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Distributed Coordinated Spectrum Sharing MAC Protocol for Cognitive Radio

Distributed Coordinated Spectrum Sharing MAC Protocol for Cognitive Radio. Advisor ： Wei-Yeh Chen Student ：楊　 于　 世 Reference

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Distributed Coordinated Spectrum Sharing MAC Protocol for Cognitive Radio

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  1. Distributed Coordinated Spectrum Sharing MAC Protocol for Cognitive Radio Advisor ：Wei-Yeh Chen Student：楊　 于　 世 • Reference • Hao Nan; Tae-In Hyon; Sang-Jo Yoo;, “Distributed Coordinated Spectrum Sharing MAC Protocol for Cognitive Radio ,” in IrelandDublinDySPAN 2007. 2nd IEEE International symposium, pp. 240 - 249 , April 2007.

  2. Outline • Introduction • Background and hidden incumbent device problem • Avoid method • Simulation • Conclusion

  3. Introduction • By adding the available channel list(表;列舉) into the RTS and CTS, the communication pair can know which data sub channels are available. • We proposed an ENNI (exchanging of neighbor nodes information) mechanism to deal with the hidden incumbent(現在的) device problem.

  4. Hidden incumbent device problem Hidden node problem A B C D Collision A B C D Data transmission Expose node problem Overhearing Hidden node and expose(暴露) node problem in single channel environment

  5. Avoid method • It has to send the RTS which includes the time duration(持續) that other node should defer to the receiver. • Upon receiving the RTS, it sends the CTS to notify(通知) the neighbor node around to defer(延遲) their transmission as well in order to avoid the possible collision. • The structure that records(紀錄) the time duration called NAV (network allocation vector), which is included in both of the RTS and CTS.

  6. A B C D Time RTS Channel 3 CTS(2) RTS Channel 2 CTS(2) Channel 2 Collision Multi-channel hidden terminal problem

  7. Avoid method(1) • MMAC (multi channel MAC) protocol to handle the multi channel hidden terminal problem. • In MMAC, periodically(定期地) transmitted beacons divide(劃分) time into beacon intervals(間格). • It uses the ATIM (ad hoc traffic indication messages) window to negotiate(通過) the channel during each beacon interval, and use the ATIM-RES (ATIM reservation(保留)) and ATIM-ACK to notify the nodes in the vicinity of sender and receiver.

  8. Transmission initiation Channel sensing Add the available channel list into the RTS N Have the same channel? Compare the ACL of source with overhearing node’s own one Y Choose one among the same channels Set the NAV of the data channel and send it back to the source by CTS Both sender and receiver switch to the agreed channel to begin the transmission end General channel selection procedure of multiple channel protocols. ACL (available channel list)

  9. incumbent system interference area SC3 DN-3 SC1 SN-1 D S SC1:DATA SC1:ACK SC1:ACK SC1:ACK SC1:DATA SC4 SN-2 SC2 DN-4 Incumbent System Device Sender/Receiver’s neighbor nodes Hidden incumbent device problem

  10. Avoid method(2) • Receiver transmits a short pulse(脈衝) during the slot time if the channel corresponding(相同的) to the slot is used by incumbent systems around themselves. • This kind of the pulse reports is generated(產生) by the neighbor node, the distance is very short. • The propagation(增加) delay can be ignored. Therefore, there is no need to use the synchronization.

  11. Avoid method(3) • The time duration of time slot of 802.11 is greater than that of the pulse. Thus, any pulse appears with the range of specific(特殊的) time slot will be regarded(當作) as the appearance of the incumbent device on that sub data channel. • Because the pulse does not need to be decoded, sender can know which sub channel has already been used. • If no pulse were detected(發現), there is no need to transmit the RTSu (RTS updated) packet to the destination node.

  12. Simulation(1) • The appearance of the incumbent devices, channel will be idle for a relatively(相對) long time interval. • The type of appearance duration follow the exponential(指數的) distribution function.

  13. ON/OFF model

  14. Calculate • We use the Eq. 9 and Eq. 10 to calculate the TimeON (time duration of the incumbent system).

  15. Simulation(2) X軸:目前設備在次資料頻道上所使用的機率 Y軸:主要使用者的鄰近節點的干擾影響

  16. Simulation(3)

  17. Conclusion • 隱藏終端問題 • 單通道與多通道隱藏終端問題 • 如何避免隱藏終端 • 避免的方法

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