WO2013081430A1

WO2013081430A1 - Method and system for station selection and link adaptation for 802.11ac compliant multi user-mimo operation

Info

Publication number: WO2013081430A1
Application number: PCT/KR2012/010345
Authority: WO
Inventors: Pradeep Dwarakanath; Young Soo Kim
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2011-11-30
Filing date: 2012-11-30
Publication date: 2013-06-06
Anticipated expiration: 2014-05-30
Also published as: KR20150077248A; KR102008426B1

Abstract

A method and system that provides enhanced link adaption in 802.11ac wireless network standard that supports Multi User-Multiple Input Multiple Output (MU-MIMO) operation in the downlink is disclosed. The method provides changes in station (STA) to Access Point (AP) feedback elements of the 801.11ac standard. These changes enable the AP to select optimal Modulation and Coding Scheme (MCS) levels to match channel and interference conditions by maintaining desired Packet Error Rate (PER). The method enables each co-scheduled station to indicate a SINR step size that enables the AP to derive optimal MCS level based on computed multi-user interference after deriving the multi-user (MU) precoder. The method further enables joint STA selection and link adaptation that appropriately minimizes transmitted power or maximizes data rate.

Description

METHOD AND SYSTEM FOR STATION SELECTION AND LINK ADAPTATION FOR 802.11AC COMPLIANT MULTI USER-MIMO OPERATION

The present invention relates to wireless communication and more particularly relates to enhancement in link adaptation techniques of 802.11ac IEEE wireless network standard which supports Multi User-Multiple Input Multiple Output (MU-MIMO) operation.

Electronic communication devices have become people's everyday companions, creating new demands for faster and more reliable wireless connectivity everywhere and all the time. IEEE 802.11ac is a fifth generation Wireless Fidelity (Wi-Fi) networking standards that brings fast, high quality video streaming and nearly instantaneous data syncing and backup to the notebooks, tablets, mobile phones and the like. Link adaptation (LA) techniques significantly increase user throughput by providing efficient ways to maximize spectral efficiency with the instantaneous quality of wireless channels.

The Wi-Fi 802.11ac specification supports Multiple User-Multiple Input Multiple Output (MU-MIMO) operations in downlink and uses link adaption with precoder design to enhance multiuser performance.

Downlink Multi-User MIMO is a technology which allows the AP to transmit to multiple clients (STAs) simultaneously using multiple spatial streams.

The mapping between the channel quality and Modulation and Coding scheme (MCS) level is one of the important design issues in the LA techniques. In a WLAN compliant with 802.11ac specification, the AP performs predefined tasks for downlink in MU-MIMO operation. The tasks such as station (STA) selection and pairing, MCS, rank selection for each STA, optimal precoder design to match the desired rate and target Packet Error Rate (PER) are performed. Currently, the feedback elements defined in 802.11ac have to be conveyed from the STAs to AP in support of MU-MIMO operation comprise STA s feedback SINR, beamforming matrices and recommended MCS level. However, these defined feedback elements in existing method are inadequate for AP to derive an optimal MCS level for each of the co-scheduled STAs. Conventionally, the AP is unaware of individual STA's receiver capability that depends on type of receiver of the respective STA.

Due to above mentioned reasons; existing methods fail to derive optimal MCS level that enables enhanced link adaption to provide stable high quality wireless channels.

The principal object of the embodiments herein is to provide a method and system to enhance the link adaption in the 802.11ac specification supporting Multi User-Multiple Input Multiple Output (MU-MIMO) operation in downlink by providing changes in the station (STA) to Access Point (AP) feedback elements that enable AP to select optimal Modulation and Coding Scheme (MCS) level to match channel and interference conditions.

Another object of the invention is to provide a method and system for feeding back SINR step size table index to the AP and enable the AP to select the appropriate SINR step size from the SINR step size table.

Another object of the invention is to provide a method to enable the STA to feedback the STA s interference suppression capability to AP.

Another object of the invention is to provide a method for optimal joint STA selection, Multi User (MU) precoder design and MCS selection.

Accordingly the invention provides a method for joint station selection and link adaptation for 802.11ac compliant Multi User-Multiple Input Multiple Output (MU-MIMO) operation in downlink, wherein the method comprises receiving Signal to Interference and Noise Ratio (SINR) step size along with feedback SINR from at least one station by an Access Point (AP), deriving post processing Signal to Interference and Noise Ratio (SINR) for the at least one station by an AP, after designing optimal Multi User (MU) precoder matrix for the at least one station, computing optimal Modulation and Coding Scheme (MCS) level for the at least one station by the AP using the post processing SINR and received feedback SINR and selecting at least one optimal station from set of stations by the AP.

