An MMSE-based MCI and MAI cancellation receiver for MIMO OVSF-OFCDMA systems

Abstract

Broadband orthogonal frequency code division multiple access (OFCDMA) with two dimensional spreading is a promising candidate for Beyond fourth Generation (B4G) networks. Since wideband channels are highly frequency-selective, orthogonality among orthogonal spreading codes are no longer maintained. Therefore, multiple code interference (MCI) is inevitable in OFCDMA-based systems. Multiple-Input Multiple-Output (MIMO) will be a key technology of future wireless communication systems. In MIMO-OFCDMA systems, in addition to MCI, inter-spatial stream interference (ISSI) will also exist. Even though maximum a posteriori probability (MAP)-based detectors provide the best performance, their computational complexity is high. Alternatively, minimum mean-square error (MMSE) detectors can be used to obtain a better tradeoff between the complexity and the performance. ; Several interference cancellation techniques were proposed under LTE Advanced, B4G standardizations and corresponding literature. One such technique is zero-forcing MAI nulling and cancellation based on QR decomposition (ZF-QRD). That can be used to cancel the MAI separately. But we are proposing a combined ISSI and MCI cancellation technique. We also compare the performance of MIMO VSFOFCDMA recursive ISSI and MCI cancellation scheme with conventional MC-CDMA, MC-DS-CDMA, MT-CDMA and OFCDMA.