1 / 108

Utilizing Beamforming Antennas for Wireless Multi-hop Networks

Utilizing Beamforming Antennas for Wireless Multi-hop Networks. Romit Roy Choudhury. Internet. Applications. Several Challenges, Protocols. Internet. Omnidirectional Antennas. RTS = Request To Send. CTS = Clear To Send. IEEE 802.11 with Omni Antenna. M. Y. S. RTS. D. CTS. X. K.

myra
Download Presentation

Utilizing Beamforming Antennas for Wireless Multi-hop Networks

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Utilizing Beamforming Antennas for Wireless Multi-hop Networks Romit Roy Choudhury

  2. Internet Applications Several Challenges, Protocols

  3. Internet Omnidirectional Antennas

  4. RTS = Request To Send CTS = Clear To Send IEEE 802.11 with Omni Antenna M Y S RTS D CTS X K

  5. IEEE 802.11 with Omni Antenna silenced M Y silenced S Data D ACK silenced X K silenced

  6. D G B F C Y A E silenced silenced silenced silenced silenced silenced silenced silenced IEEE 802.11 with Omni Antenna silenced M `` Interference management `` A crucial challenge for dense multihop networks S Data D ACK silenced X K silenced

  7. Managing Interference • Several approaches • Dividing network into different channels • Power control • Rate Control … New Approach … Exploiting antenna capabilities to improve the performance of wireless multihop networks

  8. B F C A Y D G E silenced silenced silenced silenced silenced silenced silenced silenced From Omni Antennas … silenced M S D silenced X K silenced

  9. Y D E A C F B G To Beamforming Antennas M S D X K

  10. Y D E A C F B G To Beamforming Antennas M S D X K

  11. Today • Antenna Systems  A quick look • New challenges with beamforming antennas • Design of MAC and Routing protocols • MMAC, ToneDMAC, CaDMAC • DDSR, CaRP • Cross-Layer protocols – Anycasting • Improved understanding of theoretical capacity • Experiment with prototype testbed

  12. Antenna Systems • Signal Processing and Antenna Design research • Several existing antenna systems • Switched Beam Antennas • Steerable Antennas • Reconfigurable Antennas, etc. • Many becoming commercially available For example …

  13. Electronically Steerable Antenna [ATR Japan] • Higher frequency, Smaller size, Lower cost • Capable ofOmnidirectional modeandDirectional mode

  14. Switched and Array Antennas • On poletop or vehicles • Antennas bigger • No power constraint

  15. Antenna Abstraction • 3 Possible antenna modes • Omnidirectional mode • Single Beam mode • Multi-Beam mode • Higher Layer protocols select • Antenna Mode • Direction of Beam

  16. A Antenna Beam • Energy radiated toward desired direction Main Lobe (High gain) A Sidelobes (low gain) Pictorial Model

  17. Directional Reception • Directional reception = Spatial filtering • Interference along straight line joining interferer and receiver C C Signal Signal A B A B Interference D Interference D No Collision at A Collision at A

  18. Will attaching such antennas at the radio layer yield most of the benefits ? Or Is there need for higher layer protocol support ?

  19. We design a simple baseline MAC protocol (a directional version of 802.11) We call this protocol DMAC and investigate its behavior through simulation

  20. DMAC Example • Remain omni while idle • Nodes cannot predict who will trasmit to it Y S D X

  21. RTS DMAC Example • Assume S knows direction of D Y S D X

  22. RTS CTS RTS DATA/ACK X silenced … but only toward direction of D DMAC Example Y S D X

  23. Intuitively Performance benefits appear obvious

  24. However … Throughput (Kbps) Sending Rate (Kbps)

  25. Clearly, attaching sophisticated antenna hardware is not sufficient Simulation traces revealed various new challenges Motivates higher layer protocol design

  26. Antenna Systems  A quick look • New challenges with beamforming antennas • Design of MAC and Routing protocols • MMAC, ToneDMAC, CaDMAC • DDSR, CaRP • Cross-Layer protocols – Anycasting • Improved understanding of theoretical capacity • Experiment with prototype testbed

