Efficient power allocation for outage restricted asymmetric distributed MIMO multi-hop networks

Distributed MIMO multi-hop schemes can provide high data rates through spatially distributed relaying nodes. The relaying nodes allow the deployment of MIMO techniques to enhance the throughput by utilizing uncorrelated sub-channels. However, the spatial farness of geometrically separated relaying nodes results in different path losses from the nodes of one virtual antenna array (VAA) to the nodes of another VAA. In this paper we derive an approximative expression for the end-to-end (e2e) outage probability for such asymmetric networks, where orthogonal space-time block codes (OSTBC) are utilized for transmission. Based on this analytical expression a convex optimization problem that aims to reduce the total transmission power while meeting a given e2e outage level is formulated and an efficient near-optimal power allocation approach with low complexity is proposed. This near-optimum solution leads to the interesting result, that the same power is assigned to each node of one VAA. Thus, the power allocation turns out to be symmetric with respect to the nodes of one VAA also for networks with asymmetrically distributed nodes.