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Spread Spectrum MAC Protocol with Dynamic Rate and Collision Avoidance for Mobile Ad Hoc Network

Spread Spectrum MAC Protocol with Dynamic Rate and Collision Avoidance for Mobile Ad Hoc Network. Zaihan Jian, and Mengchu Zhou Department of Electrical and Computer Engineering New Jersey Institute of Technology IEEE Transaction on Vehicular Technology, Vol. 56, No. 5, September 2007. Outline.

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Spread Spectrum MAC Protocol with Dynamic Rate and Collision Avoidance for Mobile Ad Hoc Network

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  1. Spread Spectrum MAC Protocol with Dynamic Rate and Collision Avoidance for Mobile Ad Hoc Network Zaihan Jian, and Mengchu ZhouDepartment of Electrical and Computer EngineeringNew Jersey Institute of Technology IEEE Transaction on Vehicular Technology,Vol. 56, No. 5, September 2007

  2. Outline • Introduction • DRCA protocol • Throughput analysis • Evaluation results • Conclusion

  3. Introduction • Spread spectrum (SS) has been used as one of the basic wireless access technologies • 2G, IS-95, CDMA2000, and WCDMA

  4. Introduction • Advantage of SS • Concurrent transmission in one channel without using TDMA/FDMA • SS can provide at most 1.5 times capacity compared with TDMA and 4.6 times compared with FDMA in cellular system • Is feasible to switch from signal to signal for a transmitter or receiver

  5. Introduction • MANETs become extremely useful in scenarios where fixed infrastructure is infeasible or expensive to build • Most proposed MAC protocols for MANETs are not SS based • IEEE 802.11 use only one spread code

  6. Research issues of code assignment • To assign transmission codes to network terminals to avoid packet collision as much as possible • 4 kinds of code assignment protocols • Common-code • Receiver-based • Transmitter-based • Hybrid

  7. Collision avoidance in SS • Collision can be classified into two categories • Primary collision: signals with the same spread code being received at the same receiver • Secondary collision: collision between two or more transmission that use different code • The paper only focuses on primary collision

  8. Bandwidth waste in static code allocation case Usable bandwidth = real bandwidth / spreading factor

  9. Spreading factor • Under the white Gaussian noise channel • Under the Rayleight fading channel

  10. Drawbacks of static code assignment • High peak rate for a terminal can be achieved in such contention-based MAC protocols • In static code assignment SS MAC protocol, it is hard to predict which terminal need more bandwidth • Hard to dynamically assign code

  11. Control message format

  12. Operation of DRCA Broadcast the selective code, for code reuse Broadcast the selective code, for avoiding collision Random backoff,no carrier sensing Code for CTS Code for RTS CR: code for RTS and Short Message (SM)CC: code for CTS and ACK Ci: code for data transmission

  13. Throughput analysis • N terminals in the system • Terminals are directly connected with each other • No mobility • Slot time t is chosen to accomplish RTS-CTS • An idle terminal sends out an RTS with probability p

  14. Throughput analysis • A terminal generates a packet with spreading factor Ke ,Kmin ≦ Ke ≦ Kmax • Channel transmission bit rate: m /Ke • Packet transmission time: L*Ke /m • Slots of a packet: L’= L *Ke / (m*t) • Packet length is geometrically distributed with probability q

  15. Parameter • Transmission probability from state a to state b :Pab • a/b: a/b transmission pairs is busy • a and b range from 0 to N/2 • i: number of pairs become idle from busy at the beginning of slot f • N’ = N - 2a + 2i • Number of terminals that are available to communicate

  16. Parameter • d: number of successful RTS-CST dialogs in a slot • 0 and 1 • d + a – i = b • c: number of RTS transmission at the beginning of a slot • d’ = c – d • Number of failed RTS transmission

  17. State transition in Markov chain • H: event of a transition from state a to state b • A: event of exactly one transmission occurs and is addressed to an idle terminal • B: event of one transmission occurs and is addressed to a busy terminal • C: event of zero or more than one transmission occur • Bi: event that i pairs become idle from busy

  18. State transition in Markov chain

  19. State transition in Markov chain • Simplified form • Steady state distribution Sa is given by

  20. Throughput of DRCA and static allocation

  21. Example value of Sr Sr: steady probability of r communication pairs

  22. Simulation parameters in multihop environment

  23. Throughput: 24 pairs

  24. Throughput: 9 pairs

  25. Throughput difference

  26. Conclusion • The paper proposes an SS MAC protocol with dynamic rate and collision avoidance call DRCA • Both theoretical and simulation results show that DRCA outperforms static code allocation mechanisms

  27. Thank you!!

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