Performance evaluation of algorithms for wireless medium access

Abstract

This paper evaluates the performance of a class of multiple-access algorithms for wireless medium access in shared-channel multi-cell and ad hoc network environ- ments. Based on the collision avoidance and fairness properties of the evaluated algorithms, this paper presents a wireless medium access protocol that provides significantly better channel utilization, delay, and delay variance characteris- tics compared to the IEEE 802.11 standard. In this paper, we examine two fundamental problems re- lating to wireless medium access in shared-channel multi- cellular and ad hoc network environments, and evaluate the performance of a class of multiple-access algorithms that have been proposed in contemporary literature for solving these problems. Based on our evaluation, we identify an effective combination of techniques to build a robust, effi- cient, and fair wireless medium access protocol. Wireless transmission is characterized by locality of transmission. In a shared-channel multi-cell environment, this gives rise to the well-known hidden station and exposed station scenarios. We examine two problems associated with hidden/exposed stations in wireless medium access: (a) efficient collision avoidance, and (b) fair collision reso- lution. While the hidden and exposed station problems have been well understood in the context of collision avoidance, they impact the fairness properties of wireless medium ac- cess in subtle ways that have not been adequately addressed in contemporary literature. In this paper, we first identify the problems due to hidden and exposed stations, and then evaluate possible solutions to these problems. Based on our evaluation, we propose a wireless medium access proto- col that incorporates the following two algorithms: (a) an enhanced CSMA/CA-based dual-channel collision avoid- ance algorithm which seeks to solve all cases of the hid- den/exposed and co-channel interference scenarios; and (b) a backoff-based collision resolution algorithmwhich seeks to provide fairness while taking into account spatial conges- tion. These algorithms are complementary because they ad- dress different aspects of wireless medium access. In con- cert, they effectively address the critical issues in wireless channel access. From the simulation measurements pre- sented in this paper, we conclude that a wireless MAC pro- tocol which incorporates the algorithms mentioned above can provide significantly better channel utilization and de- lay characteristics compared to the IEEE 802.11 standard. Our proposed solution does require enhancements to the typical commercially available wireless hardware, but we believe that these enhancements are both practical to imple- ment, and justified in the light of the resulting performance improvements.