CS 525M Mobile and Ubiquitous Computing Seminar Fan Wu Using - - PowerPoint PPT Presentation

CS 525M – Mobile and Ubiquitous Computing Seminar

Fan Wu

Using Directional Antennas for Medium Access Control in Ad Hoc Networks

Romit Roy ChRoudhury, Xue Yang, Ram Ramanathan and Nitin H. Vaidya

• Dept. of Electrical and Computer Engineering, and Coordinated Science

Laboratory University of Illinois at Urbana-Champaign Internetwork Research Department BBN Technologies (A Part of Verizon) Published in MOBICOM’02, Sep. 2002

Using Directional Antennas for MAC in Ad Hoc Networks

Introduction Related Works Preliminaries Basic Directional MAC (DMAC) Protocol Multi-Hop RTS MAC (MMAC) Performance Evaluation Future Work Conclusion

Contents

Using Directional Antennas for MAC in Ad Hoc Networks

The Problem of utilizing directional Antennas to improve the performance of ad hoc networks is non-trivial Pros

Higher gain (Reduced interference) Spatial Reuse

Cons

Potential possibility to interfere with communications taking place far away

Introduction

Using Directional Antennas for MAC in Ad Hoc Networks

Omni-directional Antennas

S D A B

Silenced Node

C

Using Directional Antennas for MAC in Ad Hoc Networks

Directional Antennas

S D A B C

Not possible using Omni

Using Directional Antennas for MAC in Ad Hoc Networks

MAC Proposals differ based on

How RTS/CTS transmitted (omni, directional) Transmission range of directional antennas Channel access schemes Omni or directional NAVs

Gain of directional antennas is equal to the gain of omni-directional antennas

Related Works

Using Directional Antennas for MAC in Ad Hoc Networks

Antenna Model

Two Operation modes:

Omni & Directional

Omni Mode:

Omni Gain = Go Idle node stays in Omni mode

Directional Mode:

Capable of beamforming in specified direction Directional Gain = Gd (Gd > Go)

Preliminaries

Using Directional Antennas for MAC in Ad Hoc Networks

IEEE 802.11

Preliminaries(Cont.)

IEEE 802.11 DCF – RTS/ CTS access scheme

Physical Carrier Sense

Physical Carrier Sensing Virtual Carrier Sensing

Using Directional Antennas for MAC in Ad Hoc Networks

Using directional antennas

Spatial reuse

Possible to carry out multiple simultaneous transmissions in the same neighborhood

Higher gain

Greater transmission range than omni-directional Two distant nodes can communicate with a single hop Routes with fewer hops

Problem Formulation

Using Directional Antennas for MAC in Ad Hoc Networks Channel Reservation

A node listens omni-directionally when idle

Possible to carry out multiple simultaneous

transmissions in the same neighborhood Sender transmits Directional-RTS (DRTS)

using specified transceiver profile

Physical carrier sense

Virtual carrier sense with Directional NAV

RTS received in Omni mode (only DO links used) Receiver sends Directional-CTS (DCTS) DATA,ACK transmitted and received directionally

Basic DMAC Protocol

Using Directional Antennas for MAC in Ad Hoc Networks

Directional NAV (DNAV) Table

Tables that keeps track of the directions towards which

node must not initiate a transmission

Basic DMAC Protocol(Cont.)

E H B

2*ß

e ?

e = 2ß + T

If T > 0 ,

New transmission can be initiated

DNAV

C

CTS RTS

Using Directional Antennas for MAC in Ad Hoc Networks

Hidden Terminal Problems due to asymmetry in gain

A does not get RTS/CTS from C/B

Problems w ith Basic DMAC

C A B Data RTS

Using Directional Antennas for MAC in Ad Hoc Networks

Hidden Terminal Problems due to unheard RTS/CTS

Problems w ith Basic DMAC(Cont.)

C B

D

A

Using Directional Antennas for MAC in Ad Hoc Networks

Shape of Silence Regions

Problems w ith Basic DMAC(Cont.)

Region of interference for directional transmission Region of interference for

• mnidirectional transmission

Using Directional Antennas for MAC in Ad Hoc Networks

Deafness

Problems w ith Basic DMAC(Cont.)

RTS RTS A B

X Z

DATA

X does not know node A is busy. X keeps transmitting RTSs to node A

Using Directional Antennas for MAC in Ad Hoc Networks

Attempts to exploit the extended transmission range

Make Use of DD Links

Direction-Direction (DD) Neighbor

MMAC Protocol

C A

A and C can communication each other directly

Using Directional Antennas for MAC in Ad Hoc Networks

Protocol Description : Multi-Hop RTS

Based on Basic DMAC protocol

MMAC Protocol(Cont.)

D R G S T B A C F DO neighbors DD neighbors

RTS DATA

Using Directional Antennas for MAC in Ad Hoc Networks

Channel Reservation

Send Forwarding RTS with Profile of node F

MMAC Protocol(Cont.)

R G S T B C

Forwarding RTS DATA

A F D

Using Directional Antennas for MAC in Ad Hoc Networks

Simulation Environment

Qualnet simulator 2.6.1 Beamwidth :45 degrees Main-lobe Gain : 10 dBi 802.11 transmission range : 250meters DD transmission range : 900m approx Two way propagation model Mobility : none

Performance Evaluation

Using Directional Antennas for MAC in Ad Hoc Networks

Performance Evaluation(Cont.)

A B C D E F A B C D E F

High Spatial Reuse Aggregate Throughput (Kbps) IEEE 802.11 : 1189.73 Basic DMAC : 2704.18 High Directional Interference Hidden terminal Problem Aggregate Throughput (Kbps) IEEE 802.11 : 1194.81 Basic DMAC : 1419.51

Using Directional Antennas for MAC in Ad Hoc Networks

Performance Evaluation(Cont.)

Aligned Routes

150m

Using Directional Antennas for MAC in Ad Hoc Networks

Performance Evaluation(Cont.)

Less aligned Routes

Using Directional Antennas for MAC in Ad Hoc Networks

Performance Evaluation(Cont.)

Randomly Chosen Routes

Using Directional Antennas for MAC in Ad Hoc Networks

Performance Evaluation(Cont.)

Random Topology

Using Directional Antennas for MAC in Ad Hoc Networks

Design of directional MAC protocols that incorporate transmit power control New protocols that rely less on the upper layers for beamforming information Impact of directional antennas on the performance of routing protocol

Future Work

Using Directional Antennas for MAC in Ad Hoc Networks Directional MAC protocols show improvement in aggregate throughput and delay

But not always

Performance dependent on topology

Random topology aids directional communication

MMAC outperforms DMAC & 802.11

802.11 better in some scenarios

Conclusion