Phy and mac proposal for ieee 802 11n
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PHY and MAC Proposal for IEEE 802.11n. Andreas F. Molisch, Daqing Gu, Jinyun Zhang, Neelesh Mehta Mitsubishi Electric Research Laboratories (MERL) Cambridge, MA, USA (molisch, dgu, jzhang ,mehta)@merl.com Yukimasa Nagai, Hiroyoshi Suga, Fumio Ishizu, Keishi Murakami

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PHY and MAC Proposal for IEEE 802.11n

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Phy and mac proposal for ieee 802 11n

PHY and MAC Proposal for IEEE 802.11n

Andreas F. Molisch, Daqing Gu, Jinyun Zhang, Neelesh Mehta

Mitsubishi Electric Research Laboratories (MERL)

Cambridge, MA, USA

(molisch, dgu, jzhang ,mehta)@merl.com

Yukimasa Nagai, Hiroyoshi Suga, Fumio Ishizu, KeishiMurakami

Mitsubishi Electric Corporation

5-1-1 Ofuna, Kamakura Kanagawa, Japan, 2478501

(yuki-n, hsuga, ishizu, kmurak)@isl.melco.co.jp

Jianxuan Du,

Ye (Geoffrey) Li

Georgia Institute of Technology

(jxdu, [email protected])

Jeffrey (Zhifeng) Tao

Polytechnic University

([email protected])

Yuan Yuan

University of Maryland, College Park

([email protected])

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Outline

Outline

  • Introduction

  • Proposal for High Rate PHY

    • Baseline system

    • Proposed technologies

      • Statistical rate allocation

      • RF-baseband processing for antenna selection

      • QBD-LDPC space time coding for layered structure

    • Summary

  • Proposal for High Efficiency MAC

    • MAC structure

    • ADCA mechanism for CP

    • SCCA for CFP

    • Frame aggregation

    • Block ACK enhancement

    • Summary

  • Conclusions

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Introduction

Introduction

  • Challenges

    • Dramatic increase of data rate in PHY

      • 100 Mbps required throughput at MAC SAP

    • High MAC efficiency and QoS

    • Backward compatibility

      • Compatible with existing 802.11 standards

    • Low complexity

  • Our approach

    • Maintain backward compatibility

      • Rely on mature technology & existing standard framework

    • Be innovative

      • Develop new technologies which can be easily incorporated to achieve high data rate and high efficiency

    • Focus on inexpensive solution

      • Optimize the performance/cost ratio

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Phy baseline

PHY Baseline

  • Basic MIMO-OFDM system with layered structure (VBLAST)

  • Receiver uses linear processing and successive interference cancellation

  • 2x2 antenna modes with 20 MHz channelization as mandatory, 3x3 and 4x4 as optional

  • Convolutional codes, with coding rates of ½, 2/3, ¾, and 7/8, mandatory for backward compatibility.

  • Low-density parity check (LDPC) codes as options

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


System block diagram 2x2 case

System Block Diagram (2x2 Case)

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Proposed key technologies

Proposed Key Technologies

  • Statistical rate allocation for different layers

  • RF-baseband processing for antenna selection

  • QBD-LDPC coding for layered systems

  • Each above technology, or any form of their combination can be used for performance enhancement

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Statistical rate allocation

Statistical Rate Allocation

  • Problems with existing layered systems (e.g. V-BLAST)

    • The information rates for all layers are the same

    • The first layer to be detected has low channel quality due to the loss of signal energy after linear nulling

    • The errors from previous layers propagate to later layers by successive interference cancellation (SIC)

  • Proposed solution

    • It is proved that with instantaneous rate feedback and SIC, the layered structure can achieve the open-loop capacity

    • We propose to statistically determine the optimal data rates fro different layers to avoid instantaneous rate feedback

      • Detection order is fixed

      • Different layers cycle through different transmit antennas

      • Different layers have different data rates that are statistically determined by the channel quality

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Transmitter structure with statistical rate allocation

Data

P

Channel

QAM

IFFT

Encoder

Modulator

Input

Demultiplexer

P

Channel

QAM

IFFT

Encoder

Modulator

Statistical Layer Rate

Allocation

Transmitter Structure with Statistical Rate Allocation

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Algorithm and advantages

Algorithm and Advantages

  • Algorithm

    • Compute the means and variances of different layer capacities based on the past observations,

    • Determine the data rates for each layer for a given a nominal channel data rate

    • Choose the closest rate from the supported data rates set as data transmission rate

  • Advantages

    • No instantaneous rate feedback is needed. Thus no explicit feedback mechanism is necessary.

