Implementation of MIMO downlink with perfect and imperfect CSIT

Abstract

In this paper we implement a suboptimal version of Cover - van der Meulen - Hajek - Pursley (CMHP) scheme, which is one of downlink broadcast Multiple Input Multiple Output (MIMO) schemes. We consider the vector Gaussian broadcast channel (BC) with perfect channel state information at the receiver (CSIR). For channel state information at the transmitter (CSIT), we consider two cases: perfect CSIT and imperfect CSIT (ICSIT). In the case of imperfect CSIT, the transmitter only knows channel mean and variance. In \cite{wajcer}, the achievable rate of CMHP was evaluated in 2 by 1 MISO 2 users environment with perfect CSIT and CSIR. We focus on implementation of CMHP using practical coding not assuming Gaussian signaling and performance analysis of that in ICSIT. Turbo codes described in IEEE 802.20 draft specification and QAM modulation are used to implement CMHP, MMSE beamforming and TDMA in both CSIT and ICSIT. In order to find the optimal power allocation and beamforming (BF) vector to maximize sum rate when the MIMO schemes are implemented we introduce SINR penalty factor. The SNRs for each MIMO schemes to achieve the target spectral efficiency are compared. Also, the additional signal power required to implement them is presented. Finally, we show the robustness of CMHP to channel imperfection at the transmitter.