Patent Description:
As of today, in Wireless LANs (WLANs), an access point (AP) transmits one or more PPDUs (physical layer protocol data units) to one or more stations (STAs). Thereby, only a single AP should be transmitting at a point in time. Transmissions by other APs or STAs are interfering with that transmission and are therefore undesired. Next generation Wireless LAN considers joint transmission (JTX) of PPDUs by multiple APs (MAP) at the same time. The advantage is that coverage and/or reception quality can be increased.

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.

<CIT> discloses a method and an apparatus that may be used in multi-AP and multi-wireless transmit/receive unit joint transmissions. The apparatus may be configured to transmit a joint transmission request on a first medium, and receive a joint transmission response on the first medium. In response, the apparatus my perform a joint transmission negotiation on a second medium and transmit data on the second medium based on the joint transmission negotiation.

Further prior art can be found in <CIT> and <CIT>.

It is an object to provide communication devices and methods that enable an efficient multi-AP operation. It is a further object to provide a corresponding computer program for implementing said methods.

According to an aspect there is provided a first communication device as defined in claim <NUM>.

According to a further aspect there is provided a third communication device as defined in claim <NUM>.

According to still further aspects corresponding methods and 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 are provided.

It shall be understood that the disclosed communication devices and methods and the disclosed computer program have similar and/or identical further embodiments as the claimed first communication device and as defined in the dependent claims and/or disclosed herein.

One of the aspects of the disclosure is that, in a multi-AP communication setup, the access points (generally called AP STAs or simply APs) require knowledge of the data to be transmitted to a station (generally called non-AP STA or simply STA; also called "second communication device" herein). A backhaul link is thus provided to transport the necessary information to the APs participating in a joint transmission before the actual joint transmission takes place. According to the present disclosure, an efficient backhaul operation is presented that minimizes data rate requirements of the backhaul. In particular, a concept of transferring backhaul information from a master AP (also called "first communication device" herein) to one or more slave APs (also called "third communication device" herein) is disclosed in an embodiment. Furthermore, two concepts of transmit signal construction at the master AP providing this information and the slave AP(s) receiving this information are disclosed in embodiments of the disclosure. The proposed solutions are superior to known concepts in terms of required backhaul data rate and provide seamless integration into IEEE <NUM> compliant communication systems.

As of today, in any wireless LAN, an access point (AP) transmits one or more PPDUs (physical layer protocol data units) to one or more stations (STAs). Thereby, only a single AP is transmitting at a point in time. Transmissions by other APs or STAs are interfering with that transmission and are therefore undesired.

In contrast, next generation Wireless LAN considers joint transmission (JTX) of a PPDU by multiple APs (MAP) at the same time. The advantage is that coverage and/or reception quality are increased. As a disadvantage, there is a need for synchronization between APs and advanced channel sounding.

A further important aspect for MAP is that information needs to be shared among the APs that transmit simultaneously in MAP setup. The exchange of this information is one of the objectives of this disclosure.

In the following, a brief overview of the system model will be given. <FIG> shows a system using MAP data transmission from two APs to one STA, i.e. the setup resembles a downlink scenario. Each AP as well as each STA may have multiple transmit or receive antennas, respectively. The channel transfer function from AP1 to STA1 is H<NUM>, whereas H<NUM> is the channel transfer function from AP2 to STA1. Note that both H<NUM> and H<NUM> are matrices, which are in the most general case a function of carrier or tone index, i.e. the channel can be modeled by a set of matrices. In addition, both matrices may change with time but this is not considered here, as it is assumed that a channel matrix is known to at least the respective AP with good accuracy.

The receive signal r at STA1 (for a particular carrier or tone) is <MAT> in which t<NUM> and t<NUM> denote the actual transmit signal of a respective AP. Each AP may perform a precoding with matrix Q<NUM> or Q<NUM>, respectively. Thus, the received signal r is <MAT> with <MAT> being the overall precoding matrix and s being the baseband transmit signal before precoding. In the model above, the transmit signal, receive signal, channel matrix, and precoding matrix are carrier-based. An OFDM system is assumed, where each OFDM symbol conveys the information to be transmitted on one or more subcarriers or tones. The transmit signal may consist of one or more OFDM symbols.