    • Only the first and second moment statistics of each layer capacity are used to determine the modulation and code rate for each layer.

    • Statistical information can be collected from ACK packets sent from the receiver.

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Simulation result

Simulation Result

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


The first idea antenna selection

The First Idea: Antenna Selection

  • Additional costs for MIMO

    • More antenna elements (cheap)

    • More signal processing (Moore’s law)

    • One RF chain for each antenna element

  • Basic idea of antenna selection:

    • Have many antenna elements, but select only best for down-conversion and processing

    • Diversity order is determined by number of antenna elements, not by number of RF chains

  • Hybrid antenna selection: select best L out of available N antenna elements, use those for processing

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


One step better rf preprocessing with antenna selection

One Step Better: RF-Preprocessing with Antenna Selection

  • Problem with antenna selection: significant loss of SNR in correlated channels

    • Mean SNR gain is determined by number of RF chains

  • Our solution:

    • Perform processing in RF domain, i.e., before selection is done

    • Reduce implementation cost by using only phase-shifter and adder in RF processing

    • Solution can be based on instantaneous channel state information (CSI), average CSI, or no CSI

    • Maintains diversity gain AND mean-SNR gain

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Rf pre processing block diagram

RF

Demodulator

Baseband

S

W

I

T

C

H

1

1

Sig

Proc

A/D

LNA

2

Pre-

Proc

(M)

Down

Conv

Down

Conv

.

.

.

.

L

A/D

LNA

Nr

RF Pre-Processing: Block Diagram

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Selection of the preprocessing matrix

1

2

Selection of the Preprocessing Matrix

  • No Channel Information

    • FFT based Pre-Processing

    • Simple

    • Beam pattern cannot adapt to the angle of arrival

  • Instantaneous Channel Information

    • Orient the beams with the angle of arrival of the incoming rays

    • Require continuous updating of entries of pre-processor

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Channel statistics based pre processing

Channel Statistics-Based Pre-Processing

  • Pre-processor depends on channel statistics

  • Orients the beam with the mean angle of arrival

  • Optimal Solution performs principal component decomposition on columns of H

  • Advantages

    • Continuous updating of entries of M not required

    • Optimum patterns independent of frequency!

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Transmitter structure

Transmitter Structure

Data

P

Channel

QAM

IFFT

Encoder

Modulator

Input

Joint RF-

Demultiplexer

baseband

Processing

P

Channel

QAM

IFFT

Encoder

Modulator

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Simulation result1

Simulation Result

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Why ldpc

Why LDPC?

  • Capacity approaching performance

  • Parallelizability of decoding, suitable for high speed implementation

  • Flexibility: LDPC is simply a kind of linear block code and its rate can be adjusted by puncturing, shortening, etc.

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Quasi block diagonal ldpc space time coding qbd ldpc for layered systems

Quasi-Block Diagonal LDPC Space-time Coding (QBD-LDPC) for Layered Systems

  • Feature: The encoding of different layers is correlated as compared with conventional layered systems.

  • Advantage: The space-time LDPC is designed such that the code can be decoded partially with the help of other layers (undecoded part) by the introduction of correlation between different layers

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


System diagram for qbd ldpc

System Diagram for QBD-LDPC

QAM

IFFT

Data

Modulator

Input

QBD-LDPC

P

Space-time

Encoder

QAM

IFFT

Modulator

Decoder

FFT

Soft

Output

Demodulator

-

P

1

+

QBD-LDPC

Decoder

FFT

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Parity check structure of qbd ldpc

Parity check matrix for conventional LDPC-coded V-BLAST.

Parity check matrix for QBD-LDPC.

