Spectral Efficiency of Wireless Relay Network in Frequency Non-Selective Channel

Introduction. A wireless communication system based on a relay network where a link between a source and a destination is carried out through a network of relay nodes have been considered. Relay networks operate according with amplifier-and-forward protocol where each relay node performs reception, amplifying, phase shifting and retranslation of a signal to the destination node. As a result a task of powers and phases optimization in the relay nodes (i.e. the complex weighted coefficients optimization) becomes actual. Complex weighted coefficients of the relay nodes are optimized in such a way as to ensure the maximum signal to noise ratio at the receiver while limiting a power emitted by the relay nodes. In the paper, optimization of spatial processing with different a priori channel state information (i.e. instantaneous channel state information and the second order statistics) have been considered.

Aim. Spectral efficiency analysis of a relay network in a multipath channel where the relay network was optimized by using of two types a priori information: an instantaneous channel state information and second order statistics.

Materials and methods. Optimization of spatial signal processing in the relay network was based on methods of statistical theory and optimization using analytics of linear algebra and methods of mathematical programming. Performances of the relay network were analyzed using Monte Carlo simulation. The simulation was performed in MATLAB program environment using CVX toolbox for solving convex optimization task.

Results. In the paper optimal solutions for spatial signal processing in the relay network were presented. The solutions were based on maximum of signal to noise ratio while limiting total relay power and individual power of relay nodes. Monte Carlo simulation was performed to provide performances of the relay network for different types of channel state information and channel parameters. Mean capacities versus mean source power, a budget of relay nodes power and a ratio between random and deterministic power of the channel were gained for the Rayleigh model of multipath channel.

Conclusions. The results have a practical application. Thus, the use of the second order statistics is possible in relay networks when direct visibility with a low level of background from local objects is provided. In urban areas, where shading and multipath propagation of signals occur, it is possible to use only an approach based on the knowledge of channel instantaneous state.

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