In the most general case, vector s has dimensions NSS × <NUM> with NSS denoting the number of spatial streams in JTX. Qi has dimensions NTX,i × NSS with NTX,i denoting the number of transmit chains or transmit antennas of AP i. Hi has dimensions of NRX × NTX,i with NRX denoting the number of receive antennas of STA1. The model presented here assumes a single receiver; however, it can be easily extended to a multi-user (MU) scenario. In MU context, MAP serves several STAs at the same time.

In the following, it is assumed that the data traffic ingresses at a single AP as shown in <FIG> illustrating a communication system having a master AP (AP1; generally also called first communication device herein) and a slave AP (AP2; generally also called third communication device herein; there may be further slave APs) serving a station (STA1; generally a second communication device). Thus, the (user) data to be transmitted to the STA enters one AP (the master AP) only. All other APs that participate in a JTX are referred to as slave APs. As will be explained in more detail below, backhaul information is transmitted from the master AP to one or more slave APs for joint transmission from the one or more slave APs to a STA in coordination with a transmission from the master AP to the STA.

The distribution system (DS), which may be an external entity, such as a router, a server, a network, etc., is a connection to a higher layer, which provides a source of ingress traffic and a sink for egress traffic from an AP perspective. It is the objective of the DS to deliver a MAC service data unit (MSDU) to the intended destination. The DS may contain wireline and/or even further wireless links. It should be noted that master AP and slave AP provide egress traffic to the DS as well, but this is not primarily addressed in this disclosure.

As can be seen from the equation above, the master AP (e.g. AP1) may generate s based on the ingress traffic, but AP2 cannot generate s because it is not aware of the data to be sent to STA1. It is the objective of this disclosure to provide means to convey the necessary information from the master AP to one or more slave APs so that they can generate s.

According to embodiments, two ways to provide the one or more selected MAC output data units and the associated control information to the slave AP(s), namely via wireless backhaul or via DS backhaul, are provided, i.e. the slave APs are connected via a (e.g. wired) link to the master AP or via wireless backhaul (i.e. the slave APs are wirelessly connected to the master AP). The wireless connection may use the same frequency band as the successive JTX or a different frequency band. Moreover, embodiments of how the JTX is initiated or triggered after the necessary information has been conveyed to the slave APs are presented. Generally, embodiments of the proposed solutions are very efficient in terms of required bit rate of the backhaul, because they provide only MAC layer information to the slave AP(s) instead of full PHY layer information.

Before going to the details of MAP, the general operation of WLAN shall be briefly described by reference to showing the general layout of a communication device <NUM> operating as AP and of a communication device <NUM> operating as STA. The communication device <NUM> comprises a MAC (media access control) unit <NUM> (also called MAC layer unit or MAC layer circuitry or simply MAC layer) and a PHY (physical) unit <NUM> (also called PHY layer unit or PHY layer circuitry or simply PHY layer). The communication device <NUM> comprises a MAC unit <NUM> and a PHY unit <NUM> as well. All these units may e.g. be implemented by respective circuitry, a processor or computer.

Generally, the MAC unit <NUM> processes any incoming MSDU (herein also called MAC input data unit) in several steps. The main steps may be as follows. First, the MAC unit <NUM> buffers an incoming MSDU in one or more queues depending on its priority. Once the wireless channel is free for a certain period of time, the MAC unit <NUM> starts processing one or more MSDUs: The MAC unit <NUM> encrypts user data (i.e. one or more MSDU), prepends a MAC header and appends a frame check sequence (FCS). This forms a MPDU (herein also called MAC output data unit). The MAC header contains control information for the MAC unit of the peer STA <NUM> such as type of frame, duration, source and destination (MAC) address, and sequence number. The FCS is present for the MAC unit <NUM> of the peer STA <NUM> to detect if the MSDU or the MAC header has been received in error (and to potentially request a retransmission).

