| Summary: | 碩士 === 長庚大學 === 電機工程研究所 === 89 === The maximum likelihood detection of superimposed signal in direct sequence code division multiple access (DS-CDMA) has a computational complexity, increased in exponential with numbers of active users, and its implementation is prohibitive even for a moderate number of users. Some research has applied expectation maximization (EM) algorithm to decompose the multiuser detection problem into a series of single-user problems, and presents an iterative computational efficient algorithm for detection of signals in synchronous CDMA system. The EM-based detector estimates each user’s signal to interference ratio (SIR) only by the property of cross-correlation of different users, but it does not reflect the actual SIR of each user. We propose a new detector, without increasing additional hardware circuit, can estimate signal to interference ratio (SIR) of different users directly by each user’s match filter output. Within estimated SIR, new detector changes its parameter dynamically to increase the performance of detection. Simulation result also shows that when near-far effect occurs or the power control is not perfect, the new detector can maintain performance without estimating signal amplitude of each user.
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