Parity Check Structure of QBD-LDPC

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Encoding of qbd ldpc

Encoding of QBD-LDPC

  • Wn Hn= [PnI] by Gaussian elimination.

  • The parity check bits for layer n are given by Pnun+ WnCn-1bn-1 , where is un the input information bit vector for layer n, and bn-1 is codeword for layer n-1.

  • With the given structure, the information about layer n-1 is also contained in layer n. Therefore, information from layer n can help decoding layer n-1.

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Decoder of qbd ldpc

Decoder of QBD-LDPC

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Decoding of qbd ldpc

Decoding of QBD-LDPC

  • The decoding is based on linear nulling and interference cancellation, which is made possible by the lower-triagular structure of the parity check matrix.

  • The LLR’s of bits in successfully decoded subcodes are set to maximum or minimum value, depending on the output, to avoid ambiguity caused by the introduction of connection matrices

  • The decoding of layer n is stopped as soon as is satisfied, where bn-1 is fixed based on decoded layer n-1.

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Simulation results

Simulation Results

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Summary of phy technologies

Summary of PHY Technologies

  • The proposed solution provides a good tradeoff between performance, complexity and compatibility requirements and cost.

    • Low complexity: The complexity of linear processing + SIC scales linearly with the number of layers.

    • Low cost: Joint RF-baseband processing reduces the number of RF chains needed in antenna selection.

    • Backward compatibility:

      • Existent convolutional codes can be used.

      • No explicit feedback mechanism is needed.

    • Flexibility: Multiple modes for various number of receive antennas.

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Outline1

Outline

  • Introduction

  • Proposal for High Rate PHY

    • Baseline system

    • Proposed technologies

      • Statistical rate allocation

      • RF-baseband processing for antenna selection

      • QBD-LDPC space time coding for layered structure

    • Summary

  • Proposal for High Efficiency MAC

    • MAC structure

    • ADCA mechanism for CP

    • SCCA for CFP

    • Frame aggregation

    • Block ACK enhancement

    • Summary

  • Conclusions

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Mac structure

Superframe

CFP

CP

CFP

C

F

E

N

D

B

E

A

C

O

N

B

E

A

C

O

N

SCCA

C

F

E

N

D

ADCA

CAP

ADCA

B

E

A

C

O

N

SCCA

ADCA

MAC Structure

  • Enhance 802.11e for high efficiency

  • Retain 802.11e super frame structure

  • Maintain the same QoS support as 802.11e

  • Backward compatible with IEEE 802.11/802.11e

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Mac protocol

MAC Protocol

  • ADCA (Adaptive Distributed Channel Access)

    • CSMA/CA based random access

    • Significantly boost the channel efficiency by reducing overhead

    • Ensure long-term fairness, which legacy MAC cannot accomplish

  • SCCA (Sequential Coordinated Channel Access)

    • Coordinate contention-free medium access

    • Remove polling overhead, and retain the flexibility and simplicity

    • Provide reservation-based per-flow QoS

    • Achieve high efficiency without having to maintain the stringent synchronization and timing

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Adca overview

ADCA: Overview

  • CSMA/CA Based Channel Access Mechanism

    • Defer, backoff, collision resolution

    • Proved to be a robust, scalable, wide-deployed technology

  • Adaptive Batch Transmission

    • Reference Parameter Set (RPS)

    • Supporting BlockACK

    • Leveraging Multi-Rate Capabilities

      • Select stations in good channel condition

      • Provide long-term temporal fairness among stations

  • QoS Support

    • Four access categories (AC) with different channel contention parameters, similar to IEEE 802 .11e

    • Proved to be an efficient way to provide service differentiation

Andreas F. Molisch et al, Mitsubishi (USA, Japan)


Adca algorithm details

ADCA: Algorithm Details

  • AP broadcasts the Reference Parameters Set (RPS) (includes reference rate, packet size, batch size) of the BSS in a control packet (e.g., beacon) periodically.

  • Each STA computes the number of packets that can be fit into the batch (a.k.a. actual batch size) based on its current transmission rate and packet size.

    • If the actual batch size is less than a packet, the STA skips the current transmission opportunity, and increments its batch size credit accordingly.

