend on the group of STAs which are sounded during the respectiveinterval, therefore it is better to indicate them explicitly, e.g. the number of spatial streams to be sounded by the respective APs and / or bandwidth for the feedback.

[0081] It may further be indicated within the ICF (but only applies to one coordination type, i.e. , CBF, because for the other ones the operation is implicitly sequential) if the transmission of one or more frames from AP2 should be performed simultaneously with one or more frames from AP1 or sequentially.

[0082] PHY parameters within the ICR may include one or more of the following: number of spatial streams, with which the AP2 plans to transmit the one or more frames to the bandwidth to be used by AP2 in the transmission of the one or more frames to the STA^ (should not exceed the bandwidth indicated in the ICF); bandwidth and / or feedback type and / or codebook, specifying the feedback format to be received from the STY!*1); acceptance of the configuration for LTF / GI parameters for the transmission of the frame to the STY!*1); and indication of a maximum number of spatial streams that AP1 can use during the transmission of the frame to the STA^, if a second part has been requested for sounding channels from Ap1 to the respective STA.

[0083] Based on the parameters within the ICR as listed above, particularly the fist three bullets, a final set of PHY parameters is determined by the AP1 and indicated within the second control frame (NDP-A from AP1 to STA^ and AP2). The parameters within the NDP-A are used by the AP2 to determine the configuration it shall use during the transmission of the NDP to the STY!*1). The parameters within the NDP-A, addressed to the STA^, are used by the STA^to determine the parameters of the estimation they should perform based on the subsequent frame. 0084] Fig. 17 shows a diagram of an embodiment of a null data packet announcement frame(NDP-A) (second control frame 94) that may be used for sounding in an embodiment ofthe present disclosure. It shows particularly how the new NDP-A frame may be designed and how the information may be used by the addressed STAs. Within current standards, the NDP-A frame was used by addressed non-AP STAs to determine how to format the feedback. For the purpose of the coordinated sounding, AP2 should be directly addressed and informed about the parameters it shall use in the follow-up transmission, particularly how it shall construct the training fields based on which thewill perform the estimation.

[0085] Dependent ICR indications may include one or more of the following:Indication of acceptance of the PHY parameters indicated for the transmission or alternative parameters that are respecting conditions within ICF;Indication that it can request STA® to estimate channels from AP1 ; if yes, it indicates a maximum supported number of sounding dimensions, required bandwidth and supported feedback format; further, it may indicate that this operation is conditioned by the AP1 allowing AP2 to perform training of the STA® within the obtained TXOP; indication if AP2 needs a part of the TXOP to perform sounding to STA^, it indicates a maximum duration and required channel and bandwidth; and indication that it can request ST ® to send feedback to AP1 based on estimation sequences sent by AP1 or based on a previous feedback stage (e.g., transmitting missing feedback segments corresponding to a coordinated training with an indicated identifier).

[0086] In the ICF used for sequential sounding, it is not necessary to indicate the number of sounding dimensions that will be used by AP1. However, for joint sounding, this information is necessary, because AP2 will choose the transmission parameters based on this (e.g. CSD). A final parameter adding the indication on the sounding dimensions in the ICR and in the ICF may be indicated within the second control frame (NDP-A from AP1 toAP2). For joint sounding, the AP2 has no freedom in choosing a smaller bandwidth for the training, but it should follow the ICF indication.

[0087] The ICF for joint sounding may include one or more of the following: indication to poll one or more APs if they can send NDP within the TXOP; indication of a maximum number of sounding dimensions that can be used by AP2 in the transmission to the STA^; indication of a number of sounding dimensions to be used during the training by AP1 to STd^; indication of supported feedback format; indication of sequential or joint feedback collection; joint feedback in the sense of one trigger frame from AP1 which triggers STAs to transmit the full feedback to both APs may be difficult because the STAs should have their transmissions aligned well enough to both APs; and indication that time can be allocated within the second part of the TXOP for sounding; this may include requesting a maximum number of sounded dimensions that can be sounded by the polling AP in the second part of the TXOP; this may be simplified by requesting the same configuration as in the first part.

[0088] Fig. 19 shows a diagram that illustrates different sounding examples. In a first example with multiple sounding, in a first TXOP sounding sequence AP1 and sounding Sequence AP2 may be applied. In a second TXOP, AP3 is the TXOP initiator. It may not need feedback from STA^ or only need feedback from somewhich was not received correctly in the previous training round or was not received completely during the previous training round. AP3 does not need to allow training of AP1 toduring its own (second) TXOP.

[0089] In a second example with only two APs, in a first TXOP, AP2 is the TXOP initiator performing only sounding sequence AP2 (including to enable AP1 to obtain feedback from STA®). In a second TXOP, AP1 is the TXOP initiator performing sounding sequence AP1 and requesting missing feedback from previous coordinated training sequence. It does not need AP2 training and does not need AP2 to enable AP1 to send NDPs, but only feedback.

[0090] AP1 enables AP2 to receive the feedback from one or moreby transmitting a fourth control frame which contains an indication, allowing theto align their transmissions with respect to the AP2. The fourth control frame is the BFRP frame 95 in Fig. 16. This operation and the following description refer to various options for enabling the feedback collection at AP2.

[0091] For the STA^ to align the transmissions such that the AP2 receives them at similar power levels, AP1 can include indications within the NDP-A 94, instructing the STA^ to compute pathloss based on the subsequently following sounding frame, originating from the AP2 in this case, and / or transmission parameters to be used during a follow up feedback phase. For the latter computation, a transmission power that would be used by the AP2 during the transmission of the NDP frame 96 and reception level during the feedback transmission phase should be indicated, in the NDP 96 and / or NDP- A 94. Thereafter, in the fourth control frame an indication to use the respective adjusted parameters can be transmitted.

[0092] Alternatively, AP1 may indicate the parameters of the STA^ responding to feedback request intended to the AP2 based on one or more of the SNR values of the channel from AP1 to STA^ and SNR values of the channel between AP2 tAP1 should gather both SNR values in this case. The parameters for the power precorrection can be further determined by the AP1 based on the SNR difference, the relative difference between the transmit power of AP1 and AP2 and / or relative reception levels of the feedback frame at AP1 and AP2. It will further indicate individually in user fields within the BFRP frame 95 (fourth control frame), the determined parameters requesting the feedback of the channels from the AP2 to the STA^, e.g., AP1 can indicate within an intended reception level, a reception level at AP2 which is adjusted with a factor correcting the pathloss difference between the channels from AP1 and AP2 for the respective STA. In this case, the last feedback collection phase requires two subphases: a first subphase in which a BFRP torequesting SNR of the channels from the AP2 to the STA^, and a second subphase, enabling the feedback of (potentially a subset of the STA^) to the AP2 by the new BFRP frame (with power correction parameters), 95.

[0093] An alternative to enable the AP2 to receive the feedback from theis to indicate within the fourth control frame that a sync PPDll will be transmitted, based on which precorrection parameters should be computed for a follow-up transmission of the STA^within SIFS from the reception of the sync PPDll.