In a next step, one MPDU or several MPDUs are aggregated to an A-MPDU, which forms the physical layer service data unit (PSDU; herein also called PHY input data unit). The MAC unit <NUM> forwards the PSDU to the PHY unit <NUM>, which encodes, modulates and transmits the MAC message (either MPDU or A-MPDU), i.e. the PSDU. To enable the PHY unit <NUM> of the peer STA <NUM> to demodulate a received PHY output data unit, the PHY unit <NUM> prepends a PHY preamble holding PHY configuration and channel estimation sequences. The finally obtained PPDUs (PHY output data units) are transmitted to the STA <NUM>.

The PHY unit <NUM> of the STA <NUM> receives the PPDUs and performs inverse PHY layer processing followed by inverse MAC layer processing by the MAC unit <NUM> to obtain the MSDUs, i.e. the original data provided to the AP for transmission to the STA.

The PHY unit <NUM> may combine MPDUs with different destination/receiver address in a (multi-user) MU-PPDU. In this case, orthogonal PHY layer resources such as OFDMA or MU-MIMO perform the separation of PSDUs with different destination/receiver address.

<FIG> shows a schematic diagram of an embodiment of a PHY unit <NUM> of the AP <NUM>. It includes a scrambler <NUM>, a forward error correction (FEC) encoder <NUM>, a stream parser <NUM>, NSS spatial stream processing units <NUM> (each comprising an interleaver <NUM>, a constellation mapper <NUM> and (except for the first stream) a cyclic shift delay (CSD) unit <NUM>), a spatial mapper <NUM> and NTX transmit chains <NUM> (each comprising an inverse discrete Fourier transform (IDFT) unit <NUM>, an insertion unit <NUM> for inserting a guard interval (GI) and window and an analog and RF processing unit <NUM>). It should be noted that the PHY unit <NUM> of the STA <NUM> may generally be configured in the same manner.

<FIG> shows a diagram illustrating MAC operation for transmission and reception. <FIG> shows a diagram illustrating the relationships between MSDU, A-MSDU, MPDU, A-MPDU, PSDU and PPDU. Further details of these relationships and the general configuration and operation of MAC and PHY circuitry can e.g. be found in IEEE <NUM> standards.

According to the present disclosure the processing of a MSDU is different for MAP for both master AP and slave APs as will be explained below in detail.

<FIG> shows a schematic diagram of a first communication device <NUM> to illustrate its operation as master AP according to the present disclosure. The master AP <NUM> comprises a MAC unit <NUM> and a PHY unit <NUM>. Once the master AP <NUM> receives a MSDU, it checks if that MSDU is MAP eligible, i.e. if it can be transmitted to a particular station both by the master AP and a slave AP in coordination, i.e. in a joint transmission (JTX). A MAP eligible MSDU (also called selected MSDU) thus is a MSDU which is part of a PPDU transmitted by a slave AP in a JTX. This check (or selection) can e.g. be accomplished by evaluating the destination and/or receiver address and/or user priority provided along with the MSDU. The categorization of MAP or non-MAP eligible MSDU may be done by an optional (internal or external) control unit <NUM> (e.g. station management entity, SME) or by any other entity of the master AP. The categorization may be done before or after MAC processing of MSDUs. If a MSDU is not MAP eligible, regular MAC and PHY processing is done.

It shall be noted that in an embodiment, at an earlier stage, the master AP may determine that joint transmission should be used (e. for transmission to one or more or all STAs) and a MAP mode should be entered (e. because joint transmission is beneficial regarding improved data rates or reliability). If the master AP is in that MAP mode, the eligibility check as described above may thus comprise or represent the step of selecting MSU that shall be used in a JTX. In another embodiment the step of eligibility check and the selection step may be separate steps performed subsequently.

