1. Enhanced MAC proposal for high throughput.
Tohoku University
Hiroyuki Nakase and Hiroshi Oguma

2. Outline
Background
Frame aggregation for high throughput single link using UDP – Simulation –
New MAC procedure
EDCF with CW definition for AP
Polling with static frame control
Polling with MAC frame aggregation of different IP link
Dual PHY method
Development of PHY

3. 802.11 task group n is aiming to high throughput of more than 100Mbps.
Introduction
Throughput of MAC SAP was limited by connection procedure based on CSMA/CA.
SIFS, DIFS and backoff for every packet
task group n is aiming to high throughput of more than 100Mbps.
→ New PHY and MAC proposal is needed

4. Background
MAC throughput using conventional MAC

5. Proposal 1: Frame aggregation
Frame format for aggregation
Aggregation of MAC frame to send same destination STA.
Aggregation Header is defined in addition to MAC header.
Aggregation header has informations of number of aggregation,

6. Frame structure
Aggregation flag is defined in subtype field of MAC header.
Aggregation header is defined.
Number of aggregation frames
Subheader is added to each aggregated frame.
Length of frame
Preamble
SIGNAL
Frame Body
MAC Header
Data Body
FCS
Aggregation Header
SubHeader
Frame 1
SubHeader
Frame2
SubHeader
Frame n
Less than 9000 bytes

7. Throughput with frame aggregation
Simulation results
Frame size of 1500x6 = 9,000 Byte by aggregation
Point-to-point connection using UDP packet
Wireless data rate is 324 Mbps
Throughput of more than 180 Mbps was obtained

8. Throughput using aggregation
324Mbps (54 x 6ch)
274.8Mbps (84.8%)
216Mbps (54 x 4ch)
191.2Mbps (88.5%)
162Mbps (54 x 3ch)
142.9Mbps (88.2%)
AP-STA　Point-to-Point
UDP packet
ACK : 54Mbps
SIFS: 16usec
DIFS: 32usec
Frame aggregation is effective to improve MAC throughput in the case of P-P connection.

9. MAC throughput using Scenario
Scenario 1 of usage model
Conventional DCF
Enhanced DCF with unfair contention window setting
Proposal of employment of polling connection
Proposal of FDD mode using dual PHY

10. System throughput using EDCF
PHY data rate of 216Mbps and 324Mbps
CW setting of AP and STA is the same.
Frame aggregation was employed.
6Ch,　4000Byte/CH
Throughput: 32.4 Mbps
4Ch,　4000Byte/CH
Throughput: 28.4 Mbps

11. System throughput using EDCF
Unfair CW setting for advantage of AP
CWmin_AP=15
6Ch(324Mbps),　4000Byte/CH
50.8Mbps (Downlink : 49Mbps , Uplink: 1Mbps) at CWmin_STA=255
Improvement of Throughput : 157%
4Ch(216Mbps),　4000Byte/CH
47.8Mbps (Downlink : 47Mbps , Uplink: 0.3Mbps) at CWmin_STA=255
Improvement of Throughput : 168%
Usage efficiency of PHY data rate is less than 60%

12. Proposal of Enhanced PCF
Three Types of MAC procedure
Static Beacon Timing HCF
Individual polling
MAC frame aggregation for multicast polling
Advanced HCF with dual PHY
Concept
Improvement of system throughput
AP acts full traffic control in BSS
Suppression of overhead in low data rate traffic

13. Enhanced PCF with static beacon timing
Beacon interval is fixed. (Ex. 10 msec) : Easy control with power saving
Transmission available by only AP in guard duration
Duration of alternate EPCF and EDCF
Length of EPCF is defined by AP due to request
AP broadcast information for EPCF using Beacon packet
All STAs are controlled by AP even if STA adhoc communication

14. Example procedure Guard duration EPCF duration EDCF duration Beacon
During EDCF duration, STAs are operated as standard DCF mode.
Polling request is transmitted on the rule of DCF.
EPCF duration
EDCF duration
STA-STA communication is also controlled by AP
EPCF duration is started from Beacon signal from AP.
Beacon
Poll-request
PCF Data
CF-end
DCF Data
Poll-accept

15. Definition of frame format (I)
Polling request and accept
STA sends a request frame to AP during DCF when STA has an application with fixed data rate streaming.
EX: HDTV, SDTV, VoIP, etc.
AP assigns on the polling list table for the STA, and send a acceptance frame to the SAT.
Polling List Table
AP has a polling list table for management of PDF duration.
Data rate, sequence number, STA’s address, etc.

