  Cooperative relay systems have become an active area of research during
recent years since they help cellular networks to enhance data rate and
coverage. In this paper we develop a method to jointly optimize precoding
matrices for amplify-and-forward relay station and base station. Our objective
is to increase max-min SINR fairness within co-channel users in a cell. The
main achievement of this work is avoiding any tedious alternating optimization
for joint design of RS/BS precoders, in order to save complexity. Moreover, no
convex solver is required in this method. RS precoding is done by transforming
the underlying non-convex problem into a system of nonlinear equations which is
then solved using Levenberg-Marquardt algorithm. This method for RS precoder
design is guaranteed to converge to a local optimum. For the BS precoder a
low-complexity iterative method is proposed. The efficiency of the joint
optimization method is verified by simulations.
