Loss Differentiated Channel Aware Rate Adaptation for IEEE 802.11n Wireless Links

Abstract

Rate adaptation in wireless network adapts the transmission rate to the estimated quality of the channel as a single rate is not suitable over large period of time. Key limitation of existing closed loop Rate Adaptation Algorithm is its slow speed of adaptation due to the analysis of several frames for a reliable judgment, especially when the error rate is low. This is detrimental to the real time multimedia streaming applications. Implementation of a closed loop system is challenging in heterogeneous, power constrained networks. Adaptation is affected by collisions, faded channel and hidden nodes, which contribute differently to loss of data. Absence of loss differentiation may increase the transmission time, congesting the network further. This paper proposes an open loop, per packet, Loss Differentiated-Channel Aware Rate Adaptation (LD-CARA) for IEEE 802.11n. It uses block acknowledgement and other inherent features of 802.11n to differentiate losses and optimize the system throughput. Signal to noise ratio of the received signal, the raw measurement of the link, is directly related to the bit/frame error rate in the link. Use of SNR measurements characterize the instantaneous channel behavior and make the design agile. The performance is evaluated using network simulator NS3, and compared prevalent adaptations. It is found that LD-CARA is a stable algorithm and improves network throughput in static, mobile and interfered channels; however node mobility has an adverse effect on the protocol and the dropping ratio of mobile nodes deteriorates in the congested environment and results for the same are comparable to other protocols.