Achievable Rates and Power Loading in MIMO-THP Systems

Nonlinear Tomlinson Harashima precoding (THP), considered in this paper, is an attractive solution for a scenario in which multiple antenna are deployed at both the transmitter and receiver side so that cooperation among them is possible. In literature THP filters has been calculated and optimized with zero forcing (ZF) and minimum mean square error (MMSE) criteria with the assumption that complete Channel State Information (CSI) is available in transmitter side. In this paper we compute maximum achievable rate of this system by means of information theory concepts. A good solution for maximum achievable rate and optimum as well as suboptimum solutions are presented. For simplicity of calculations, closed form upper bound is attained by neglecting spatially interference term. Moreover, lower bound is obtained by some extra computations on mutual information. Generalization of THP (GTHP) in structure of spatial THP is considered, too. GTHP structure enables different transmission power per antenna so we attained an optimal power allocation to minimize Symbol Error Rate (SER) of each sub channels. In addition the maximum achievable rate of GTHP is calculated for general case.