[0094] A further alternative to enable AP2 to receive the feedback from STA^, is to enable AP1 to transmit directly to AP2, a frame containing aggregated feedback information from the respective STAs. This is particularly useful for CSR or a loose coordination scheme (e.g., CBF partial).

[0095] The AP1 enables the AP2 to transmit one or more frames to the ST ® by including a third control frame, which indicates the ID of the AP2 and / or a duration information regarding the duration of the TXOP which can be used by the second AP. The third control frame is depicted as the “AP2 Allocation 81” in Fig. 15. This operation refers to the operation of the sounding sequence at AP2, which is performed during the obtained TXOP. The following steps relate to actions that can be performed, depending on the ICF / ICR indications.

[0096] If the AP1 requires feedback from the ST ® and has indicated this in the IGF, it may indicate a set of parameters to be used for the feedback format. If the AP1 has received an ICR from the AP1 , indicating a request from the AP2 to the AP1 to sound channels from the AP1 to the ST ®, then the AP1 should transmit upon request of the AP2 an NDP with PHY parameters indicated by the AP2.

[0097] Fig. 20 shows a flowchart of another embodiment of a first communication method 400 according to the present disclosure. In a first step 401 , a TXOP is obtained. In a second step 402, an initial control frame is transmitted to one or more second communication devices. The initial control frame indicates that at least a part of the obtained TXOP may be used by the second communication device to transmit one or more frames to one or more third and / or fourth communication devices and including conditioning information prioritizing or restricting frame transmissions of the second communication device during the obtainedTXOP to one or more parameters. In a third step 403, an initial control response frame is received from one or more of the second communication devices, the initial control response frame indicating whether the second communication device can participate in the obtained TXOP. In a fourth step 404, within at least a part of the obtained TXOP one of the one or more second communication devices are enabled to transmit one or more frames to one or more third and / or fourth communication devices based on the conditioning information.

[0098] Fig. 21 shows a flowchart of another embodiment of a second communication method 500 according to the present disclosure. In a first step 501 , an initial control frame is received from a first communication device. The initial control frame indicates that a TXOP obtained by the first communication device may be used by the second communication device to transmit one or more frames to one or more third and / or fourth communication devices and including conditioning information prioritizing or restricting frame transmissions of the second communication device during the obtained TXOP to one or more parameters. In a second step 502, an initial control response frame is transmitted to the first communication device, the initial control response frame indicating whether the second communication device can participate in the obtained TXOP. In a third step 503, an enablement is received within at least a part of the obtained TXOP from the first communication device allowing the second communication device to transmit one or more frames to one or more third and / or fourth communication devices based on the conditioning information.

[0099] The obtained TXOP may be used by the second communication device to transmit one or more frames to one or more third communication devices or even perform a frame exchange. This means, in the simplest form, just a transmission from the second communication device of the NDP frames. The second communication device may receive feedback from the third communication device, if triggered by the first communication device or may receive the feedback of the channels from the second communication device to the third communication devices in one or more frames transmitted by the first communication device.

[0100] The device may be implemented by respective units or circuitry, e.g. a processor, processing circuitry, a computer, dedicated hardware, etc., that carries out the functions ofthe device. Alternatively, a common unit or circuitry, e.g. a common processor or computer, may implement the various functions of the device, or separate units or elements may be used that together represent the circuitry.

[0101] 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 disclosure may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosure of the present disclosure is intended to be illustrative, but not limiting 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 subject matter is dedicated to the public.

[0102] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite 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 combination of these measures cannot be used to advantage.

[0103] 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 distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0104] The elements of the disclosed devices, apparatus and systems may be implemented by corresponding hardware and / or software elements, for instance appropriate circuits or circuitry. A circuit is a structural assemblage of electronic components including conventional circuit elements, integrated circuits including application specific integrated circuits, standard integrated circuits, application specific standard products, and field programmablegate 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).