  27. New Challenges [Mobicom 02] Self Interference with Directional MAC

  28. Unutilized Range • Longer range causes interference downstream • Offsets benefits • Network layer needs to utilize the long range • Or, MAC protocol needs to reduce transmit power Data A D B C route

  29. Utilize Range – MMAC • Learn far away neighbor via ngbr discovery • Approaches proposed in literature • Send RTS packets over multiple DO links • Request Rx to beamform back toward Tx • Tx sends Data over DD link, followed by DD Ack

  30. New Challenges II … New Hidden Terminal Problems with Directional MAC

  31. New Hidden Terminal Problem • Due to gain asymmetry • Node A may not receive CTS from C • i.e., A might be out of DO-range from C CTS RTS Data B A C

  32. New Hidden Terminal Problem • Due to gain asymmetry • Node A later intends to transmit to node B • A cannot carrier-sense B’s transmission to C CTS RTS Data Carrier Sense B A C

  33. New Hidden Terminal Problem • Due to gain asymmetry • Node A may initiate RTS meant for B • A can interfere at C causing collision Collision Data RTS B A C

  34. New Challenges II … New Hidden Terminal Problems with Directional MAC

  35. New Hidden Terminal Problem II • While node pairs communicate • X misses D’s CTS to S  No DNAV toward D Y S Data Data D X

  36. New Hidden Terminal Problem II • While node pairs communicate • X misses D’s CTS to S  No DNAV toward D • X may later initiate RTS toward D, causing collision Collision Y S Data D RTS X

  37. New Challenges III … Deafness with Directional MAC

  38. Deafness • Node N initiates communication to S • S does not respond as S is beamformed toward D • N cannot classify cause of failure • Can be collision or deafness M Data S D RTS N

  39. Channel Underutilized • Collision: N must attempt less often • Deafness: N should attempt more often • Misclassification incurs penalty (similar to TCP) M Data S D RTS N Deafness not a problem with omnidirectional antennas

  40. Deafness and “Deadlock” • Directional sensing and backoff ... • Causes S to always stay beamformed to D • X keeps retransmitting to S without success • Similarly Z to X  a “deadlock” Z DATA RTS S D RTS X

  41. New Challenges IV … MAC-Layer Capture The bottleneck to spatial reuse

  42. Capture • Typically, idle nodes remain in omni mode • When signal arrives, nodes get engaged in receiving the packet • Received packet passed to MAC • If packet not meant for that node, it is dropped Wastage because the receiver could accomplish useful communication instead of receiving the unproductive packet

  43. C C D D A B A B B and D beamform to receive arriving signal Capture Example Both B and D are omni when signal arrives from A

  44. Outline / Contribution • Antenna Systems  A closer look • New challenges with beamforming antennas • Design of MAC and Routing protocols • MMAC, ToneDMAC, CaDMAC • DDSR, CaRP • Cross-Layer protocols – Anycasting • Improved understanding of theoretical capacity • Experiment with prototype testbed

  45. C C D D A B A B Impact of Capture Beamforming for transmission and reception only is not sufficient Antenna control necessary during idle state also

  46. MAC Layer Solution • Capture-Aware MAC (CaDMAC) • D monitors all incident traffic • Identifies unproductive traffic • Beams that receive only unproductive packets are turned off • However, turning beams off can prevent useful communication in future C D A B

  47. CaDMAC Time Cycles • CaDMAC turns off beams periodically • Time divided into cycles • Each cycle consists of • Monitoring window + 2.Filtering window cycle 1 2 1 2 1 2 time All beams remain ON, monitors unproductive beams Node turns OFF unproductive beams while it is idle. Can avoid capture

  48. C D A B CaDMAC Communication C • Transmission / Reception uses only necessary single beam • When node becomes idle, it switches back to appropriate beam pattern • Depending upon current time window D A B

  49. Spatial Reuse in CaDMAC • During Monitoring window, idle nodes are omni C D E A B F

  50. Spatial Reuse in CaDMAC • At the end of Monitoring window CaDMAC identifies unproductive links C D E A B F

More Related