Abstract
Multiuser detection is the demodulation of signals of different users interfering with each other. This phenomena known as multiple access interference occurs mostly in code division multiple access (CDMA) systems. In this paper the study and analysis of the blind adaptive multiuser detection algorithm is achieved for directsequence code division multiple access (DS-CDMA) communication systems. The goal is to obtain multiuser detectors that require only knowledge of the signature waveform and timing of the desired user. Comparison is performed of the blind adaptive technique with the conventional detector (matched filter detector) or (M.F.D) in perfect power control and in the presence of the near-far effect. In the present simulation, the blind adaptive multiuser detection showed an excellent bit error rate as compared to the conventional detection with the same requirements. Also the blind detector showed an immunity towards the near-far problem. In this simulation the use of adaptive variable step size is used in contrast to the constant step size shows improvement in speed convergence and stability of the algorithm adapte
Highlights
Conventional communication models use time or frequency division multiplexing
Continuous-time Model The basic synchronous K-user code division multiple access (CDMA) model describes the received signal of a CDMA system in which K synchronous bit streams antipodally modulate K signature waveforms, which are transmitted over an Additive White Gaussian Noise (AWGN) channel
Results and Discussion: a description of the simulation model for synchronous directsequence code division multiple access (DS-CDMA) for K=10-user, processing gain N=31 short code [the period of the signature sequence is equal to the duration of a bit], gold code sequence is used, with Additive White Gaussian Noise (AWGN) [3]
Summary
Conventional communication models use time or frequency division multiplexing. In time division multiple access (TDMA) systems a unique time slot is reserved for each user. Each user is assigned a unique "code" and by using this code receiver can demodulated the desired signal. In a mobile environment a particular user's signal may be received more strongly than the desired user This effect is known as the near-far effect. The optimum detector was proposed by Verdu This receiver has a very high computational complexity that increases exponentially with the number of active users. Adaptive MMSE detector is a typical detector that uses training sequences to minimize the square error between the transmitted bit and the filter output. Each time the channel goes through drastic changes the training sequence must be retransmitted which is a very costly operation for fastly changing channels like the wireless environment To overcome this problem blind detectors are proposed. The blind detectors only require the signature waveform and the timing of the desired user [2]
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