Complexity reduction using QRD-M or SD in MIMO Interleaved SC-FDMA receiver with iterative detection

The maximum likelihood detection (MLD) is known as the optimum separation method of spatially multiplexed signals in MIMO (Multiple Input Multiple Output) communication schemes. However, when the number of transmit antenna and the level of modulation are increased, the complexity of MLD becomes quite large and the reduction of complexity is the important issue. For reducing the complexity of MLD, QRD-M (QR Decomposition with M-Algorithm) was proposed, but it is a quasi-ML method and could not obtain the ML solution although the complexity is largely reduced. On the other hand, Sphere Decoding (SD) can obtain the ML solution like MLD with reduced complexity. In this paper, we propose the receiver structure for MIMO Interleaved SC-FDMA (MIMO Interleaved Single Carrier-Frequency Division Multiple Access) where the FDE (Frequency Domain Equalization) is firstly done for obtaining the tentative decision results and secondly using the tentative results the ISI (Inter-Symbol Interference) is cancelled by ISI canceller and then the MLD is made for separating the spatially multiplexed signals. Furthermore the output from MLD is fed back to ISI canceller and this feedback is iteratively for improving the BER. In order to reduce the complexity of the proposed receiver, we replace the MLD by QRD-M or SD. By examining the BER characteristics and the complexity reduction through computer simulations, we have verified the effectiveness of proposed receiver in which MLD is replaced by SD.