Frequency-Domain Backoff Mechanism for OFDM-Based Wireless LANs

Abstract

Modern wireless communication technologies enabled high data rate support which stands in need of proficient MAC protocols. In WLANs, the fair channel access and collision avoidance are achieved by employing contention. The contention period degrades bandwidth utilization and longer delays; the network performance worsens for high data rates. Previously, this problem is addressed by modifying or adaptively selecting contention time using the same time-domain- based backoff mechanism. In this paper, we propose a backoff scheme, FD-Backoff, in which backoff is taken in the frequency domain. Therein, an integer is assigned to every data subcarrier, and then, a random data subcarrier (integer) is chosen to transmit a RTS packet. Since OFDM-based data subcarriers are orthogonal, thus simultaneous transmission of multiple RTS packets is possible. Every nontransmitter node listens on the whole channel bandwidth to observe any active subcarriers. The transmitter who chose smallest subcarrier for RTS transmission wins channel access and receiver replies it with a CTS packet. Contrary to the IEEE 802.11 backoff mechanism, the proposed backoff scheme offers lesser and relatively fixed contention overhead. Performance analysis based on analytical and simulation study suggests that the proposed scheme promises lower contention overhead and higher efficiency gain (up to 35 %) as compared to standard channel access mechanism.