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협업 통신에서의 매체액세스제어 Cooperative Communication MAC

협업 통신에서의 매체액세스제어 Cooperative Communication MAC. 2006. 02 Chungnam National University Byung Chul Kim byckim@cnu.ac.kr. Cooperative Communication. Cooperative communication

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협업 통신에서의 매체액세스제어 Cooperative Communication MAC

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  1. 협업 통신에서의 매체액세스제어Cooperative Communication MAC 2006. 02 Chungnam National University Byung Chul Kim byckim@cnu.ac.kr

  2. Cooperative Communication • Cooperative communication • Different wireless nodes cooperate to increase their robustness by decreasing the bit error rate and outage probabilities • Use another mobile to relay information

  3. Cooperative Communication • Broadcast Wireless Channel • Omni-directional wireless antennas • Signals transmitted towards the destination can be overheard at the relay partner • Partner can process this overheard information and re-transmit towards the destination • Destination processes signals from both mobiles • Benefits • Spatial Diversity • Higher Data rates and throughput • Lower Delay • Power Efficient • Lower interference • Increased Coverage

  4. Cooperative Communication • Spatial diversity gain • Store and forward: traditional relay • Amplify and forward • Coded cooperation • Multi-hop Communication

  5. Problems of wireless communication • Problems of multi-rate IEEE 802.11b • 3 different modulation scheme • 1Mbps: DBPSK, 2Mbps: DQPSK, 5.5 & 11Mbps: CCK • Fairness problem: equal channel access probabilities • Performance anomaly: low data rate nodes (say 1Mbps) will occupy the channel for longer duration for the same size frame • Reduced overall network throughput • Shortest path routing: Low data rate • Adaptive Modulation and Coding • Data rate based on the distance between the AP and STA • Service quality enhancement method is required at the boundary

  6. Cooperative Communication MAC • Goals • Reduce the channel time for low data rate node by assisting its transmission • Enhance the robustness of the WLAN operation • New Algorithm • Relay node Selection Algorithm • Relay node 고려한 new CSMA/CA Algorithm • Backoff and Retransmission Algorithm

  7. Cooperative Communication MAC • CMAC Protocol • The partner retransmits the MAC frame that it received from the source when the frame is received in error at the destination • The backoff window size of partner << that of source  priority to the relaying data • direct link : 오류 확률 p • Ndirect = 1/(1-p) • NCMAC = 1*(1-p)+2*p = 1+p

  8. Cooperative Communication MAC • Shortest path algorithm • (1/11+1/5.5) • = 3.7Mbps

  9. Cooperative Communication MAC • Relay node 선택 - I • Physical node table에 각 modulation type에 대한 threshold SNR 존재  수신한 SNR에 근거해서 최적의 modulation scheme 선택 • AP와 다른 노드 간 통신 overhearing해 header내에 있는 relay node와 AP간 전송 속도 계산 • 수신한 신호 세기로부터 자신과 relay 간의 path loss 계산

  10. Cooperative Communication MAC • Relay node 선택 - II • Sender-receiver channel quality: extract the piggybacked transmission rate in the CTS • Sender-relay node, relay node-receiver channel quality: sense the signal strength of RTS or CTS, respectively • Sender-receiver flow가 주어진 경우 MAC layer relay를 통해 더 빨리 전달 가능한 경우 willing list에 해당 송, 수신 노드의 MAC 주소를 포함 • 각 노드는 주기적으로 자신의 willing list를 one-hop 이웃에게 광고

  11. Cooperative Communication MAC

  12. Cooperative Communication MAC • 모든 노드는 helper table 관리 • Table 구성 • ID : MAC address of (helper) • Time : time the last packet from is heard. • : Transmission rate between and the destination • : Transmission rate between the current station and

  13. Cooperative Communication MAC • Table Update • : can hear the RTS/CTS exchanged between AP and • : measuring the received power level • Selecting a helper • Check the helper table and calculates the time needed to transmit via each helper • two hop transmission via the helper

  14. Cooperative Communication MAC • Reserving the channel • RTS frame에 새로운 필드 포함. • The ID of , and • RTS 수신한 helper • SIFS후 helper ready to send (HTS) 송신. • HTS packet은 CTS packet과 같음. • RTS 수신한 • 에 의해 HTS를 수신할 경우 • CTS 전송 : 를 경유하여 전송하기 위해 필요한 시간을 예약 • HTS를 수신하지 못했을 경우 • CTS 전송 : 직접 전송할 때 필요한 시간을 예약 • RTS를 전송하고 CTS 받은 • Helper table에서 삭제

  15. Cooperative Communication MAC • CTS를 수신한 • RTS후 HTS를 수신했을 경우 • 로 데이터 전송 • 는 CRC 체크 , SIFS후 에게 전송 • RTS후 HTS를 수신하지 못했을 경우 • 로 직접 전송 • Helper table에서 삭제 • Data 수신한 • 에 직접 ACK을 전송

  16. Cooperative Communication MAC

  17. Cooperative Communication MAC With Helper Without Helper

  18. Cooperative Communication MAC • Adaptively changed transmission rate • Sender does not know the transmission rate of the impending packet in advance • Solution • Sender first calculate the duration of the RTS and CTS transmissions only(basic rate, 2Mbps) • After the sender receives CTS (or RCTS), it calculates the durations of the data packet and the ACK

  19. Cooperative Communication MAC • Comparison of two carrier sensing mechanism

  20. Cooperative Communication MAC • Different transmission rates  different transmission ranges • When the sender sends data at high rate, some one-hop neighbors may stay within its carrier sensing range but cannot extract the information of the duration • Solution • Reservation-sub-header(RSH) • RSH is inserted preceding the data frame • Sent at the same or lower rate compared to RTS

  21. Cooperative Communication MAC

  22. Cooperative Communication MAC • Dynamic channel condition • Adaptive decision when to perform relay • Credit ranging in [0.0, 1.0] • Choose the relay node with the largest credit • Successful relaying node increment the credit by 0.1 • Fail  decrement by 0.1 • Willing list 수신  increment by 0.5

  23. Cooperative Communication MAC • Impacts of Relay • 망의 Spatial Reuse에 영향을 미침

  24. Cooperative Communication MAC • Throughput Increase

  25. Cooperative Communication MAC • Energy Efficiency

  26. Cooperative Communication MAC • Energy Efficiency

  27. Conclusions • Significant improvement enabled by cooperation • Capacity, delay, energy consumption, and interference reduction • Enhance the robustness of the WLAN operation • Heals the anomaly problem of 802.11 multi-rate STAs • Enhance the WiBro STA’s QoS at the boundary of the cell

  28. References • A Cooperative MAC Protocol for Wireless Local Area Network • Pei Liu, Zhifeng Tao, and Shivendra Panwar • Cooperative Communication MAC (CMAC) – A New MAC Protocol for Next Generation Wireless LANs • Sai Shankar, Chun-Ting Chou, and Monisha Ghosh • rDCF: A Relay-enabled Medium Access Control Protocol for Wireless Ad Hoc Networks • Hao Zhu and Guohong Cao • Cooperative Communication in Wireless Networks • Aria Nosratinia, Todd E. Hunter, and Ahmadreza Hedayat

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