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Receiver-Initiated Channel Hopping (RICH)

Receiver-Initiated Channel Hopping (RICH). Makis Tzamaloukas (jamal@cse.ucsc.edu) Computer and Communications Research Group (CCRG) http://www.cse.ucsc.edu/research/ccrg. Computer Engineering Department Jack Baskin School of Engineering University of California Santa Cruz, CA 95064.

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Receiver-Initiated Channel Hopping (RICH)

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  1. Receiver-Initiated Channel Hopping (RICH) Makis Tzamaloukas (jamal@cse.ucsc.edu)Computer and Communications Research Group (CCRG)http://www.cse.ucsc.edu/research/ccrg Computer Engineering DepartmentJack Baskin School of EngineeringUniversity of CaliforniaSanta Cruz, CA 95064

  2. Presentation Outline • Introduction • Physical Layer • Motivation • Polling Issues • RICH • RICH-SP • RICH-DP • Throughput Analysis • Delay Analysis • Simulations • Conclusions A. E. Tzamaloukas

  3. Physical Layer - Unlicensed RF • FCC regulations require the use of frequency hopping (FH) or direct sequence (DS) spread spectrum modulation to operate in an ISM band • Multiple users can share the available bandwidth at the same time at a minimal increase of complexity and cost A. E. Tzamaloukas

  4. Physical Layer - FHSS • Frequency Hopping Spread Spectrum (FHSS) On the right, two pairs of nodes exchange DATA packets by following a unique hopping pattern In the USA the: 915 MHz band has 52 FH channels 2.4 GHz band has 79 FH channels 5.8 GHz band has 125 FH channels A. E. Tzamaloukas

  5. Physical Layer - FHSS • Hopping sequence: The pattern with which nodes use the channels • Advantages: robustness against multi-path propagation, minimize hidden node terminal problems, increased security, not prone to fading, capable to capture a packet even when multiple packets overlap • Most commercially available ISM radios are FH A. E. Tzamaloukas

  6. Motivation • The receiver of a data packet is the point of interest • Recast the collision avoidance dialogues so that the receiver, sender or both can have control of the dialogue • Provide correct floor acquisition without carrier sensing and code assignment • Be applicable to multi-channel frequency-hopping or direct-sequence spread-spectrum radios A. E. Tzamaloukas

  7. Polling Issues • When to poll: whether or not the polling rate is independent of the data rate at polling nodes • independent polling • data-driven polling • To whom: whether the poll is sent to a particular neighbor or to all neighbors; for dense networks a schedule may have to be provided to the poll recipients • How: whether the polling packet asks for permission to transmit as well A. E. Tzamaloukas

  8. RICH Characteristics • Dwell time should be long enough to transmit a pair of MAC addresses, a CRC and framing bits • Use synchronous frequency hopping to ensure that all radios hop to different frequency hops at the same time • Nodes do not need carrier sensing or code assignment • Commercially available radios can be used A. E. Tzamaloukas

  9. RTR DATA RTR CTS DATA RTR silence RTR RTR backoff RICH-SP All the nodes follow a common channel-hopping sequence. If a node receives an RTR then it sends its data to the polling node over the same channel hop; all the other nodes hop to the next channel hop. time t1 t2 t3 t4 t5 t6 hop h1 h2 h3 h4 A. E. Tzamaloukas

  10. RTR DATA DATA RTR CTS DATA RTR silence RTR RTR backoff RICH-DP • The key difference from RICH-SP is that now an RTR is an invitation to receive and transmit; therefore, two data packets can be exchanged in the same busy period time t1 t2 t3 t4 t5 t6 t6 hop h1 h2 h3 h4 A. E. Tzamaloukas

  11. Throughput Analysis Model • ad-hoc network of N nodes • multiple channels, error-free • the size of an RTR and CTS is less than one slot; the size for a data packet is derived from a geometric pdf • the turn-around time is considered to be part of the duration of control and data packet • a polled node receiving an RTR always has a data packet to send • the probability that the packet is addressed to the polling node is 1/N • Analysis is based on a model first introduced by Sousa and Silvester [Trans. On Communications - March 1988] A. E. Tzamaloukas

  12. Fixed packet length Fixed number of nodes --- MACA-CT --- MACA-CT --- RICH-SP --- RICH-SP Throughput analysis results • Throughput vs. probability of transmission. Results for RICH-SP are compared against MACA-CT [Joa-Ng and Lu - INFOCOM 1999] A. E. Tzamaloukas

  13. Throughput analysis results • Throughput vs. probability of transmission. The packet length is fixed equal to 10 hops and the number of nodes in the network is a parameter. Results for RICH-DP are compared against RICH-SP. A. E. Tzamaloukas

  14. Delay analysis results Normalized delay Actual delay A. E. Tzamaloukas

  15. Network Topologies Base N1 N1 N1 N2 (b) Base (a) N1 N1 (c) B2 B1 A. E. Tzamaloukas

  16. Simulated Radio Model • Radio features • 2.4GHz FHSS, no capture, no power control • 80 channels, 1Mbps each • 120us dwell time • half-duplex operation • RICH MAC protocol • omni-directional antenna A. E. Tzamaloukas

  17. Simulation Results A. E. Tzamaloukas

  18. Simulation Results aggregate data rate < available bandwidth A. E. Tzamaloukas

  19. Simulation Results aggregate data rate > available bandwidth A. E. Tzamaloukas

  20. Simulation Results Comparison A. E. Tzamaloukas

  21. Conclusions • By reversing the collision avoidance handshake we improved the performance of MAC protocols for ad-hoc networks • RICH protocols achieve correct floor acquisition without carrier sensing or code assignment • RICH outperforms any other multi-channel collision avoidance MAC protocol to date in terms of throughput and delay • Extensive simulations verified our analytical results A. E. Tzamaloukas

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