Winter 2004 UCSC CMPE252B1 CMPE 257: Wireless and Mobile Networking SET 3d: Medium Access Control Protocols

Spring 2005CMPE257 UCSC2 MAC Protocol Topics n MAC protocols using directional antennas p Basic protocols p Directional Virtual Carrier Sensing (DVCS) p Directional MAC (D-MAC) in UDAAN

Spring 2005CMPE257 UCSC3 MAC Protocols Using Directional Antennas The MAC protocols so far assume that a node ’ s transmissions reach all of its neighbors. n With powerful antenna systems, it is possible to limit transmissions and receptions to desired directions only. n This can increase spatial reuse and reduce interferences to neighbors nodes. n Caveat: p Not all neighbor nodes defer access. p Directional receiving is not always desired.

Spring 2005CMPE257 UCSC4 Omni-Directional and Directional Transmissions Node A Node B Node C Node A Node B Node C  Omni-directional transmissionDirectional transmission

Spring 2005CMPE257 UCSC5 Directional Antenna Models n Antenna systems  Switched beam – fixed orientation  Adaptive beam forming – any direction n Simulation models: p Complete signal attenuation outside the directional transmission beamwidth (  )  ``Cone plus ball ’’ model n Directional transmissions have higher gains p Possible to use power control to reduce the gain n Various medium access control schemes have been proposed and/or investigated (see Refs).Refs

Spring 2005CMPE257 UCSC6 Basic Scheme One n OTOR (omni-transmit, omni-receive) p The usual omni RTS/CTS based collision avoidance p All packets are transmitted and received omni-directionally. p IEEE MAC protocol uses such scheme.

Spring 2005CMPE257 UCSC7 Basic Scheme Two n DTOR (directional-transmit, omni-receive) p Packets are transmitted directionally. p Packets are received omni-directionally. p Increased spatial reuse (+) and collisions (-). Talks btw. A & B, C & D can go on concurrently; – More collisions may occur; + Spatial reuse is increased; + Nodes spend less time waiting.

Spring 2005CMPE257 UCSC8 Basic Scheme Three n DTDR (directional-transmit, directional- receive) p All packets are transmitted and received directionally. p Aggressive spatial reuse Talks btw. A & B, C & D can go on concurrently; – More collisions may occur; – Channel status info. is incomplete; + Aggressive spatial reuse; + Nodes spend less time waiting.

Spring 2005CMPE257 UCSC9 Basic Scheme Four n MTDR (mixed transmit, directional receive) p CTS packets are transmitted omni-directionally while other packets are transmitted directionally. p Tradeoff between spatial reuse and collision avoidance D sends RTS to C directionally; C replies with omni-CTS; + A and G defer their access and won’t cause collisions; – However, A cannot talk with B at the same time.

Spring 2005CMPE257 UCSC10 Predictions from the Analysis [WG03] n The DTDR scheme performs the best among the schemes analyzed. p Increased spatial reuse and reduced interference through directional transmissions. p Directional receiving cancels much interferences from neighbors and hidden terminals. n Throughput of the DTDR scheme with narraw beamwidth θ has a slightly increase when N increases. p Spatial reuse effect is more conspicuous. p Scalability problem is mitigated.

Spring 2005CMPE257 UCSC11 Simulation Results [WG03] n Higher-gain directional transmissions have negative effects on throughput and delay. p More nodes are affected. n Influence of side lobes can be almost canceled out if: p The level of side lobes is reasonably low through the advancement of antenna systems. p Carrier sensing threshold is raised such that nodes are less sensitive to channel activities.

Spring 2005CMPE257 UCSC12 Advanced Schemes n Directional Virtual Carrier Sensing ([TMRB02]) p Angle-of-Arrival (AoA) information available p Nodes record direction information and defer only to non-free directions (directional NAV) n UDAAN ([RRSWP05]) p Switched beam antenna p Experimental system was built to test the effectiveness of directional antenna systems

Spring 2005CMPE257 UCSC13 Details on Directional NAV n Physical carrier sensing still omni- directional Virtual carrier sensing be directional – directional NAV p When RTS/CTS received from a particular direction, record the direction of arrival and duration of proposed transfer r Channel assumed to be busy in the direction from which RTS/CTS received

Spring 2005CMPE257 UCSC14 n Nodes overhearing RTS or CTS set up directional NAV (DNAV) for that Direction of Arrival (DoA) X D Y C CTS Directional NAV (DNAV)

Spring 2005CMPE257 UCSC15 n Nodes overhearing RTS or CTS set up directional NAV (DNAV) for that Direction of Arrival (DoA) X Y Directional NAV (DNAV) D C DNAV

Spring 2005CMPE257 UCSC16 Directional NAV (DNAV) A B C θ DNAV D n New transmission initiated only if direction of transmission does not overlap with DNAV, i.e., if (θ > 0) RTS

Spring 2005CMPE257 UCSC17 D-MAC  Forced Idle is to avoid starvation  FI-Busy ``aggressive’’  Tight integration with power control

Spring 2005CMPE257 UCSC18 Directional Neighbor Discovery n Three kinds of links (neighbors) p N-BF, without beam forming p T-BF, using only transmit-only beamforming p TR-BF, using transmit and receive beamforming n Two methods for discovery p Informed discovery p Blind discovery

Spring 2005CMPE257 UCSC19 Directional Packet Transmission A B B’s omni receive range D-O transmission AB B’s directional receive beam D-D transmission

Spring 2005CMPE257 UCSC20 Related topics n Neighbor protocol and topology management n Energy efficiency n Routing

Spring 2005CMPE257 UCSC21 References  [KSV00] Ko et al., Medium Access Control Protocols Using Directional Antennas in Ad Hoc Networks, in IEEE INFOCOM  [NYH00] Nasipuri et al., A MAC Protocol for Mobile Ad Hoc Networks Using Directional Antennas, in IEEE WCNC  [R01] R. Ramanathan, On the Performance of Ad Hoc Networks with Beamforming Antennas, ACM MobiHoc '01, Oct  [TMRB02] Takai et al., Directional Virtual Carrier Sensing for Directional Antennas in Mobile Ad Hoc Networks, ACM MobiHoc ’ 02, June  [CYRV02] Choudhury et al., Medium Access Control in Ad Hoc Networks Using Directional Antennas, ACM MobiCom '02, Sept  [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 2005CMPE257 UCSC22 Acknowledgments n Parts of the presentation are adapted from the following sources: p Prasant Mohapatra, UC Davis, /NOTES/Adhoc-Sensor.ppt /NOTES/Adhoc-Sensor.ppt