Multi-code wireless packet random access

Abstract

Spread spectrum multiple-access packetized wireless communications systems are considered. Although very efficient in low traffic (or low-rate) and low signal-to-noise ratio scenarios, the traditional and well-known spread ALOHA multiple access (SAMA) quickly collapses when both traffic and signal power increase. In certain situations, such as wireless sensor network traffic towards a sink, this severely limits the system data collection rates. Multi-packet reception (MPR), on the other hand, offers significant improvements in maximum throughput with respect to SAMA, whose performance is limited by the channel's collision mechanism. To enable MPR we propose to use multiple code CDMA, where different data packets are assigned individual (pseudo-random) spreading sequences. Several types of multiuser detector, such as the popular minimum mean-square error receiver are studied with respect to achievable system throughput and (system) power efficiencies. Due to the inherent asynchronicity of random access, we discuss asynchronous implementations of these receivers based on iterative cancelation processing. Basic queue behaviour utilizing a simplified MAC protocol, and analytical and numerical results are presented for a concept wireless sensor network with a central data collection sink, a setup that is also appropriate for last-mile relaying networks.