Accordingly the invention provides an Access Point (AP) for providing joint station selection and link adaptation for 802.11ac compliant Multi User-Multiple Input Multiple Output (MU-MIMO) operation in downlink, wherein the AP comprises an integrated circuit further comprising at least one processor, at least one memory having a computer program code within the circuit, at least one memory and the computer program code with the at least one processor cause the AP to receive Signal to Interference and Noise Ratio (SINR) step size along with feedback SINR from at least one station, derive post processing Signal to Interference and Noise Ratio (SINR) for the at least one station, after designing optimal Multi User (MU) precoder matrix for the at least one station, compute optimal Modulation and Coding Scheme (MCS) level for the at least one station using the post processing SINR and received feedback SINR and select at least one optimal station from set of stations.

Accordingly the invention provides a station for supporting joint station selection and link adaptation for 802.11ac compliant Multi User-Multiple Input Multiple Output (MU-MIMO) operation in downlink, wherein the station is configured to feedback Signal to Interference and Noise Ratio (SINR) step size according to the station s receiver capability to an Access Point (AP), store plurality of the SINR step size tables and feedback interference suppression capability to the AP.

These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

This invention is illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:

FIG. 1 illustrates an exemplary MU-MIMO feedback and STA selection during link adaptation in 802.11ac specification;

FIG. 2 illustrates an exemplary Packet Error Rate (PER) versus Signal to Noise Ratio (SNR) curve complying to 802.11ac specification;

FIG. 3 illustrates a flow diagram for deriving the optimal Modulation and Coding Scheme (MCS) level, according to embodiments as disclosed herein;

FIG. 4 illustrates proposed changes to Very High Throughput (VHT) format High Throughput (HT) Control field of 802.11ac specification D1.1, according to embodiments as disclosed herein;

FIG. 5 illustrates joint encoding of Signal to interference and noise ratio (SINR) step sizes and the MCS levels using proposed change in MCS field in MFB sub-field of the VHT format HT control field, according to embodiments as disclosed herein;

FIG. 6 illustrates exemplary SINR step size tables that are stored at the AP and STA, according to embodiments as disclosed herein;

FIG. 7 illustrates changes to VHT supported MCS Set field of 802.11ac specification D1.2, according to embodiments as disclosed herein;

FIG. 8 illustrates changes to VHT capabilities Info field of 802.11ac D1.2, according to embodiments as disclosed herein; and

FIG. 9 illustrates flow diagram explaining the process of joint STA selection and link adaption, according to embodiments as disclosed herein.

The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein can be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

The embodiments herein achieve a method and system that provides an enhanced link adaption in 802.11ac wireless network standard, which supports Multi User-Multiple Input Multiple Output (MU-MIMO) operation in the downlink. The method provides changes in station (STA) to Access Point (AP) feedback elements of the 801.11ac standard. These changes enables AP to select optimal Modulation and coding scheme (MCS) levels to match channel and interference conditions by maintaining desired Packet Error Rate (PER).

The method enables each co-scheduled STA to indicate a Signal to interference noise ratio (SINR) step size that enables the AP to derive optimal MCS level based on computed multi-user interference after deriving the MU-precoder. The method further enables joint STA selection and link adaptation that appropriately minimizes transmitted power or maximizes data rate.

Throughout the description STA refers to a non-AP STA.

In an embodiment, the station (STA) comprises a mobile device, laptop, tablet, personal computer, media player, digital camera, smart phone, TV or the like which supports Wireless Local Area Network (WLAN).

Referring now to the drawings, and more particularly to FIGS. 1 through 9, where similar reference characters denote corresponding features consistently throughout the figures, there are shown preferred embodiments.

FIG. 1 illustrates an exemplary MU-MIMO feedback and STA selection during link adaptation in 802.11ac specification. The figure depicts feedback elements from the STAs to the AP0's link adaptation and scheduling algorithm and output of the link adaptation and scheduling algorithm. In a Wireless Local Area Network (WLAN) system compliant with the existing 802.11ac specification, during the downlink MU-MIMO operation the AP performs STA selection and pairing, MCS and rank selection for each STA along with optimal precoder design to match the desired data rate and target Packet Error Rate (PER) of each co-scheduled STA. In the existing method, the AP receives feedback from STAs. Based on the various feedback parameters received, the AP selects a set of STAs to be scheduled in the designated time interval and subsequently derive an optimal precoder at each subcarrier of the OFDM frame. Further, the AP computes the optimal MCS levels for each of the STA (User Equipment) that may satisfy desired PER targets as per their individual Quality of Service (QoS) requirements.

