Communication devices and methods

Abstract

A first communication device is configured to communicate with one or more second communication devices, the first communication device comprising circuitry configured to detect a collision detection indication in a data unit received from one or more of the second communication devices configured to transmit a data unit including a collision detection indication; determine, based on one or more received collision detection indications, whether a collision or reception failure has occurred; and transmit, if it is determined that a collision or reception failure has occurred, a collision resolution indication indicating that a collision or reception failure has occurred and / or indicating at least one of the one or more second communication devices which transmitted a data unit that caused the collision or had a reception failure.

Description

WITTEWELLERP A T E N T A N W A L T EApplicants:Sony Group Corporation 17 December 20241-7-1 Konan 4727P369WO - SKMinato-KuTokyo 108-0075JAPANSony Europe B.V.The Heights, BrooklandsWeybridge, SurreyKT13 0XWUNITED KINGDOMCOMMUNICATION DEVICES AND METHODSBACKGROUNDFIELD OF THE DISCLOSURE

[0001] The present disclosure relates to first and second communication devices, in particular for collision detection and resolution.DESCRIPTION OF RELATED ART

[0002] Enhanced distributed channel access (EDCA) is a main channel access protocol used in WLAN. This protocol is efficient when the number of stations (STA; also called non-AP STA) contending for channel access is low, but it can create very long channel accessdelays when the number of STAs grows. On the other hand, trigger based (TB) channel access is more efficient when the number of STAs is larger, which, however, can also create long delays when the access point (AP) is not aware of data traffic arrival at the STAs. Despite the use of this protocol and the need for performing a backoff procedure, collisions and delays of channel access can occur when multiple STAs access the same channel.

[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 reduce the probability of collisions and / or channel access delays, in particular in WLAN systems. It is a further object to provide a corresponding method as well as a corresponding computer program and a non-transitory computer-readable recording medium that stores therein a computer program product for implementing said method.

[0005] According to an aspect there is provided a first communication device configured to communicate with one or more second communication devices, the first communication device comprising circuitry configured to: detect a collision detection indication in a data unit received from one or more of the second communication devices configured to transmit a data unit including a collision detection indication; determine, based on one or more received collision detection indications, whether a collision or reception failure has occurred; and transmit, if it is determined that a collision or reception failure has occurred, a collision resolution indication indicating that a collision or reception failure has occurred and / or indicating at least one of the one or more second communication devices which transmitted a data unit that caused the collision or had a reception failure.

[0006] According to a further aspect there is provided a second communication device configured to communicate with a first communication device that is configured to communicate with one or more second communication devices, the second communication device comprising circuitry configured to transmit a data unit including a collision detection indication; and receive from the first communication device a response to the transmitted data unit or a collision resolution indication indicating that a collision or reception failure has occurred and / or indicating at least one of one or more second communication devices which transmitted a data unit that caused the collision or had a reception failure.

[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 a collision detection indication that is transmitted from a second communication device (which may be a STA, i.e. operate as STA in an embodiment, but may be an AP, i.e. operate as AP in another embodiment) to a first communication device (which may be an AP, i.e. operate as AP in an embodiment, but may be an STA, i.e. operate as STA in another embodiment). The collision detection indication may, for instance, be transmitted in the form of a collision detection field (CoF), such as a physical layer (PHY) field, in a data unit (e.g. a physical layer protocol data unit (PPDll)). The collision resolution indication, e.g., in the form of a collision resolution field (CRF), thus indicates to the second communication device(s) that a collision or reception failure has occurred. Furthermore, it may indicate the second communication device(s) that caused the collision or reception failure. This enables a second communicationdevice to detect a collision and, optionally, to take measures for collision resolution, which may be instructed from the first communication device.

[0010] Herein, the term “collision” shall be understood as an event where two or more transmissions by different second communication devices or between a second communication device and another communication device (e.g., a legacy or interfering device that does not use the collision detection indication) are fully or partially overlapped in time and / or frequency domain. For instance, an event where two or more STAs transmit PPDlls that are fully or partially overlapped in time represents a collision. This can occur, for example, when the devices access the wireless medium simultaneously after performing contention-based channel access or receiving an indication from the AP allowing simultaneous transmissions. A reception failure may not only be caused by the device transmitting but rather external factors like interference, channel conditions, etc. that affect the reception of a data unit.

[0011] A collision detection indication shall be broadly understood as an indication that is utilized within a wireless medium where collisions or packet reception failure may occur. Some exemplary applications of a collision detection indication are one or more of detecting collisions and identify colliding STAs during distributed channel access and preemption scenarios and identifying the transmitter of a data unit with a failed packet reception. The collision detection indication may be a signal inserted as a PHY field and composed of one or more OFDM symbols. These OFDM symbols may be truncated to form other periodic signals.

[0012] Contention-based channel access refers to a distributed channel access mechanism like EDCA where the STA that needs to access the channel (or wireless medium) performs carrier sense (CS) and / or clear channel assessment (CCA) to determine if the channel is busy before transmitting. If the channel is busy, a backoff procedure is invoked and the channel access is performed when the backoff counter reaches zero.

[0013] 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, togetherwith 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

[0014] 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 of a communication scheme using collision resolution with EDCA legacy behavior.Fig. 2 shows a diagram of a communication scheme illustrating an example of a collision in frame-based preemption in a downlink scenario.Fig. 3 shows a diagram of a first embodiment of a communication scheme according to the present disclosure illustrating collision resolution in uplink via a collision detection indication by means of trigger based channel access.Fig. 4 shows a flowchart illustrating an embodiment of the general process of collision detection and resolution via a collision detection field (CoF) at the AP.Fig. 5 shows a diagram of a second embodiment of a communication scheme according to the present disclosure illustrating collision resolution in uplink via CoF by means of a shared TXOP operation.Fig. 6 shows a diagram of a third embodiment of a communication scheme according to the present disclosure illustrating collision resolution in uplink via CoF by means of deferred channel access.Fig. 7 shows a diagram of a fourth embodiment of a communication scheme according to the present disclosure illustrating a response indication to CRF to confirm CoF detection.Fig. 8 shows a flowchart illustrating an embodiment of the general operation of a colliding STA.Fig. 9 shows a diagram of a fifth embodiment of a communication scheme according to the present disclosure illustrating collision resolution with CoF for framebased preemption.Fig. 10 shows a diagram of a sixth embodiment of a communication scheme according to the present disclosure illustrating AP contention before transmitting a collision resolution field (CRF).Fig. 11 show a diagram illustrating an embodiment of the process to set up CoF operation.Fig. 12 shows a flow chart of an embodiment of a first communication method according to the present disclosure.Fig. 13 shows a flow chart of an embodiment of a second communication method according to the present disclosure.Fig. 14 shows a diagram of a seventh embodiment of a communication scheme according to the present disclosure illustrating collision resolution in downlink.Fig. 15 shows a diagram of an eighth embodiment of a communication scheme according to the present disclosure illustrating collision resolution in uplink in case of a collision between communication devices of different basic service sets.Fig. 16 shows a diagram of a ninth embodiment of a communication scheme according to the present disclosure illustrating collision resolution in downlink in case of a collision between communication devices of different basic service sets.Fig. 17 shows a diagram of a tenth embodiment of a communication scheme according to the present disclosure illustrating collision resolution in uplink and downlink in case of a collision between communication devices of different basic service sets.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0015] Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, Fig. 1 shows a diagram of a communication scheme using collision resolution with EDCA legacy behavior. A first communication device (in this embodiment an AP) communicates with two second communication devices (in this embodiment stations STA1 and STA2). For Low latency applications the use of EDCA is advantageous because each STA can start contending to access the channel as soon as they have data to transmit, avoiding potential delays of waiting to be triggered by the AP. To avoid collisions, a STA using EDCA must invoke a backoff procedure when the channel is busy. Thus, before transmitting, a STA must sense the channel to be idle for an arbitration interframe space (AIFS) duration and draw a random backoff counter from an interval [0, nCW] where nCW is an integer number that defines the size of the contention window (CW). The STA decrements its backoff counter for each specific time slot durations. When the backoff counter reaches zero, the STA is allowed to transmit. If the STA transmission fails, for example due to a collision or a temporary loss of coverage, the STA must invoke the backoff procedure again, but this time it must double its CW, meaning to draw a new backoff counter from an interval [0, 2 x nCW - 1], This is done to reduce the collision probability, but it may lead to even longer delays as shown in Fig. 1.

