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

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

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 802.11 task group n is aiming to high throughput of more than 100Mbps. → New PHY and MAC proposal is needed

Background MAC throughput using conventional MAC

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,

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

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

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.

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

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

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%

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

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

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

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.

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%.

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 + FCS @ 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

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

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

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

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%.

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

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

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

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.

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

Implementation of 5GHz modem

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

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.