| Summary: | 碩士 === 國立中興大學 === 電機工程學系 === 88 === In this thesis, we introduce the Blocked MMSE (B-MMSE) multiuser detection scheme for asynchronous DS/CDMA systems, it can be considered as a modified version of conventional MMSE. In the B-MMSE multiuser detector, the information data stream is divided into blocks by inserted silence bits. Since the block length in the B-MMSE detection is controllable, it provides a great flexibility for practical implementations without destroying the optimality of the MMSE detection. Therefore, the adaptive B-MMSE detector retains the advantages of the MMSE detection.
In order to avoid estimation users’ power and track the time-variant channel, the B-MMSE is implemented in an adaptive way. The Least Mean Square (LMS) and Recursive Least Squares (RLS) algorithms are introduced in adaptive B-MMSE detector. We compare the convergence properties and estimation error between the two adaptive algorithms. It is shown that the RLS algorithm offers a consistently fast convergence regardless of the received power, making it ideal for the use in a time-varying channel with near-far effect.
To get the better performance, the antenna array is used in adaptive B-MMSE detector. The LMS and RLS algorithm are also used to control the weights of antenna array. The BER performance of adaptive B-MMSE detector is reduced drastically as the No. of antenna element increased. We also consider using minimum variance distortionless response (MVDR) beamformer but the angle of interest is required. For the practical implementation, we introduce the DOA pre-processor followed by the MVDR beamformer. The BER performance is better than using RLS beamformer if without angle estimation error. Finally, the conclusions and future work are given.
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