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Directional Antennas in Mobile Ad Hoc Networks:

Directional Antennas in Mobile Ad Hoc Networks:. MAC and Routing Issues Prepared by: Yi Zhang. Why Directional Antennas?. Omni-directional Antennas. Silenced Node. B. D. S. C. A. Directional Antennas. Not possible using Omni. B. D. S. C. A.

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Directional Antennas in Mobile Ad Hoc Networks:

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  1. Directional Antennas in Mobile Ad Hoc Networks: MAC and Routing Issues Prepared by: Yi Zhang

  2. Why Directional Antennas?

  3. Omni-directional Antennas Silenced Node B D S C A

  4. Directional Antennas Not possible using Omni B D S C A

  5. Classification of directional MAC protocols

  6. Pure-RTS/CTS protocols • Directional MAC(DMAC): Y.B.Ko et al., Medium Access Control Protocols Using Directional Antennas in Ad Hoc Networks (Infocom2000) • A.Nasipuri et al., A MAC Protocol for Mobile Ad Hoc Networks Using Directional Antennas (WCNC 2000) • Directional Virtual Carrier Sensing (DVCS): M.Takai et al., Directional Virtual Carrier Sensing for Directional Antennas in Mobile Ad Hoc Networks (MobiHoc2002) • Multihop Medium Acces Control (MMAC): R.R.Choudhury et al., Using Directional Antennas for Medium Access Control in Ad Hoc Networks (MobiCom2002) • Circular-DMAC: T.Korakis et al., A MAC protocol for full exploitation of Directional Antennas in Ad-hoc Wireless Networks (MobiHoc2003)

  7. Tone-based directional MAC protocols • Dual Busy Tone Multiple Access with Directional Antennas (DBTMA/DA): C. S. Z. Huang et al., A busy-tone based directional mac protocol for ad hoc networks (Milcom 2002) • Tone-based directional MAC (ToneDMAC): Choudhury et al., Deafness: a mac problem in ad hoc networks when using directional antennas (ICNP 2004) • Smart-802.11b: H.Singh et al., Smart-802.11b MAC protocol for use with smart antennas (ICC 2004) • Smart-Aloha: H.Singh et al., Smart-802.11b MAC protocol for use with smart antennas (ICC 2004) • DOA-MAC: H.Singh et al., A MAC protocol based on adaptive beamforming for ad hoc networks (PIMRC 2003) • Tone-based 802.11b: H.Singh et al., Tone based MAC protocol for use with adaptive array antennas (WCNC 2004)

  8. Other directional MAC protocols using additional control packets: • Lal et al., A novel MAC layer protocol for space division multiple access in wireless ad hoc networks (IC3N 2002) • Ready to Receive (RTR) Packet

  9. Scheduling MAC protocols for directional antennas • Receiver-Oriented Multiple Access (ROMA) protocol: L. Bao et al., Transmission scheduling in ad hoc networks with directional antennas (MobiCom 2002) • DTRA: Z. Zhang et al., DTRA: Directional transmission and reception algorithms in WLANS with directional antennas for qos support (ICC 2005, IEEE Network 2005[J]) • 2P: B. Raman et al., Design and evaluation of a new MAC protocol for long-distance 802.11 mesh networks (MobiCom2005)

  10. But what if we have no location information?

  11. Directional Virtual Carrier Sensing (R. Bagrodia et. Al) • Main Advantage: No additional hardware is required to get location information. • Each node estimates the position of its neighbors by the “Angle of Arrival” information, i.e. by noting the antenna which received the highest signal. • Operation can be summarized in 3 main processes:

  12. 1. AOA(Angle of Arrival) Caching • Each node caches an estimated angle of arrival from neighboring nodes even if the signal is not sent to it. • When that node has data to send, it searches its cache for an angle of arrival information, if the AOA is found, the node will send a directional RTS, otherwise, the RTS is send omni-directionally.

  13. 1. AOA Caching (cont’d) • The node updates its AOA information each time it receives a newer signal from the same neighbor. • It also invalidates the cache in case if it fails to get the CTS after 4 directional RTS transmissions. • The CTS is sent directionally.

  14. 2. Beam Locking and Unlocking • When a node gets an RTS, it locks its beam pattern towards the source to transmit the CTS. • The transmitting node only locks its pattern once it received the CTS. • Beam Patterns are formed at both the transmitter and the receiver to maximize signal power.

  15. (2) CTS (3) DATA (4) ACK (1)RTS Example • Node A has data to transmit to node B and finds an AOA field for B in its cache. • The AOA field is currently a little outdated since B has moved since the last update. A B B

  16. (2) CTS (3) DATA (4) ACK (1)RTS Example (cont’d) • Node B senses the RTS from node A, and then adapts its antenna pattern to maximize the gain for the signal coming from node A. • Node A locks its antenna pattern after the reception of the CTS from B. A B B

  17. 3. DNAV Setting • DNAV (Directional Network Allocation Vector) instead of NAV used in the classical 802.11 • DNAV also contains direction information of neighboring nodes. It is updated each time the physical layer provides new information about the location of a neighboring node.