[0105] It follows a list of further embodiments of the disclosed subject matter:1. First communication device configured to communicate with one or more third communication device, the first communication device comprising circuitry configured to: obtain a transmission opportunity (TXOP); transmit an initial control frame to a second communication device, the initial control frame indicating that the obtained TXOP may be shared with the second communication device and including conditioning information prioritizing or restricting the use of the obtained TXOP to an operating mode and / or restricting frame exchanges of the second communication device during the obtained TXOP to one or more parameters; receive an initial control response frame from the second communication device, the initial control response an indication whether the second communication device can participate in the obtained TXOP; and allocate at least a part of the obtained TXOP to the second communication device allowing it to exchange one or more frames with one or more fourth communication devices taking account of the conditioning information.2. First communication device according to embodiment 1 , wherein the conditioning information includes a request for schedule-relevant information for the obtained TXOP and / or a parameter indication indicating one or more parameters based on which the second communication device determines conditions to be respected during a shared transmission within the obtained TXOP; and / or wherein the initial control response includes requested schedule-relevant information and an indication whether the second communication device can respect the one or more parameters indicated by the parameter indication.3. First communication device according to embodiment 2,wherein circuitry is configured to determine a point in time of allocating at least a part of the TXOP and / or a duration of the allocation of at least a part of the TXOP to the second communication device based on the request for schedule-relevant information.4. First communication device according to embodiment 2 or 3, wherein the request for schedule-relevant information includes one or more of: size of data units corresponding to an indicated traffic identifier and / or to a particular fourth communication device; size of data units corresponding to data flows associated with a data path that is no longer active at the second communication device; size of data units destined to a fourth communication device for which a roaming procedure from the second communication device is ongoing; sounding related parameters, in particular number of sounding dimensions, type of estimation sequences, feedback format or number of fourth communication devices to be sounded planned duration of a transmission for data units whose size is indicated or a part of the data units, whose size is indicated, and a transmission should be accommodated in the obtained TXOP; planned duration of a transmission respecting the conditioning information; and duration needed to prepare a transmission respecting the one or more parameters within the obtained TXOP.5. First communication device according to any one of embodiments 2 to 4, wherein the parameter indication includes one or more of: indication that the obtained TXOP may be shared for a particular operating mode and / or only frames corresponding to the particular operating mode may be transmitted; indication of a particular operating mode, based on which a set of conditions are defined or can be derived, in particular an indication that the obtained TXOP should be used for sequential sounding or joint sounding or coordinated measurement or roaming; indication of a set of parameters which restrict the type of traffic transmitted by the second communication device; indication of a subset of channels to be used during the obtained TXOP by the second communication device;indication of a set of one or more fourth communication devices which should be addressed by the second communication device; indication of a set of physical layer (PHY) parameters that should be used, in particular number of sounding dimensions, type of estimation sequences and / or feedback format and indication of whether the shared transmission should be for uplink data traffic and / or downlink data traffic or can be left at the decision of the second communication device.6. First communication device according to any one of the preceding embodiments, wherein the third communication device is within the same basic service set (BSS) as the first communication device and / or the fourth communication device is within the same basic service set (BSS) as the second communication device.7. First communication device according to any one of the preceding embodiments, wherein the circuitry is configured to: receive a roaming notification from a second communication device or a roaming fourth communication device that the roaming fourth communication device intends to roam to the basic service set (BSS) of the first communication device; obtain a TXOP; allocate at least a part of the obtained TXOP to the second communication device enabling the second communication device to transmit remaining or buffered data units to the roaming fourth communication device during the allocated part of the obtained TXOP.8. First communication device according to embodiment 2 and 5, wherein the request for schedule-relevant information includes a request for one or more of: information about the size of the remaining or buffered data units of the second communication device for the roaming fourth communication device; estimated duration of transmission of the remaining or buffered data units from the second communication device towards the roaming fourth communication device; an estimate of the start time when the second communication device could start the transmission within the obtained TXOP; andan estimate of the required duration of the transmission of the first communication device within the obtained TXOP.9. First communication device according to embodiment 2 and 7, wherein the parameter indication includes one or more of: indication that the second communication device shall transmit at least one data unit towards the roaming fourth communication device; indication that the second communication device shall transmit at least one data unit containing traffic corresponding to a particular traffic identifier; indication that the second communication device shall only transmit data units containing traffic corresponding to a particular traffic identifier; indication of a roaming mode; and indication that the second communication device may transmit a Link Disable indication towards the roaming fourth communication device indicating that there are no more data units destined for the fourth communication device and / or the fourth communication device should switch to a link of the first communication device.10. First communication device according to embodiment 8, wherein the initial control response includes one or more of: information about the size of buffered units for the roaming fourth communication device; estimated duration of transmission of data units towards the roaming fourth communication device; estimated duration of the transmission of the second communication device with the constraints indicated in the parameter indication; and whether the second communication device is ready for transmission, or which is the earliest time when the second communication device can perform the transmission towards the roaming fourth communication device.11 . First communication device according to any one of embodiments 7 to 10, wherein the circuitry is configured to perform channel sounding with the roaming fourth communication device and / or obtain buffer status of uplink traffic from the roaming fourth communication device and / or accommodate uplink transmissions.12. First communication device according to embodiment 11 , wherein the circuitry is configured to transmit an indication to the roaming fourth communication device to switch to monitoring links from the first and second communication device or a link from the second communication device.13. First communication device according to any one of embodiments 7 to 12, wherein the circuitry is configured to allocate transmission time for the second communication device to perform data exchange with the fourth communication device within the obtained TXOP before the data exchange between the first and third communication devices; or, if the first communication device has data to transmit to the roaming fourth communication device, corresponding to a particular traffic identifier or traffic identifier set to transmit an indication to the second communication device to discard remaining data units corresponding to the particular traffic identifier or traffic identifier set or to transmit data units to the roaming fourth communication device which correspond to one traffic identifier set and allow the second communication device to send data units corresponding to a second traffic identifier set that is non-overlapping with the first traffic identifier set.14. First communication device according to embodiments 2 and 13, wherein, if the first communication device can accommodate transmission of buffered data units from the second communication device, the request for schedule-relevant information includes one or more of: indication of whether data units for the intended one or more traffic identifiers are buffered and transmission can be performed within the current TXOP or within an indicated interval; and indication of whether data units are buffered for the intended roaming fourth communication device from different traffic identifiers and can be transmitted within the current TXOP or within an indicated interval.15. First communication device according to embodiments 2 and 13, wherein the parameter indication includes one or more of:intended roaming fourth communication device and / or traffic identifiers which are intended for transmission within the TXOP; indication whether the second communication device should discard the buffered data units corresponding to the roaming fourth communication device and / or the indicated traffic identifier or may inform about the status of the buffered data units; and indication of a first set of traffic identifiers for which the transmission is intended for the roaming fourth communication device and a second set of traffic identifiers, which indicate the traffic identifiers of the traffic that the second communication device may transmit to the roaming fourth communication device.16. First communication device according to any one of embodiments 7 to 15, wherein the circuitry is configured to perform a control message exchange with the roaming fourth communication device by transmitting an indication that a downlink transmission from the second communication device will follow and / or inquiring whether the roaming fourth communication device can receive the transmission.17. First communication device according to any one of embodiments 7 to 16, wherein the circuitry is configured to: receive a roaming notification from a third communication device that the third communication device intends to roam to the basic service set (BSS) of a second communication device or the signal quality has degraded at the third communication device; obtain a TXOP; allocate at least a part of the TXOP to one or more second communication devices to perform control and / or data message exchange with the third communication device.18. First communication device according to embodiment 17, wherein the circuitry is configured to allocate at least a part of the obtained TXOP to one or more second communication devices to transmit measurement signals preferably allowing a collection of one or more potential target communication devices to which a roaming third communication device may roam.19. First communication device according to embodiment 18, wherein the circuitry is configured to include in the initial control frame one or more of:an indication of the one or more potential target communication devices; in case of more than one potential target communication devices, a schedule of transmission within the obtained TXOP; and the type of channel measurement that should be performed.20. First communication device according to any one of the preceding embodiments, wherein the circuitry is configured to allocate the transmission time within the obtained TXOP for the second communication device to enable the second communication device to transmit data units corresponding to a traffic with time constraints to a fourth communication device