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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
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)

slide32

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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