    • If the actual batch size is equal or larger than one packet, the STA can transmit a batch of packets up to the actual packet size, if packets available.

  • During the batch transmission, the NAV in each data packet is set so that the channel time for the next packet in the same batch is reserved.

  • Once the batch transmission is completed, the transmitting STA releases the channel.

  • Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Phy and mac proposal for ieee 802 11n

    DIFS

    DIFS

    SIFS

    SIFS

    . . . . .

    Backoff

    Frame

    ACK

    Backoff

    Frame

    ACK

    Adaptive Packet Batch Transmission

    DIFS

    SIFS

    SIFS

    SIFS

    SIFS

    SIFS

    . . . . .

    Backoff

    Frame

    ACK

    Frame

    ACK

    Frame

    ACK

    Adaptive Batch Transmission: Illustration

    IEEE 802.11

    MAC

    IEEE 802.11n

    MAC

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Adca performance evaluation

    SIFS

    16us

    AIFS[AC0,1]

    54us

    DIFS

    34us

    CWmin[AC0,1]

    31

    Slot Time

    9us

    CWmax[AC0,1]

    1023

    ACK Size

    14B

    AIFS[AC2]

    43us

    MAC Header

    28B

    CWmin[AC2]

    15

    Peak Data-Rate

    216Mb/s

    CWmax[AC2]

    500

    Base Data-Rate

    24Mb/s

    AIFS[AC3]

    34us

    PLCP Preamble Length

    20us

    CWmin[AC3]

    7

    PLCP Header Length

    4us

    CWmax[AC3]

    100

    ADCA Performance Evaluation

    • Simulation Environments

      • Simulation platform: Ns-2 (version 2.26)

      • Physical parameters are based upon the MERL PHY layer proposal.

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Adca throughput gain

    ADCA Throughput Gain

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Effect of reference batch size b f

    Effect of Reference Batch Size(Bf)

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Adca comprehensive simulation

    ADCA Comprehensive Simulation

    • We have conducted extensive simulations according to the usage model (UM) released by IEEE 802.11n TG. The results prove that ADCA satisfies the most stringent requirements set aside in UM.

    • The throughput observed at MAC SAP on a point to point link is 106Mbps, which exceeds the 100Mbps requirement.

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Sample simulation results

    Sample Simulation Results

    • Home Scenario

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Sample simulation results1

    Sample Simulation Results

    • Home Scenario Cont’

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Effect of increasing frame size

    Effect of Increasing Frame Size

    • Large frame size and frame aggregation, among other technologies can be integrated with ADCA to achieve even higher throughput

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Related message format

    EDCA parameter set element in IEEE 802.11e

    1

    1

    1

    4

    4

    4

    4

    1

    Octet

    Element

    ID (12)

    Length

    (18)

    QoS

    Info

    Reserved

    Octet

    1

    2

    1

    1

    1

    1

    1

    AC_BK

    Parameter

    Record

    AC_VI

    Parameter

    Record

    AC_VO

    Parameter

    Record

    AC_BE

    Parameter

    Record

    ACI/

    AIFSN

    ECWmin/

    ECWmax

    TXOP

    Limit

    Reference

    Packet Size

    (Sf)

    Reference

    Data Rate

    (Rf)

    Reference

    Batch Size

    (Bf)

    Reference

    BlockACK Size

    (Af)

    Modified EDCA parameter set element for ADCA

    Related Message Format

    • Need to modify the EDCA parameter set element in the beacon

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Scca overview

    SCCA: Overview

    • Highly efficient and flexible channel utilization

    • Ensure parameterized QoS

    • Combine the merits of TMDA and polling mechanisms

      • Eliminate the overhead of polling, and retain its flexibility

      • Avoid the rigidity of TDMA, and achieve its efficiency

    • Consist of five distinct phases

      • Resource request

      • Resource allocation

      • Data transmission

      • Resource renegotiation

      • Resource relinquishment

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Scca algorithm details

    SCCA: Algorithm Details

    • To join SCCA, STAs need to send a resource reservation packet to AP .

    • Based on reservation request received from the STAs, AP assigns a TXDT, and an integer sequence index value (SIV) to each STA sequentially. SIV starts from 1 to N (Max. number of admitted).