If the MSDU is MAP eligible, the MAC unit <NUM> may perform the following steps illustrated in the flowchart shown in <FIG>.

Initially, MAC output data units are generated by performing MAC layer processing of MAC input data units to be transmitted to a STA. In particular, in a first step S101, the MAC unit <NUM> processes the MSDU (MAC input data unit) regularly, i.e. it performs steps such as encryption, MAC header and FCS addition as well as aggregation to an A-MPDU (this is indicated by the block <NUM> in <FIG>). The output is either a MPDU or A-MPDU (MAC output data unit). This MAC processing for MAP eligible MSDUs can be done although the channel is busy.

The master AP <NUM> stores (step S102) the MAC output data units that are selected for later transmission in the joint transmission (also called "selected MAC output data units") in a memory <NUM> (these are later the PSDU or at least part of it).

Subsequently, control information for one or more selected MAC output data units is generated. The control information indicates that the one or more selected MAC output data units are to be PHY layer processed by slave AP and to be transmitted to the STA from the slave AP and from the master AP.

In particular, in step S103, the MAC unit <NUM> interprets the selected MAC output data units (i.e. the MPDU or A-MPDU) as a new MSDU (called MAP-MSDU in the following) but sets source and destination address differently: The new source address is the master AP address (i.e. the address of the master AP <NUM>) and the new destination address is the slave AP address (i.e. the address of a slave AP (<NUM> and <NUM>; see <FIG> and <FIG>).

Further, in step S104 the MAC unit <NUM> adds further control information to that MAP-MSDU, for instance a unique identifier. This can e.g. be another header, a MAP header or a MAP (control) frame. Details will be explained below in more detail. Steps <NUM> and <NUM> are performed in the block <NUM> in <FIG>. The MAP information ("control information") may be provided by the control unit (e.g. the SME <NUM>). In another embodiment, S103 and S104 may be combined, i.e. the addresses may be set in the control information.

Subsequently, the one or more selected MAC output data units and the associated control information are provided to the slave AP. In an embodiment using wireless backhaul, as provided in step S105, once the channel is free, the MAC unit <NUM> processes this MAP-MSDU regularly but considers the source-destination (e.g. master AP-slave AP) specific parameters such as MAC (e.g. encryption) and PHY (e.g. encoding, modulation) parameters and triggers the PHY unit <NUM> to process them to generate selected PHY output data units for transmission. Because source and destination address have changed, the selected PHY output data units (i.e. the corresponding MSDU) are transmitted to the slave AP (the third communication device) and not to the intended STA (the second communication device).

In another embodiment for providing the one or more selected MAC output data units and the associated control information are provided to the slave AP using DS or wireline backhaul, as provided in step S106, the MAC unit <NUM> provides the MAP-MSDU to a higher layer (DS) together with destination address (DA), source address (SA), and length information. Consequently, DA is set to slave AP, and SA is set to master AP. It is the objective of the DS to convey this information (i.e. the selected MAC output data units and the control information) to the slave AP.

The master AP <NUM> may await an acknowledgement (ACK) (step S107) indicating successful reception of one or more MAP-MSDUs and may even retransmit MAP-MSDUs if needed.

Once the master AP conveyed all MAP-MSDUs to all slave APs needed for a JTX, possibly having received an acknowledgement, the master AP <NUM> may decide to initiate a JTX in step S108. The master AP <NUM> thus sends announcement information (an announcement frame) to all slave APs including at least the unique identifiers of the MAP-MSDUs that are going to be jointly transmitted in the following. Additionally, PHY layer configuration data may be added and spatial mapping matrices Q may be indicated (details will be explained below).

The master AP <NUM> then transmits in step S109 a PPDU with the PSDU(s) saved in step <NUM>, either after a predefined time after the announcement information (frame) transmitted in step S107 has been transmitted or following a trigger transmitted by the master AP <NUM> to the slave APs. This is illustrated in <FIG> by the JTX trigger that may be provided by the control unit (e.g. the SME <NUM>). It shall be noted that the announcement and the JTX may be transmitted separately or the information may be combined into a combined trigger.

