Spatial Multiplexing for Heterogeneously Equipped Nodes in Wireless Ad Hoc Networks

Ad hoc wireless multihop networks inherently suffer from interference when several nodes communicate in parallel in a close vicinity. This problem can be alleviated, if the nodes apply multiple antennas and appropriate techniques like beamforming or layered space-time processing. While such techniques are well studied in cellular networks, it is not straight forward to apply them to ad hoc networks due to the distributed nature of the latter. In this paper we propose a novel MAC protocol, the Fully Distributed Spatial Multiplexing (FDSM)-MAC, which allows for spatial multiplexing on the basis of a LAyered Space Time Multiuser Detector (LASTMUD) at the physical layer. FDSM-MAC operates fully distributed and enables multiple streams per node. Moreover, within the same network, it supports nodes with different numbers of antennas, including the extreme case of single antenna nodes. FDSM-MAC can be operated with and without spreading, where spreading further increases the supported traffic density. We evaluate FDSM-MAC by means of system simulations including a detailed channel model. We present results for different spreading factors and different numbers of antennas. Moreover, we provide a comparison with another MAC protocol, which uses multiple antennas solely for interference suppression rather than for spatial multiplexing.