[0016] Collisions can also occur in the special scenario of frame-based preemption where protocol changes have been introduced to provide channel access for low latency applications. Fig. 2 shows a diagram of a communication scheme illustrating an example of a collisionin frame-based preemption in a downlink scenario. The AP starts a transmit opportunity (TXOP), and in between specific frames, an IFS gap (denoted as preemption IFS (pIFS) in Fig. 2) is added which has a longer duration than the commonly used short interframe space (SIFS). In these pIFS gaps, other STAs may send a preemptive PPDll (pPPDll) carrying a preemption indication or data. Typically, there is an indication in previous PPDlls announcing an upcoming pIFS gap to STAs with preemptive traffic. Collisions can occur when more than one STA send a pPPDll in the same pIFS gap as illustrated in Fig. 2 for STA2 and STA3.

[0017] Since there are specific pIFS gaps where STAs are allowed to send pPPDlls, collisions can happen more frequently than in regular contention scenarios. This can introduce unwanted delays and reduce the efficiency of the TXOP. The frame-based preemption mechanism already has an inherent decrease in efficiency because PPDlls need to have a limited duration to offer regular preemption gaps and support low latency traffic constraints.

[0018] In many cases, when there is a collision, the frames are lost because they cannot be decoded, and it is not known who collided until later. In the case of EDCA, the STAs involved in the collision need to wait for a predetermined timeout, as shown in Fig. 1 , without obtaining a response before they can realize that their transmission failed. Afterwards, the colliding STAs contend again with a new backoff counter having double CW (in Fig. 1 the AIFS is included in the timeout). The collision can be detected at the AP only after one of the STAs is able to successfully transmit a frame containing a retransmission indication.

[0019] In the case of frame-based preemption shown in Fig. 2, the AP needs to start a buffer status report (BSR) procedure to find out which STAs collided. In addition, the collisions can occur in several pIFS gaps during the TXOP. Thus, using BSR procedures to resolve collisions in frame-based preemption cases introduces more delays and reduces the efficiency of the data exchange in the TXOP.

[0020] Fig. 3 shows a diagram of a first embodiment of a communication scheme according to the present disclosure illustrating collision resolution in uplink via a collision detectionindication by means of trigger based (TB) channel access. According to this embodiment a collision detection field (CoF) 10, 20, representing an embodiment of the collision detection indication, is added as a PHY field in a PPDll 11 , 21 which identifies the STA transmitting the PPDll. This enables a receiver STA (i.e. , in this embodiment the AP) to detect a collision. The CoF 10, 20 may, e.g., be located in the preamble of the PPDll 11 , 21 after a legacy portion and at least one signaling field. In an example, the CoF may be added to the first PPDU used to obtain a TXOP, which avoids further delays due to the exponential backoff procedure. The CoF further enables a receiver STA (the AP) to identify which STAs collided even if no other information (including SIG and data fields) can be decoded from the PPDUs 11 , 21 that collided.

[0021] It shall be noted that the AP is assumed to be the intended receiver of a CoF. If the AP identifies at least one of the STAs (STA1 , STA2) that collided, it can modify the channel access to resolve the collision (at least partly) and reduce the channel access delay. For this purpose, it can transmit a collision resolution indication indicating that a collision or reception failure has occurred and / or indicating at least one of the STAs which transmitted a PPDU that caused the collision or had a reception failure. In this embodiment, a collision resolution field (CRF) 30 represents the collision resolution indication. A receiver may generally determine that a failed detection has occurred when the likelihood values for the detection test do not reach a certain threshold within the selected detection window. This does not mean that a CoF is present or not, but it simply means that the detection test did not detect a CoF. When this happens a second lower threshold may be used to trigger the start of a detection window adjustment or employ successive interference cancellation methods.

[0022] To support collision resolution mechanisms via CoF the following considerations may be taken. This can be done as part of an initialization or (re-)configuration phase or within the association process for each STA:• Generation and distribution of CoF to all STAs: The AP should know all CoFs and their assignment to each STA. A CoF can be assigned to a single STA or to a group of STAs. A CoF can also be used to indicate a simplified traffic priority of buffer status. For instance, each STAs may have two CoFs, each indicating if the traffic buffer is below or above certain level.• Configuration of CoF to be used by each STA: Duration of CoF, modulation parameters of CoF, sequence type of CoF.• Definition of TB-PPDU or TXOP duration that the AP can set following a collision detection.

[0023] In an embodiment a mode of operation is provided where STAs including CoF in PPDlls to request for channel access, also configure such PPDlls to have equal duration. This makes the legacy signaling field (L-SIG) have equal content and increases their decoding reliability. In case of collisions, if the AP can extract this duration information from the L- SIG, it can adjust the duration of scheduled TB-PPDUs or TXOPs.

[0024] Fig. 4 shows a flowchart illustrating an embodiment of the general process 100 of collision detection and resolution via CoF at the AP. In the following, the proposed mechanisms to detect and resolve collisions with CoF are explained.

[0025] In an embodiment, there are two main assumptions being made about the format of PPDlls carrying a CoF, that is, the PPDU can contain a data field or not. In the first case, a PPDU with data field carries MPDUs containing medium access control (MAC) information in the header like transmitting address (TA) and network allocation vector (NAV) setting indication. Thus, in cases explained below where MAC information items are mentioned, it is assumed that the PPDU contains a data field. In the second case, the PPDU carrying a CoF only contains physical layer (PHY) information and resulting behaviors do not rely on MAC information.

[0026] First, with reference to Fig. 4, a potential AP behavior shall be explained. When energy is detected (L-STF detection), which can be part of carrier sense (CS) or clear channel assessment (CCA) procedures (step 101), the AP process the PPDU as usual (decode preamble and data field; steps 102 and 105, respectively). In addition, it may run (step 103) a detection process for CoF (based on its configuration) in one or more of the following: for first PPDU of a non-established TXOP, for PPDUs transmitted in a service period where specific STAs are allowed to transmit, and for PPDUs within a TXOP where preemptionoperation is allowed (in particular, to PPDlls carrying a preemptive indication or preemptive data). Further, it transmits (step 104) in a subsequent frame an indication if a CoF was detected or not. This indication can be part of the contention resolution / recovery frame (CRF) (30 in Fig. 3), which will be explained below in more detail. The absence of such a transmission may also be an indication. If a CoF is detected, STA ID or ID group is preferably identified by the CoF as well. This frame may also be included in a response PPDll in case the PPDll with CoF also has a data field carrying an MPDll that was successfully decoded.

[0027] The evaluation if a collision has occurred may be done as follows. A collision or packet decoding failure is detected via CoF in the following cases (AP actions follow below). Generally, the CoF can be detected sequentially after the preamble decoding and before the data field decoding or in parallel based on the result from CS or CCA procedures. If one CoF is detected, one of the following cases may occur.

[0028] In a first case, a PPDll including a data field is correctly decoded (step 105) containing at least one MPDU with transmitter address (TA) identifying a transmitter STA that does not match the STA identified or contained in the group of STAs identified by the CoF, which is checked in step 106. In this case a collision is detected (step 107), but the TXOP of the STA sending the correctly decoded MPDU can be established. The AP can send a response frame (step 104) to TXOP initiating STA and allow TXOP to be established. In the response frame the AP can include channel access information to a STA identified by the CoF. Further mechanisms are explained below.

