A Congestion-aware Medium Access Control Protocol for Multi-rate Ad-hoc Networks

This paper investigates the problem of how to improve TCP performance in multi-rate Ad-hoc networks with con-gested links. To improve network performance, different rate adaptation algorithms, such as Automatic Rate Fall-back (ARF) and Receiver-Based AutoRate (RBAR), have been proposed to adapt the data rate according to the cur-rent channel quality. Opportunistic Auto Rate (OAR) pro-tocol is an optimisation for any existing rate adaptation al-gorithm which leads to a significant performance gain by providing temporal fairness. We analyze the reasons for the high performance gain obtained using OAR, and show that the OAR protocol does not work well for TCP com-munications in Ad-hoc networks where nodes use different data rates to communicate with each other (heterogeneous). Based on these analysis, we propose a Congestion Reac-tive Opportunistic Auto Rate (CROAR) protocol, which is a new rate adaption enhancement tailored to improve TCP performance in heterogeneous multi-hop Ad-hoc networks. Extensive simulations show that CROAR, compared to OAR and RBAR, produces significant throughput and end-to-end transmission latency improvements while only marginally relaxing temporal fairness. 1