1. Effects of Directional Antennas on 802.11e Muhammad Mahmudul Islam Ronald Pose Carlo Kopp School of Computer Science & Software Engineering Monash University Melbourne, Australia

2. Agenda An analytical model & Simulation results to show the effect of directional antennas on network performance using 802.11e

3. Assumptions in this Work  Only the interference related effect on network performance is considered  Scheme O: single channel and omni-directional antenna  Scheme MO-x: x NICs, x distinct channels and omnidirectional antennas  Scheme MD-x: x NICs and x directional antennas  All antenna configurations had the same TX range  Simulated with GloMoSim (ver 2.02)  The effect of secondary lobes on the primary lobe has been ignored while using directional antennas  EDCA of IEEE 802.11e has been used as MAC protocol  DSR has been used as the routing protocol  Adjacent nodes have been separated by 240 metres  Traffic was generated with CBR UDP packets  Ad-hoc networks similar to a SAHN are considered

4. SAHN  Multi-hop ad-hoc network  Ideal for cooperative nodes, e.g. connecting houses and business  Topology is quasi-static  Uses wireless technology  Multi-hop QoS routing  Decentralized  Multi Mbps broadband service  No charges for SAHN traffic  Can run alongside TCP/IP  Conceived by Ronald Pose & Carlo Kopp in 1997

5. Omni-directional Antennas Advantages  Directional orientation is not required  May provide more connecting links  Installation is easy and quick  Ideal for ad-hoc networks with high mobility Drawbacks  Power radiates in all directions  Increases hidden and exposed terminal problems  Increases multiple access intereferences (MAI)  Increases collisions and packet loss  Degrades network performance  Easy to eavesdrop

6. Directional Antennas Drawbacks  Requires antenna direction alignment  May provide fewer links  Installation may be complicated  Network planning is more difficult Advantages  Power can be beam formed  Reduces hidden and exposed terminal problems  Reduces multiple access intereferences (MAI)  Reduces collisions and packet loss  Improves network performance  Eavesdropping is limited to the direction of communication  Ideal for ad-hoc networks with less mobility

7. Analytical Model (1/7) Basic of data transmission with directional antenna Basic of data transmission with omnidirectional antenna

8. Analytical Model (2/7) Data transmission with single channel & omnidirectional antenna TX interval 3  T

9. Analytical Model (3/7) Data transmission with multi-channel & omnidirectional antenna (1/2) TX interval 3  T

10. Analytical Model (4/7) Data transmission with multi-channel & omnidirectional antenna (2/2) TX interval 2  T

11. Analytical Model (5/7) Data transmission with directional antenna TX interval 1  T

12. Analytical Model (6/7) Summary

13. Simulation Setup  7 nodes are placed along a straight line  Each node has at most 2 neighbors  Schemes O, MO-2 and MD-2 are used  Channel allocation for MO-2 is similar to Analytical Model (4/7)  Single session for each pair  Number of hops varied between 1-6  Each session is offered a load of 400 kbps  Each UDP payload is 400 bytes long

14. Simulation Result 1  T 2  T 3  T

15. Analytical Model (7/7) Lets consider  Two sessions with AC_VO and AC_BK  Packet Tx interval of each session = 3xT More than one AC may result in virtual colission For multi-hop ad-hoc networks using 802.11e if there is a chance of real colission, there can be a circular dependecy between virtual colission and real colission Our model shows, Scheme MD-x has least chances of real colission So with multiple AC, MD-2 is expected to perform better than MO-2 & O

16. Simulation Result (1/3) Processing delay of each node + delays for virtual & real collisions Processing delay of each node + delay for virtual collision

17. Simulation Result (2/3) virtual + real collisions Only virtual collision

18. Simulation Result (3/3) virtual + real collisions Only virtual collision

19. Simulation Setup  77 nodes are placed on a 3000  3000 sq m flat terrain  Each node has at most 6 neighbors  Schemes O, MO-3 and MD-3 are used  Channel allocation for MO-3 was random  In MO-3, on average each channel connected 2 neighbors  In MD-3 each antenna was connected at most 1 neighbor  MD-3 reduced the degree of connectivity per node  4 sessions/pair of source & destination with different AC  Each session is offered a load of 400 kbps  Each UDP payload is 400 bytes long  New sessions were introduced every 20 ms

20. Simulation Result (3/3) AC = AC_VO Path length for O & MO-3 = 5 Avg path length for MD-3 = 8.5

21. Simulation Result (3/3) AC = AC_VO Path length for O & MO-3 = 5 Avg path length for MD-3 = 8.5

22. Simulation Result (3/3) AC = AC_VO Path length for O & MO-3 = 5 Avg path length for MD-3 = 8.5

23. Conclusions  If no route exists in configured directions, antennas may need to be redirected & it may be difficult with multiple fixed directional antennas  Multiple fixed directional antennas may be expensive to buy & install  A smart directional antenna can be an alternative solution at low cost  The performance results encourages us to build a SAHN specific MAC protocol that is capable of integrating smart directional antennas efficiently

24. Thank You ?