Blind adaptive constrained moe receiver for uplink MC-CDMA systems with real signaling in multi-cell environments
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A blind adaptive constrained minimum output energy (MOE) receiver has been proposed for the uplink multicarrier code-division multiple access (MC-CDMA) system in a multicell environment when some users, including the desired user, employ real-valued modulation such as binary phase-shift keying (BPSK) or amplitude-shift keying (ASK). Since the imaginary part of residual interference at the filter output does not affect the decision of the desired user's data in this case, the proposed receiver has been designed to perfectly eliminate the real part of residual in-cell interference using the information of the spreading sequence and to reduce the real part of residual intercell interference by minimizing the constrained output energy. Results of analysis and simulation show that the proposed blind adaptive algorithm converges faster and has a higher steadystate signal-to-interference and noise ratio (SINR) than those of conventional schemes.Multiple access interference (MAI) limits the capacity of Direct Sequence Code Division Multiple Access (DS-CDMA) systems. In CDMA systems MAI is considered as additive noise and a matched filter bank is employed. Traditionally, multiuser detectors—a code-matched and a multiuser linear filter—are used which increases the complexity of the system due to its nature of operation. Multiuser detection is an approach which uses both these filters for the optimization. However, the main drawback of the optimal multiuser detection is one of complexity so that suboptimal approaches are being sought. Much of the present research is aimed at finding an appropriate tradeoff between complexity and performance. These suboptimal techniques have linear and non-linear algorithms. In this work, we introduce Successive Interference Cancellation (SIC) which is a nonlinear suboptimal method of MUD and is based upon successively subtracting off the strongest remaining signal. Further analysis is to be carried out and simulations to be done for better understanding of SIC.
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This paper describes a successive multiuser detection technique for Direct Sequence Code Division Multiple Access (DS-CDMA) systems. In conventional CDMA system, single-user detection is employed, so that the interference between users or multiple access interference (MAI) component is considered as noise, which contributes to the statistics of detection variables affecting the quality of detection. In this paper a successive multiuser detection scheeme is proposed to cancell inter user interference. In multiuser detections, the MAI component can be eliminated or cancelled by the use of all user's spreading code in the system. The basic concept of successive multiuser detection technique are described in a simple model and the performance for various number of users is simulated and eavaluated. The performnce of successive multiuser detection is then compared with that of the single-user detection to show a significant improvement.
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Semi-blind multiuser detection for the reverse link of a multi-cell code-division multiple-access (CDMA) system is considered. In such a system, although active users are present in the home cell and neighbouring cells, the base station receiver only knows the signal information of the users in its own cell. Three new adaptive semi-blind linear multiuser detectors are proposed, based on a parallel interference cancellation approach. Compared with some known semi-blind detectors, the proposed detectors share a rather simple implementation structure and involve reduced latency for processing, which are of particular importance in a time-varying CDMA system. Numerical results are presented to show that the detection performance of the proposed detectors is superior to that of some existing semi-blind multiuser detectors.
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We consider a synchronous code division multiple access (CDMA) system where all users share an additive white Gaussian noise channel. For this multiuser communication system a new so-called hybrid multiuser detection scheme based on a favourable link of multistage multiuser detection algorithms and maximum likelihood detection is presented. It is shown that this scheme yields a profitable tradeoff between computational expense and detection performance. In addition, the hybrid detection scheme offers the possibility of parallel computations such that computational delay can be limited to a reasonable size.
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This paper describes the effect of power imbalance on multiuser detection of Direct Sequence Code Division Multiple Access (DS-CDMA) systems. Unlike the conventional single-user detection technique which considers interference between users or multiple access interference (MAI) as noise, in multiuser detection schemes of DS-CDMA systems MAI is eliminated successively. However in the present of near-far problems and fading channels, where received power among different users are of different levels, the performance of multiuser detection methods degrade due to unreliable detections of users with low power levels. In this paper multiuser detection is described in a simple model and the performance for various number of users is evaluated using computer simulation. The effect of power imbalance among different users is presented to show the performance degradation.
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Semiblind multiuser detection for the reverse link of a multicell code-division multiple-access (CDMA) system is considered. In such a system, although active users are present in the home cell and neighboring cells, the base station receiver only knows the signature information of the users in its own cell. Three new semiblind linear multiuser detectors are proposed based on parallel interference cancellation approach. Compared with some known semiblind detectors, the proposed detectors share a rather simple implementation structure and involve reduced latency for processing, which are of particular importance in a time-varying CDMA system. Numerical results are presented to compare the detection performance of the proposed detectors with that of some existing semiblind multiuser detectors.
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The conventional single user detector in DS-CDMA (direct sequence code division multiple access) systems involves multiple access interference and the near-far effect which cause the limitation of capacity. On the other hand, the computational complexity of the optimum multiuser detector grows exponentially with the number of users. There has been a lot of interest in suboptimal multiuser detectors with less complexity and reasonable performance. In this paper we apply the classic and new modified genetic algorithms for multiuser detection of DS/CDMA signals. It is shown that the classic genetic algorithm (GA) reaches an error floor at high signal to noise ratios while the proposed method has higher performance than the classic one and is comparable to the optimum single user detector with much less complexity than the optimum multiuser detector.
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An improved pseudo parallel genetic algorithm based on multiuser detection(MUD) is proposed for the multicarrier code-division multiple-access(MC-CDMA) system in the frequency-selective fading channel.The pseudo parallel genetic algorithm based on the allied strategy of human being is used in MUD technology.Simulation analysis shows that the pseudo parallel genetic algorithm based on allied strategy of human being has better performance than DEC,MMSE and tradition GA used in MUD for MC-CDMA systems,and it can provide 97.5% in computational complexity than the optimal multiuser detection.
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