Coherence time-based cooperative MAC protocol 1 for wireless ad hoc networks

Murad Khalid,Yufeng Wang,Ravi Sankar,Hyung-Jin Kim,In-Ho Ra,Ismail Butun

doi:10.1186/1687-1499-2011-3

Abstract

In this article, we address the goal of achieving performance gains under heavy-load and fast fading conditions. CoopMACI protocol proposed in Proceedings of the IEEE International Conference on Communications (ICC), Seoul, Korea, picks either direct path or relay path based on rate comparison to enhance average throughput and delay performances. However, CoopMACI performance deteriorates under fading conditions because of lower direct path or relay path reliability compared to UtdMAC (Agarwal et al. LNCS, 4479, 415-426, 2007). UtdMAC was shown to perform better than CoopMACI in terms of average throughput and delay performances because of improved transmission reliability provided by the backup relay path. Although better than CoopMACI, UtdMAC does not fully benefit from higher throughput relay path (compared to the direct path), since it uses relay path only as a secondary backup path. In this article, we develop a cooperative MAC protocol (termed as instantaneous relay-based cooperative MAC--IrcMAC) that uses channel coherence time and estimates signal-to-noise ratio (SNR) of source-to-relay, relay-to-destination, and source-to-destination links, to reliably choose between relay path or direct path for enhanced throughput and delay performances. Unique handshaking is used to estimate SNR and single bit feedbacks resolve contentions among relay nodes, which further provides source node with rate (based on SNR) information on source-to-destination, source-to-relay, and relay-to-destination links. Simulation results clearly show that IrcMAC significantly outperforms the existing CoopMACI and the UtdMAC protocols in wireless ad hoc network. Results show average throughput improvements of 41% and 64% and average delay improvementd of 98.5% and 99.7% compared with UtdMAC and CoopMACI, respectively.

Highlights

Ever-increasing demand for higher throughput and lower delay in wireless ad hoc networks led to an extensive research into newer techniques, algorithms, and technologies
For single hop ad hoc networks cooperative MAC protocols can be classified into two major categories: (1) protocols that invoke relay node when transmission time via relay path is better than the direct path, and (2) protocols that invoke the relay node for backup transmission when direct transmission fails due to fading or interference
Only relays that can decode both RTS and CTS packets respond in the RR frame; (3) each relay with total transmission time less than the channel coherence time can only respond in RR frame; (4) each relay responds with a single bit at random bit interval location in an appropriate slot; and (5) source invokes relay with logical addressing by using Address 4 field in IEEE 802.11 MAC header

Summary

Introduction

Ever-increasing demand for higher throughput and lower delay in wireless ad hoc networks led to an extensive research into newer techniques, algorithms, and technologies. IrcMAC protocol fully exploits available relays and further resolves contention between relays under fading conditions as follows: (1) all the nodes passively monitor and estimate channel coherence time; (2) RTS and CTS messages are exchanged before relays can respond By this way, only relays that can decode both RTS and CTS packets respond in the RR frame; (3) each relay with total transmission time less than the channel coherence time can only respond in RR frame; (4) each relay responds with a single bit at random bit interval location in an appropriate slot; and (5) source invokes relay with logical addressing by using Address 4 field in IEEE 802.11 MAC header. CoopMACI and IrcMAC protocols are capable of handling such contentions

Simulation setup

Simulation results and discussion

Findings

Conclusion