1. Performance Evaluation of Multiple Access Protocols for Ad hoc Networks Using Directional Antenna Tamer ElBatt, Timothy Anderson, Bo Ryu WCNC 2003, March 2003 speaker ： Chen-Chi Hsieh

2. Outline Introduction Introduction System Model System Model Channel Reservation Based on Directional Antennas Information Channel Reservation Based on Directional Antennas Information Results and Discussion Results and Discussion

3. Introduction The broadcast nature of omni-directional antenna The broadcast nature of omni-directional antenna causes multi-user interference causes multi-user interference thus limit the spatial reuse thus limit the spatial reuse

4. Introduction – Related Work Three schemes Three schemes Omni-directional reservation (802.11) Omni-directional reservation (802.11) Directional reservation (DRTS/DCTS) Directional reservation (DRTS/DCTS) Hybrid reservation (DMAC using DRTS/OCTS) Hybrid reservation (DMAC using DRTS/OCTS) Decide whether to proceed with a transmission in a specific direction or not Decide whether to proceed with a transmission in a specific direction or not Rely on hearing/not hearing a reservation message Rely on hearing/not hearing a reservation message

5. Introduction – Related Work (cont.) Neighbor Neighbor N(x) ： Area covered by the radiation patterns of all N(x) ： Area covered by the radiation patterns of all beams at node x beams at node x Partition N(x) into Block-Neighbor BN(x) and Unblock-Neighbor UBN(x) Partition N(x) into Block-Neighbor BN(x) and Unblock-Neighbor UBN(x) BN(x) ： at least one of its beams is blocked from transmission BN(x) ： at least one of its beams is blocked from transmission UBN(x) ： not hear any reservation message UBN(x) ： not hear any reservation message Cause collision to the ongoing transmission Cause collision to the ongoing transmission

6. Introduction – Related Work (cont.) Omni-directional Reservation(802.11) All neighbors become aware of the ongoing transmission All neighbors become aware of the ongoing transmission N(S)= ｛ 1,2,3,4,5,6,D ｝ BN(S)=N(S) UNB(S)=Φ BN(S)=N(S) UNB(S)=Φ N(D)= ｛ 1,4,5,6,7,8,9,S ｝ BN(D)=N(D) UNB(D)=Φ BN(D)=N(D) UNB(D)=Φ Advantage ：Advantage ： Minimize the possibility of collisionsMinimize the possibility of collisions Drawback ：Drawback ： Too conservativeToo conservative

7. Introduction – Related Work (cont.) Directional Reservation D-RTS/D-CTS D-RTS/D-CTS Advantages ：Advantages ： Initiates more simultaneousInitiates more simultaneous reservation attempts reservation attempts Trade-off between collisions andTrade-off between collisions and spatial reuse spatial reuse Drawbacks ：Drawbacks ： Unaware of each otherUnaware of each other Highly subject to collisionsHighly subject to collisions N(S)= ｛ 1,2,3,4,5,6,D ｝ BN(S)= ｛ 4,5,6,D ｝ UBN(S)= ｛ 1,2,3 ｝ N(D)= ｛ 1,4,5,6,7,8,9,S ｝ BN(D)= ｛ 4,5,S ｝ UBN(D)= ｛ 1,6,7,8,9 ｝

8. Introduction – Related Work (cont.) Hybrid Reservation Use different combinations of omni-directional and directional reservation messages (D-RTS/O-CTS) Use different combinations of omni-directional and directional reservation messages (D-RTS/O-CTS) N(S)= ｛ 1,2,3,4,5,6,D ｝ BN(S)= ｛ 4,5,6,D ｝ UBN(S)= ｛ 1,2,3 ｝ N(D)= ｛ 1,4,5,6,7,8,9,S ｝ Φ BN(D)= ｛ 1,4,5,6,7,8,9,S ｝ UBN(D)=Φ

9. Introduction – Related works (cont.) Hybrid Reservation “ Medium Access Control Protocols Using Directional Antennas in Ad Hoc Networks ” IEEE INFOCON 2000 “ Medium Access Control Protocols Using Directional Antennas in Ad Hoc Networks ” IEEE INFOCON 2000 ABCDE DRTS(B) OCTS(B,C) DATA ACK DRTS(D) OCTS(D,E) DATA ACK OCTS(D,E) Exploit the spatial reuse but raise collision problem

10. Introduction – Related works (cont.) Hybrid Reservation (cont.) Drawbacks Drawbacks Doesn ’ t strike a balance minimizing control packet collisions May lead to further collisions May lead to further collisions

11. Introduction (cont.) New concepts in this paper New concepts in this paper All neighbors of the source and the destination should be aware of the intended transmission ， if possible All neighbors of the source and the destination should be aware of the intended transmission ， if possible Antenna blocking decisions should be based on the information included in the RTS/CTS packets Antenna blocking decisions should be based on the information included in the RTS/CTS packets

12. Introduction (cont.) The contributions of this paper The contributions of this paper Balance the trade-off Balance the trade-off between omni-directional and directional reservations between omni-directional and directional reservations Resolve new type of collisions Resolve new type of collisions Concept Concept Sending reservation packets carrying “ directional antennas information ” to as many neighbors as possible Sending reservation packets carrying “ directional antennas information ” to as many neighbors as possible Knowing their locations relative to the transmitter- receiver pair Knowing their locations relative to the transmitter- receiver pair