    • AP distributes SIVs and TXDTs in a control packet at the beginning of each CFP period.

    • STAs listen to the channel, retrieves its own SIV and TXDT from the control frame and then accesses the channel in CFP period as follows

      • Start to backoff SIV time after the channel is idle for PIFS time

      • Stop the backoff once channel becomes busy. Restart it again when the channel is cleared

      • Transmit for a duration of TXDT if SIV is decremented to zero

  • The controller inside AP schedules the downlink traffic (from AP to STA) in the same way as uplink traffic.

  • Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Scca resource request allocation

    SCCA: Resource Request & Allocation

    STA

    SCCA Controller

    Resource Request (RRQ)

    ADCA Period

    SIFS

    ACK

    Resource Reservation and Allocation

    . . .

    Beacon

    SIFS

    Resource Allocation (RAL)

    . . .

    SCCA Period

    Data

    Data Transmission

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Scca data transmission

    TXDT

    0

    1 frame

    2 frame

    TXDT

    1 frame

    1 frame

    2 frame

    TXDT

    0

    0

    0

    TXDT

    0

    0

    2 frame

    At time t0

    SIV

    NA

    1

    2

    SIV

    1

    2

    3

    At time t3

    At time t2

    At time t1

    SIV

    NA

    NA

    NA

    SIV

    NA

    NA

    1

    STA

    S1

    S2

    AP

    STA

    S1

    S2

    AP

    STA

    S1

    S2

    AP

    STA

    S1

    S2

    AP

    D

    A

    T

    A

    P

    I

    F

    S

    S

    L

    O

    T

    S1

    C

    F

    E

    N

    D

    AP

    B

    E

    A

    C

    O

    N

    R

    A

    L

    S

    L

    O

    T

    D

    A

    T

    A

    S

    I

    F

    S

    D

    A

    T

    A

    S

    I

    F

    S

    S

    I

    F

    S

    P

    I

    F

    S

    P

    I

    F

    S

    t1

    t3

    P

    I

    F

    S

    P

    I

    F

    S

    A

    C

    K

    A

    C

    K

    D

    A

    T

    A

    P

    I

    F

    S

    S

    L

    O

    T

    S

    I

    F

    S

    A

    C

    K

    t2

    t0

    S2

    CP: ADCA

    CP: ADCA

    CFP: SCCA

    SCCA: Data Transmission

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Scca resource renegotiation

    SCCA: Resource Renegotiation

    STA

    SCCA Controller

    Beacon

    SIFS

    Resource Allocation (RAL)

    . . .

    Data

    Data

    from

    STA x

    SCCA Period

    Resource Request (RRQ)

    ACK

    . . .

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Scca resource relinquishment

    SCCA: Resource Relinquishment

    SCCA Controller

    STA

    Beacon

    SIFS

    Resource Allocation (RAL)

    . . .

    Resource Relinquishment (RRL)

    SCCA Period

    Resource Relinquishment

    SIFS

    ACK

    . . .

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Scca throughput

    SCCA Throughput

    • Identical simulation settings

    • Simplified scenario and focus solely the core SCCA mechanism

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Effect of increasing frame size1

    Effect of Increasing Frame Size

    • SCCA can achieve even higher throughout, with other augmentations such as large frame size, frame aggregation, etc.

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Related message format1

    2

    6

    6

    6

    2

    4

    2

    Frame

    Control

    Duration

    DA

    SA

    BSSID

    Sequence

    Control

    Frame

    Body

    FCS

    MAC Header

    Related Message Format

    • Introduce 3 signaling messages

      • Resource request (RRQ)

      • Resource allocation (RAL)

      • Resource relinquishment (RRL)

    • Share common frame format

    • Designed based upon IEEE 802.11e ADDTS request, ADDTS response and DELTS

    Common frame format

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Related message format rrq

    Order

    Information

    1

    Category

    2

    Action

    3

    Dialog Token

    4 ~n

    Multi-TSPEC

    Related Message Format: RRQ

    RRQ Message Format

    Octet

    1

    2

    x

    1

    2

    y

    Frame format of Multi-TSPEC

    Element

    ID

    Length

    TSPEC

    Bitmap 1

    TSPEC 1

    . . .

