1. An Opportunistic Directional MAC Protocol for Multi-hop Wireless Networks with Switched Beam Directional Antennas Osama Bazan and Muhammad Jaseemuddin Department of Electrical and Computer Engineering, Ryerson University, Toronto, Canada IEEE ICC 2008

2. Outline Introduction Proposed Mechanism – OPDMAC Evaluation Conclusion

3. Introduction Recently, the use of directional antennas in multi-hop wireless networks has received increasing attention in the research community due to their potential benefits and numerous advantages over omni-directional antennas. Increase spatial reuse Reduce interference Extend transmission range Reduce power consumptions S1S1 D1D1 D2D2 S2S2 Communication Range of S 1 Spatial Reuse Example – S 1 communicates with D 1, and S 2 communicates with D 2.

4. DMAC R.R. Choudhury, X. Yang, R. Ramanathan and N.H. Vaidya, “Using Directional Antennas for Medium Access Control in Ad Hoc Networks”, ACM Mobicom, 2002 All messages are sent in uni-direction. An idle node listens to the channel omnidirectionally. The Directional NAV Table (DNAV) is a table that keeps track of the directions (and the corresponding durations) towards which a node must not initiate a transmission. Introduction – Related Work

5. DNAV S 2 – 10 slots DRTS (10 slots) DCTS Related Work - DMAC D2D2 S1S1 D1D1 S2S2 Sensing Range of S 1 DCTS S1S1 D1D1 S2S2 ACK DRTSData DRTSBackoffDRTSBackoff 10 slots DNAV D 2 – 10 slots Data

6. Related Work – Problems Unsuccessful transmission The collision problem The deafness problem

7. DRTS Collision D3D3 S1S1 D1D1 S2S2 D2D2 DCTS

8. Deafness S1S1 D1D1 S2S2 DNAV S 2 – 10 slots DRTS (10 slots) DCTS Sensing Range of S 1 DCTS S1S1 D1D1 S2S2 ACK DRTSData DRTSBackoffDRTSBackoff 10 slots DNAV D 2 – 10 slots DRTS DCTS D2D2 D3D3

9. Introduction – Goal To fully exploit the benefits of spatial reuse, the MAC protocol for directional antennas should not force a node to undergo idle wait time while it has outstanding packets for transmissions in other directions.

10. Proposed Mechanism - OPDMAC In OPDMAC, the node always backoffs in an omni-directional mode for a random time derived from the minimum contention window. Thus, it does not exponentially increase contention window with every round of backoff. After each successful transmission, the node is forced to remain idle for a certain period of time called the listening period (LP) even if it has packets outstanding for transmission. The LP is essential to mitigate persistent deafness by allowing other nodes to communicate with this node.

11. DRTS (10 slots) Proposed Mechanism - OPDMAC D2D2 S1S1 D1D1 S2S2 Sensing Range of S 1 S1S1 D1D1 S2S2 DRTS 10 slots Data D3D3 Request LP Listen Period DCTS Request for D 1 is earlier than D 3

12. DNAV S 2 – 10 slots DRTS (10 slots) DCTS Proposed Mechanism - OPDMAC D2D2 S1S1 D1D1 S2S2 Sensing Range of S 1 DCTS S1S1 D1D1 S2S2 ACK DRTSData DRTSBackoffRTS 10 slots DNAV D 2 – 10 slots Data D3D3 Backoff Request LP Listen Period DNAV D 1 – 6 slots D 3 – 15 slots

13. Proposed Mechanism - OPDMAC D2D2 S1S1 D1D1 S2S2 Sensing Range of S 1 DCTS S1S1 D1D1 S2S2 ACK DRTSData DRTSBackoffDRTS 10 slots Data D3D3 Backoff Request LP Listen Period DRTS

14. DNAV S 2 – 10 slots DRTS (10 slots) DCTS Proposed Mechanism - OPDMAC D2D2 S1S1 D1D1 S2S2 Sensing Range of S 1 DCTS S1S1 D1D1 S2S2 ACK DRTSData DRTS 10 slots DNAV D 2 – 10 slots Data D3D3 Request LP Listen Period DNAV D 1 – 6 slots D 3 – 4 slots DCTS D3D3 ACK Data

15. Evaluation Simulator: OPNET Directional Gain: 10 dB Beamwidth 60 o Omni-directional transmission range: 250m Directional transmission range: 250m (power controlled) Scenario Collision Deafness

16. Average Delay Scenario Collision D3D3 S1S1 D1D1 S2S2 D2D2 Request

17. Average Delay Scenario Deafness D2D2 S1S1 D1D1 S2S2 D3D3 Request

18. Evaluation in Multi-hop Parameters Nodes: 30 Area: 800m X 800m Random deployment 10 nodes randomly chosen as sources CBR Scenario Multi-hop

19. Aggregate Throughput

20. Average Delay

21. Conclusion Proposed an opportunistic directional MAC protocol (OPDMAC) for multihop wireless networks with switched beam directional antennas. In case of a missing response (CTS or ACK), OPDMAC does not force the node to undergo idle backoff while it has outstanding packets for transmissions in other directions. This increases the channel utilization significantly.