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CMPE 257: Wireless and Mobile Networking SET 3d:

CMPE 257: Wireless and Mobile Networking SET 3d: . Medium Access Control Protocols. MAC Protocol Topics. MAC protocols using directional antennas Basic protocols Directional Virtual Carrier Sensing (DVCS) Directional MAC (D-MAC) in UDAAN. MAC Protocols Using Directional Antennas.

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CMPE 257: Wireless and Mobile Networking SET 3d:

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  1. CMPE 257: Wireless and Mobile NetworkingSET 3d: Medium Access Control Protocols UCSC CMPE252B

  2. MAC Protocol Topics • MAC protocols using directional antennas • Basic protocols • Directional Virtual Carrier Sensing (DVCS) • Directional MAC (D-MAC) in UDAAN CMPE257 UCSC

  3. 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. CMPE257 UCSC

  4. Omni-Directional and Directional Transmissions  Node B Node B Node C Node C Node A Node A Omni-directional transmission Directional transmission CMPE257 UCSC

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

  6. 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. CMPE257 UCSC

  7. Basic Scheme Two • DTOR (directional-transmit, omni-receive) • Packets are transmitted directionally. • Packets are received omni-directionally. • 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. CMPE257 UCSC

  8. Basic Scheme Three • DTDR (directional-transmit, directional-receive) • All packets are transmitted and received directionally. • 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. CMPE257 UCSC

  9. 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 omni-CTS; • + A and G defer their access and won’t cause collisions; • –However, A cannot talk with B at the same time. CMPE257 UCSC

  10. 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 θ has a slightly increase when N increases. • Spatial reuse effect is more conspicuous. • Scalability problem is mitigated. CMPE257 UCSC

  11. 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. CMPE257 UCSC

  12. 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 CMPE257 UCSC

  13. Details on Directional NAV • Physical carrier sensing still omni-directional • 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 CMPE257 UCSC

  14. Directional NAV (DNAV) • Nodes overhearing RTS or CTS set up directional NAV(DNAV)for thatDirection of Arrival (DoA) D CTS C X Y CMPE257 UCSC

  15. Directional NAV (DNAV) • Nodes overhearing RTS or CTS set up directional NAV(DNAV)for thatDirection of Arrival (DoA) D C DNAV X Y CMPE257 UCSC

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

  17. D-MAC • Forced Idle is to avoid starvation • FI-Busy ``aggressive’’ • Tight integration with power control CMPE257 UCSC

  18. 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 CMPE257 UCSC

  19. Directional Packet Transmission B D-O transmission A B’s omni receive range D-D transmission A B B’s directional receive beam CMPE257 UCSC

  20. Related topics • Neighbor protocol and topology management • Energy efficiency • Routing CMPE257 UCSC

  21. 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. CMPE257 UCSC

  22. Acknowledgments • Parts of the presentation are adapted from the following sources: • Prasant Mohapatra, UC Davis,http://www.cs.ucdavis.edu/~prasant/ECS257/NOTES/Adhoc-Sensor.ppt CMPE257 UCSC

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