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IEEE 802 . 11 Rate Control Algorithms : Experimentation and Performance Evaluation in Infrastructure Mode

This paper evaluates the performance of practical Rate Control Algorithms (RCAs) operating at the Media Access Control (MAC) layer in IEEE 802.11 networks built on Atheros chipsets. Using a dual band 32bit cardbus based wireless network interface card (WNIC) on a laptop running vanilla Linux 2.6.13.3 kernel, we explore the capabilities of each of the three different RCAs under varying wireless channel conditions. We observe their link layer response by using a closely monitored and controlled step function generated inside a microwave operating at 2450 MHz. The resultant link layer performance is quantified by the Kullback-Leibler (KL) distance that exposes the degree of divergence between the received signal strength indicator (RSSI) distribution and that of the adapted transmission rate. Our findings indicate that both Adaptive Multi Rate Retry (AMRR) algorithm and SampleRate are sensitive enough to detect short term variations of RSSI values while Onoe is practically immune to such short term signal strength variations. In order to expose the effect of RCA on application layer, we conducted experiments with heterogeneous traffic (Voice, Streaming, Interactive, Background) in controlled network subnets. The average application level throughput, packet inter-arrival time and jitter observed with different RCAs is reported in our study. Our experiments show that the aggressive adaptation behavior of AMRR and SampleRate to RSSI variations does not bode well for delay sensitive traffic like VoIP applications. The conservative Onoe is more suitable in such cases. However, for other traffic types, both AMRR and SampleRate compete neck-and-neck in providing high application throughput.