In accordance with 802.11ac specification, the feedback elements to be conveyed from each STA to AP in support of downlink MU-MIMO operation comprise MCS feedback message and beamforming report. The MCS feedback message comprises the STA recommended MCS level (MCS_fb) and feedback SINR from the STA to AP called Average SINR (AvgSINR) over all Spatial Streams (SS) and subcarriers (SC). The beamforming report comprises compressed per subcarrier Beamforming matrix (V_sc), quantized SINR per SC & SS ( △SINR_sc,ss), quantized per spatial stream SINR averaged over all subcarriers (Avg SINR_ss). The AP processes the received feedback elements to output STA specific MCS, STA specific rank and per SC MU-precoder matrix (Q).

The disadvantage with the existing method is that the feedback SINR (Avg SINR) differs drastically from the actual SINR (post processing SINR or effective SINR) experienced by the STA during full swing downlink MU-MIMO operation. Thus, the STA recommended MCS level (MCS_fb) is insufficient to decide the STA specific MCS. The various factors that lead to this variation in fed back SINR (Avg SINR) and actual experienced SINR are explained below.

Multi User interference: Null Data Packet (NDP) frames are training frames that are transmitted in Single User-MIMO (SU-MIMO) mode to individual STAs. Due to absence of multiple users during transmission of NDP frames, STAs experience a communication channel that is free from multi-user interference. Thus SINR feedback from STAs does not consider SINR degradation due to multi-user interference when the AP actually transmits data packets in MU-MIMO mode.

Partial Channel State Information at Transmitter (CSIT): AP receives per subcarrier partial CSIT from each STA in the form of SINR S (Diagonal matrix of per stream SINR) and beamforming matrix (V_sc). The two matrices could be used to construct the diagonal matrix of singular values and the right singular matrix of an SVD (H = USV ^H). However, the receiver side rotation matrix U is not known to the AP. Multi user (MU) precoders designed with such partial CSIT cause degradation in post-processing SINR experienced at the STA receiver.

Noisy CSIT: The STAs feedback per subcarrier SINR and beamforming matrix (V_sc), through compression and quantization. Compression, quantization of beamforming matrix introduces errors in the final decoded beamforming matrix at AP. When such corrupted beamforming matrix (V_sc), is used at the AP to derive MU-precoders, the post-processing SINR experienced at the STA degrades.

Subcarrier Grouping: In order to reduce feedback overhead from STA to AP, sub-carrier grouping is used in feedback, where beamforming matrix (V_sc), and SINR are communicated for a specific set of subcarriers instead of all subcarriers. This causes a single feedback to be sent for a group of subcarriers. At the AP, the CSIT for other subcarriers are derived through interpolation. Such interpolation schemes introduce significant CSIT errors that further degrade the post-processing SINR experienced at the STA.

Thus, in existing method AP fails to re-select an optimal MCS based on the post processing SINR. The existing method also fails to provide a mechanism to derive post processing SINR and further use it for processing by link adaption and scheduling algorithm to enhance link adaption in existing 802.11ac specification. In the existing method, post processing SINR at STA which is lower than the feedback SINR is not taken into consideration. Also, the receiver capability of STA using receivers such as Minimum Mean Square Error (MMSE) receiver, interference suppression receivers, successive interference cancellation receivers and Maximum Likelihood (ML) vector symbol detector and so on that have different PER capabilities is not taken into account.

FIG. 2 illustrates an exemplary PER versus SNR curve complying with 802.11ac specification. The figure depicts PER to SNR curve for a 4x4 MIMO system for MCS levels 0 - 9 at 80MHz channel bandwidth for channel model D for Minimum Mean Square Error (MMSE) receiver. PER vs. SNR curve for 80MHz, 4x4, Number of spatial streams (NSS)=4, MCS 0 - 9, BCC, TxBF with perfect CSIT, Channel D-NLOS. At a target PER of 10^-2, the SNR step size required for subsequent MCS levels is shown. Graphs from left to right represent MCS level 0 to 9 respectively. The SINR difference between MCS level 0 and MCS level 1 is 2.5 dB, the SINR difference between MCS level 1 and MCS level 2 is 3 dB, the SINR difference between MCS level 2 and MCS level 3 is 4 dB and so on. This indicates that for a desired PER target of a STA, the SINR difference (in dB) between subsequent MCS levels are not uniform. Thus, the AP requires the knowledge of MCS vs. SINR tables for different PER targets for all combinations of SS, bandwidth and receiver types.

