1. The 2014 APSIPA ASC Conference December 9-12, 2014, Siem Reap, city of Angkor Wat, Cambodia Improved Cross-Layer Cooperative MAC Protocol for Wireless Ad hoc Networks Quang Trung Hoang, Xuan Nam Tran Faculty of Radio-Electronics Le Quy Don Technical University, Vietnam.

2. Outline of Presentation  Introduction  Network model  Proposed cooperative MAC protocol  Performance analysis  Simulation and numerical results  Conclusions 2/19

3. Introduction Cooperative communications and wireless networks Designs of the previous cooperative protocols: enhancing the system performance through the best relay selected. However, the contending problem of best relays is not focused much. The cross-layer cooperative MAC protocol [14]: achieving higher diversity gain. However, relay contending time can increase because of length of the Ready-To-Help (RTH) frame and retransmission of this frame.  it is necessary to optimize or redesign the MAC protocols for selecting the best relay effectively, improving the system performance. [14] H. Shan, T. H. Cheng, W. Zhauang, “Cross-Layer Cooperative MAC Protocol in Distributed Wireless Networks, ”IEEE Trans. on Wireless Commun., vol. 10, no. 8, pp. 2603–2615, August 2011.

4. Our contributions:  Proposal of an improved cross-layer cooperative MAC protocol:  improving the system throughput and reducing the end-to-end packet latency for wireless ad hoc networks.  Detailed mathematical analysis of the network performance in terms of the system throughput and the end-to-end packet latency for both cases of error-free and erroneous channel. 4/19

5. Network model  Each node uses a single ant.  Data frames : multi-rate mode. (6, 9, 12, 18, 24, 36, 48, 54) Mbps.  Control frames: 2 Mbps.  Available data rate depends on the instant received SNR.  Channels: with log-normal shadowing path loss and Rayleigh fading. Fig.1. Cooperative wireless ad hoc network 5/19

6. 6/19 Network model (cont.) A. MAC layer operation:  Designed based on the IEEE 802.11 DCF.  The effective payload transmission rate (EPTR) is determined by (1)  By designing to reduce T P and/or T O, the system throughput can be enhanced. B. Physical Layer Operation Fig.2. Transmission scheme The cooperative mode is implemented by using the distributed Alamouti space-time coding scheme. higher cooperative data rate (R h ) => decreasing data transmission time duration T D or T P => increasing (EPTR).

7. 7/19 Proposed cooperative MAC protocol Fig.3. Proposed cooperative MAC protocol. helpers calculate the cooperative rate R h based on CSI received through RTS/CTS. Cooperative rate allocation: (g th prior group, m th member) HI, GI, MI

8. 8/19 Performance analysis A. Payload and Overhead Transmission Time  Direct ransmission: T 1,p = W/R 1; T 1,o = T RTS + T CTS + T d,o + T ACK + 4T SIFS + 4t prop  Cooperation Without Collision T 2,p = W/R C1 + W/R C2 = W/R h T 2o (g,m,k) = T 1,o + T HI + T fb1 (g) + T GI + T fb2 (g,m) + T MI + kt fb + T HRP + T d,o + 2T SIFS + 2t prop  Cooperation With Optimal Helper Contention T 3,p = T 2,p ; T 3,o = T 2,o However, given K mini-slots, the probability that one of n optimal helpers wins the contention to choose the k-th mini-slot is given by.  Unsuccessful Cooperation T 4,o = T 1,o + T HI + T fb1 (g) + T GI + T fb2 (g,m) + T MI +kt fb + T SIFS T 4,p = T 1,p ; (2) (3) (4) (5) The probability that the contention fails due to more than one optimal helper selecting the same k th mini-slot is given by P f (n,k).

9. 9/19 Performance analysis (cont.) B. Throughput Under Error-Free Transmission C. Throughput Under Erroneous Transmission (6) (7) (7’) With given W, R 1, K the system throughput is determined by formula (6), (7).

10. 10/19 Simulation and numerical results  The network topology is created as in Fig. 1 with 20 helpers distributed randomly between the source and the destination. W = 2000 bytes; ρ = 1; K=20.  In order to compare with the previous protocol in [14], we use the same channel conditions and assume that there is no packet transmission error. Fig. 4. the system performance versus network radius under error-free channel (a) (b)

11. 11/19 Simulation and numerical results (cont.) Fig. 5. Comparing the system performance under error-free and erroneous channels (a) erroneous channel (b) (d) Error-free channel (c)

12. 12/19 Conclusions  We have presented an improved cross-layer design of cooperative MAC protocols for wireless ad hoc networks.  Decreasing signaling overhead by reducing the relay contending times in only fixed K mini-slots.  Increasing the channel accessing ability as well as the controlling signal decoding capability by using the helper response pulse (HRP) signal instead of the control frame RTH in previous protocol.  We also offer the mathematical analysis for the system performance.

13. Thank you for your attention! 13/19

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