1. A MAC protocol for full exploitation of Directional Antennas in Ad-hoc Wireless Networks

2. Outline 1. INTRODUCTION 2. PRELIMINARIES 3.THE PROPOSED PROTOCOL
4. SIMULATIONS
5. Simulation Results
6. CONCLUSIONS

3. 1. INTRODUCTION Omnimode is over a large region,
But sometimes a small portion is intended to receive.
Directional antennas can solve this problem.
Omnidirectional antenna
Directional antenna

4. 1. INTRODUCTION Directional Antennas Advantages Disadvantages
Increase the signal energy.
Increase of the coverage area.
Increase of the channel capacity.
Disadvantages
Deafness
Determination of neighbors’ location.
Hidden terminal problem

5. 1. INTRODUCTION

6. 2. PRELIMINARIES
Directional Antennas

7. 3.THE PROPOSED PROTOCOL
Some principles principles govern the design of a MAC protocol.
Fully exploit the increase in coverage range.
Deal with deafness problem.
Identify the neighbors’ location and maintain this information.
Decreasing hidden terminal problem.

8. 3.THE PROPOSED PROTOCOL The problem of deafness Directional Antennas A
Can’t hear C

9. 3.THE PROPOSED PROTOCOL Circular Directional RTS
RTS and CTS are transmitted directional consecutively, in a circular way.

10. 3.THE PROPOSED PROTOCOL

11. 3.THE PROPOSED PROTOCOL Neighbors’ location
every node maintains a table, called Location Table

12. 3.THE PROPOSED PROTOCOL

13. 3.THE PROPOSED PROTOCOL
Directional transmissions in ad-hoc networks is the increase of the hidden terminal problem.

14. 3.THE PROPOSED PROTOCOL CTS !!! packet collision RTS Idle
Ready to send a fram
Hear Nothing…

15. 3.THE PROPOSED PROTOCOL Use of D-NAV
D-NAV(Directional Network Allocation Vector) uses a table that keeps track of the directions and the corresponding durations.

16. 3.THE PROPOSED PROTOCOL

17. 3.THE PROPOSED PROTOCOL

18. 3.THE PROPOSED PROTOCOL Some protocol details
These are the necessary changes in some time periods.
A is the transmitter node and B is the receiver.

19. 3.THE PROPOSED PROTOCOL CTS is transmitted after the circular RTS
T = k * RTS transmission time + SIFS, where k = M - A’s beam number. A 3 4
Receive RTS and after SIFS,CTS ready to send B 2 1
RTS
CTS 3 4 2 1

20. 3.THE PROPOSED PROTOCOL
An idle node hears the channel for longer time than DIFS before transmission
Defined an idle node to hear the medium for M*RTS transmission time before its transmission.

21. 3.THE PROPOSED PROTOCOL
Duration period = RTS trans time +SIFS + CTS trans. Time +SIFS +Data trans time +SIFS +Ack trans time.

22. 4. SIMULATIONS Simulation Model
Channel is error free and the propagation delay is zero.
Destination of each packet is chosen randomly
The packet length is 1024 bytes.
Runs for 200 seconds with a warm up period of 50 seconds.
Antenna arrays of 1, 4 and 8 elements.
Location Table of each station is empty

23. 5. Simulation Results(3 nodes)

24. 5. Simulation Results(3 nodes)

25. 5. Simulation Results(3 nodes)
In D-MAC, node C can not be aware for the communication between A and B.
RTS again and again. As it does not receive a respond from A.
Back off again and again resulting in large periods.

26. 5. Simulation Results(7 nodes)

27. 5. Simulation Results(7 nodes)

28. 5. Simulation Results(15 stations)

29. 5. Simulation Results(9 nodes)10

30. 5. Simulation Results(9 nodes)11 10

31. 6. CONCLUSIONS
We propose a MAC protocol that is a strong decrease in the hidden terminal problem.
The previous features result in an efficient, integrated scheme that can be implemented easily.