Existing method fails to provide the information of the STA receiver capability. Thus, the AP is unaware of the receiver capabilities at the STA, and cannot correctly estimate an optimal MCS level corresponding to the post-processing SINR. Any MCS down scaling applied by the AP without knowledge of receiver capabilities will risk the stability and efficiency of the communication link.

Hence the defined feedback elements are inadequate for the AP to derive an optimal MCS level for each of the co-scheduled STAs.

FIG. 3 illustrates a flow diagram for deriving the optimal MCS level, according to embodiments as disclosed herein. The method disclosed enhances feedback from STA to the AP by providing a mechanism to feedback SINR step size (dB) and further estimate the post processing SINR likely to be experienced at STA receiver. In the downlink MU-MIMO scenario AP accepts the feedback SINR from the co-scheduled STA.

Access Point (AP) computes (301) optimal MU-precoder matrix (Q). Then, AP forms the MU-precoder matrix (Q) to compute (302) post processing SINR for each co-scheduled STA. For example, consider a non-limiting downlink scenario with an AP equipped with N _Tx antennas and serving one SS to each of the K STAs, each equipped with N _Rx receive antennas. The channel between transmitter and k ^th STA is represented as

[001] and the transmit vector is represented by X and is drawn from a square constellation. The received signal at STA_k with AP using a MU-precoder matrix (Q) is expressed in equation (1) below.

Since the AP has the knowledge of H_k and Q, it computes post processing SINR that STA_k is likely to experience using equation (2) below.

Knowledge of STA's interference suppression capability will assist the AP in constructing an optimal receiver matrix G corresponding to each STA and use it in computation in the post processing SINR. The G matrix is formed by factoring the interference suppression capability of each STA. The post-processing SINR thus derived will be lower than the STA feedback SINR.

The method enables the co―cheduled STA to feedback SINR step size to the AP. As described in FIG. 2, the SINR difference between immediate MCS levels is not uniform and the SINR difference varies with bandwidth, Number of Spatial Streams (NSS) and receiver type at the STA. Hence, the method defines multiple SINR step sizes to cover most SINR differences.

In an embodiment, the method pre-communicates the SINR step sizes (SINR step size table) to the AP at the time of association.

In an embodiment, the SINR step size table is stored at both AP and STA and an index to the SINR step size table can be communicated in the feedback messages.

The method enables AP to select appropriate step size from the SINR step size table. The SINR step size selected is used at the AP to select the immediate lower MCS levels to suit the post processing SINR. Thereafter, the method computes (303) number of MCS levels (N_levels) to downgrade the MCS_fb (recommended MCS level by the STA) using the selected SINR step size from the SINR step size table. The N_levelsare computed using the equation (3) given below.

Further, the method derives (304) optimal MCS level (MCS_optimal) using the STA recommended MCS level (MCS_fb) and the N_levels computed from equation (3). The equation (4) below gives the MCS optimal level to be used by the AP that enables AP to better match the channel and interference conditions.

The various actions in flow diagram 300 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions listed in FIG. 3 may be omitted.

FIG. 4 illustrates changes to Very High Throughput (VHT) format High Throughput (HT) Control field of 802.11ac specification

according to embodiments as disclosed herein. The FIG 4 depicts changes to the VHT format HT control field, where reserved bit (B1) of the existing 802.11ac specification is removed. This acquired bit is used in the MFB sub-field of the VHT format HT control field. The method changes the MFB sub-field size to 16 bits (B8-B23). The remaining fields of VHT format HT control field are unchanged and remain in accordance with the existing 802.11ac specification.

FIG. 4 depicts changes to MCS field of the MFB sub-field in the VHT format HT Control field of 802.11ac specification. The acquired bit in the MFB sub-field is used to change size of MCS field to five bits (B11-B15) as depicted in the figure. With MCS field having five bit size, the method supports 32 unique MCS levels.

FIG. 5 illustrates joint encoding of Signal to interference and noise ratio (SINR) step sizes and the MCS levels using proposed MCS field in MFB sub-field of the VHT format HT control field, according to embodiments as disclosed herein. The figure depicts a combined interpretation of MCS level and SINR step size. The method enables to define three step sizes as given below.

