1. On Reservation-Based MAC Protocol for IEEE 802.11 Wireless Ad Hoc Networks With Directional Antenna Author : Jin-Jia Chang, Student Member, IEEE Wanjiun Liao, Fellow, IEEE Jiunn-Ru Lai, Member, IEEE Speaker : Huei-Rung Tsai IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY 2011

2. Outline Introduction Minor-Lobe Problem in Directional Antennas Goals RDMAC Protocol Performance Evaluation Conclusions

3. Introduction The antenna of wireless network device – Omnidirectional antennas – Directional antennas The advantage of using directional antennas – Reduce the interference problem – Reduce energy consumption – Increase the network throughput (spatial reuse)

4. R R Introduction The communication condition of directional antennas – Data-link layer – Physical layer T T R R T T Data-link Layer Physical Layer

5. Introduction In the IEEE 802.11 – Collision avoidance Carrier sense multiple access with collision avoidance (CSMA/CA) – Hidden terminal problem RTS/CTS exchange before each data transmission – For omnidirectional antenna system In directional antenna system – New problems of location-dependent carrier sensing Directional hidden terminal problem Deafness problem A A B B DATA RTS C

6. Introduction Several protocols have been proposed to solve the location dependent carrier-sensing problem [3] T. Korakis, G. Jakllari, and L. Tassiulas, “A MAC protocol for full exploitation of directional antennas in ad hoc wireless networks,” in Proc. ACM MobiHoc, 2003, pp. 98–107. Circular directional RTS/CTS [4] H. Gossain, C. Cordeiro, and D. P. Agrawal, “MDA: An efficient directional MAC scheme for wireless ad hoc networks,” in Proc. IEEE Globecom, 2005, p. 3637. Diametrically opposite directional RTS/CTS Criticism – Every node known the location information of its neighbor in a priori – Do not take into account the effect of the minor-lobe problem

7. Minor-Lobe Problem in Directional Antennas Main-lobe Minor-lobes Back lobe Side lobe

8. Interference From Minor Lobes Minor-Lobe Problem in Directional Antennas T T R R N N

9. Interference From Minor Lobes – When transmitter’s main lobe overlaps with receiver’s minor lobe, the node pair is regarded as within the interference Minor-Lobe Problem in Directional Antennas R R Interference T T

10. Interference From Minor Lobes Minor-Lobe Problem in Directional Antennas N N T T R R T T R R N N Interference

11. Minor-Lobe Problem in Directional Antennas Mitigating Interference From Minor Lobes – Virtual Carrier Sensing (VCS) – Physical Carrier Sensing (PCS)

12. VCS in Practical Directional Antenna Systems – Requires successfully decoding frames – VCS cannot identify the existence of minor lobes Minor-Lobe Problem in Directional Antennas T T R R Safe !! N N

13. Minor-Lobe Problem in Directional Antennas PCS in Practical Directional Antenna Systems – Energy-detection-based mechanism – When the signal strength exceeds a threshold, then we consider that existence of an ongoing transmission PCS is faster and more sensitivity than VCS, but when a node detects no signal, it doesn’t mean that it is real safe

14. Goals Propose a MAC protocol called reservation-based directional medium access control (RDMAC), solved these problems – Location-dependent carrier sensing – Minor-lobe interference RDMAC can operate without – Prior information on neighboring nodes’ location – Centralized synchronization mechanism

15. Assumption The network environment exist two kinds of node – Omnidirectional antenna nodes – RDMAC nodes Each RDMAC node can display two kinds of transmission – Omnidirectional transmission (ORTS/OCTS) – Directional transmission (DRTS/DCTS/DDATA/DACK) Each RDMAC node maintains three table – Network access vector (NAV) table – Directional network access vector (DNAV) table – Neighbor table

16. RDMAC protocol E E D D C C Omnidirectional antenna nodes RDMAC node F F B B ORTS: Notify receiver node and neighboring node DRTS: Let neighboring nodes test the antenna gain threshold OCTS: Response transmitter node Notify the direction of the antenna beam to transmitter and neighboring node DRTS DCTS ORTSOCTS A A Contention Period

17. RDMAC protocol E E D D C C Omnidirectional antenna nodes RDMAC node F F B B A A DRTS DCTS ORTS OCTS

18. RDMAC protocol E E D D C C Omnidirectional antenna nodes RDMAC node F F B B A A Transmission Period DDATA

19. RDMAC protocol E E D D C C Omnidirectional antenna nodes RDMAC node F F B B A A Transmission Period DACK

20. RDMAC protocol A Contention Period(t CP ) Transmission Period(t TP ) B C D E F OR OC NAV DR DC NAV OR OC DR DC Back off DDATA DAC K time

21. RDMAC protocol A Contention Period(t CP ) Transmission Period(t TP ) B C D E F Free Period (t FP ) NAV OR OC DATA ACK NAV OR OC time

22. Performance Evaluation Evaluate the performance result through ns-2 simulations Static nodes50 Area2000 × 2000 m 2 Frame size1460 Byte Physical data rate54 Mb/s Transmission range250 m Sidelobe beamwidthmain beamwidth × 2 Backlobe beamwidthmain beamwidth × 1 Interference rangemain beamwidth × 2 DIFS28 μs Contention period500 μs

23. Performance Evaluation

28. Conclusions This paper proposed a new MAC mechanism called RDMAC for IEEE 802.11 DCF-based multihop wireless networks with directional antennas – Reduce the location-dependent carrier-sensing – Reduce the interference problems caused by minor lobes – Eliminates the requirements of a centralized synchronization mechanism and prior location information on neighboring nodes

30. Performance Evaluation