Full auto rate MAC protocol for wireless ad hoc networks

Z. Li, A. Das, A.K. Gupta and S. NandiSchool of Computer Engineering

Nanyang Technological University Singapore

IEE Proceedings-Communications, Vol. 152, No. 3, June 2005

Outlines

Introduction Motivation Modified Virtual Carrier Sensing (MVCS) Full Auto Rate (FAR) algorithm Analytical modeling Simulation Conclusion

Introduction

IEEE 802.11 standards provide high raw bandwidth and support multiple transmission rates

Several rate-adaptation algorithms had been proposed to improve the throughput Increase the utilization of bandwidthSuit the channel condition

Introduction (cont.)

However, these schemes considered the rate adaptation for the data frame only

The overhead of control frames which transmitted in the basic rate is considerable

Motivation

Motivation (cont.)

Motivation (cont.)

We could estimate the throughput by

Maximum throughput in IEEE 802.11b

Bandwidth utilization

Objective

In this paper, the protocol aims to transmit the control frames at an acceptable higher rate

MVCS

MVCS (cont.)

When a MAC frame did not correctly be received with a correct FCS value, EIFS shall be used

Since EIFS = SIFS + DIFS + Tx(ACK) EIFS is long enough for transmitting any control frame

at any rate RTS and ACK should be always transmitted at the hig

hest rate under the given channel conditions

MVCS (cont.)

If (Ldata / Rdata) < EIFSCTS should be transmitted at acceptable high

est rateThe higher data rate, the higher probability

Otherwise, CTS should be transmitted at the lowest basic rate

FAR

RTS

CTS

S

R

Data

ACK

SIFS SIFS SIFS

RTS CTS DATA ACK

Cached Cached or basic-rate

Piggy backed in CTS

Piggy backed in Data

Data length L/Chosen rate ACK/Chosen rate 0

CTS*Basic-rate Duration value Duration value Duration value

Tx Rate

Duration Field

Defer Time

Analytical modeling

Throughput : RBAR+MVCS vs. RBAR

Improvements of MVCS

Analytical modeling (cont.)

Throughput : FAR vs. RBAR+MVCS

FAR vs. RBAR+MVCS

Analytical modeling (cont.)

Throughput : FAR vs. RBAR

FAR vs. RBAR

Simulation

NS-2 Transmission range/Carrier sensing range

250m Mobility

Random way-point mobility modelPause time = 0Maximum speed = 5m/s

Single flow within single-hop2 nodes

200 * 200

Multiple flows within single-hop10 nodes200 * 200

Multiple flows within multi-hop20 nodes

1000 * 500

Conclusion

This paper proposed a new rate adaptation algorithm: FARTransmit all the frames at the highest rate

under the given channel conditions To ensure the correct operation of VCS,

MVCS is proposed

Conclusion (cont.)

Both analytical and simulation show that the FAR algorithm greatly improves the performance of IEEE 802.11

Routing protocol should be considered in the future work

Thank you !