| CDMA (Code Division Multiple Access) is a promising technology for future mobile communication system because of its several features with which other multiple access technology can not compare: higher efficiency of frequency allocation, robust anti-multipath effect, macro diversity, mitigating interference, soft capacity, low power, soft handoff, simple frequency design, easy access, and so on. In CDMA communication system, the users are identified by their different spread spectrum codes which are unique to each user, namely they are identified by the cross correlation of spread spectrum codes. If the correlation of different spread spectrum codes is not zero, there would be multi-access interference. Additionally, CDMA communication system is a interference-limited system, that is to say that the interference directly influences the capacity of this system and the QoS of the user in the system. In order to rid the multi-access interference, multi-user detection (MUD) plays a important role. Traditional CDMA detector executes the correlation operation on the receivers signal to get the user' symbol, but this method does not considered the difference between the multi-user interference and the white noise. Multi-user detection executes the jointly detection fully using the spreading sequence, time delay x phase information and amplitude, the performance has enhanced as a whole. It overcomes the multi-user interference, the uplink frequency resource is used efficiently, so the capacity of system has been increased notably.In this paper, the principle of spread sequence communication and all kind of the current multi-user detection techniques and the independent component analysis (ICA) algorithm are respectively analyzed completely in chapter II , chapter III and chapter IV. Based on the statistical feature of multi-user signal that the signal of every user's and every channel is statistical independent with each other and take the same distribution, the mathematical model of the received multi-user signal is fully researched, then the blind signal detection algorithm is introduced into the multi-user signal detection, two new algorithms of multi-user detection are proposed: multi-user detection based on the delay estimation of downlink using ICA in DS-CDMA and based on ICA post processing matched filter multi-user detection.In the fifth chapter, these two algorithms are recommended in detail. Traditional delay estimation based on ICA requires the trail sequences to initialize the receiver, but the new algorithm based on ICA does not need the trail sequences. It is based on the channel character of downlink,using the ICA algorithm to estimate the multi-path mixture matrix, then, find the delay information which is embodied by the column vector of the mixture matrix. The simulation results show that it does enhance the performance of traditional detector without wasting the invaluable frequency resource. Based on ICA post processing matched filter multi-user detection lets the output of traditional matched filter to initialize the ICA iterations, not only the known spread information of interesting user is used to overcome the uncertainness of ICA, but also the character of statistical independence is used. The simulation results show that it advances the ability of traditional detector when the signal-noise-ratio is large.Keywords Code Division Multiple Access; Independent Component Analysis; Channel Estimation; Matched Filter; Blind Multi-user Detection... |
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