Space-Time Codes Versus Random Beamforming in Cooperative Multi-Hop Wireless Networks

We consider a multi-hop wireless sensor network in which a large number of sensor nodes are grouped into cooperative clusters. Multi-hop transmission is carried out between the source and the destination nodes by concatenating consecutive cluster-to-cluster hops. For each hop, both the transmit and the receive clusters can exploit node cooperation such that cooperative distributed multiple-input multiple-output (MIMO) channels can be formed. As proposed in [1], a time-division protocol is employed for transmissions within a cluster and between clusters, i.e., the intra-cluster slot is used for broadcasting within the transmit cluster, and the inter-cluster slot is used for transmissions between clusters. Distinguished from the scheme in [1] that space-time codes (STC) are utilized for inter-cluster transmissions, random beamforming is proposed in this paper, which is shown to outperform STC in term of energy efficiency provided that the number of nodes within receive cluster is adequately large. We demonstrate that even with moderate number of nodes within receive cluster, e.g., 10 nodes, random beamforming can offer higher energy efficiency for inter-cluster links, at 5% outage rate. The "random" nature incorporated in random beamforming scheme assigns the clusterhead node within receive cluster in an alternate manner, thus balancing energy consumption within receive cluster.