Wireless Channel is shared

1. 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 4 4 4 4 4 4 4 4 4 3 3 3 3 3 3 3 3 3 Using Directional Antennas in Multihop Wireless Networks: Deafness and Directional Hidden Terminal Problems Anand Prabhu Subramanian, Samir R. Das, Computer Science Department, SUNY at Stony Brook http://www.wings.cs.sunysb.edu Motivation Directional Hidden Terminal Problem - Control window to avoid hidden terminal problem • Use MACA-P based technique [Acharya et al] • RTS/CTS packets carry an additional field called control window • The control window is adaptive • Wireless Channel is shared • A single transmission in a multi-hop path inhibits a number of surrounding transmissions • Culprit – OMNI DIRECTIONAL TRANSMISSION • Solution – DIRECTIONAL ANTENNA • Advantages - Higher spatial reuse - Increased coverage - Better link reliability - Increased capacity • New problems - Deafness - Directional Hidden Terminal Problem D S RTS DATA A collision ACK CTS B A RTS DATA S DATA ACK CTS B D Antenna Model and Assumptions - Negative CTS • To solve deafness scenario (ii) a nodes sends a NCTS omni-directionally when it cannot send a CTS • The node which receives the NCTS cancels the transmission and sends a TC packet • This informs the neighboring nodes of the sender about the cancellation Goal • Switched beam Antenna model which consists of N beams covering entire 360 degrees. • Two modes: Omni and Directional mode • We assume two passive antenna elements attached to a single radio • Assumptions: - Directional Gain = Omni Directional Gain - Location information known • Identify various scenarios of deafness and directional hidden terminal problem • Design a MAC protocol that uses a single channel and single radio that solves both the problems Simulation • Random network with 30 nodes in 1500x1500m • 5 simultaneous flows Deafness Scenarios Directional MAC Protocol - Omni-directional RTS/CTS with directional Information • RTS/CTS packets sent omni-directionally • DATA/ACK packets sent directionally • RTS/CTS packets carry the beam index used to transmit DATA/ACK packets respectively • Any node receiving RTS/CTS packet will block its beam only when the beam index in the packet is same as the beam used by the sender of RTS/CTS to communicate with it • Each node maintains a neighborhood transmission table and records the neighboring transmissions D A S S Future Work Deafness Deafness B • Analyze more scenarios that cause deafness and directional hidden terminal problems • Evaluate performance with other directional MAC protocols 1 1 2 2 S X D 3 4 4 3 Scenario (i) Scenario(ii) ICNP 2005 Anand Prabhu Subramanian { anandps@cs.sunysb.edu }