13. System Model - Antenna Model Antenna Model Antenna Model Each node Each node a fixed number (B) of switched beams a fixed number (B) of switched beams Each of width θ ＝ 2π/B radians Each of width θ ＝ 2π/B radians Transmitted energy Transmitted energy uniformly in a beam of width θ uniformly in a beam of width θ Nodes receive omni-directionally Nodes receive omni-directionally Beams are non-overlapping Beams are non-overlapping

14. System Model – Network Assumptions (cont.) Each node obtains neighboring information by a node-discovery scheme Each node obtains neighboring information by a node-discovery scheme Information of each node Information of each node The identities of all neighbors The identities of all neighbors The identities of neighbors that lie within the coverage of each beam The identities of neighbors that lie within the coverage of each beam Location of a node Location of a node R S A not allowed to engage in any communications A transmit on any directional beam except the one pointing towards the transmitter

15. Channel Reservation Based on Directional Antennas Information Balance the aforementioned trade-off Balance the aforementioned trade-off Send RTS/CTS packets over all unblocked beams Send RTS/CTS packets over all unblocked beams Add two fields to the RTS/CTS messages Add two fields to the RTS/CTS messages the index of the directional beam currently being used the index of the directional beam currently being used the index of the directional beam intended to be used the index of the directional beam intended to be used

16. Channel Reservation Based on Directional Antennas Information (cont.) 10 2 3 1 5 4 6 7 8 9 11 SD O-RTS O-CTS Node 5 ： not engage in any communications Node 2 ： (1)block only the beam pointing towards node S (2)can initiate a transmission with node 10

17. Channel Reservation Based on Directional Antennas Information (cont.) New types of collisions New types of collisions A neighbor may miss reservation messages due to lying in the coverage of a blocked beam A neighbor may miss reservation messages due to lying in the coverage of a blocked beam A RTS SD Node A ： it may be active or inactive ， May cause collision later

18. Channel Reservation Based on Directional Antennas Information (cont.) Solution of collision Solution of collision Use auxiliary channel to transmit special reservation packets on blocked beams Use auxiliary channel to transmit special reservation packets on blocked beams Suffering collisions from active users Suffering collisions from active users Special reservation packets RTS SD A ： inactive

19. Channel Reservation Based on Directional Antennas Information (cont.) Two solutions for solving collision problem Two solutions for solving collision problem Use auxiliary channel(s) to transmit special reservation packets on blocked beams Use auxiliary channel(s) to transmit special reservation packets on blocked beams Suffering collisions from active users Suffering collisions from active users Send “ pending ” RTS/CTS packets once the blocked beam becomes unblocked Send “ pending ” RTS/CTS packets once the blocked beam becomes unblocked Involves synchronization complexity Involves synchronization complexity

20. D1 S2 Special RTS/CTS S1 RTS DATA S1 ： unaware the ongoing transmission DATA D2

21. S2D1 S1 RTS Pending RTS/CTS

22. Channel Reservation Based on Directional Antennas Information (cont.) Solution of collision Solution of collision Use auxiliary channel(s) to transmit special reservation packets on blocked beams Use auxiliary channel(s) to transmit special reservation packets on blocked beams Suffering collisions from active users Suffering collisions from active users Send “ pending ” RTS/CTS packets once the blocked beam becomes unblocked Send “ pending ” RTS/CTS packets once the blocked beam becomes unblocked Involves synchronization complexity Involves synchronization complexity Transmit different packets on multiple beams at the same time Transmit different packets on multiple beams at the same time

23. Results and Discussion NS-2 simulator NS-2 simulator Under a wide variety of network loads Under a wide variety of network loads Schemes Schemes omni-directional reservation omni-directional reservation directional reservation directional reservation hybrid reservation hybrid reservation

24. Results and Discussion – Simulation Setup Small networks ： n = 50 nodes Small networks ： n = 50 nodes A rectangular area ： 500 meters x 500 meters A rectangular area ： 500 meters x 500 meters Data packet size ： 500 bytes Data packet size ： 500 bytes No mobility No mobility B = 6 switched beams per node Each of 60 0 width duration ： 900 sec.

25. Results and Discussion – Simulation Results Packet arrival rate/node λ(packets/sec) Average number of data packets transmitted/sec

26. Results and Discussion – Simulation Results (cont.) Packet arrival rate/node λ(packets/sec) Average number of data packets collisions/sec

27. Results and Discussion – Simulation Results (cont.) Packet arrival rate/node λ(packets/sec) MAC throughput (Kbps)

28. Results and Discussion – Simulation Results (cont.) MAC throughput (Kbps) Number of beams/node (B)

29. Results and Discussion – Simulation Results (cont.) Drawbacks Drawbacks Real switched beam antennas experience some overlapping Real switched beam antennas experience some overlapping Solutions Solutions minimizes beam overlap minimizes beam overlap Physical layer algorithms “ captures ” the strongest signal from interference in the overlapped areas Physical layer algorithms “ captures ” the strongest signal from interference in the overlapped areas Carrying out reservations in a round-robin fashion over the course of K phases ， where K may take values between 2 and B Carrying out reservations in a round-robin fashion over the course of K phases ， where K may take values between 2 and B

30. Conclusions Incorporating aggressiveness in the reservation scheme Incorporating aggressiveness in the reservation scheme Modifying the channel occupancy criterion to depend on information carried by the RTS/CTS messages Modifying the channel occupancy criterion to depend on information carried by the RTS/CTS messages Candidate solutions for combating new types of collisions inherent to directional antennas Candidate solutions for combating new types of collisions inherent to directional antennas