Cross-layer design of uplink multiple-antenna interference cancellation for WLAN with CSMA/CA in open access networks
24 June 2007
The potential of multi-antenna interference cancellation receiver algorithms for increasing the uplink throughput in WLAN systems such as 802.11 is investigated. The medium access control (MAC) in such systems is based on carrier sensing multiple- access with collision avoidance (CSMA/CA), which itself is a powerful tool for the mitigation of intra-system interference. However, due to the spatial dependence of received signal strengths, it is possible for the collision avoidance mechanism to fail resulting in packet collisions at the receiver and a reduction in system throughput. The CSMA/CA MAC protocol can be complemented in such scenarios by interference cancellation (IC) algorithms at the physical (PHY) layer. The corresponding gains in throughput are a result of the complex interplay between the PHY and MAC layers. It is shown that semi-blind interference cancellation techniques are essential for mitigating the impact of interference bursts, in particular since these are typically asynchronous with respect to the desired signal burst. Semi-blind IC algorithms based on second- and higher-order statistics are compared to the conventional no-IC and training-based IC techniques in an open access network (OAN) scenario involving home and visiting users. It is found that the semi-blind IC algorithms significantly outperform the other techniques due to the bursty and asynchronous nature of the interference, caused by the MAC interference avoidance scheme.