Efficient Detection Algorithm for a Multiple-Input and Multiple-Output Multiuser Multi-Carrier Code Division Multiple Access in Time-Varying Channels

Problem statement: Maximum Likelihood (ML) decoding has been applied for the uplink of a Multi-Carrier Code Division Multiple Access (MC-CDMA) system based on Orthogonal Frequency Division Multiplexing (OFDM). Multiple-Input Multiple-Output (MIMO) channel from k users, which moves at vehicular speed, to the Base-Station (BS) is time-varying. For time-varying channels, Sphere Decoding (SD) was introduced to perform ML decoding. Whereas, computational complexity of SD (due to a QR-factorization for each symbol), is nevertheless high. Modified SD had been proposed to achieve near optimum solutions that called Subspace-Sphere Decoder (SPSD). Approach: Proposed algorithm was based on subspace and orthogonal projection with very small dimensionality as robustness scheme in an iterative Multi-User Detection (MUD) and Parallel Interference Cancelation (PIC) method. Results: This approach had been achieved intense reduction of computational complexity for time-varying channel via one and more than one order of magnitude at channel estimation and multiuser detection respectively. Furthermore, SPSD was robustness to channel estimation error (about 3.8 dB) as compared to the representative counterparts in literature. Conclusion: Effectiveness of proposed method was demonstrated by simulations.