It shall be noted that MSDUs may exist, which are to be transmitted by a master AP in a JTX and are not MAP eligible. These MSDUs may be stored in a memory at the master AP until the JTX starts. Conceptually, these can be stored either in the memory <NUM> or in memories, which are contained in the MAC unit <NUM> anyway, e.g. in a transmit queue.

<FIG> shows a diagram illustrating a MAP-MSDU comprising a MAP header (MAP hdr) and a data portion comprising the MPDU or A-MPDU.

<FIG> and <FIG> show schematic diagrams of different embodiments of a third communication device <NUM> and <NUM> (each having a MAC unit <NUM> and a PHY unit <NUM>) to illustrate its operation as slave AP according to the present disclosure in JTX. Once a slave AP receives a MAP-MSDU either via a received PPDU for wireless backhaul (<FIG>) or via a higher layer interface for wireline backhaul (<FIG>), it performs the following steps illustrated in the flowchart shown in <FIG>.

Initially, one or more selected MAC output data units and the associated control information is obtained by the slave AP from the master AP. In particular, in a first step S201 the MAC unit <NUM> extracts the MPDU or A-MPDU and the identifier present in the MAP-MSDU (indicated by block <NUM>). In case of wireless backhaul this may contain various steps: The PPDU holding the MAP-MSDU is demodulated, decoded, analyzed, defragmented and decrypted just as a regular PPDU is processed. In step S202 an acknowledgement may be transmitted according to the settings in the PPDU received.

The additional control information residing in the MAP-MSDU is extracted (indicated by block <NUM>) in step S203 and the MPDU or A-MPDU together with the identifier are stored in a memory <NUM> in step S204. In step S203, the source address may be set to the master AP <NUM> and the destination address may be set to the station(s) that receives data in JTX.

Subsequently, the slave AP generates selected PHY output data units by performing PHY layer processing of the selected MAC output data units for transmission to the STA from the slave AP in coordination with the transmission of selected PHY output data units generated by the master AP from selected MAC output data units. In particular, once the slave AP <NUM> / <NUM> receives announcement information (frame), it configures its PHY unit <NUM> and spatial mapping matrix as indicated in the announcement and forwards the PSDU content, i.e. one or more MPDU or A-MPDU to the PHY unit <NUM> (step S205). The PHY unit <NUM> transmits a PPDU with the PSDUs either after a predefined time after the announcement information (frame) or after a trigger received from the master AP (step S206), which is illustrated by the JTX trigger triggering the memory <NUM> in <FIG> and <FIG>.

<FIG> shows a diagram illustrating the temporal operation of the master AP <NUM> and the slave AP <NUM> / <NUM> including dependencies between master AP and slave AP.

<FIG> shows a schematic diagram of the master AP <NUM> (as shown in <FIG>) and the slave AP <NUM> (as shown in <FIG>) illustrating - for the wireless backhaul case - the sequence of the steps of their operation and the flow of the information through the master AP <NUM> and the slave AP <NUM>, indicated by encircled numbers from <NUM> to <NUM>.

As shown in <FIG>, after the backhaul operation, same MAC output data unit resides in memory at master and slave AP (assuming there are only MSDUs that are transmitted from both APs; otherwise, the memory content is a subset of each other). The dashed lines show the transmit and receive PHY MAC operation. Both cancel each other (If there is no transmission error; as this is a regular link, all features such as acknowledgement, retransmissions, etc. can be applied). This is a regular wireless link. The PHY configuration of this link is different to that in JTX. For JTX both APs send at the same time that MAC output data units by PHY layer processing as a PHY output data unit.

<FIG> shows a schematic diagram of the master AP <NUM> (as shown in <FIG>) and the slave AP <NUM> (as shown in <FIG>) illustrating - for the DS / wireline backhaul case - the sequence of the steps of their operation and the flow of the information through the master AP <NUM> and the slave AP <NUM>, indicated by encircled numbers from <NUM> to <NUM>.

