A Systematic Design of Multiuser Space-Frequency Codes for MIMO-OFDM Systems

While a great number of space-time (ST) code and space-frequency (SF) code designs have been extensively studied for point-to-point single-user links and directly applied to each user for multiuser links, little effort has been dedicated to multiuser ST/SF code design. Recently, this issue was considered by Gartner and Bolcskei and from a perspective of increasing system throughput, they proposed a joint code design for a 2-user scenario. In this paper, by applying a signal space diversity technique and a judicious phase rotation to each of a group of uncoordinated users, we propose a systematic design of SF codes for multiuser MIMO-OFDM systems over frequency-selective fading channels. We prove that multiuser SF codes with maximum-likelihood (ML) detection can achieve the maximum diversity for each user while minimizing the interference introduced from all the other users.