On the side effects of packet detection sensitivity in IEEE 802.11 interference management

Interference management is one of the most critical operations for CSMA/CA protocols. In this paper we investigate how specific PHY-layer operations, designed to mitigate the effect of interference, can cause the radio-receiver circuitry to over-estimate the channel occupation status, thus unnecessarily limiting the overall spatial reuse or impeding the synchronization to incoming frames. We individuated the root of this problem in the surprising effectiveness of the overall packet detection procedure of WLAN PHY, which allows for the demodulation of strongly attenuated 802.11 frames. The transmit spectrum mask for the IEEE 802.11 standard allows limited power leakage over adjacent channels. Such a low power signal from adjacent channels nowadays can be correctly recognized by recent OFDM/CCK receive circuitry, which has an important impact on WLAN performance. A receiver may miss the reception of packets destined to it, whenever a frame capture of a transmission on a partially overlapping channel occurs. A similar effect occurs in the transmit phase. In carrier sense mode, the OFDM/CCK receiver of the WLAN device is capable of synchronizing to the preamble of low SNR signals, thus unnecessarily deferring the channel access in case of transmissions on partially overlapping channels.