or to receive data units from a fourth communication device within an interval corresponding to the time constraints.21 . First communication device according to any one of the preceding embodiments, wherein the circuitry is configured to: check the status of the transmission of data units corresponding to a particular traffic identifier for the roaming fourth communication device; if it can accommodate transmission of buffered data units from the second communication device, assist the second communication device to finish transmission of the buffered data units; if it cannot accommodate transmission of buffered data units from the second communication device, inform the second communication device to discard the respective data units; and if the transmission from the first communication device is for a traffic with priorities corresponding to a first set of traffic identifiers and the remaining data units at the second communication device for the roaming fourth communication device correspond to a nonoverlapping second set of traffic identifiers, perform the transmission of traffic with priorities corresponding to a first set of traffic identifiers first.22. Second communication device configured to communicate with one or more fourth communication device, the second communication device comprising circuitry configured to: receive an initial control frame from a first communication device, the initial control frame indicating that a TXOP obtained by the first communication device may be sharedwith the second communication device, and including conditioning information prioritizing or restricting the use of the obtained TXOP to an operating mode and / or restricting frame exchanges of the second communication device during the obtained TXOP to one or more parameters; transmit an initial control response frame to the first communication device, the initial control response including an indication whether the second communication device can participate in the obtained TXOP; and receive an allocation of at least a part of the obtained TXOP from the first communication device allowing the second communication device to exchange one or more frames with one or more fourth communication devices taking account of the conditioning information.23. Second communication device according to embodiment 22, wherein the initial control response includes an indication whether the second communication device can respect the one or more parameters indicated by the conditioning information.24. Second communication device according to embodiment 22 or 23, wherein, if the conditioning information contains an indication of a sounding mode, the circuitry is configured to exchange with the one or more fourth communication devices one or more of sounding frame, sounding announcement frames, feedback frames, request for feedback.25. Second communication device according to any one of embodiments 22 to 24, wherein circuitry is configured to be ready to transmit first within the obtained TXOP and / or inform via a control entity if the data units towards a fourth communication device are ready for transmission or discard the data units corresponding to a roaming fourth communication device and an indicated traffic identifier.26. Second communication device according to any one of embodiments 22 to 25, wherein the circuitry is configured to obtain, from the received conditioning information, a parameter indication indicating one or more parameters; andtransmit within the obtained TXOP one or more of:- at least one data unit towards a roaming fourth communication device,- at least one data unit containing traffic corresponding to a particular traffic identifier,-at least one data unit containing traffic corresponding to a data path that is no longer active at the second communication device,-a data unit triggering the fourth communication device to send control and or data units towards the second and / or first communication device,-at least one data unit towards a fourth communication device, indicated by the first communication device, and- a Link Disable indication towards the roaming fourth communication device indicating that there are no more data units destined for the fourth communication device and / or the fourth communication device should switch to a link of the first communication device.27. First communication method of a first communication device configured to communicate with one or more third communication device, the first communication method comprising: obtaining a transmission opportunity (TXOP); transmitting an initial control frame to a second communication device, the initial control frame indicating that the obtained TXOP may be shared with the second communication device and including conditioning information prioritizing or restricting the use of the obtained TXOP to an operating mode and / or restricting frame exchanges of the second communication device during the obtained TXOP to one or more parameters; receiving an initial control response frame from the second communication device, the initial control response including an indication whether the second communication device can participate in the obtained TXOP; and allocating at least a part of the obtained TXOP to the second communication device allowing it to exchange one or more frames with one or more fourth communication devices taking account of the conditioning information.28. Second communication method of a second communication device configured to communicate with one or more fourth communication device, the second communication method comprising: receiving an initial control frame from the first communication device, the initial control frame indicating that a TXOP obtained by the first communication device may be shared with the second communication device, and including conditioning information prioritizing or restricting the use of the obtained TXOP to an operating mode and / or restricting frame exchanges of the second communication device during the obtained TXOP to one or more parameters; transmitting an initial control response frame to the first communication device, the initial control response including an indication whether the second communication device can participate in the obtained TXOP; and receiving an allocation of at least a part of the obtained TXOP from the first communication device allowing it to exchange one or more frames with one or more fourth communication devices taking account of the conditioning information.29. A non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method according to embodiment 27 or 28 to be performed.30. A computer program comprising program code means for causing a computer to perform the steps of said method according to embodiment 27 or 28 when said computer program is carried out on a computer.A1. First communication device configured to communicate with one or more third communication device, the first communication device comprising circuitry configured to: obtain a transmission opportunity (TXOP); transmit an initial control frame to one or more second communication devices, the initial control frame indicating that at least a part of the obtained TXOP may be used by the second communication device to transmit one or more frames to one or more third and / or fourth communication devices and including conditioning information prioritizing or restricting frame transmissions of the second communication device during the obtained TXOP to one or more parameters;receive an initial control response frame from one or more of the second communication devices, the initial control response frame indicating whether the second communication device can participate in the obtained TXOP; and enable within at least a part of the obtained TXOP one or more of the second communication devices to transmit one or more frames to one or more third and / or fourth communication devices based on the conditioning information.A2. First communication device according to embodiment A1 , wherein the circuitry is configured to enable one or more of the second communication devices, from which an initial control response frame has been received, to transmit one or more frames to one or more third and / or fourth communication devices.A3. First communication device according to any one of embodiments A1 to A2, wherein the conditioning information or the initial control frame includes one or more of the following: coordination identifier that identifies one or more first and / or second communication devices which can share time / spatial resources at a particular time;Coordination Group Identifier that identifies a group of communication devices, which should be sounded together; sounding scheduling interval identifier representing an interval within which one or more first and / or second communication devices can cooperate to identify coordinated transmission schemes and / or train channel parameters; coordinated transmission schedule interval representing an interval within which one or more first and / or second communication devices can coordinate their transmissions based on previously negotiated arrangements; coordination type including one or more of coordinated spatial reuse with transmit power control, coordination spatial reuse without transmit power control, and coordinated beamforming; one or more PHY parameters; indication of whether the transmission of the one or more sounding frames from a second communication device to the one or more third communication devices should be performed simultaneously with the transmission of one or moresounding frames from the first communication device to the one or more third communication devices; indication that only sounding related frames can be sent by the second communication device; and enabling information for the second communication device.A4. First communication device according to embodiment A3, wherein the PHY parameters include one or more of the following: number of spatial streams which the first communication device plans to use in the transmission of the one or more sounding frames to the one or more third communication devices; maximum number of spatial streams that can be transmitted by the second communication device in the one or more sounding frame to the 3rdcommunication devices; total number of spatial streams that can be used in the transmission of the one or more sounding frames from the first and / or second communication devices; supported bandwidth of the one or more third communication devices which should be sounded in the obtained TXOP; bandwidth with which the sounding frames should be sent; bandwidth for which the feedback from the one or more third communication devices to the first communication device should be sent; indication of supported feedback format; indication of sequential or joint feedback collection; andLTF type, Gl type, number of subcarriers to be grouped within the feedback, and codebook size.A5. First communication device according to any one of embodiments A1 to A4, wherein the initial control frame further includes one or more of the following: indication that within a second part of the TXOP, the second communication device should enable the first communication device to receive feedback of channel information from the first communication device to one or more fourth communication devices with a format based on predefined parameters or parametersindicated within the initial control frame or to receive feedback corresponding to a previous training session with an identifier indicated within the initial control frame; indication that a second part of the TXOP can be used by the second communication device to exchange sounding frames with one or more fourth communication devices; and indication that within a second part of the TXOP, the second communication device may enable the first communication device to transmit one or more null data packet frames to one or more fourth communication devices.A6. First communication device according to any one of embodiments A1 to A5, wherein the initial control frame for joint sounding includes one or more of the following: indication to poll one or more second communication devices if they can send null data packets within the TXOP; indication of a maximum number of sounding dimensions that can be used by one or more second communication devices in the transmission to one or more third communication devices; indication of a number of sounding dimensions to be used during the training by the first communication devices to the one or more third communication devices; indication of supported feedback format; indication of sequential or joint feedback collection; and indication that time can be allocated