As shown in <FIG>, after the backhaul operation, the same MAC output data unit resides in memory at the master AP and the slave AP. For JTX both APs send at the same time these MAC output data units by PHY layer processing as a PHY output data unit.

In some embodiments, a slave AP may actually comprise an AP and a STA. The STA is collocated with the AP and both exchange data internally (e.g. via a station management entity, SME). This is to enable data exchange between AP and STA at all times, because AP to AP communication is not defined for WLAN devices. In this regard, the master AP sends wireless backhaul information to a STA, which is collocated with a slave AP. This STA is configuring the slave AP via internal data exchange as described above.

A MAP-MSDU contains the MPDU or A-MPDU to be transmitted by a slave AP during a JTX. Furthermore, it holds control information. The control information may reside in a frame that is aggregated to the MPDU or A-MPDU or that may be added in the form of a MAP header.

The control information may contain at least an identifier of the MAP-MSDU. This identifier is required for the master AP to indicate to the slave AP prior to JTX which MPDU or A-MPDU within a MAP-MSDU it is supposed to transmit. A slave AP may transmit multiple MPDU or A-MPDU of a MAP-MSDUs in a JTX. Thus, the set of identifiers may arrange the order of MPDU or A-MPDU of MAP-MSDUs to be sent.

In order for a JTX to be successful, more control information may be provided to the slave AP by the master AP. This information may either reside in control information described above or in the announcement frame or in the trigger, which precedes a JTX. The information may include one or more of.

The announcement or trigger frame may include one or more identifiers of the MPDU or A-MPDU within a MAP-MSDUs to be transmitted by the slave APs in the upcoming JTX.

There are various options for the PHY operation. They are different in the tasks each AP needs to perform in JTX. The assumption is that each AP has two transmit antennas and that four transmit antennas are used in joint transmission of two APs.

First, in <FIG>, a schematic diagram of an embodiment of a PHY unit <NUM> (indicated here as 102a) of the AP <NUM> is illustrated in non-MAP mode, i.e. regular mode in which there is no JTX, but all MSDUs are transmitted to the STA from the master AP only. It shall be noted that the PHY unit of slave APs <NUM> and <NUM> is configured accordingly in the non-MAP mode.

<FIG> shows a schematic diagram of a first embodiment of the PHY unit <NUM> (indicated here as 102b) of the AP <NUM> in MAP mode. <FIG> shows a schematic diagram of a first embodiment of the PHY unit <NUM> (indicated here as 202b) of the AP <NUM> in MAP mode. In an alternative embodiment the embodiment shown in <FIG> may be used in the slave AP <NUM> and the embodiment shown in <FIG> may be used in the master AP <NUM>.

The first embodiment shown in <FIG> and <FIG> uses the most general approach. It is more complex, but provides most MAP gain. Each PHY unit 102b, 202b performs scrambling, FEC encoding, stream parsing, interleaving (optional), constellation mapping and CSD for all NSS spatial streams in MAP. These operations are performed in each AP at same time. Following the CSD operation, each PHY unit 102b, 202b multiplies with its Qi matrix, which maps NSS spatial streams to NTX,i transmit streams. NTX,i corresponds to the number of active transmit chains or transmit antennas used. After that, each PHY unit 102b, 202b performs IDFT operation, insertion of GI, windowing, and analog & RF processing for its own NTX,i active transmit chains. If NSS > NTX,i, the processing capabilities of the PHY unit needed before the spatial mapping are greater than after the spatial mapping.

<FIG> shows a schematic diagram of a second embodiment of the PHY unit <NUM> (indicated here as 102c) of the AP <NUM> in MAP mode. <FIG> shows a schematic diagram of a second embodiment of the PHY unit <NUM> (indicated here as 212c) of the AP <NUM> in MAP mode. In an alternative embodiment the embodiment shown in <FIG> may be used in the slave AP <NUM> and the embodiment shown in <FIG> may be used in the master AP <NUM>.

