An efficient scheduling scheme for hybrid TDMA and SDMA systems with smart antennas in WLANs

Abstract

Smart antennas are an emerging technology that exploits spatial diversity and allows an access point (AP) to simultaneously transmit downlink packets to multiple stations (STAs). In this paper, we propose a new AP scheduling scheme for hybrid TDMA (Time Division Multiple Access) and SDMA (Spatial Division Multiple Access). Our scheduling scheme aims at maximizing the system throughput while maintaining the fairness among STAs and guaranteeing Quality of Service of different traffic classes. The original contributions of our scheduling scheme include: (1) We propose a transmission framework that allows TDMA STAs to transmit in the TDMA fashion, and non-TDMA STAs to compete channel access in the CSMA/CA fashion. (2) We analyze the performance of CSMA/CA STAs and determine the optimal contention window size for each STA to minimize the collision rate subject to the contention period constraint. (3) We propose an analysis to determine the minimal length of time allocated to non-TDMA STAs during a transmission period such that each STA will have a success transmission probability above a specified threshold in each period. (4) We propose a scheduling algorithm that schedules simultaneous packet transmission to multiple STAs such that maximal number of packets can be transmitted to multiple STAs without causing unacceptable interference. © 2012 Springer Science+Business Media, LLC.