The initial ten MCS levels (0 - 9) indicate MCS 0 - 9 with step size-1

The next ten MCS levels (10-19) indicate MCS 0 - 9 with step size-2

The next ten MCS levels (20-29) indicate MCS 0 - 9 with step size-3

The remaining two levels (30 and 31) are unused and reserved for future use.

FIG. 6 illustrates exemplary SINR step size tables that are stored at the AP and STA, according to embodiments as disclosed herein. The figure depicts four SINR step size with each table defining three different step sizes. The SINR step size table 1 defines three SINR step sizes of 1dB, 2dB, 3dB while the SINR step size table 2 defines three step sizes as 1dB, 2.5dB, 4dB. The SINR step size table 3 and SINR step size table 4 define plurality of SINR step sizes. The method enables AP to be aware of this information of the defined SINR step size tables. The AP is informed about the appropriate SINR step size table to be used through a SINR step size table index.

FIG. 7 illustrates changes to VHT supported MCS Set field of 802.11ac specification D1.2, according to embodiments as disclosed herein. The figure depicts a MCS set field (B0-B63). The method defines SINR step size table index field (B29-B31) in the MCS set field. With index field of size 3 bits, eight step size tables of varying granularity are supported. These eight tables are sufficient to cover most SINR step sizes. The STAs feedback the index of desired SINR step size table to be later used by the AP to derive the optimal MCS level.

FIG. 8 illustrates changes to VHT capabilities Info field of IEEE 802.11ac D1.2, according to embodiments as disclosed herein. The method enables the STA to feed back its interference suppression capability to the AP. The knowledge of the STA's interference suppression capability enables AP to construct the optimal receiver matrix G corresponding to each STA that is later used to compute the post processing SINR.

The method provides changes in the VHT capabilities info field (32 bit) by using one of the reserved bits (bit B28) to enable STA to communicate its interference suppression capability to the AP at the time of association. The remaining fields of VHT capabilities info field are unchanged and remain in accordance with the existing 802.11ac specification.

FIG. 9 illustrates flow diagram explaining the process of joint STA selection and link adaption, according to embodiments as disclosed herein. The AP performs station selection and pairing for plurality of STA's. For example, K stations STA₁to STA_k are considered by the AP. Each of STA₁to STA_k has its own defined or desired QoS, target PER, data rate, rank, and MCS level.

As depicted in flow diagram 900, the AP selects (901) a set of STAs (STA₁to STA_k) based on data availability in AP s queue. The AP is aware of each STA's QoS. Thus, AP asses each STA's target PER and data rate required based on the STA specific QoS. Further, for each STA the AP derives the rank (NSS) and the required MCS level to support their required data rate. The AP arrives at each STA's required SINR to meet STA's desired target PER by using the stored PER versus SINR tables. Thereafter, the AP applies (902) the per user SINR constraint and per antenna power constraint and checks (903) if an optimal precoder exists. If the optimal precoder does not exist for the set of STAs selected the method loops back to step (901) to select new set of STAs. If the optimal precoder exists, the AP further designs (904) the optimal precoder. Then, the AP derives the post processing SINR of each co-scheduled. Thereafter, using the feedback elements MCS_fb, feedback SINR (Avg SINR) from the STAs and SINR step size, the AP derives (905) the optimal MCS level (MCS_optimal) for each co-scheduled STA. The AP also computes the data rate achievable for all the co-scheduled STAs and the power required for serving this achievable data rate. The AP stores the power required and achievable data rate. Thereafter, the AP loops (906) through all combinations of STAs and selects the combination that maximizes achievable data rate or minimizes transmit power satisfying delay constraints. Thus, AP arrives (907) at optimal STA set along with MCS, MU-precoder and rank (NSS) to provide joint STA selection and link adaption. The various actions in flow diagram 900 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions listed in FIG. 9 may be omitted.

The embodiments disclosed herein can be implemented through at least one software program running on at least one hardware device and performing network management functions to control the elements. The elements shown in Fig. 9 include blocks which can be at least one of a hardware device, or a combination of hardware device and software module.