    TSPEC

    Bitmap n

    TSPEC n

    3

    2

    2

    4

    4

    4

    4

    4

    Maximum

    Service

    Interval

    Inactivity

    Interval

    Suspension

    Interval

    Service

    Start

    Time

    TS

    Info

    Nominal

    MSDU

    Size

    Maximum

    MSDU

    Size

    Minimum

    Service

    Interval

    Frame format of TSPEC

    Octet

    4

    4

    4

    4

    2

    2

    4

    4

    Minimum

    Data

    Rate

    Medium

    Time

    Mean

    Data

    Rate

    Peak

    Data

    Rate

    Maximum

    Burst

    Size

    Delay

    Bound

    Minimum

    PHY

    Rate

    Surplus

    Bandwidth

    Allowance

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Related message format ral

    Order

    Information

    1

    Category

    2

    Action

    14

    1

    2

    14

    3

    Dialog Token

    Multi-Schedule

    Element n

    Element

    ID

    Length

    Multi-Schedule

    Element 1

    4 ~n

    Multi-Schedule

    2

    2

    2

    4

    2

    2

    AID

    Specification

    Interval

    Schedule

    Info

    SIV

    Service

    Interval

    TXDT

    Bit 0

    Bit 1 - 4

    Bit 5 - 6

    Bit 7 - 15

    Reserved

    TSID

    Direction

    Reserved

    Related Message Format: RAL

    RAL

    Message Format

    Multi-Schedule

    Schedule Information subfield

    Schedule Information subfield

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Related message format rrl

    Order

    Information

    1

    Category

    2

    Action

    3 ~ n

    RRL element

    Bit 0

    Bit 11 - 13

    Bit 1 - 4

    Bit 5 - 6

    Bit 7 - 8

    Bit 9

    Bit 10

    Bit 14 - 15

    Bit 16

    Bit 17 - 23

    Traffic

    Type

    APSD

    User

    Priority

    TSID

    Direction

    Access

    Policy

    Aggregation

    TS Info

    ACK Policy

    Schedule

    Reserved

    2

    3

    AID

    TS Info

    5 Bytes

    Related Message Format: RRL

    RRL

    Message Format

    RRL

    element

    TS Info

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Frame aggregation

    MAC header

    Frame

    Control

    Duration

    /ID

    Addr1

    Addr2

    Addr3

    Starting Sequence

    Control

    Addr4

    QoS

    Control

    Aggregated

    Frame Body

    . . .

    AL-1

    Hdr 1

    MSDU

    1

    FCS

    1

    AL-1

    Hdr 2

    MSDU

    2

    FCS

    2

    AL-1

    Hdr n

    MSDU

    n

    FCS

    n

    LLC

    b11

    b12

    b0

    b10

    b15

    b16

    b32

    MSDU

    Length

    More MSDU

    Reserved

    Sequence Control

    MAC

    MPDU

    PSDU

    PHY

    PPDU

    Frame Aggregation

    • Frame aggregation at multilevel

      • At MSDU and/or PSDU level

      • In both contention period and contention free period

      • Flexible and efficient BlockACK mechanism for frame aggregation

      • Novel internal collision resolution mechanism

    • Frame aggregation at MSDU level

      • Aggregation condition: With identical traffic class (TID) and same <source, destination> pair

    Format of frame aggregation at MSDU level

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Frame aggregation psdu level

    1 OFDM symbol

    PLCP

    Preamble

    PLCP

    Hdr 1

    PSDU

    1

    PLCP

    Hdr 2

    PSDU

    2

    PLCP

    Hdr n

    PSDU

    n

    PLCP

    Hdr n+1

    Aggregated

    BlockACK

    Request

    Tail

    Pad

    AL2

    parameter

    Scrambling

    Initialization

    Reserved

    0

    1

    2

    3

    4

    5

    6

    7

    8

    9

    10

    11

    12

    13

    14

    15

    Rate

    4bits

    Length

    13bits

    Parity

    1bit

    Tail

    6bits

    Service

    16bits

    Frame Aggregation: PSDU Level

    • Aggregation condition:

      • Frames can have different destination addresses, but they must have the same TIDs.