[0029] In a second case, the PHY preamble decoding fails (step 108) or, if the PPDU contains a data field, all MPDUs in the PPDU failed to be successfully decoded (step 105). This case does not necessarily mean that a collision occurred since decoding failure could also be due to an outage in coverage. However, since the CoF is detected, the transmitting STA can be identified (step 109), and the AP can decide to provide channel access or not (step 104) (collision resolution item for mechanism the AP can be used to give channel access).

[0030] If at least two CoFs are detected in step 103, this is interpreted as a collision and the following mechanism explained below for collision resolution may be applied (steps 109, 104, 110).

[0031] In case no collision occurred, it is assumed that the PPDll can be successfully decoded The AP can know (which is detected in step 111) if a CoF was added by an indication in the PPDll preamble or by a previous negotiation phase where it is fixed which STAs will use CoF. If no CoF is detected in step 111 and if a CoF was added in the PPDll, the AP can request (step 110) a CoF configuration change to the STA sending the PPDU or a group of STAs sharing the same CoF configuration or to all STAs in the BSS (step 1 10). Further, the AP can send a CoF report (step 110) to the STA identified by the TA in the decoded PPDU, in a separate frame containing information regarding detection values of CoF (e.g., likelihood ratios of detection test, probability of detection and / or probability of false alarm). It shall be noted that CoF is designed to be as robust or more as the PHY preamble to ensure that a correctly decoded PPDU with no CoF detection should happen with very low probability. Assuming the PPDU contains a data field, if a CoF is detected and if the CoF identifies the same STA identified by the TA of a MPDU carried in the PPDU, no further action with respect to CoF processing is needed, except (optionally) to send a CoF report to the transmitting STA for collecting statistics of CoF detection performance. The PPDU processing shall continue as usual.

[0032] If, in step 105, at least one MPDU has been successfully decoded, an acknowledgement is transmitted if the MPDU is addressed to this STA and the acknowledgement policy requires it (step 112).

[0033] In the following, an embodiment of collision resolution according to the present disclosure will be explained. If a collision or a packet failure is detected via CoF, the AP sends a contention resolution / recovery frame (CRF) a predetermined inter frame space (IFS), denoted as IFS1 in Fig. 3, after the medium is idle (e.g., after the collision occurred) to resolve the collision, or attempts to recover the channel access failure.

[0034] The CRF can enable an uplink TB channel access as illustrated in Fig. 3. The AP triggers (using the CRF itself 30 and / or a trigger frame TF 31) the STAs that were identified in the CoFs 10, 20 to send data in a TB-PPDU 12, 12a, 22, 22a where the TB-PPDU duration can be determined by one of the following: the time duration of the collision (this duration can be estimated as the difference between the end of the collision taken as the point in time the wireless medium is sensed as idle, and the start of the colliding PPDll detection (from e.g., CS / CCA)), or a predetermined fixed value set by the AP or previously negotiated, or duration information in successfully decoded L-SIG in case the colliding PPDlls have equal length. Further, the AP triggers the STAs to collect BSR and continue with uplink TB channel access.

[0035] As shown in Fig. 3, the CRF 30 may act as a trigger frame that schedules the first two PPDlls 12, 22. Since the AP does not fully know how much traffic STA1 and STA2 need to transmit, the length of the first PPDlls 12, 22 may not be sufficient. Thus, a second trigger 31 may be used to allow STA1 and STA2 to finish or continue their data transmission. It can also be that the CRF 30 acts as a trigger but it first collects buffer status from the STAs, so first PPDUs 12, 22, and then triggers the uplink data, i.e. , second PPDUs 12a, 22a.

[0036] In another embodiment the CRF can start a shared TXOP operation with one or more colliding STAs, or other STAs needing to transmit. Fig. 5 shows a diagram of a second embodiment of a communication scheme according to the present disclosure illustrating collision resolution in uplink via CoF by means of a shared TXOP operation. Further, a TXOP can be shared between downlink and / or peer-to-peer (P2P) traffic. The AP can give priority to one or more specific STAs, for example, based on the access category (AC) or Traffic identifier (TID).

[0037] In another embodiment the CRF can defer channel access of a specific group of STAs, e.g., with low priority traffic. Fig. 6 shows a diagram of a third embodiment of a communication scheme according to the present disclosure illustrating collision resolution in uplink via CoF by means of deferred channel access. The AP can ask STA2 to not duplicate CWs 24, 25 compared to the original CW23 to avoid additional delays resulting from the exponential backoff increase.

[0038] In the example illustrated in Fig. 6, STA2 was deferred in favor of STA1 , which gives priority to STA1 . The next TXOP 32 is started by the AP since it typically has short backoff counter. At this point, STA2 starts contending for channel access with a new backoff counter 24 that is not doubled. This modification allows STA2 to avoid having a long waiting time before transmitting. For example, in this case STA1 had a data arrival during the AP’s TXOP 32. Without this modification of the length of the CW 24, it would have been likely for STA1 to win contention before STA2.

[0039] In still another embodiment, the AP can move frame exchange to another link.

[0040] In addition, CRF can also indicate on or more of the following:• NAV resetting for all other STAs in case other STAs could extract NAV information from colliding PPDlls, assuming the colliding PPDlls contained a data field carrying MPDlls;• The STAs that participated in the collision (or failed transmission) extracted from detected CoFs and in addition an indication if these STAs are allowed to draw a new backoff counter without doubling CW, an indication if one or more of these STA can use other EDCA parameters (e.g., reduced AIFS), and / or an indication if one or more of these STAs will be triggered in an upcoming TXOP;• to colliding STAs whose CoF were not detected (AP does not know who they are) that they can draw a new backoff counter without double CW, which can only be allowed if a collision is resolved (at least partly), meaning that the CRF gives channel access to at least one colliding STA;• to deferred and / or unscheduled STAs to use only a short frame to start their TXOPs with a mandatory CoF and, in addition, a more robust CoF configuration.

[0041] The expected response to a CRF frame may be configured as follows. Depending on the collision resolution mechanism triggered by the CRF, STAs can reply with a PPDll containing data, or no response as shown in Fig. 6, or with a short response as shown in Fig. 7 showing a diagram of a fourth embodiment of a communication scheme according to the present disclosure illustrating a response indication to CRF to confirm CoF detection.

[0042] In very seldom cases, it can occur that the CoF detected by the AP was incorrect and a wrong STA is identified as a colliding STA. For example, in the example shown in Fig. 7, STA3 is identified as a colliding STA but only STA1 and STA2 collided. To account for this case, the AP can request STAs that are identified as colliding STAs in the CRF 30 to always respond with an indication of whether they participated in the collision or not. This request may be in the form of an additional reply field 36 included in or added to the CRF 30. This response indication can be in a separate short PPDll as shown in Fig. 7 illustrated by the response frame R 16, 46.

[0043] The colliding STAs not identified in the CRF 30 may be allowed to redraw a backoff counter without doubling the CW or optionally with a short AIFS. In the example of Fig. 7, this mechanism allows STA2 to have a shorter contention (compared to double CW) avoiding further delays (e.g., otherwise STA3 would gain channel access before STA2).

[0044] If there is no response to the CRF, the AP should fall back to standard EDCA rules, e.g., to start a new backoff procedure to schedule colliding STAs. No response may, e.g., occur if the STAs addressed in the CRF 30 suffer a momentarily outage (e.g., shadowing effects or external interference prevented them from decoding the CRF).