The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

Claims

A method for joint station selection and link adaptation for 802.11ac compliant Multi User-Multiple Input Multiple Output (MU-MIMO) operation in downlink, wherein said method comprises:

receiving Signal to Interference and Noise Ratio (SINR) step size along with feedback SINR from at least one station by an Access Point (AP);

deriving post processing Signal to Interference and Noise Ratio (SINR) for said at least one station by an AP, after designing optimal Multi User (MU) precoder matrix for said at least one station;

computing optimal Modulation and Coding Scheme (MCS) level for said at least one station by said AP using said post processing SINR and received feedback SINR; and

selecting at least one optimal station from set of stations by said AP.
The method as in claim 1, wherein said method derives said post processing SINR using at least one of: channel matrix between a transmitter of said AP, receiver of said at least one station, said optimal MU-precoder matrix and interference suppression capability of said at least one station.
The method as in claim 2, wherein said method receives indication of said interference suppression capability through a reserved bit of Very High Throughput (VHT) capabilities info field.
The method as in claim 1, wherein said method computes optimal MCS level further comprises:

selecting appropriate said SINR step size from said SINR step size table indicated by said SINR step size index field in said VHT supported said MCS set field received by said AP from said at least one station;

computing number of said MCS level using at least one of: said SINR step size, said feedback SINR, said post processing SINR; and

computing optimal said MCS level using at least one of: said at least one station recommended said MCS level, said number of MCS levels for said at least one station.
The method as in claim 4, wherein said method computes said optimal MCS level by using encoded said MCS level and said encoded SINR step size.
The method as in claim 5, wherein method uses reserved bit in said VHT format High Throughput (HT) control field for said MCS field of MFB sub-field to encode plurality of said MCS level and said SINR step size.
The method as in claim 4, wherein said SINR step size index is communicated through reserved bits of said VHT supported MCS set field.
The method as in claim 4 wherein said method stores plurality of said SINR step size tables in at least one of: said AP, said at least one station.
A system for joint station selection and link adaption for 802.11ac compliant Multi User-Multiple Input Multiple Output (MU-MIMO) operation in downlink, wherein said system comprises at least one access point (AP), at least one station, further said system is configured for performing steps as claimed in claims 1 to 8.
An Access Point (AP) for providing joint station selection and link adaptation for 802.11ac compliant Multi User-Multiple Input Multiple Output (MU-MIMO) operation in downlink, wherein said AP comprises

an integrated circuit further comprising at least one processor;

at least one memory having a computer program code within said circuit;

said at least one memory and said computer program code with said at least one processor cause said AP to:

receive Signal to Interference and Noise Ratio (SINR) step size along with feedback SINR from at least one station;

derive post processing Signal to Interference and Noise Ratio (SINR) for said at least one station, after designing optimal Multi User (MU) precoder matrix for said at least one station;

compute optimal Modulation and Coding Scheme (MCS) level for said at least one station

using said post processing SINR and received feedback SINR; and

select at least one optimal station from set of stations.
The Access Point as in claim 10, wherein said AP is configured to derive said post processing SINR using at least one of: channel matrix between transmitter of said AP, receiver of said at least one station, said MU-precoder matrix and interference suppression capability of said at least one station.
The Access Point as in claim 10, wherein said AP is configured to receive said SINR step size from said SINR step size table indicated in said SINR step size index field in Very High Throughput (VHT) supported said MCS set field received from said at least one station.
The Access Point as in claim 12, wherein said AP is configured to:

compute number of said MCS level using at least one of: said SINR step size, said feedback SINR, said post processing SINR; and

compute optimal said MCS level using at least one of: said at least one station recommended said MCS level, said number of MCS levels for said at least one station.
The Access Point as in claim 13, wherein said AP is configured to compute said optimal MCS level by using encoded said MCS level said encoded SINR step size.
The Access Point as in claim 14, wherein said AP is configured to use reserved bit in said VHT format High Throughput (HT) control field for said MCS field of MFB sub-field to encode plurality of said MCS level and said SINR step size.
The Access Point as in claim 10, wherein said AP is configured to store plurality of said SINR step size tables.
A station for supporting joint station selection and link adaptation for 802.11ac compliant Multi User-Multiple Input Multiple Output (MU-MIMO) operation in downlink, wherein said station is configured to:

feedback Signal to Interference and Noise Ratio (SINR) step size according to said station s receiver capability to an Access Point (AP);

store plurality of said SINR step size tables; and

feedback interference suppression capability to said AP.
The station as in claim 17, wherein said station is configured to communicate said SINR step size index to said AP through reserved bits of Very High Throughput (VHT) supported Modulation and Coding Scheme (MCS) set field.