      • Frames can have different TIDs, but they must be involved in the same internal collision internal collision resolution.

    Frame format of frame aggregation at PSDU level

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Blockack for frame aggregation

    Transmission of an

    aggregated frame

    S

    I

    F

    S

    S

    I

    F

    S

    MAC header

    S

    L

    O

    T

    S

    L

    O

    T

    BlockACK

    from STA k

    BlockACK

    from STA k+1

    Frame

    Control

    Duration

    RA

    TA

    Aggregated BlockACK

    Request Frame Body

    2

    6

    2

    2

    2

    4

    Duration

    RA

    BAR

    Control

    Block ACK Starting

    Sequence Control (TIDj)

    Block ACK Starting

    Sequence Control (TIDk)

    FCS

    Octets

    b0

    b1

    b2

    b5

    b6

    b11

    b12

    b15

    Type

    TID Bitmap

    IBV

    Reserved

    BlockACK for Frame Aggregation

    • BlockACK mechanism is specially tailored for frame aggregation.

      • Aggregated BlockACK request

      • Resolution to potential collision of multiple BlockACK messages

        • CSMA-alike backoff

        • No collision

    Aggregated BlockACK Request

    Resolution to potential collision of multiple BlockACK messages

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Blockack for frame aggregation1

    Octets

    2

    2

    6

    6

    2

    2

    2

    2xN

    4

    Frame

    Control

    Duration

    RA

    TA

    BA

    Control

    Block ACK

    Starting Sequence

    Control (TIDj)

    Block ACK

    Starting Sequence

    Control (TIDk)

    BlockACK

    Bitmap

    FCS

    M 1-byte-long relative sequence number = M Bytes

    . . .

    b0

    b1

    b2

    b5

    b6

    b7

    b15

    Type

    TID Bitmap

    NAK

    Reserved

    Relative Sequence

    Number (6bits)

    Relative Sequence

    Number (6bits)

    Encoded TID

    (2bits)

    Encoded TID

    (2bits)

    BlockACK for Frame Aggregation

    BlockACK for frame aggregation in contention period

    • Contention period

      • Support multiple TIDs

      • Relative sequence number

    • Contention free period

      • Similar to our streamlined BlockACK proposal

      • Explained in the next slide.

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Streamlined blockack

    b0

    b1

    b2

    b7

    b8

    b11

    b12

    b15

    Type

    Block Size

    Reserved

    TID

    Streamlined BlockACK

    • The blockACK bitmap field in the legacy BlockACK frame contains more than it needs

    • A more streamlined BlockACK frame design can save more than 90% of bandwidth

      • Single TID

      • Sequence number bitmap (at most 8-byte long) for acknowledgement to 64 frames

      • Readily extensible to support acknowledgement to more than 64 frames

        • Enlarge the block size field in BAR/BA field

        • Extend the sequence number bitmap to accommodate the number of frames to be acknowledged.

      • The 2-bit type field in BAR/BA field

        • 0x02: streamlined BlockACK

        • 0x03: BlockACK for frame aggregation in contention free period.

    BAR/BA

    field

    BlockACK Bitmap

    Padded to the boundary of byte

    Sequence Number Bitmap

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Summary of proposed mac technologies

    Summary of Proposed MAC Technologies

    • We proposed four major enhancements for 802.11e MAC

      • Adaptive Batch transmission

      • Sequentially coordinated channel access & frame format

      • Efficient and flexible frame aggregation at MSDU and/or PSDU level

      • Streamlined BlockACK

    • All these enhancements improve 802.11e MAC efficiency while retaining the reliability, simplicity, interoperability and QoS support of 802.11/802.11e MAC

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


    Conclusions

    Conclusions

    • We have proposed a variety of important techniques for performance enhancements to both PHY and MAC

    • These techniques can be individually or jointly included in the upcoming 802.11n standard

    • We will continue to develop further enhancements for possible adoption

    • We are open for any collaboration to establish a baseline proposal for 802.11n standard

    Andreas F. Molisch et al, Mitsubishi (USA, Japan)


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