[0045] The behavior of a colliding STA shall now be explained with reference to Fig. 8 showing a flowchart illustrating an embodiment of the general operation 200 of a colliding STA. Initially, the STA agrees with the AP on CoF usage and configuration. To start, the STA contends for channel access via EDCA (step 201) or obtains channel access in a preemption pIFS gap (step 202). In step 203, the STA adds CoF to a PPDll in one or more of the following cases: for the first PPDll of a non-established TXOP, for PPDUs transmitted in a service period where specific STAs are allowed to transmit, or for PPDUs within TXOP where preemption operation is allowed (as shown in Fig. 9 showing a diagram of a fifth embodiment of a communication scheme according to the present disclosure illustrating collision resolution with CoF for frame-based preemption), in particular to PPDUs carrying a preemptive indication or preemptive data.

[0046] If the colliding STA receives a response frame as usual, which is checked in step 204, and the STA receives an indication that CoF was successfully detected (step 205), this means that there was no collision and the CoF detection works as intended so that no further action is needed, i.e. , the frame exchange can be continued within the TXOP (step 206). If the colliding STA receives an indication that the CoF failed (or absence of CoF information), this means that a PPDll was correctly decoded at the receiver, but the CoF was not detected. Then the colliding STA can modify the CoF configuration at the request of the AP (step 207).

[0047] If the CRF is received (step 208) and conveys actions addressed to the colliding STA, the colliding STA follows instructions of the AP (step 209), for example: respond to TF, respond to frame that schedules a shared TXOP operation (e.g., Mll-RTS), defer channel access by drawing a new backoff counter and (if allowed) do not double the CW and optionally modify AIFs before contending again (this can be in the same channel after the current TXOP ends or can be in a separate link if indicated in the CRF), or modify EDCA parameters, e.g., no doubling of CW, change AIFS duration.

[0048] If the CRF is received but it does not contain actions or information for the colliding STA (step 210) it means the AP does not know that this STA was also part of the collision. If allowed (indicated in the CRF), the STA may not increase CW, draw a new backoff counter, and optionally change EDCA parameters as indicated in CRF. If indicated in the CRF, a short frame with mandatory CoF may be used in the next channel access attempt and a more robust CoF configuration.

[0049] If no response frame is received within a predetermined timeout, the STA shall fall back to the standard backoff (2 x CW - 1) operation (step 201 or 202). the timeout value is set based on the time duration required for an expected response to be received. This can include AIFS, receiver PHY delays and length of response frame.

[0050] For the frame-based preemption case, a collision resolution example is shown in Fig. 9, where STA2 and STA3 are colliding STAs. In this case, the STAs with preemption traffic (STA2, STA3) should include a CoF 20, 40 in the PPDll 27, 47 carrying a preemptionindication or data. This allows the AP to identify which STAs participated in the collision and start a collision resolution mechanism from the ones defined above (as explained for the collision resolution). In the example shown in Fig. 9, the CRF 30 triggers the colliding STAs to reduce the delay that occurs from additional BSR procedures.

[0051] Generally, if there is a collision on the CRF, all STAs should fall back to legacy behavior, doubling CW and waiting AIFS before counting down the backoff counter.

[0052] In the IEEE 802.11 standards, typically, a TXOP is established by a successful exchange of two PPDlls where the STA initiating the exchange obtains channel access via EDCA. To comply with standard operation one of the following rules may be implemented. In the event of a collision that is detected via CoF detection, the AP may perform a backoff procedure before sending the CRF as illustrated in Fig. 10 showing a diagram of a sixth embodiment of a communication scheme according to the present disclosure illustrating AP contention 33 before transmitting CRF 30. In the event of a collision that is detected at the AP via CoF detection, the AP may start a TXOP without performing a backoff procedure as shown, for example, in Fig. 5. In addition, at least one frame in the TXOP should be scheduled to resolve the collision and allow at least one colliding STA to transmit data (e.g., a TF and / or CRF should schedule a colliding STA). The duration of the TXOP that contains transmissions of colliding STAs can be set up to a predetermined duration.

[0053] As explained above, the AP should determine the ID of STAs based on the CoF detection. To achieve this, the AP may correlate the received signal with all possible CoF signals and select the ones whose likelihood values are above a predetermined threshold. This operation can have high complexity if the number of possible CoFs is too large (e.g., more than hundreds). To reduce complexity, it is possible to group several STAs into one CoF signal, and after detection, the AP can trigger the STAs corresponding to this group in other to identify the transmitting STAs.

[0054] In an embodiment of the operation, each CoF signal may identify a different transmitting STA so that several different CoF signals need to be generated. The cross-correlation between CoF signals determines the performance of the detection at the receiver; lowercross-correlation means higher detection reliability. In addition, colliding transmissions are in general not synchronous so that the cross-correlation between CoF signals should also be low in the presence of time and frequency shifts.

[0055] There are two main design parameters for the generation of CoF signals: the time duration of the CoF signal and the number of distinct CoF signals, denoted as Ncof, that shall be generated.

[0056] The time duration of the CoF signal determines the number of samples that the CoF signals has (based, e.g., on the PPDll bandwidth). The more CoF samples, the higher the detection reliability that can be achieved. Furthermore, the greater the number of CoF samples, the easier is it to separate the Ncof signals, in particular, it is desirable that the number of CoF samples is larger or equal to Ncof.

[0057] Fig. 11 show a diagram illustrating an embodiment of the process 300 to set up CoF operation. This process involves the definition of main parameters (e.g., number of STAs), CoF configuration, signal generation and distribution.

[0058] The general procedure to generate and distribute CoF signal may be as follows. In block 302, the time duration of CoF signals within PPDll is defined. Several time durations can be defined to be mapped to several CoF configurations. Thus, it is beneficial to define the time duration in predetermined steps. For example, for a bandwidth of 20MHz, 4ps is a practical step size which contains 80 samples that would correspond to one OFDM symbol for a FFT size of NFFT = 64 plus a guard interval (Gl) of 16 samples.

[0059] In block 301 , the number of distinct CoF signals, denoted as Ncof, is defined that need to be generated. They can be computed as:Ncof = ( ceil (N_contending_STAs I N_STA_groups ) x N_ind_per_STA ) where ceil() denotes a rounding operation to the nearest largest integer value. N_contend- ing_STAs is the number of STAs contending for channel access. N_ind_per_STA is thenumber of indications per STA in case more information than STA identification is to be provided with the CoF, for example: buffer status indications per each STA (each STA can have, for example, two CoFs, one indicating short packets below certain threshold, and the other indicating larger packets above said threshold) and priority level of data needed to be transmitted which can be defined based on TID, AC or stream classification service (SCS) characteristics. N_STA_groups is the number of groups into which several STAs are pulled together for a common CoF assignment.

[0060] In block 303, CoF signals are generated. In particular, complex-value sequences are generated by one of the following:• Create binary sequences and modulate them with PSK modulation (e.g., BPSK or QPSK) to obtain complex-value sequences with low cross-correlation properties.The binary sequences can be common sequences with low cross-correlation properties, like, Gold sequences, or randomly generated sequences where the PSK modulated complex-value sequences have a cross-correlation below a predetermined threshold.• Create complex-value sequences based on DFT or Hadamard matrices.• Encode the bits corresponding to each STA ID using a robust channel coding operation (e.g., BCC with code rate 1 / 2 or 1 / 3) and modulate the encoded bits with a robust modulation (e.g., BPSK) to create complex-value sequences.

[0061] In block 304, the complex-value sequences are modulated into waveforms to be transmitted. This may be done using time domain waveforms, wherein the complex-value sequences can be phase shifted and transmitted with pulse amplitude modulation (PAM). Alternatively, this may be done using OFDM waveforms, wherein the complex-value sequences can be phase shifted and mapped into tones in an OFDM grid that are modulated into OFDM symbols and transmitted.