within the second part of the TXOP for sounding.A7. First communication device according to any one of embodiments A1 to A6, wherein the initial control frame includes an indication of whether the transmission of one or more frames from the second communication device should be performed simultaneously with one or more frames from the first communication device or sequentially, in particular in the case of coordinated beamforming sounding.A8. First communication device according to embodiment A4, wherein the circuitry is configured to determine, based on one or more one or more parameters indicated within the initial control frame and / or the initial control response frame a final set of PHY parameters and to indicate the final set of PHY parameters within asecond control frame, in particular an NDP-A frame, to the second communication device and the one or more third communication devices.A9. First communication device according to any one of embodiments A1 to A8, wherein the circuitry is configured to enable the second communication device to transmit one or more sounding frames to the one or more third communication devices by transmitting a second control frame, in particular an NDP-A frame, including a user field identifying the respective communication unit and the final set of PHY parameters to be used in the transmission of the one or more frames by the second communication device.A10. First communication device according to embodiment A9, wherein the final set of PHY parameters includes one or more of: index of the first spatial stream to be transmitted by the second communication device; the total number of spatial streams to be transmitted by the second communication device; bandwidth to be used in the transmission; the format in which the feedback, in particular one or more of type, codebook, grouping, postprocessed, bandwidth, will be transmitted by the one or more third communication devices;LTF type;Gl type; and sounding token; and / or wherein the user field of the one or more third communication devices includes an indication of the format of the feedback of the channel from the second to the fourth communication device and, optionally, one or more of a transmission power to be used by the second communication device, an expected receiver power expected by the second communication device to receive the feedback, an indication that pathloss information for the channels between the second and third communication devices should be computed, an indication that a transmit power to be used in the transmission of the report containing the feedback of the channel to be estimated based on the subsequent sounding frame, shall be determined.A11. First communication device according to any one of embodiments A1 to A10, wherein the circuitry is configured to enable the second communication device to receive the feedback from one or more third communication devices by transmitting a fourth control frame, in particular an BFRP frame, which contains an indication, allowing the one or more third communication devices to align their transmissions with respect to the second communication device, in particular an indication including adjusted transmit power levels or adjusted expected receive power per user, or an indication that the transmit power determined during the estimation of the reported channels shall be used in the transmission of the feedback reports.A12. First communication device according to embodiment A11 , wherein the circuitry is configured to enable the second communication device to receive the feedback from one or more third communication devices by transmitting a fourth control frame, in particular an BFRP frame, which contains an indication, allowing the one or more third communication devices to align their transmissions with respect to the second communication device based on one or more of relative SNR values of the transmissions from the first and second communication devices to the third communication devices, transmission power of the second communication device, and expected reception power at the second communication device.A13. First communication device according to any one of embodiments A1 to A12, wherein the circuitry is configured to enable the second communication device to receive the feedback from one or more third communication devices by transmitting a frame containing aggregated feedback information from the respective third communication devices; and / or enable the second communication device to transmit one or more frames to the one or more fourth communication devices by including a third control frame, in particular an allocation frame, which indicates the ID of the second communication device and / or a duration information regarding the duration of the TXOP which can be used by the second communication device.A14. First communication device according to any one of embodiments A1 to A13,wherein the conditioning information conditions the use of the TXOP by the one or more second communication devices to one or more of: transmission of one or more sounding frames from the second communication device to one or more third communication devices; transmission of one or more control frames from the second communication device to the first communication device and to the one or more fourth communication devices, indicating a set of parameters to be used by the first communication device in a subsequent transmission to the one or more fourth communication devices; transmission of one or more sounding frames from the second communication device to the one or more fourth communication devices; transmission of one or more control frames from the second communication device to one or more fourth communication devices, requesting for feedback information; and transmission of one or more control frames from the second communication device to the one or more fourth communication devices, indicating correction parameters to be used by the one or more fourth communication devices in a follow up transmission to the first communication device.A15. Second communication device configured to communicate with one or more fourth communication device, the second communication device comprising circuitry configured to: receive an initial control frame from a first communication device, the initial control frame indicating that a TXOP obtained by the first communication device may be used by the second communication device to transmit one or more frames to one or more third and / or fourth communication devices and including conditioning information prioritizing or restricting frame transmissions of the second communication device during the obtained TXOP to one or more parameters; transmit an initial control response frame to the first communication device, the initial control response frame indicating whether the second communication device can participate in the obtained TXOP; and receive an enablement within at least a part of the obtained TXOP from the first communication device allowing the second communication device to transmit one or more frames to one or more third and / or fourth communication devices based on the conditioning information.A16. Second communication device according to embodiment A15, wherein, if the conditioning information contains an indication of a sounding mode, the circuitry is configured to exchange with the one or more fourth communication devices one or more of sounding frame, sounding announcement frames, feedback frames, request for feedback.A17. Second communication device according to any one of embodiments A15 to A16, wherein the initial control response frame includes one or more of the following: indication of acceptance of PHY parameters indicated for the transmission or indication of alternative parameters that are respecting conditions within the initial control frame; indication that the second communication device can request one or more fourth communication devices to estimate channels from the first communication device; indication if the second communication device needs a part of the TXOP to perform sounding to one or more fourth communication devices; and indication that the second communication device can request one or more fourth communication devices to send feedback to the first communication device based on estimation sequences sent by the first communication device within the obtained TXOP or based on a previous feedback stage.A18. Second communication device according to any one of embodiments A15 to A17, wherein the initial control response frame includes PHY parameters including one or more of the following: number of spatial streams, with which the second communication device plans to transmit one or more frames to the one or more third communication devices; bandwidth to be used by the second communication device in the transmission of the one or more frames to one or more third communication devices; bandwidth and / or feedback type and / or codebook, specifying the feedback format to be received from one or more third communication devices; acceptance of the configuration for LTF / GI parameters for the transmission of the frame to one or more third communication devices; transmission power to be used during the transmission of the sounding frames;expected reception level of the signals from the third to the second communication device; indication of a maximum number of spatial streams that the first communication device can use during the transmission of the frame to the one or more fourth communication devices; and a supported feedback format of the fourth communication devices, for reporting the channel information related to the channels between the first and fourth communication devices.A19. Second communication device according to any one of embodiments A15 to A18, wherein the circuitry is further configured to determine, based on a final set of PHY parameters indicated in a second control frame, in particular an NDP-A frame, received from the first communication device, a configuration for use during the transmission of one or more NDP frames to the one or more second communication devices.A20. First communication method of a first communication device configured to communicate with one or more third communication device, the first communication comprising: obtaining a transmission opportunity (TXOP); transmitting an initial control frame to one or more second communication devices, the initial control frame indicating that at least a part of the obtained TXOP may be used by the second communication device to transmit one or more frames to one or more third and / or fourth communication devices and including conditioning information prioritizing or restricting frame transmissions of the second communication device during the obtained TXOP to one or more parameters; receiving an initial control response frame from one or more of the second communication devices, the initial control response frame indicating whether the second communication device can participate in the obtained TXOP; and enabling within at least a part of the obtained TXOP one or more of the second communication devices to transmit one or more frames to one or more third and / or fourth communication devices based on the conditioning information.A21. Second communication method of a second communication device configured to communicate with one or more fourth communication device, the second communication method comprising: receiving an initial control frame from a first communication device, the initial control frame indicating that a TXOP obtained by the first communication device may be used by the second communication device to transmit one or more frames to one or more third and / or fourth communication devices and including conditioning information prioritizing or restricting frame transmissions of the second communication device during the obtained TXOP to one or more parameters; transmitting an initial control response frame to the first communication device, the initial control response frame indicating whether the second communication device can participate in the obtained TXOP; and receiving an enablement within at least a part of the obtained TXOP from the first communication device allowing the second communication device to transmit one or more frames to one or more third and / or fourth communication devices based on the conditioning information.A22. A non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method according to embodiment A20 or A21 to be performed.A23. A computer program comprising program code means for causing a computer to perform the steps of said method according to embodiment A20 or A21 when said computer program is carried out on a computer.