The second embodiment shown in <FIG> and <FIG> uses a less general approach. It is less complex, but provides a less positive MAP gain. Each PHY unit 102c, 212c performs scrambling, FEC encoding, and stream parsing. These operations are performed in each AP at same time. Following the stream parser operation, each PHY unit 102c, 212c performs interleaving (optional), constellation mapping, CSD (optional), spatial mapping with its Qi matrix, IDFT operation, insertion of GI, windowing, and analog & RF processing for its own NTX,i active transmit chains. If NSS > NTX,i, the required processing capabilities of the PHY unit are significantly lower compared to the first embodiment.

The Qi matrix has a different size compared to the first embodiment. In the first embodiment Qi is of size NTX,i × NSS, whereas in the second embodiment the size is NTX,i × NTX,i. The overall Q is <MAT> for the first embodiment, whereas Q is Q = <MAT> for the second embodiment when NSS > NTX,i. Thus, the second embodiment assumes zero entries on the anti-diagonal to be present in overall Q matrix.

For the first embodiment, the stream parser operates conventionally. It assigns in a round robin fashion consecutive bits to a first spatial stream. Following that, it further assigns following consecutive bits to second spatial stream and so on. When bits to the last spatial stream have been assigned, it continues with the first spatial stream. However, for the second embodiment, only the relevant output of the stream parser is processed further and non-relevant spatial streams for a particular AP are not further considered. This means that an AP discards some outputs of the stream parser.

In principle, the first and second embodiments may be combined in the sense that the master AP operates according to the first embodiment whereas a slave AP operates according to the second embodiment, for example.

All PHY components in all APs preferably use the same settings. These settings may be shared by the master AP with the slave APs and include all or a subset of the TXVECTOR parameters. The TXVECTOR parameters are configuring the PHY for a transmission. Compression schemes for the TXVECTOR may be applicable. One method comprises in transmitting the PHY headers for the JTX as they contain all relevant TXVECTOR information for the receiver to process the incoming PPDU.

For preambles as well as for the second embodiment, an AP should know what the spatial streams are that it is supposed to serve in JTX. This is indicated by a spatial stream index number. For the example in <FIG> and <FIG> the master AP transmits spatial streams <NUM> and <NUM>, whereas a slave AP serves spatial streams <NUM> and <NUM>.

Either the master AP may compute the overall spatial mapping matrix Q or each AP may compute its own spatial mapping matrix. In the first case, at least that part of the Q matrix, which is relevant to a slave AP, is signaled, whereas in the second case, Q matrix signaling is not needed.

Embodiments of the present disclosure have been explained in detail. In the following a short summary of essential aspects of the present disclosure shall be provided.

The present disclosure seeks to provide an enhancement of reliability, latency, and throughput of wireless communication, which are recently required for applications such as UHD video transfer including AR/VR. It is assumed that Multiple APs (multi-AP) transmit jointly to one or more STAs at same time (also known as network MIMO). Each AP's transmit signal in joint transmission originates from (at least partly) the same data. Multiple APs are categorized in one master AP and one or more slave APs. STAs are (at least) logically associated to the master AP.

The backhaul transmission of the PHY waveform is very inefficient because the PHY waveform is an analog signal and it holds PHY redundancy. The required backhaul bit rate demand is thus very high, which is undesired because it limits the throughput and applicability of multi-AP. It is an object to minimize the rate requirements for the backhaul. The presented solution can thus be seen as a backhaul compression. Further, a very simple compression and decompression of the backhaul data by master and slave AP, respectively, shall be enabled.

The main concept of a known communication scheme is illustrated in <FIG>. The master AP generates the PPDU (waveform) for the slave AP and transmits the digitized PPDU waveform to the slave AP via the backhaul (step <NUM>). The slave AP transmits the received waveform once it receives a trigger (step <NUM>) for joint transmission (step <NUM>). Thus, the backhaul conveys the PPDU waveform.