[0062] In block 305, CoF signals are assigned to STAs. In case each STA has several distinct CoF signals assigned to it (e.g., each having additional indications), signals are chosen that have the larger cross-correlation in comparison to their cross-correlation with CoF signals assigned to other STAs. In case more than one STA is identified by a distinct CoFsignal, STAs that are less likely to contend for channel access at the same time (e.g., if they have regular activity intervals that do not overlap) are grouped.

[0063] In block 306, information is exchanged between AP and all STAs in the BSS so that each STA knows which CoF signal to use (and which additional indications can be conveyed), and the AP knows all CoFs corresponding to each STA. For the AP, all CoF signals and their STA assignment plus additional indications should be known. The generation of CoF signals can be done in a centralized manner at the AP, which in turns sends indications to each STA with information about how to generate its own CoF signal, or the CoF signals themselves.

[0064] Based on the general procedure to create CoF signals explained above, it may be desirable to have several CoF configurations available to dynamically balance reliability, signaling overhead and complexity. Different CoF configurations are obtained by changing one or more of the following parameters: The duration of the CoF signal and / or length of the CoF signal, modulation parameters (the modulation and coding scheme in case the encoded STA ID is used for generating CoF signals; the FFT size, guard interval and tone map to be used in case of OFDM modulation), and sequence type as one of low-cross correlation pseudo random sequence type (e.g., Gold, Kasami, JPL) and orthogonal sequence DTF or Hadamard.

[0065] Fig. 12 shows a flow chart of an embodiment of a first communication method 400 of the first communication device (the AP) according to the present disclosure, which may be performed by circuitry or separate units or a programmed computer of processor of the first communication device. In a first step 401 , a collision detection indication is detected in a data unit received from one or more of the second communication devices (STAs) configured to transmit a data unit including a collision detection indication. In a second step 402, it is determined, based on one or more received collision detection indications, whether a collision or reception failure has occurred. In a third step 403, if it is determined that a collision or reception failure has occurred, a collision resolution indication is transmitted indicating that a collision or reception failure has occurred and / or indicating at least one of the one or more second communication devices which transmitted a data unit that caused the collision or had a reception failure.

[0066] Fig. 13 shows a flow chart of an embodiment of a second communication method 500 of the second communication device (any one of the STAs) according to the present disclosure, which may be performed by circuitry or separate units or a programmed computer of processor of the second communication device. In a first step 501 , a data unit is transmitted including a collision detection indication. In a second step 502, from the first communication device a response to the transmitted data unit is received or a collision resolution indication is received indicating that a collision or reception failure has occurred and / or indicating at least one of one or more second communication devices which transmitted a data unit that caused the collision or had a reception failure.

[0067] In the embodiments illustrated with reference to Figs. 3 to 11 , the first communication device is configured to operate as AP and the second communication device (s) is (are) configured to operate as STA I non-AP STA. These embodiments dealt with uplink (UL) scenarios. In the following, embodiments of the present disclosure will be presented dealing with a downlink (DL) scenario, in which the first communication device is configured to operate as STA I non-AP STA and a second communication device is configured to operate as AP and further second communication devices are configures as STA I non-AP STA as well. Furthermore, embodiments of the present disclosure will be presented dealing with a mixed UL / DL scenario, in which a collision occurs between communication devices of different (overlapping) basic service sets ((O)BSS).

[0068] Fig. 14 shows a diagram of a seventh embodiment of a communication scheme according to the present disclosure illustrating collision resolution in downlink. The AP includes a collision detection field (CoF) 50 into its PPDU 51 , e.g. into the PPDU preamble. The CoF 50 corresponds to the one assigned to the receiver STA or collision responder (STA that is supposed to reply with a CRF), in this case STA2 (the first communication device in this embodiment). The non-AP STA (STA2) only replies with CRF if detects the CoF that has been assigned to itself. Since this particular CoF 50 can only be used by this non-AP STA2 it implicitly means that the AP sent it (i.e. , it implicitly identifies the AP as the transmitter). The non-AP STA2 is supposed to reply with a CRF 60. The colliding non-AP STA1 may transmit another CoF 70 in a PPDU 71 , which may be configured and / or contain information as explained above for CoF 10.

[0069] According to this collision resolution mechanism, the CRF 60 informs all other STAs (STA1 , STA3 ... STAN, representing further second communication devices in this embodiment, and the AP) of a DL collision or packet failure. Consequently, all non-AP STAs (STA1 , STA3 ... STAN) defer channel access for a fixed period. Colliding STAs can contend again after the current DL TXOP ends without increasing the contention window (CW).

[0070] The AP gets channel access and starts its TXOP. The AP can start TXOP by triggering a buffer status report from colliding STAs. The CRF 60 may also contain an identification of other colliding STAs so that the AP can trigger them or start a shared TXOP. This may add complexity at the non-AP STA because it needs to detect more CoFs and not just the ones to identify itself.

[0071] Fig. 15 shows a diagram of an eighth embodiment of a communication scheme according to the present disclosure illustrating collision resolution in uplink in case of a collision between communication devices of different basic service sets (BSS). In this embodiment, the APs AP1 and AP2 represent first communication devices and the STAs represent second communication devices. The CoF designs may be limited so that communication devices in different OBSS may use the same CoF to identify different non-AP STAs. To overcome this potential problem, a service set information indicating the BSS to which the device belongs may be included within the CoF or added to the CoF. In Fig. 15 the CoF(1 ,1) 72 transmitted by STA1 (present in BSS1) identifies STA1 as transmitter of the CoF 72 and the BSS1 as the BSS to which the STA1 belongs to. CoF(3,2) 82 transmitted by STA3 (present in BSS2, which is an OBSS of BSS1) identifies STA3 as transmitter of the CoF 82 and the BSS2 as the BSS to which the STA3 belongs to. CoF 72 and CoF 82 may be transmitted in respective PPDlls 73, 83.

[0072] For non-AP STAs, the CoF 72, 82 identifies itself as transmitter and the BSS that it is part of. For AP STAs, the CoF 72, 82 identifies the target receiver within its BSS and the BSS it is part of. As explained above with reference to Fig. 14, the receiving STAs implicitly understand that the AP sent the CoF when it uses the CoF assigned to themselves.

[0073] In Fig. 15, the case UL vs. UL is particularly illustrated, i.e. , there is a collision between STA1 (of BSS1) and STA3 (of BSS2), which is also referred to as OBSS collision herein (i.e. two communication devices belong to different BSSs). To resolve this collision, it is proposed to allow APs to identify an OBSS collision. If the OBSS collision is detected (e.g., by evaluation of CoF 82 by AP1, CoF 82 identifying BSS2), one or more of the following steps may be taken.

[0074] As a first option, one designated AP may reply with a ORF 52. Therein, the AP priority order may be fixed (e.g., AP 1> AP2 > AP3 ,...), i.e., the sequence in which the APs may transmit may be set, and only the highest priority AP can then reply with ORF. Further, the order may be changed in round robin fashion every certain amount of time to avoid a fairness issue. As a second option, a short backoff may be done so that only APs are contending for channel access, which reduces the likelihood of collisions of CRFs. This short backoff can be done with different EDCA parameters than the ones during regular EDCA operation. If there is CRF collision, it may be fallen back to Enhanced Distributed Channel Access (EDCA) (for non-AP STAs it means to wait for a specific amount of time (e.g., EIFS) and start a backoff procedure with an increase CW it they wants to access the channel again; for APs it means that they will not get an answers to the CRF before a timeout timer has elapsed, meaning that the collision resolution failed and they need to wait a certain amount of time and start another backoff procedure if they need to access the channel.). As a third option, a BSS-specific short waiting time (e.g. Inter Frame space, IFS) may be set, which are different. This gives a priority order between APs so that the likelihood of a CRF collision is reduced. The IFS can change in round robin fashion every certain amount of time to avoid a fairness issue.