  18. 3. DNAV Setting (cont’d) • DNAV reserves the channel only in specified range of directions. • The algorithm selectively excludes directions included in DNAV for transmission in which the node may cause interference with other transmissions in progress. • Meanwhile it allows transmitting frames along other free directions.

  19. 3. DNAV Setting

  20. Performance PDR and throughput of the network in the no mobility scenario (without the physical CS in the IEEE 802.11). PDR and throughput of the network in the mobility scenario (without the physical CS in the IEEE 802.11).

  21. Performance Cntd. PDRs with and without the physical CS

  22. Channel frequency 2.4 [GHz] Signal reception BER based(with DBPSK modulation) Data rate 2 [Mbps] Noise figure 10.0 [dB] TX power 15.0 [dBm] TX power (directional) 0.0 [dBm] RX threshold (RXT) -81.0 [dBm] CS threshold (CST) -91.0 [dBm] AOA cache expiration time 2 [s] Performance Cntd. Set of parameters used in the simulation

  23. Problems with Bagrodia et al. • Basically this scheme suffers from the same problem as Vaidya’s scheme. This is a result of the directional RTS,i.e. a node can not know that a neighboring node is busy if that node sent a directional RTS to another neighbor.

  24. Routing with Directional Antennas

  25. On Demand Routing with Directional Antennas (Nasipuri et al) • Motivation: Trying to reduce the routing overhead associated with the flooding of Route Request Packets associated with on demand protocols such as AODV and DSR. • Directional antennas are exploited to limit the flooding to a specific region of the network thus reducing routing overhead.

  26. Underlying MAC Protocol • There is no use in modifying a routing algorithm for directional antennas if the underlying MAC protocol itself was not modified. • The MAC protocol used is very similar to IEEE 802.11.The RTS and CTS are sent omni-directionally, but data is sent directionally. • 2 Routing Protocols were proposed:

  27. Routing Protocol 1 • If a node S has a packet to send to node D, it transmits a query packet on the directional antenna which it had been using earlier to communicate with D. • Assuming that D has not moved too far since the last communication instant, the flooding is restricted to the region containing the last known location to D.

  28. Routing Protocol 1 (cont’d) • If D has moved out of range, and S did NOT receive a Route Reply from D after a suitable timeout period, then S will generate a Route Request on all antennas (Omni- Directional), this time flooding the whole network. • Result: a decrease in Routing Overhead at the cost of increased latency.

  29. Routing Protocol 1 (cont’d)

  30. Drawbacks of Protocol 1 • The angular span of the antenna in S that was used to transmit data packets on the first hop of the last valid route to D may not necessarily include D. • This happens if the first intermediate node on the path to D and the node D do not lie within the angular span of the same directional antenna of S. • Solution: Routing Protocol 2 …

  31. Routing Protocol 2 • At the end of every successful route discovery, the source records the directions of the antennas to be used on every hop of the newly discovered route. • The information is made available to the source if each node on the route adds to the header of the Route Reply packet, the antenna identifier which it used to receive the packet while forwarding it back to the source.

  32. Routing Protocol 2 (cont’d) • This allows the source to get a rough estimate about the angular location of the destination by simply counting the number of times each antenna was used on the route that has been found.

  33. Routing Protocol 2 (cont’d)

  34. Performance Tradeoffs • If directional route search was successful from the first attempt, then both protocols have the advantage of remarkably reducing routing overhead. • However, as node mobility increases, the chances of finding a route from a directional search drastically decrease.

  35. Performance Tradeoffs (cont’d) • Another disadvantage is that a directional route request may not always find the shortest route. • This happens if the destination is not included in the search zone but an intermediate node which received the request has a route to the destination and positively responds.

  36. Finally … Comparisons and conclusions …

  37. RTS CTS Data Ack. 802.11 Omni Omni Omni Omni Nasipuri Omni Omni Directional Directional Vaidya 1 Directional Omni Directional Directional Vaidya 2 Dir./Omni Omni Directional Directional Bagrodia Dir/Omni Directional Directional Directional Performance Comparison

  38. Conclusion • We have seen aMAC protocol and a routing protocol that take advantage of the spatial reuse capabilities offered by directional antennas. • All of the discussed protocols deliver optimum performance under no mobility conditions. Their performance degrade drastically as mobility increases

  39. Conclusions (cont’d) • The use of directional antenna in ad hoc and large scalable networks is still unclear due to technical and physical difficulties of implementing directional antennas on each node. • Those protocols are designed to increase network throughput at the cost of some increased design complexity … • … Which brings us back to the popular saying …

  40. There is no such thing as a free lunch!

  41. Based on the work of: • N. Vaidya, Y.b. Ko, and V. Shankarkumar, Texas A&M University; “Medium Access Control Protocols for Directional Antennas in Ad Hoc Networks” • A. Nasipuri et. Al , University of Texas, San Antonio; “A Medium Access Protocol for Ad hoc Networks with Directional Antennas” • A. Nasipuri et. Al, University of Texas, San Antonio; “On Demand Routing Using Directional Antennas in Mobile Ad Hoc Networks” • R. Bagrodia, J. Martin, A. Ren, M. Takai, Computer Science Department, UCLA; “Directional Virtual Carrier Sensing for Directional Antennas in Mobile Ad Hoc Networks”

  42. THANK YOU!

  43. Questions???

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