The main concept of communication scheme according to the present disclosure is illustrated in <FIG>. The master AP transmits (step <NUM>) MDPU or A-MPDU in conjunction with PHY configuration that shall be applied for JTX. The slave AP processes the received MPDU or A-MPDU in its PHY layer according to the PHY configuration received and generates the PPDU waveform which it is transmitted once it receives (step <NUM>) a trigger for JTX (step <NUM>).

In more detail, and as illustrated in <FIG>, according to the present disclosure the master AP generates an A-MPDU that is stored in memory for later joint transmission and M-AP info (e.g. PHY config, identifier) is added. The A-MPDU and M-AP info forms a MAP-MSDU that can either go to the DS or be interpreted as a regular MSDU for wireless transmission. After the JTX trigger, the A-MPDU in memory is processed by the master AP PHY and the PPDU is transmitted. In one embodiment the slave AP (DS) receives a MAP-MSDU from DS and extracts M-AP info. The A-MPDU is then stored in memory for later joint transmission. When JTX trigger is received the slave AP PHY processes the A-MPDU according to the PHY config in M-AP info and the PPDU is transmitted. In another embodiment the slave AP (wireless) receives a PPDU from master AP that contains the MAP-MSDU. The MAP-MSDU is extracted from the backhaul PPDU. The following processing is as in the first embodiment. It shall be noted that the PHY configuration is different for backhaul and JTX PPDU.

Thus, to summarize this disclosure, the backhaul consist of data units (MPDU/A-MPDU or PSDU) to be transmitted by the slave AP plus configuration data. In known systems, the master AP generates the transmit signal for the slave AP and the backhaul conveys the PPDU of a slave AP. According to the present disclosure, the backhaul consist of data units (MPDU/A-MPDU or PSDU) to be transmitted by the slave AP plus configuration data.

Implementing the backhaul on MPDU/A-MPDU level is much more efficient than doing on PPDU level, which would need quantization of I and Q components for each sample and redundancy due to channel coding. Assuming <NUM> bit quantization for each I and Q component and channel code rate of ½, the overhead in terms of backhaul bitrate requirement is reduced by factor of (<NUM>*<NUM>*<NUM>=<NUM>).

The presented backhaul proposal may further seamlessly integrated into a regular <NUM> link, thus all MAC features such as BAck or Ack can be used.

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 essential characteristics thereof.

Further, such a software may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

Claim 1:
First communication device (AP1, <NUM>) comprising:
- MAC layer circuitry (<NUM>) configured to
- generate MAC output data units by performing media access control (MAC) layer processing of MAC input data units to be transmitted to a second communication device (STA1), and
- generate control information for one or more selected MAC output data units, the control information indicating that the one or more selected MAC output data units are to be physical (PHY) layer processed by a third communication device (AP2, <NUM>, <NUM>) and to be transmitted to the second communication device from the third communication device and from the first communication device; and
- PHY layer circuitry (<NUM>) configured to generate PHY output data units by performing PHY layer processing of the MAC output data units, wherein selected PHY output data units are generated from the selected MAC output data units for transmission to the second communication device from the first communication device in coordination with the transmission of selected PHY output data units generated by the third communication device from the selected MAC output data units,
wherein the first communication device is configured to provide the one or more selected MAC output data units and the associated control information to the third communication device,
characterized in that the PHY layer circuitry (102b, 102c) is further configured to divide the MAC output data units into N spatial streams, and either
i) perform, per spatial stream and in parallel, interleaving and/or constellation mapping processing, perform spatial stream mapping to map the processed N spatial streams onto M transmit streams, and perform inverse Fourier transforming and analog and RF processing of the M transmit streams to generate M transmit signals, or
ii) perform, for M of the N spatial streams, per spatial stream and in parallel, interleaving and/or constellation mapping, spatial stream mapping, inverse Fourier transforming, and analog and RF processing to generate M transmit signals,
wherein M corresponds to the number of active transmit chains of the first communication device and is smaller than N.