[0075] The CRF 52 thus indicates an OBSS collision and indicates the STA identity of the STA (here STA1) that should start TXOP, while other STAs should defer channel access and start of a TXOP. Optionally, the CRF 92, which may be a copy of the CRF 52, can be broadcasted by AP2 to avoid further OBSS collisions.

[0076] Fig. 16 shows a diagram of a ninth embodiment of a communication scheme according to the present disclosure illustrating collision resolution in downlink in case of a collision between communication devices of different basic service sets. In this embodiment, theSTAs STA1 and STA3 represent first communication devices and the APs and other STAs represent second communication devices.

[0077] In Fig. 16, the case DL vs. DL is particularly illustrated, i.e. , there is a collision between AP1 (of BSS1) and AP2 (of BSS2), which is referred to as OBSS collision as well. To resolve this collision, non-AP STAs (e.g. STA1 , STA3) detect the CoFs 50, 90 in the PPDlls 51 , 91 and identify their BSS and themselves as intended receivers. If a non-AP STA (STA1 , STA3) identifies an OBSS collision, the approach described above with reference to Fig. 15 may be used before sending a CRF 74, 84. Otherwise, the ORF 74, 84 may be transmitted with a CoF 75, 85 identifying their respective BSS. APs can thus identify an OBSS collision and follow the options described above with reference to Fig. 15.

[0078] Fig. 17 shows a diagram of a tenth embodiment of a communication scheme according to the present disclosure illustrating collision resolution in uplink and downlink in case of a collision between communication devices of different basic service sets. In this embodiment, STA1 and AP2 represent first communication devices and AP1 and the other STAs represent second communication devices.

[0079] In Fig. 17, the case UL vs. DL is particularly illustrated, i.e., there is a collision between AP1 (of BSS1) and STA3 (of BSS2), which is referred to as OBSS collision as well. If AP2 identifies the OBSS collision with AP1 , it does not respond to it with a CRF. To resolve this collision, a non-AP STA (STA1) correctly detects the CoF 50 and identifies its BSS and itself as intended receiver. If a non-AP STA identifies an OBSS collision, the approach described above with reference to Fig. 15 may be used. Otherwise, it may transmit a CRF 74 with CoF 75 identifying itself as transmitter and its respective BSS. AP1 then decodes the CRF 74, and if it does not identify another CoF within the CRF, meaning that there is no CRF collision, it can start its TXOP.

[0080] Thus, according to the embodiments illustrated with reference to Figs. 14 to 17, the collision indication may include an implicit receiver identifier to account for DL cases and / or a BSS identifier to account for OBSS cases. The STA receiving the collision indication identifying itself replies with CRF, which identifies the collision as a DL. If the STA receivingthe collision indication identifies its BSS and another BSS from an overlapping transmission, the CRF can indicate that an OBSS collision occurred. Generally, the CRF can include a collision indication in its preamble, in particular if it is a non-AP STA.

[0081] In summary, according to embodiment of the present disclosure, a communication device, such as an AP, may detect PHY indications in received PPDlls and extract information identifying the transmitting device for each transmitted PPDll, determine whether a collision between PPDlls or a packet reception failure has occurred, and, if a collision or packet failure occurred, transmit indication to transmitting STAs and other STAs, indicating that a collision or a packet failure has occurred and / or which were the STAs identified in the detected PHY indication. A transm itting / colliding communication device, such as a STA, may include a PHY indication at least in a first PPDll transmitted to establish a TXOP or in a service period where specific STAs are allowed to transmit or in a predetermined IFS gap within an established TXOP where preemptive data transmission is allowed, the PHY indication including information identifying the STA as the transmitter, and receive an indication from the AP and determine if it has participated in a collision or a packet failure occurred when transmitting said PPDll.

[0082] 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 of the 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.

[0083] 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 of the scope of the disclosure, as well as other claims. The disclosure, including any readily discernible variants of the teachings herein, defines, in part, the scope of the foregoing claim terminology such that no inventive subject matter is dedicated to the public.

[0084] 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.

[0085] 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.

[0086] 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 programmable gate arrays. Further, a circuit includes central processing units, graphics processing units, and microprocessors which are programmed or configured according to software code. A circuit does not include pure software, although a circuit includes the above-described hardware executing software. A circuit or circuitry may be implemented by a single device or unit or multiple devices or units, or chipset(s), or processor(s).

