On the 20/40 MHz Coexistence of Overlapping BSSs in WLANs

We investigate the impact of 20/40 MHz coexistence on the performance of wireless local area networks (WLANs). To that end, we present simulation results of overlapping basic service sets (BSSs), a 802.11n BSS operating in 20/40 MHz mode and a legacy BSS operating in 20 MHz mode, where the overlapping channel is the extension channel of the 20/40 MHz BSS. Our results show that if clear channel assessment (CCA) is not used in the overlapping channel, the throughput in legacy BSS is almost zero, while the throughput of 20/40 MHz BSS decreases drastically. If CCA is used in the overlapping channel, the throughput of legacy and 20/40 MHz BSSs increase dramatically compared to the case when no CCA is used. In addition, when stations (STAs)/AP that operate in 20/40 MHz BSS are able to dynamically switch between 20 MHz and 40 MHz transmit/receive modes and CCA is used in the extension channel, the throughput of both BSSs further increases. We also report the impact of 40 MHz operation on legacy BSS when the 20/40 MHz BSS employs IEEE 802.11e enhancements. In addition, the impact on the network performance of RTS/CTS protection mechanism for 40 MHz transmissions are also shown. Reducing transmission opportunity (TXOP) interval for 40 MHz transmissions also improves fairness and throughput for legacy BSSs.