Claims

CLAIMS1. First communication device configured to communicate with one or more third communication device, the first communication device comprising circuitry configured to: obtain a transmission opportunity (TXOP); transmit an initial control frame to a second communication device, the initial control frame indicating that the obtained TXOP may be shared with the second communication device and including conditioning information prioritizing or restricting the use of the obtained TXOP to an operating mode and / or restricting frame exchanges of the second communication device during the obtained TXOP to one or more parameters; receive an initial control response frame from the second communication device, the initial control response an indication whether the second communication device can participate in the obtained TXOP; and allocate at least a part of the obtained TXOP to the second communication device allowing it to exchange one or more frames with one or more fourth communication devices taking account of the conditioning information.

2. First communication device as claimed in claim 1 , wherein the conditioning information includes a request for schedule-relevant information for the obtained TXOP and / or a parameter indication indicating one or more parameters based on which the second communication device determines conditions to be respected during a shared transmission within the obtained TXOP; and / or wherein the initial control response includes requested schedule-relevant information and an indication whether the second communication device can respect the one or more parameters indicated by the parameter indication.

3. First communication device as claimed in claim 2, wherein circuitry is configured to determine a point in time of allocating at least a part of the TXOP and / or a duration of the allocation of at least a part of the TXOP to the second communication device based on the request for schedule-relevant information.

4. First communication device as claimed in claim 2, wherein the request for schedule-relevant information includes one or more of:size of data units corresponding to an indicated traffic identifier and / or to a particular fourth communication device; size of data units corresponding to data flows associated with a data path that is no longer active at the second communication device; size of data units destined to a fourth communication device for which a roaming procedure from the second communication device is ongoing; sounding related parameters, in particular number of sounding dimensions, type of estimation sequences, feedback format or number of fourth communication devices to be sounded; planned duration of a transmission for data units whose size is indicated or a part of the data units, whose size is indicated, and a transmission should be accommodated in the obtained TXOP; planned duration of a transmission respecting the conditioning information; and duration needed to prepare a transmission respecting the one or more parameters within the obtained TXOP.

5. First communication device as claimed in claim 2, wherein the parameter indication includes one or more of: indication that the obtained TXOP may be shared for a particular operating mode and / or only frames corresponding to the particular operating mode may be transmitted; indication of a particular operating mode, based on which a set of conditions are defined or can be derived, in particular an indication that the obtained TXOP should be used for sequential sounding or joint sounding or coordinated measurement or roaming; indication of a set of parameters which restrict the type of traffic transmitted by the second communication device; indication of a subset of channels to be used during the obtained TXOP by the second communication device; indication of a set of one or more fourth communication devices which should be addressed by the second communication device; indication of a set of physical layer (PHY) parameters that should be used, in particular number of sounding dimensions, type of estimation sequences and / or feedback format; andindication of whether the shared transmission should be for uplink data traffic and / or downlink data traffic or can be left at the decision of the second communication device.

6. First communication device as claimed in claim 1 , wherein the third communication device is within the same basic service set (BSS) as the first communication device and / or the fourth communication device is within the same basic service set (BSS) as the second communication device.

7. First communication device as claimed in claim 1 , wherein the circuitry is configured to: receive a roaming notification from a second communication device or a roaming fourth communication device that the roaming fourth communication device intends to roam to the basic service set (BSS) of the first communication device; obtain a TXOP; allocate at least a part of the obtained TXOP to the second communication device enabling the second communication device to transmit remaining or buffered data units to the roaming fourth communication device during the allocated part of the obtained TXOP.

8. First communication device as claimed in claim 2 and 7, wherein the request for schedule-relevant information includes a request for one or more of: information about the size of the remaining or buffered data units of the second communication device for the roaming fourth communication device; estimated duration of transmission of the remaining or buffered data units from the second communication device towards the roaming fourth communication device; an estimate of the start time when the second communication device could start the transmission within the obtained TXOP; and an estimate of the required duration of the transmission of the first communication device within the obtained TXOP.

9. First communication device as claimed in claim 2 and 7, wherein the parameter indication includes one or more of:indication that the second communication device shall transmit at least one data unit towards the roaming fourth communication device; indication that the second communication device shall transmit at least one data unit containing traffic corresponding to a particular traffic identifier; indication that the second communication device shall only transmit data units containing traffic corresponding to a particular traffic identifier; indication of a roaming mode; and indication that the second communication device may transmit a Link Disable indication towards the roaming fourth communication device indicating that there are no more data units destined for the fourth communication device and / or the fourth communication device should switch to a link of the first communication device.

10. First communication device as claimed in claim 8, wherein the initial control response includes one or more of: information about the size of buffered units for the roaming fourth communication device; estimated duration of transmission of data units towards the roaming fourth communication device; estimated duration of the transmission of the second communication device with the constraints indicated in the parameter indication; and whether the second communication device is ready for transmission, or which is the earliest time when the second communication device can perform the transmission towards the roaming fourth communication device.11 . First communication device as claimed in claim 7, wherein the circuitry is configured to allocate transmission time for the second communication device to perform data exchange with the fourth communication device within the obtained TXOP before the data exchange between the first and third communication devices; or, if the first communication device has data to transmit to the roaming fourth communication device, corresponding to a particular traffic identifier or traffic identifier set to transmit an indication to the second communication device to discard remaining data units corresponding to the particular traffic identifier or traffic identifier set or to transmit dataunits to the roaming fourth communication device which correspond to one traffic identifier set and allow the second communication device to send data units corresponding to a second traffic identifier set that is non-overlapping with the first traffic identifier set.

12. First communication device as claimed in claim 7, wherein the circuitry is configured to: receive a roaming notification from a third communication device that the third communication device intends to roam to the basic service set (BSS) of a second communication device or the signal quality has degraded at the third communication device; obtain a TXOP; allocate at least a part of the TXOP to one or more second communication devices to perform control and / or data message exchange with the third communication device.

13. First communication device as claimed in claim 12, wherein the circuitry is configured to allocate at least a part of the obtained TXOP to one or more second communication devices to transmit measurement signals preferably allowing a collection of one or more potential target communication devices to which a roaming third communication device may roam.

14. First communication device as claimed in claim 1 , wherein the circuitry is configured to allocate the transmission time within the obtained TXOP for the second communication device to enable the second communication device to transmit data units corresponding to a traffic with time constraints to a fourth communication device or to receive data units from a fourth communication device within an interval corresponding to the time constraints.