[0087] It follows a list of further embodiments of the disclosed subject matter:1. First communication device configured to communicate with one or more second communication devices, the first communication device comprising circuitry configured to detect a collision detection indication in a data unit received from one or more of the second communication devices configured to transmit a data unit including a collision detection indication;determine, based on one or more received collision detection indications, whether a collision or reception failure has occurred; and transmit, if it is determined that a collision or reception failure has occurred, a collision resolution indication indicating that a collision or reception failure has occurred and / or indicating at least one of the one or more second communication devices which transmitted a data unit that caused the collision or had a reception failure.2. First communication device according to embodiment 1 , wherein the circuitry is configured to detect a collision detection indication in a data unit received from one or more of the second communication devices configured to transmit a data unit including a collision detection indication after performing contention-based channel access, during a predetermined service period or during a predetermined time gap within an established transmit opportunity.3. First communication device according to any one of embodiments 1 to 2, wherein the circuitry is configured to obtain and / or indicate and / or exchange with the one or more second communication devices information indicating one or more of: the assignment of collision detection indications to the one or more second communication devices; if a collision detection indication shall be included in a subsequent data unit transmitted by one or more second communication devices; if said subsequent data unit can start a transmit opportunity; if a collision detection indication indicates traffic priority and / or buffer status of the respective second communication device; the configuration of collision detection indications; and the maximum length of a data unit including a collision detection indication.4. First communication device according to embodiment 3, wherein the circuitry is configured to obtain and / or indicate and / or exchange with the one or more second communication devices information indicating the configuration of collision detection indications including one or more of duration, modulation parameters, sequence type, tone index allocation, time / symbol sequence index allocation, definition of atrigger based data unit and / or transmit opportunity duration that the first communication device can set following the detection of a collision or reception failure.5. First communication device according to any one of embodiments 1 to 4, wherein the circuitry is configured to determine, based on the one or more received collision detection indications, that a collision or reception failure has occurred by detecting one or more of: transmit information included in the collision detection indication indicating the second communication device as transmitter of the collision detection indication does not match transmit information included in a data unit received and correctly decoded by the first communication device; at least one collision detection indication has been detected and decoding of a preamble and / or data field of one or more data units failed; at least two collision detection indications have been received from different second communication devices.6. First communication device according to any one of embodiments 1 to 5, wherein the circuitry is configured, if no collision detection indication has been detected from a second communication device, but the first communication device is aware that a collision detection indication should have been transmitted by the second communication device, to perform one or more of: transmit a request to change the configuration of the collision detection indication to one or more second communication devices; and transmit a collision detection report to one or more second communication devices including information regarding detection values of collision detection indications.7. First communication device according to any one of embodiments 1 to 6, wherein the circuitry is configured, if a collision or reception failure has occurred, to transmit a collision resolution indication that is configured to inform at least the one or more second communication devices indicated by the received collision detection indications of one or more of the following: enable trigger-based channel access; schedule transmissions by one or more second communication devices;start a shared TXOP operation with the first communication device; defer channel access; move data exchange to another link; modify network allocation vector settings; transmit a response if the second communication device participated in the collision or not; indicate if an OBSS collision occurred, meaning a collision with a transmission of a first or second communication device of an overlapping BSS (OBSS); indicate if a second communication device is allowed to draw a new backoff counter and / or if it is allowed to draw a new backoff counter without increase of contention window; indicate if a second communication device can use other channel access parameters; indicate if a second communication device will be triggered in an upcoming transmit opportunity; and indicate if a second communication device may use only a short frame to start a transmit opportunity with a mandatory collision detection indication and / or a more robust configuration of the collision detection indication.8. First communication device according to any one of embodiments 1 to 7, wherein the circuitry is configured, if a collision or reception failure has occurred, to transmit a collision resolution indication in a broadcast data unit that is configured to inform second communication devices that transmitted a data unit before of one or more of the following: modify network allocation vector settings; defer channel access; if a second communication device is allowed to draw a new backoff counter and / or if it is allowed to draw a new backoff counter without increase of contention window; indicate if a second communication device can use other channel access parameters; and indicate if a second communication device may use only a short frame to start a transmit opportunity with a mandatory collision detection indication and / or a more robust configuration of the collision detection indication.9. First communication device according to any one of embodiments 1 to 8, wherein the circuitry is configured to perform a backoff procedure before the transmission of the collision resolution indication; or start a transmit opportunity, after the wireless medium is identified as idle after a collision or packet error has been determined, without performing a backoff procedure by transmitting a data unit carrying a collision resolution indication that schedules the transmission of a data unit by a second communication device; or preempt an existing transmit opportunity to schedule the transmission of a data unit by a second communication device after transmission of the collision resolution indication by the first communication device.10. First communication device according to any one of embodiments 1 to 9, wherein the circuitry is configured to generate and / or indicate to one or more second communication devices one or more configurations of collision detection indications by one or more of: defining the time duration of a collision detection indication within a data unit; defining the number of distinct collision detection indications; creating complex-valued sequences representing or being included in collision detection indications; modulating complex-valued sequences into waveforms to be transmitted as collision detection indications; assigning one or more collision detection indications to one or more second communication devices; and informing the second communication devices associated with the first communication device of the assignment of one or more collision detection indications to one or more second communication devices.11 . Second communication device configured to communicate with a first communication device that is configured to communicate with one or more second communication devices, the second communication device comprising circuitry configured to transmit a data unit including a collision detection indication; andreceive from the first communication device a response to the transmitted data unit or a collision resolution indication indicating that a collision or reception failure has occurred and / or indicating at least one of one or more second communication devices which transmitted a data unit that caused the collision or had a reception failure.12. Second communication device according to embodiment 11 , wherein the circuitry is configured to receive from the first communication device a collision resolution indication identifying the second communication device as a participant in a collision determined by the first communication device by detecting a collision detection indication.13. Second communication device according to embodiment 11 or 12, wherein the circuitry is configured to include the collision detection indication into a preamble of a data unit, in particular into a physical layer preamble of a physical layer protocol data unit.14. Second communication device according to any one of embodiments 11 to 13, wherein the circuitry is configured to transmit the data unit including the collision detection indication after performing contention-based channel access or during a predetermined service period or during a predetermined time gap within an established transmit opportunity and / or to include the collision detection indication into one or more of a first data unit transmitted after performing contention-based channel access; a data unit transmitted in a service period in which one or more second communication devices are allowed to transmit; and a data unit carrying a preemptive indication and / or preemptive data.15. Second communication device according to any one of embodiments 11 to 14, wherein the circuitry is configured to include, into the collision detection indication, one or more of transmit information indicating the second communication device as transmitter of the collision detection indication; target information indicating the first communication device as receiver of the collision detection information and / or as the device that shall resolve the collision; andservice set information indicating its basic service set.16. Second communication device according to any one of embodiments 11 to 15, wherein the circuitry is configured to perform, in response to the received collision resolution indication, one or more of the following: transmit a response and / or a data unit containing data; perform trigger-based channel access by transmitting a trigger-based data unit; transmit traffic according to a received schedule; start a shared TXOP operation with the first communication device; defer channel access; move data exchange to another link; modify network allocation vector settings; transmit a response if the second communication device participated in the collision or not; draw a new backoff counter; draw a new backoff counter without increase of contention window if the second communication device is not indicated or its channel access is deferred in the collision detection indication; use other channel access parameters; use only a short frame to start a transmit opportunity with a mandatory collision detection indication; and use a more robust configuration of the collision detection indication.17. Second communication device according to any one of embodiments 11 to 16, wherein the circuitry is configured to modulate one or more complex-valued sequences into waveforms to be transmitted as collision detection indication.18. First communication method of a first communication device configured to communicate with one or more second communication devices, the first communication method comprising: detecting a collision detection indication in a data unit received from one or more of the second communication devices configured to transmit a data unit including a collision detection indication;determining, based on one or more received collision detection indications, whether a collision or reception failure has occurred; and transmitting, if it is determined that a collision or reception failure has occurred, a collision resolution indication indicating that a collision or reception failure has occurred and / or indicating at least one of the one or more second communication devices which transmitted a data unit that caused the collision or had a reception failure.19. Second communication method of a second communication device configured to communicate with a first communication device that is configured to communicate with one or more second communication devices, the second communication method comprising: transmitting a data unit including a collision detection indication; and receiving from the first communication device a response to the transmitted data unit or a collision resolution indication indicating that a collision or reception failure has occurred and / or indicating at least one of one or more second communication devices which transmitted a data unit that caused the collision or had a reception failure.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 embodiment 18 or 19 to be performed.21 . A computer program comprising program code means for causing a computer to perform the steps of said method according to embodiment 18 or 19 when said computer program is carried out on a computer.22. First communication device according to any one of embodiments 1 to 10, wherein the circuitry is configured to: determine, if the detected collision detection indication is assigned to the first communication device and / or indicates that the first communication device shall resolve a collision; and perform the steps of determining whether a collision or reception failure has occurred and / or transmitting a collision resolution indication if it has determined that the detected collision detection indication is assigned to the first communication device.23. First communication device according to any one of embodiments 1 to 11 and 22, wherein the first communication device is configured to operate as station; and wherein the collision resolution indication is configured to inform second communication devices that are configured to operate as stations to defer channel access and to inform a second communication device that is configured to operate as access point to start a transmit opportunity and / or to trigger a buffer status report from other second communication devices.24. First communication device according to any one of embodiments 1 to 12 and 22 to 23, wherein the circuitry is configured to: determine, based on one or more received collision detection indications including a service set information indicating the basic service set (BSS) of the second communication device, whether an OBSS collision has occurred, meaning a collision with a transmission of a first or second communication device of an overlapping BSS (OBSS); and perform, if an OBSS collision has occurred, one or more of the following:- transmit a collision resolution indication indicating one or more of the priority of subsequent transmissions, the identity of the second communication device that is allowed to start a transmit opportunity, the one or more second communication devices that should defer to start a transmit opportunity; and the own BSS;- defer channel access;- initiate a backoff; and- include a BSS-specific interframe space.25. First communication device according to embodiment 24, wherein, if the first communication device is configured to operate as access point, the circuitry is configured not to transmit a collision resolution indication if an OBSS collision with another first communication device of the OBSS has occurred; and / or wherein, if the first communication device is configured to operate as station, the circuitry is configured to transmit a collision resolution indicating itself as transmitter and its BSS.26. Second communication device according to any one of embodiments 11 to 17,wherein the circuitry is configured to start a transmit opportunity if a service set information included in the received collision detection indication indicates its own basic service set, BSS, and if no collision detection indication has been received from an overlapping BSS (OBSS).

Claims

CLAIMS1. First communication device configured to communicate with one or more second communication devices, the first communication device comprising circuitry configured to detect a collision detection indication in a data unit received from one or more of the second communication devices configured to transmit a data unit including a collision detection indication; determine, based on one or more received collision detection indications, whether a collision or reception failure has occurred; and transmit, if it is determined that a collision or reception failure has occurred, a collision resolution indication indicating that a collision or reception failure has occurred and / or indicating at least one of the one or more second communication devices which transmitted a data unit that caused the collision or had a reception failure.

