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

Using Directional Antennas for MAC in Ad Hoc Networks Introduction � 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

Using Directional Antennas for MAC in Ad Hoc Networks Omni-directional Antennas Silenced Node B D S C A

Using Directional Antennas for MAC in Ad Hoc Networks Directional Antennas Not possible using Omni B D S C A

Using Directional Antennas for MAC in Ad Hoc Networks Related Works � 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

Using Directional Antennas for MAC in Ad Hoc Networks Preliminaries � 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)

Using Directional Antennas for MAC in Ad Hoc Networks Preliminaries(Cont.) � IEEE 802.11 Physical Physical Carrier Sensing Carrier Sense Virtual Carrier Sensing IEEE 802.11 DCF – RTS/ CTS access scheme

Using Directional Antennas for MAC in Ad Hoc Networks Problem Formulation � 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

Using Directional Antennas for MAC in Ad Hoc Networks Basic DMAC Protocol � 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

Using Directional Antennas for MAC in Ad Hoc Networks Basic DMAC Protocol(Cont.) � Directional NAV (DNAV) Table � Tables that keeps track of the directions towards which node must not initiate a transmission H e = 2ß + T RTS 2*ß If T > 0 , e ? E New transmission can be initiated B DNAV CTS C

Using Directional Antennas for MAC in Ad Hoc Networks Problems w ith Basic DMAC � Hidden Terminal Problems due to asymmetry in gain � A does not get RTS/CTS from C/B Data RTS C B A

Using Directional Antennas for MAC in Ad Hoc Networks Problems w ith Basic DMAC(Cont.) � Hidden Terminal Problems due to unheard RTS/CTS D A B C

Using Directional Antennas for MAC in Ad Hoc Networks Problems w ith Basic DMAC(Cont.) � Shape of Silence Regions Region of interference for Region of interference for directional transmission omnidirectional transmission

Using Directional Antennas for MAC in Ad Hoc Networks Problems w ith Basic DMAC(Cont.) � Deafness Z RTS A B DATA RTS X X does not know node A is busy. X keeps transmitting RTSs to node A

Using Directional Antennas for MAC in Ad Hoc Networks MMAC Protocol � Attempts to exploit the extended transmission range � Make Use of DD Links � Direction-Direction (DD) Neighbor C A A and C can communication each other directly

Using Directional Antennas for MAC in Ad Hoc Networks MMAC Protocol(Cont.) � Protocol Description : Multi-Hop RTS � Based on Basic DMAC protocol DO neighbors DD neighbors RTS C B G T D F A DATA S R

Using Directional Antennas for MAC in Ad Hoc Networks MMAC Protocol(Cont.) � Channel Reservation � Send Forwarding RTS with Profile of node F Forwarding RTS C B G T D F A DATA S R

Using Directional Antennas for MAC in Ad Hoc Networks Performance Evaluation � 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

Using Directional Antennas for MAC in Ad Hoc Networks Performance Evaluation(Cont.) High Spatial Reuse D E F Aggregate Throughput (Kbps) C A B IEEE 802.11 : 1189.73 Basic DMAC : 2704.18 High Directional Interference Hidden terminal Problem Aggregate Throughput A D B C F E (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 Future Work � 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

Using Directional Antennas for MAC in Ad Hoc Networks Conclusion � 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