15. Second communication device configured to communicate with one or more fourth communication device, the second communication device comprising circuitry configured to: receive an initial control frame from a first communication device, the initial control frame indicating that a TXOP obtained by the first communication device may be shared with the second communication device, and including conditioning information prioritizing or restricting the use of the obtained TXOP to an operating mode and / or restricting frameexchanges of the second communication device during the obtained TXOP to one or more parameters; transmit an initial control response frame to the first communication device, the initial control response including an indication whether the second communication device can participate in the obtained TXOP; and receive an allocation of at least a part of the obtained TXOP from the first communication device allowing the second communication device to exchange one or more frames with one or more fourth communication devices taking account of the conditioning information.

16. Second communication device according to claim 15, wherein the circuitry is configured to be ready to transmit first within the obtained TXOP and / or inform via a control entity if the data units towards a fourth communication device are ready for transmission or discard the data units corresponding to a roaming fourth communication device and an indicated traffic identifier.

17. Second communication device according to claim 15, wherein the circuitry is configured to obtain, from the received conditioning information, a parameter indication indicating one or more parameters; and transmit within the obtained TXOP one or more of:- at least one data unit towards a roaming fourth communication device,- at least one data unit containing traffic corresponding to a particular traffic identifier,-at least one data unit containing traffic corresponding to a data path that is no longer active at the second communication device,-a data unit triggering the fourth communication device to send control and or data units towards the second and / or first communication device,- at least one data unit towards a fourth communication device, indicated by the first communication device, and- a Link Disable indication towards the roaming fourth communication device indicating that there are no more data units destined for the fourth communication deviceand / or the fourth communication device should switch to a link of the first communication device.

18. First communication method of a first communication device configured to communicate with one or more third communication device, the first communication method comprising: obtaining a transmission opportunity (TXOP); transmitting an initial control frame to a second communication device, the initial control frame indicating that the obtained TXOP may be shared with the second communication device and including conditioning information prioritizing or restricting the use of the obtained TXOP to an operating mode and / or restricting frame exchanges of the second communication device during the obtained TXOP to one or more parameters; receiving an initial control response frame from the second communication device, the initial control response including an indication whether the second communication device can participate in the obtained TXOP; and allocating at least a part of the obtained TXOP to the second communication device allowing it to exchange one or more frames with one or more fourth communication devices taking account of the conditioning information.

19. Second communication method of a second communication device configured to communicate with one or more fourth communication device, the second communication method comprising: receiving an initial control frame from the first communication device, the initial control frame indicating that a TXOP obtained by the first communication device may be shared with the second communication device, and including conditioning information prioritizing or restricting the use of the obtained TXOP to an operating mode and / or restricting frame exchanges of the second communication device during the obtained TXOP to one or more parameters; transmitting an initial control response frame to the first communication device, the initial control response including an indication whether the second communication device can participate in the obtained TXOP; andreceiving an allocation of at least a part of the obtained TXOP from the first communication device allowing it to exchange one or more frames with one or more fourth communication devices taking account of the conditioning information.

20. A non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method according to claim 18 or 19 to be performed.21 . First communication device configured to communicate with one or more third communication device, the first communication device comprising circuitry configured to: obtain a transmission opportunity (TXOP); transmit an initial control frame to one or more second communication devices, the initial control frame indicating that at least a part of the obtained TXOP may be used by the second communication device to transmit one or more frames to one or more third and / or fourth communication devices and including conditioning information prioritizing or restricting frame transmissions of the second communication device during the obtained TXOP to one or more parameters; receive an initial control response frame from one or more of the second communication devices, the initial control response frame indicating whether the second communication device can participate in the obtained TXOP; and enable within at least a part of the obtained TXOP one or more of the second communication devices to transmit one or more frames to one or more third and / or fourth communication devices based on the conditioning information.

22. First communication device according to claim 21 , wherein the conditioning information or the initial control frame includes one or more of the following: coordination identifier that identifies one or more first and / or second communication devices which can share time / spatial resources at a particular time;Coordination Group Identifier that identifies a group of communication devices, which should be sounded together;sounding scheduling interval identifier representing an interval within which one or more first and / or second communication devices can cooperate to identify coordinated transmission schemes and / or train channel parameters; coordinated transmission schedule interval representing an interval within which one or more first and / or second communication devices can coordinate their transmissions based on previously negotiated arrangements; coordination type including one or more of coordinated spatial reuse with transmit power control, coordination spatial reuse without transmit power control, and coordinated beamforming; one or more PHY parameters; indication of whether the transmission of the one or more sounding frames from a second communication device to the one or more third communication devices should be performed simultaneously with the transmission of one or more sounding frames from the first communication device to the one or more third communication devices; indication that only sounding related frames can be sent by the second communication device; and enabling information for the second communication device.

23. First communication device according to claim 22, wherein the PHY parameters include one or more of the following: number of spatial streams which the first communication device plans to use in the transmission of the one or more sounding frames to the one or more third communication devices; maximum number of spatial streams that can be transmitted by the second communication device in the one or more sounding frame to the 3rdcommunication devices; total number of spatial streams that can be used in the transmission of the one or more sounding frames from the first and / or second communication devices; supported bandwidth of the one or more third communication devices which should be sounded in the obtained TXOP; bandwidth with which the sounding frames should be sent;bandwidth for which the feedback from the one or more third communication devices to the first communication device should be sent; indication of supported feedback format; indication of sequential or joint feedback collection; andLTF type, Gl type, number of subcarriers to be grouped within the feedback, and codebook size.

24. First communication device according to claim 21 , wherein the initial control frame further includes one or more of the following: indication that within a second part of the TXOP, the second communication device should enable the first communication device to receive feedback of channel information from the first communication device to one or more fourth communication devices with a format based on predefined parameters or parameters indicated within the initial control frame or to receive feedback corresponding to a previous training session with an identifier indicated within the initial control frame; indication that a second part of the TXOP can be used by the second communication device to exchange sounding frames with one or more fourth communication devices; and indication that within a second part of the TXOP, the second communication device may enable the first communication device to transmit one or more null data packet frames to one or more fourth communication devices.

25. First communication device according to claim 21 , wherein the initial control frame for joint sounding includes one or more of the following: indication to poll one or more second communication devices if they can send null data packets within the TXOP; indication of a maximum number of sounding dimensions that can be used by one or more second communication devices in the transmission to one or more third communication devices; indication of a number of sounding dimensions to be used during the training by the first communication devices to the one or more third communication devices; indication of supported feedback format; indication of sequential or joint feedback collection; andindication that time can be allocated within the second part of the TXOP for sounding.

26. First communication device according to claim 21 , wherein the initial control frame includes an indication of whether the transmission of one or more frames from the second communication device should be performed simultaneously with one or more frames from the first communication device or sequentially, in particular in the case of coordinated beamforming sounding.

