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 TranFaculty of Radio-Electronics

Le Quy Don Technical University, Vietnam.

Outline of Presentation

Introduction Network model Proposed cooperative MAC protocol Performance analysis Simulation and numerical results Conclusions

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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.

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.

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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

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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 TP and/or TO, 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 (Rh) => decreasing data transmission time duration TD or TP => increasing (EPTR).

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Proposed cooperative MAC protocol

Fig.3. Proposed cooperative MAC protocol.

helpers calculate the cooperative rate Rh based on CSI received through RTS/CTS.

Cooperative rate allocation: (gth prior group, mth member)

HI, GI, MI

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Performance analysisA. Payload and Overhead Transmission Time Direct ransmission:

T1,p = W/R1;

T1,o = TRTS + TCTS + Td,o + TACK + 4TSIFS + 4tprop

Cooperation Without CollisionT2,p = W/RC1 + W/RC2 = W/Rh

T2o(g,m,k) = T1,o + THI + Tfb1(g) + TGI + Tfb2(g,m) + TMI + ktfb + THRP + Td,o + 2TSIFS + 2tprop

Cooperation With Optimal Helper Contention T3,p = T2,p; T3,o = T2,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 CooperationT4,o = T1,o + THI + Tfb1(g) + TGI + Tfb2(g,m) + TMI +ktfb + TSIFS

T4,p = T1,p;

(2)

(3)

(4)

(5)

The probability that the contention fails due to more than one optimal helper selecting the same kth mini-slot is given by Pf(n,k).

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Performance analysis (cont.)B. Throughput Under Error-Free Transmission

C. Throughput Under Erroneous Transmission

(6)

(7)

(7’)

With given W, R1, K the system throughput is determined by formula (6), (7).

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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)

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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)

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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.

Thank you for your attention!

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