A thesis submitted in partial fulfillment of the requirement for the degree of Master of Engineering, School of Engineering and Technology

Thesis (M.Eng.) - Asian Institute of Technology, 2001

The future generation networks are supposed to have capability to support multimedia and high data rate services. Proposed third generation systems such as UMTS have indorsed W-CDMA as the access technique. In addition to third generation systems, MC-CDMA has been proposed as the signaling technique for future generation broadband wireless networks, since it offers robustness to channel impairments, relatively low complexity, flexibility in bandwidth assignment and efficient spectrum use. It has also been shown that multicarrier allocation scheme can provide radio links with different rates suitable for multimedia communications. To achieve such a diverse traffic requirements, problems of multiple access interference and channel-introduced impairments have to be solved. MC-CDMA signaling incorporating powerful performance improving techniques is currently the topic of various research activities. OFDM at the physical layer with interference suppression, multiuser detection, advanced error control coding and frequency diversity as well as smart antenna are the possible techniques to obtain variable bit rates, spectral efficiency and robustness. In this thesis, performance of asynchronous as well as synchronous MC-CDMA uplink system with antenna array and multiuser detection technique is studied over a Rayleigh multipath fading channel through simulation. Main focus is given to antenna array processing algorithms for spatially correlated as well as spatially independent fading cases. A simplified algorithm suitable for slow fading situation is investigated to overcome the problem associated with Eigen analysis methods. Multiuser detection with interference cancellation detectors are studied in conjunction with antenna array. The effectiveness of different frequency diversity combining methods in antenna array platform is studied. The effect of variable data rate in the system is studied and effectiveness of antenna array to handle high data rate is discussed briefly. A brief investigation on the performance degradation of the system due to correlated channel is also carried out. Based on the simulation results, the performance in asynchronous uplink of the system is found to improve dramatically with the use of antenna arrays and multiuser detection techniques. Asynchronicity and channel correlation are found to affect the system performance significantly. The investigated simplified algorithm is found to produce similar result as with other array processing algorithms in slow fading situation with much reduced complexity. Role of spatial correlation among antenna element is found to be critical. The difference of MMSEC and MRC combining techniques in MCCDMA receiver is found to be insignificant in conjunction with antenna arrays. It is found that variable data rate transmission using MC-CDMA is possible with the assistance of antenna array and multiuser detection techniques.