Spectrum Sharing MAC-layer Protocols：MAC层协议的频谱共享

1、Spectrum Sharing MAC-layer ProtocolsSang-Yoon ChangECE 439 Spring 2010MotivationBandwidth becoming scarcer and more valuableIncreased demands on wireless applicationsUsers demand higher performanceDynamically accessing multiple channels can increase spectrum efficiencyOur goal is to support multiple

2、 transmissions and increase performance by mitigating interference FCC Spectrum Allocation ChartSpectrum UtilizationA snapshot of spectrum utilization up to 6 GHz in an urban area at mid-day 1BackgroundCognitive radioSecondary users operating on licensed BandRequired to detect primary users signals

3、(physical-layer)Avoid and yield the channel use to primary users (MAC-layer)In addition, coordination with other secondary usersOther Spectrum Sharing Techniques Ultra WideBand (UWB) CommunicationUnlicensed Band, e.g., ISM bandProject OverviewRandom access protocol without coordination 2Centralized

4、channel allocation algorithm 3Distributed channel allocation algorithm 4,5Single radio per user 6,7Sensing overhead / limitations 7,8Diverging from traditional slotted channelization 7,10,11,12Selfish users 14MMAC 6, HMAC 7 SWIFT 10 Hidden-Terminal ProblemIn single-channel environment, IEEE 802.11 D

5、CF, busy-toneAssumed single radio per userIEEE 802.11 DCF in multi-channel environmentC does not hear the CTS(2) from B, and thus collisionIf multiple radios per user, Dynamic Channel Assignment (DCA) by Wu 9Needs complex hardwareMMAC ProtocolMulti-Channel MAC (MMAC) by So and Vaidya 6Single radio p

6、er userBuild on IEEE 802.11 PSM protocol (beacon interval, ATIM)Requires global synchronizationIn ATIM window, Agree on a channel according to Preferable Channel List (High, Medium, Low)ATIM-RES to notify the channel reservationBeacon IntervalMMAC PerformanceWLAN (above) and multi-hop (below) enviro

7、nmentAlso observed packet delayCBR trafficPacket size = 512 BytesBeacon interval = 100 msATIM window size = 20 ms3 channelsHC-MAC ProtocolHardware-Constrained Cognitive MAC (HC-MAC) by Jia et al. 7Single radio, partial spectrum sensing, spectrum aggregation limitConstruct a stopping problem to decid

8、e whether or not to sense further channels Robust to multi-channel hidden terminal problemHC-MAC: Sensing DecisionsB = Transmission Rate, T = Packet Duration, t = Sensing Time*HC-MAC: Control PacketsContention (C-RTS / C-CTS)Competing for common control channel accessSensing (S-RTS / S-CTS)Exchange

9、channel availability and agree on data channel Transmission (T-RTS / T-CTS)Notify neighboring nodes the completion of transmissionSWIFT ProtocolSplit Wideband Interferer Friendly Technology (SWIFT), Rahul 10Unlike UWB, no need to sacrifice transmission power, rateCognitive aggregation of non-contigu

10、ous frequency bandAdaptive sensing (probe the spectrum and observe reaction)SWIFT: Adaptive Sensing(sec)SWIFT Bin Sync. ProblemSWIFT: Bin Synchronization SWIFT users independently decide which bands that they can use.i) If drastic disagreement on usable bands, or boot upSends usable bins in all freq

11、uency binsTxer and Rxer agrees at least on one of the binsii) If limited disagreement,Stripes data across the previously agreed bins, but transmits only in the subset that is still usableTransform the potential disagreement to bit errorsError correcting codesDiscussion and ConclusionSecurity issues

12、arise, e.g., Denial-of-Services (primary user emulation, jamming, etc.)Analyzed correctness and performance of schemes assuming rational users (who care for their performances)With smart radio becoming reality, burgeoning interest in MAC protocols that are designed for multi-channel environmentRefer

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15、amic Spectrum Allocation Networks,” IEEE CrownCom, 2007.6 J. So and N. Vaidya, “Multi-Channel MAC for Ad Hoc Networks: Handling Multi-Channel Hidden Terminals Using a Single Transceiver,” ACM MobiHoc, 2004.7 J. Jia, Q. Zhang, and X. Shen, “HC-MAC: A Hardware-Constrained Cognitive MAC for Efficient S

16、pectrum Management,” IEEE Journal on Selected Areas in Communications, vol. 26, no. 1, pp. 106-117, 2008.8 S. Shetty, M. Song, C. Xin, and E. K. Park, “A Learning-Based Multiuser Opportunistic Spectrum Access Approach in Unslotted Primary Networks,” IEEE Infocom, 2009.9 S.-L. Wu, C.-Y. Lin, Y.-C. Ts

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