Decoupling method for low complexity turbo equalization of frequency-selective MIMO wireless systems

This paper proposes a decoupling method for low complexity turbo equalization of frequency selective multiple-input multiple-output (MIMO) wireless systems. A coded MIMO system can be viewed as a serially concatenated coding (SCC) system where the encoder for the transmitted signals and the MIMO channel take on the roles of inner code and outer code, respectively. Several MIMO turbo equalization methods have been proposed for detecting coded signals transmitted by multiple antennas in the presence of interchannel interference (ICI) and intersymbol interference (ISI). However these methods use MAP or MMSE-based MIMO inner equalizers in the turbo iteration. The complexity of such equalizers grows rapidly as the number of transmit or receive antennas increases, or as the order of the MIMO channel increases. To overcome this difficulty, we propose to use a MIMO FIR decoupler on either the transmit or receive side in order to transform the MIMO channel into parallel single-input single-output (SISO) subchannels. Turbo equalization can then be applied separately to each scalar subchannel, resulting in a low complexity receiver. Transmit or noise power constraints can be included in the decoupler design. Simulations demonstrating the effectiveness of the proposed low-complexity turbo equalizer are presented.