27. First communication device according to claim 23, wherein the circuitry is configured to determine, based on one or more one or more parameters indicated within the initial control frame and / or the initial control response frame a final set of PHY parameters and to indicate the final set of PHY parameters within a second control frame, in particular an NDP-A frame, to the second communication device and the one or more third communication devices.

28. First communication device according to claim 21 , wherein the circuitry is configured to enable the second communication device to transmit one or more sounding frames to the one or more third communication devices by transmitting a second control frame, in particular an NDP-A frame, including a user field identifying the respective communication unit and the final set of PHY parameters to be used in the transmission of the one or more frames by the second communication device.

29. First communication device according to claim 28, wherein the final set of PHY parameters includes one or more of: index of the first spatial stream to be transmitted by the second communication device; the total number of spatial streams to be transmitted by the second communication device; bandwidth to be used in the transmission; the format in which the feedback, in particular one or more of type, codebook, grouping, postprocessed, bandwidth, will be transmitted by the one or more third communication devices;LTF type;Gl type; and sounding token; and / or wherein the user field of the one or more third communication devices includes an indication of the format of the feedback of the channel from the second to the fourth communication device and, optionally, one or more of a transmission power to be used by the second communication device, an expected receiver power expected by the second communication device to receive the feedback, an indication that pathloss information for the channels between the second and third communication devices should be computed, an indication that a transmit power to be used in the transmission of the report containing the feedback of the channel to be estimated based on the subsequent sounding frame, shall be determined.

30. First communication device according to claim 21 , wherein the circuitry is configured to enable the second communication device to receive the feedback from one or more third communication devices by transmitting a fourth control frame, in particular an BFRP frame, which contains an indication, allowing the one or more third communication devices to align their transmissions with respect to the second communication device, in particular an indication including adjusted transmit power levels or adjusted expected receive power per user, or an indication that the transmit power determined during the estimation of the reported channels shall be used in the transmission of the feedback reports.

31. First communication device according to claim 21 , wherein the circuitry is configured to enable the second communication device to receive the feedback from one or more third communication devices by transmitting a frame containing aggregated feedback information from the respective third communication devices; and / or enable the second communication device to transmit one or more frames to the one or more fourth communication devices by including a third control frame, in particular an allocation frame, which indicates the ID of the second communication device and / or aduration information regarding the duration of the TXOP which can be used by the second communication device.

32. First communication device according to claim 21 , wherein the conditioning information conditions the use of the TXOP by the one or more second communication devices to one or more of: transmission of one or more sounding frames from the second communication device to one or more third communication devices; transmission of one or more control frames from the second communication device to the first communication device and to the one or more fourth communication devices, indicating a set of parameters to be used by the first communication device in a subsequent transmission to the one or more fourth communication devices; transmission of one or more sounding frames from the second communication device to the one or more fourth communication devices; transmission of one or more control frames from the second communication device to one or more fourth communication devices, requesting for feedback information; and transmission of one or more control frames from the second communication device to the one or more fourth communication devices, indicating correction parameters to be used by the one or more fourth communication devices in a follow up transmission to the first communication device.

33. Second communication device configured to communicate with one or more fourth communication device, the second communication device comprising circuitry configured to: receive an initial control frame from a first communication device, the initial control frame indicating that a TXOP obtained by the first communication device may be used by the second communication device to transmit one or more frames to one or more third and / or fourth communication devices and including conditioning information prioritizing or restricting frame transmissions of the second communication device during the obtained TXOP to one or more parameters; transmit an initial control response frame to the first communication device, the initial control response frame indicating whether the second communication device can participate in the obtained TXOP; andreceive an enablement within at least a part of the obtained TXOP from the first communication device allowing the second communication device to transmit one or more frames to one or more third and / or fourth communication devices based on the conditioning information.

34. Second communication device according to claim 33, wherein, if the conditioning information contains an indication of a sounding mode, the circuitry is configured to exchange with the one or more fourth communication devices one or more of sounding frame, sounding announcement frames, feedback frames, request for feedback.

35. Second communication device according to claim 33, wherein the initial control response frame includes one or more of the following: indication of acceptance of PHY parameters indicated for the transmission or indication of alternative parameters that are respecting conditions within the initial control frame; indication that the second communication device can request one or more fourth communication devices to estimate channels from the first communication device; indication if the second communication device needs a part of the TXOP to perform sounding to one or more fourth communication devices; and indication that the second communication device can request one or more fourth communication devices to send feedback to the first communication device based on estimation sequences sent by the first communication device within the obtained TXOP or based on a previous feedback stage.

36. Second communication device according to claim 33, wherein the initial control response frame includes PHY parameters including one or more of the following: number of spatial streams, with which the second communication device plans to transmit one or more frames to the one or more third communication devices; bandwidth to be used by the second communication device in the transmission of the one or more frames to one or more third communication devices;bandwidth and / or feedback type and / or codebook, specifying the feedback format to be received from one or more third communication devices; acceptance of the configuration for LTF / GI parameters for the transmission of the frame to one or more third communication devices; transmission power to be used during the transmission of the sounding frames; expected reception level of the signals from the third to the second communication device; indication of a maximum number of spatial streams that the first communication device can use during the transmission of the frame to the one or more fourth communication devices; and a supported feedback format of the fourth communication devices, for reporting the channel information related to the channels between the first and fourth communication devices.

37. Second communication device according to claim 33, wherein the circuitry is further configured to determine, based on a final set of PHY parameters indicated in a second control frame, in particular an NDP-A frame, received from the first communication device, a configuration for use during the transmission of one or more NDP frames to the one or more second communication devices.

38. First communication method of a first communication device configured to communicate with one or more third communication device, the first communication comprising: obtaining a transmission opportunity (TXOP); transmitting an initial control frame to one or more second communication devices, the initial control frame indicating that at least a part of the obtained TXOP may be used by the second communication device to transmit one or more frames to one or more third and / or fourth communication devices and including conditioning information prioritizing or restricting frame transmissions of the second communication device during the obtained TXOP to one or more parameters; receiving an initial control response frame from one or more of the second communication devices, the initial control response frame indicating whether the second communication device can participate in the obtained TXOP; andenabling within at least a part of the obtained TXOP one or more of the second communication devices to transmit one or more frames to one or more third and / or fourth communication devices based on the conditioning information.

39. Second communication method of a second communication device configured to communicate with one or more fourth communication device, the second communication method comprising: receiving an initial control frame from a first communication device, the initial control frame indicating that a TXOP obtained by the first communication device may be used by the second communication device to transmit one or more frames to one or more third and / or fourth communication devices and including conditioning information prioritizing or restricting frame transmissions of the second communication device during the obtained TXOP to one or more parameters; transmitting an initial control response frame to the first communication device, the initial control response frame indicating whether the second communication device can participate in the obtained TXOP; and receiving an enablement within at least a part of the obtained TXOP from the first communication device allowing the second communication device to transmit one or more frames to one or more third and / or fourth communication devices based on the conditioning information.

40. A non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method according to claim 38 or 39 to be performed.

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