CMPE 257 Wireless and Mobile Networking SET 3d Medium Access Control Protocols Winter 2004 UCSC CMPE252B 1 MAC Protocol Topics MAC protocols using directional antennas Basic protocols Directional Virtual Carrier Sensing DVCS Directional MAC D MAC in UDAAN Spring 2005 CMPE257 UCSC 2 MAC Protocols Using Directional Antennas The MAC protocols so far assume that a node s transmissions reach all of its neighbors With powerful antenna systems it is possible to limit transmissions and receptions to desired directions only This can increase spatial reuse and reduce interferences to neighbors nodes Caveat Not all neighbor nodes defer access Directional receiving is not always desired Spring 2005 CMPE257 UCSC 3 Omni Directional and Directional Transmissions Node B Node B Node C Node C Node A Node A Omni directional transmission Spring 2005 Directional transmission CMPE257 UCSC 4 Directional Antenna Models Antenna systems Simulation models Complete signal attenuation outside the directional transmission beamwidth Cone plus ball model Directional transmissions have higher gains Switched beam fixed orientation Adaptive beam forming any direction Possible to use power control to reduce the gain Various medium access control schemes have been proposed and or investigated see Refs Spring 2005 CMPE257 UCSC 5 Basic Scheme One OTOR omni transmit omni receive The usual omni RTS CTS based collision avoidance All packets are transmitted and received omni directionally IEEE 802 11 MAC protocol uses such scheme DIFS RTS DATA SRC SIFS SIFS SIFS ACK CTS DEST DIFS NAV RTS OTHER NAV CTS Defer Access Spring 2005 CMPE257 UCSC 6 Basic Scheme Two DTOR directional transmit omni receive Packets are transmitted directionally Packets are received omni directionally Increased spatial reuse and collisions Spring 2005 CMPE257 UCSC Talks btw A B C D can go on concurrently More collisions may occur Spatial reuse is increased Nodes spend less time waiting 7 Basic Scheme Three DTDR directional transmit directionalreceive All packets are transmitted and received directionally Talks btw A B C Aggressive spatial reuse D can go on concurrently Spring 2005 CMPE257 UCSC More collisions may occur Channel status info is incomplete Aggressive spatial reuse Nodes spend less time waiting 8 Basic Scheme Four MTDR mixed transmit directional receive CTS packets are transmitted omni directionally while other packets are transmitted directionally Tradeoff between spatial reuse and collision avoidance D sends RTS to C directionally C replies with omniCTS A and G defer their access and won t cause collisions However A cannot talk with B at the same time Spring 2005 CMPE257 UCSC 9 Predictions from the Analysis WG03 The DTDR scheme performs the best among the schemes analyzed Increased spatial reuse and reduced interference through directional transmissions Directional receiving cancels much interferences from neighbors and hidden terminals Throughput of the DTDR scheme with narraw beamwidth has a slightly increase when N increases Spatial reuse effect is more conspicuous Scalability problem is mitigated Spring 2005 CMPE257 UCSC 10 Simulation Results WG03 Higher gain directional transmissions have negative effects on throughput and delay More nodes are affected Influence of side lobes can be almost canceled out if The level of side lobes is reasonably low through the advancement of antenna systems Carrier sensing threshold is raised such that nodes are less sensitive to channel activities 11 Spring 2005 CMPE257 UCSC Advanced Schemes Directional Virtual Carrier Sensing TMRB02 Angle of Arrival AoA information available Nodes record direction information and defer only to non free directions directional NAV UDAAN RRSWP05 Switched beam antenna Experimental system was built to test the effectiveness of directional antenna systems Spring 2005 CMPE257 UCSC 12 Details on Directional NAV Physical carrier sensing still omnidirectional Virtual carrier sensing be directional directional NAV When RTS CTS received from a particular direction record the direction of arrival and duration of proposed transfer Channel assumed to be busy in the direction from which RTS CTS received Spring 2005 CMPE257 UCSC 13 Directional NAV DNAV Nodes overhearing RTS or CTS set up directional NAV DNAV for that Direction of Arrival DoA D CTS C X Spring 2005 Y CMPE257 UCSC 14 Directional NAV DNAV Nodes overhearing RTS or CTS set up directional NAV DNAV for that Direction of Arrival DoA D C DNAV X Spring 2005 Y CMPE257 UCSC 15 Directional NAV DNAV New transmission initiated only if direction of transmission does not overlap with DNAV i e if 0 B D A DNAV C RTS Spring 2005 CMPE257 UCSC 16 D MAC Forced Idle is to avoid starvation FI Busy aggressive Tight integration with power control Spring 2005 CMPE257 UCSC 17 Directional Neighbor Discovery Three kinds of links neighbors N BF without beam forming T BF using only transmit only beamforming TR BF using transmit and receive beamforming Two methods for discovery Informed discovery Blind discovery Spring 2005 CMPE257 UCSC 18 Directional Packet Transmission B A D O transmission B s omni receive range A B D D transmission B s directional receive beam Spring 2005 CMPE257 UCSC 19 Related topics Neighbor protocol and topology management Energy efficiency Routing Spring 2005 CMPE257 UCSC 20 References KSV00 Ko et al Medium Access Control Protocols Using Directional Antennas in Ad Hoc Networks in IEEE INFOCOM 2000 NYH00 Nasipuri et al A MAC Protocol for Mobile Ad Hoc Networks Using Directional Antennas in IEEE WCNC 2000 R01 R Ramanathan On the Performance of Ad Hoc Networks with Beamforming Antennas ACM MobiHoc 01 Oct 2001 TMRB02 Takai et al Directional Virtual Carrier Sensing for Directional Antennas in Mobile Ad Hoc Networks ACM MobiHoc 02 June 2002 CYRV02 Choudhury et al Medium Access Control in Ad Hoc Networks Using Directional Antennas ACM MobiCom 02 Sept 2002 WG03 Yu Wang and JJ Collision Avoidance in Single Channel Ad Hoc Networks Using Directional Antennas in IEEE ICDCS 03 RRSWP05 Ramanathan et al Ad Hoc Networking With Directional Antennas A Complete System Solution IEEE JSAC 2005 Spring 2005 CMPE257 UCSC 21 Acknowledgments Parts of the presentation are adapted from the following sources Prasant Mohapatra UC Davis http www cs ucdavis edu prasant ECS257 NOTES Spring 2005 CMPE257 UCSC 22