2. First communication device according to claim 1 , wherein the circuitry is configured to detect a collision detection indication in a data unit received from one or more of the second communication devices configured to transmit a data unit including a collision detection indication after performing contention-based channel access, during a predetermined service period or during a predetermined time gap within an established transmit opportunity.

3. First communication device according to claim 1 , wherein the circuitry is configured to obtain and / or indicate and / or exchange with the one or more second communication devices information indicating one or more of: the assignment of collision detection indications to the one or more second communication devices; if a collision detection indication shall be included in a subsequent data unit transmitted by one or more second communication devices; if said subsequent data unit can start a transmit opportunity; if a collision detection indication indicates traffic priority and / or buffer status of the respective second communication device; the configuration of collision detection indications; and the maximum length of a data unit including a collision detection indication.

4. First communication device according to claim 3, wherein the circuitry is configured to obtain and / or indicate and / or exchange with the one or more second communication devices information indicating the configuration of collision detection indications including one or more of duration, modulation parameters, sequence type, tone index allocation, time / symbol sequence index allocation, definition of a trigger based data unit and / or transmit opportunity duration that the first communication device can set following the detection of a collision or reception failure.

5. First communication device according to claim 1 , wherein the circuitry is configured to determine, based on the one or more received collision detection indications, that a collision or reception failure has occurred by detecting one or more of: transmit information included in the collision detection indication indicating the second communication device as transmitter of the collision detection indication does not match transmit information included in a data unit received and correctly decoded by the first communication device; at least one collision detection indication has been detected and decoding of a preamble and / or data field of one or more data units failed; at least two collision detection indications have been received from different second communication devices.

6. First communication device according to claim 1 , wherein the circuitry is configured, if no collision detection indication has been detected from a second communication device, but the first communication device is aware that a collision detection indication should have been transmitted by the second communication device, to perform one or more of: transmit a request to change the configuration of the collision detection indication to one or more second communication devices; and transmit a collision detection report to one or more second communication devices including information regarding detection values of collision detection indications.

7. First communication device according to claim 1 ,wherein the circuitry is configured, if a collision or reception failure has occurred, to transmit a collision resolution indication that is configured to inform at least the one or more second communication devices indicated by the received collision detection indications of one or more of the following: enable trigger-based channel access; schedule transmissions by one or more second communication devices; start a shared TXOP operation with the first communication device; defer channel access; move data exchange to another link; modify network allocation vector settings; transmit a response if the second communication device participated in the collision or not; indicate if an OBSS collision occurred, meaning a collision with a transmission of a first or second communication device of an overlapping BSS (OBSS); indicate if a second communication device is allowed to draw a new backoff counter and / or if it is allowed to draw a new backoff counter without increase of contention window; indicate if a second communication device can use other channel access parameters; indicate if a second communication device will be triggered in an upcoming transmit opportunity; and indicate if a second communication device may use only a short frame to start a transmit opportunity with a mandatory collision detection indication and / or a more robust configuration of the collision detection indication.

8. First communication device according to claim 1 , wherein the circuitry is configured, if a collision or reception failure has occurred, to transmit a collision resolution indication in a broadcast data unit that is configured to inform second communication devices that transmitted a data unit before of one or more of the following: modify network allocation vector settings; defer channel access;if a second communication device is allowed to draw a new backoff counter and / or if it is allowed to draw a new backoff counter without increase of contention window; indicate if a second communication device can use other channel access parameters; and indicate if a second communication device may use only a short frame to start a transmit opportunity with a mandatory collision detection indication and / or a more robust configuration of the collision detection indication.

9. First communication device according to claim 1 , wherein the circuitry is configured to perform a backoff procedure before the transmission of the collision resolution indication; or start a transmit opportunity, after the wireless medium is identified as idle after a collision or packet error has been determined, without performing a backoff procedure by transmitting a data unit carrying a collision resolution indication that schedules the transmission of a data unit by a second communication device; or preempt an existing transmit opportunity to schedule the transmission of a data unit by a second communication device after transmission of the collision resolution indication by the first communication device.

10. First communication device according to claim 1 , wherein the circuitry is configured to generate and / or indicate to one or more second communication devices one or more configurations of collision detection indications by one or more of: defining the time duration of a collision detection indication within a data unit; defining the number of distinct collision detection indications; creating complex-valued sequences representing or being included in collision detection indications; modulating complex-valued sequences into waveforms to be transmitted as collision detection indications; assigning one or more collision detection indications to one or more second communication devices; andinforming the second communication devices associated with the first communication device of the assignment of one or more collision detection indications to one or more second communication devices.

11. Second communication device configured to communicate with a first communication device that is configured to communicate with one or more second communication devices, the second communication device comprising circuitry configured to transmit a data unit including a collision detection indication; and receive from the first communication device a response to the transmitted data unit or a collision resolution indication indicating that a collision or reception failure has occurred and / or indicating at least one of one or more second communication devices which transmitted a data unit that caused the collision or had a reception failure.

12. Second communication device according to claim 11 , wherein the circuitry is configured to receive from the first communication device a collision resolution indication identifying the second communication device as a participant in a collision determined by the first communication device by detecting a collision detection indication.

13. Second communication device according to claim 11 , wherein the circuitry is configured to include the collision detection indication into a preamble of a data unit, in particular into a physical layer preamble of a physical layer protocol data unit.

14. Second communication device according to claim 11 , wherein the circuitry is configured to transmit the data unit including the collision detection indication after performing contention-based channel access or during a predetermined service period or during a predetermined time gap within an established transmit opportunity and / or to include the collision detection indication into one or more of a first data unit transmitted after performing contention-based channel access; a data unit transmitted in a service period in which one or more second communication devices are allowed to transmit; and a data unit carrying a preemptive indication and / or preemptive data.

15. Second communication device according to claim 11 , wherein the circuitry is configured to include, into the collision detection indication, one or more of transmit information indicating the second communication device as transmitter of the collision detection indication; target information indicating the first communication device as receiver of the collision detection information and / or as the device that shall resolve the collision; and service set information indicating its basic service set.

16. Second communication device according to claim 11 , wherein the circuitry is configured to perform, in response to the received collision resolution indication, one or more of the following: transmit a response and / or a data unit containing data; perform trigger-based channel access by transmitting a trigger-based data unit; transmit traffic according to a received schedule; start a shared TXOP operation with the first communication device; defer channel access; move data exchange to another link; modify network allocation vector settings; transmit a response if the second communication device participated in the collision or not; draw a new backoff counter; draw a new backoff counter without increase of contention window if the second communication device is not indicated or its channel access is deferred in the collision detection indication; use other channel access parameters; use only a short frame to start a transmit opportunity with a mandatory collision detection indication; and use a more robust configuration of the collision detection indication.

17. Second communication device according to claim 11 ,wherein the circuitry is configured to modulate one or more complex-valued sequences into waveforms to be transmitted as collision detection indication.

18. First communication method of a first communication device configured to communicate with one or more second communication devices, the first communication method comprising: detecting a collision detection indication in a data unit received from one or more of the second communication devices configured to transmit a data unit including a collision detection indication; determining, based on one or more received collision detection indications, whether a collision or reception failure has occurred; and transmitting, if it is determined that a collision or reception failure has occurred, a collision resolution indication indicating that a collision or reception failure has occurred and / or indicating at least one of the one or more second communication devices which transmitted a data unit that caused the collision or had a reception failure.

19. Second communication method of a second communication device configured to communicate with a first communication device that is configured to communicate with one or more second communication devices, the second communication method comprising: transmitting a data unit including a collision detection indication; and receiving from the first communication device a response to the transmitted data unit or a collision resolution indication indicating that a collision or reception failure has occurred and / or indicating at least one of one or more second communication devices which transmitted a data unit that caused the collision or had a reception failure.

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.

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