MMSE filtering for amplify & forward simo multiple access channel with ill-conditioned second hop

Relaying has been extensively studied during the last decades and has found numerous applications in wireless communications. The simplest relaying method, namely amplify and forward, has shown potential in MIMO multiple access systems, when Gaussian fading channels are assumed for both hops. However, in some cases ill conditioned channels may appear on the second hop. For example, this impairment could affect cooperative BS systems with microwave link backhauling, which involves strong line of sight channels with insufficient scattering. In this paper, we consider a large system analysis of such as system model focusing on the joint MMSE filtering receiver. Analytical methods based on free probability are presented for calculating the MMSE error and average SINR, while the performance degradation of the system throughput due to second hop ill-conditioning is studied.