16. Simulation results of EPCF
Scenario 1
10msec Beacon interval is assumed.
HDTV, SDTV, VoIP, MP3, VideoPhone is communicated under polling streaming.
Internet file transfer is under DCF.
Necessary duration for polling : 4.8 msec
Without re-transmission for packet error
Estimated throughput more than 81Mbps.
MAC efficiency is more than 96%.

17. Problem
Waste duration of PHY preamble and SIGNAL field of 16+4usec in low data rate frame.
Ex: 0.096Mbps (VoIP)
Preamble and SIGNAL: 20usec
MAC Header + Data + 216Mbps: 16usec
(36Byte + 120Byte + 4Byte)/(216Mbps)
Solution :Reduce the number of PHY preamble
Merging downstream for low data rate!!
MAC frame Aggregation for low data stream of < 1Mbps

18. Enhanced PCF with MAC frame aggregation
Employment of MAC frame aggregation of AP-to-STAs frame during EPCF
STA-to-AP frame is sending by reserved slot in Poll-accept packet
Expansion of duration for EDCF due to suppression of EPCF overhead
Guard duration
Beacon
PCF Data
Poll-request
Poll-accept
CF-end
DCF Data

19. Aggregation MAC Header
Frame format
Preamble
SIGNAL
Aggregation MAC Header
MAC SubHeader 1
Body + FCS
MAC SubHeader 2
Body + FCS
MAC SubHeader 3
Body + FCS
FCS
Frame Control 2
Duration 2
Source Address 6
BSSID 6
Aggregation header has four fields of Frame Control, Duration, Source Address, BSSID and Sequence Control.
Sequence Control 1
Duration 2
Destination Address 6
MAC SubHeader has fields of Sequence Number, Duration and Destination Address

20. Control Field Definition
Frame Control Field
First 1 Byte is the same as conventional MAC header.
Number of aggregated MAC frames is represented.
Protocol Version 2
Type 2
Subtype 4
Number of Aggregation 4
Researved 4
Sequence Control Field
Sequence number for identification
MAC information for individual terminal
Sequence Number 4
Retry 1
Pwr
Mgt 1
WEP 1
Order 1

21. Throughput Estimation (Scenario 1)
10msec Beacon interval is assumed.
HDTV, SDTV, VoIP, MP3, VideoPhone is communicated under polling streaming.
Internet file transfer is under DCF.
Necessary duration for polling : 4.4 msec
Without re-transmission for packet error
Estimated throughput more than 82Mbps.
MAC efficiency is more than 98%.

22. Dual PHY communication
IFS for ACK, low rate AP-STA are wasted duration for 11n.
AP-STA and STA-AP connection are used the same frequency band : Time Division Duplex (TDD)
In order to increase throughput, different band is used for STA-AP connection : Employment of Freqency Division Duplex (FDD) using 11a/b/g
Ack, low rate packet for STA-AP connection

23. Dual PHY protocol stack
Definition of MAC sub-layer for merging different PHY
MAC
STA-AP AP-STA
MAC
11n
MAC
11b/g/n
PHY
11b/g/n
PHY
11n

24. Dual PHY communication
Employment of 11b/g/n PHY for low data rate traffic of less than 1 Mbps
High data rate of 11n PHY for large streaming such as HDTV, Gaming, etc.
AP-to-STA streaming without IFS to achieve higher throughput.
IFS is not needed for AP-STA
ACK is transmitted immediately from STA

25. PHY and MAC implementation
We have a national project to implement 5GHz high throughput WLAN terminal.
Development with Mitsubishi Electric Co. and NetCleus Systems Co.
Band expansion based on 11a PHY format.
6 channels expansion available
Xillinx VertexIIPro was used for MAC implementation.

26. Block diagram of implemented modem
Wireless LAN
Gbit Ethernet
14bit 160Msps
TX RF/IF
DAC
Modulation
MAC
MAC
PHY LSI
RJ45
RX RF/IF
ADC
Demodulation
12bit 160Msps
Implemented on Virtex2Pro
With dual processor of PowerPC450

27. Implementation of 5GHz modem

28. Implementation of modem
MAC board : throughput of more than 100Mbps

29. Conclusion
New MAC Proposal with effective polling procedure is indispensable for high system throughput using 11n.
Our proposals are based on
1 Enhanced DCF with unfair contention window setting
2 Proposal of employment of polling connection
3 Proposal of FDD mode using dual PHY
Every proposal has improvement of MAC-SAP throughput superior to conventional MAC procedure.