Multiuser Detection In DS-CDMA Systems Research Articles

Multi-user Detection in DS-CDMA System Using Biogeography Based Optimization

To attain large information rates, code division multiple access (CDMA) is a well-built aspirant for the downlink of cell phone communications. However, while transmitting any signal over fading channel, the performance of CDMA system is highly affected. For that reason, Multiuser detection (MUD) and channel estimation play a significant function for overcoming the interference and characterizing the channel. In this paper, biogeography base optimization (BBO) algorithm introduced for multiuser detection CDMA system. The objective of BBO algorithm is used to minimize the error rate of the user transmitting signal. According to immigration rate and emigration rate, the optimal solution of the detection problem is decided. Therefore, the user detection complexity and the interference of user transmitting signal are resolved. Proposed multiuser detection algorithm is appropriate for run time user identification process; since the detection complication and the required time are concentrated. The proposed approach is implemented in MATLAB working platform and the performance measures are examined. The error rate of proposed algorithm is compared with harmony search algorithm, enhanced harmony search algorithm, and without multiuser detection procedure.

Non Iterative Algorithm for Multi-user Detection in DS-CDMA System: An Enhanced Harmony Search Algorithm

paper, a non iterative algorithm for MUD in DS-CDMA system is proposed. The proposed multiuser algorithm is performed based on harmony search algorithm. In the proposed algorithm, a new harmony memory updating is based on the random and mean operation. So, the proposed harmony search algorithm is reduced the complexity and the user information interference. Hence, the bit error rate of the transmitted code reduced. In the enhanced harmony search algorithm, the marginal distribution for each observed and unobserved node are calculated. The proposed multiuser detection algorithm is applicable in run time user identification process, so the MUD complexity and the required time are concentrated. Also, the iteration can be predefined based on the number of users, signal interference and signal to noise ratio. This improves the multi- user efficiency, reduce the information losses and power corruption in CDMA channel. The proposed technique is implemented in MATLAB and the performance is evaluated. Keywords-CDMA system, multiuser detection, enhanced harmony search algorithm, bit error rate.

Gaussian process regressors for multiuser detection in DS-CDMA systems

In this paper we present Gaussian processes for Regression (GPR) as a novel detector for CDMA digital communications. Particularly, we propose GPR for constructing analytical nonlinear multiuser detectors in CDMA communication systems. GPR can easily compute the parameters that describe its nonlinearities by maximum likelihood. Thereby, no cross-validation is needed, as it is typically used in nonlinear estimation procedures. The GPR solution is analytical, given its parameters, and it does not need to solve an optimization problem for building the nonlinear estimator. These properties provide fast and accurate learning, two major issues in digital communications. The GPR with a linear decision function can be understood as a regularized MMSE detector, in which the regularization parameter is optimally set. We also show the GPR receiver to be a straightforward nonlinear extension of the linear minimum mean square error (MMSE) criterion, widely used in the design of these receivers. We argue the benefits of this new approach in short codes CDMA systems where little information on the users' codes, users' amplitudes or the channel is available. The paper includes some experiments to show that GPR outperforms linear (MMSE) and nonlinear (SVM) state-ofthe- art solutions.

A Switching Mechanism Detection to Reduce Complexity in Multiuser Detection for DS-CDMA Systems

We present a reduced complexity switching mechanism which uses either matched filter or Parallel Interference Cancellation (PIC) detector based on channel characteristics. The main criterion of taking PIC detector is that it has less Bit Error Rate (BER) and less processing delay than other nonlinear multiuser detectors. This proposed detector reduces overall complexity while maintaining the same performance as PIC detector. The switching mechanism is exploited by performance complexity tradeoff between matched filter detector and PIC detector.

Adaptive Step-size Constant Modulus Algorithm for blind multiuser detection in DS-CDMA systems

Blind Adaptive Step-size Constant Modulus Algorithm (AS-CMA) for multiuser detection in DS-CDMA systems is presented. It combines the CMA and the concept of variable step-size, uses a second LMS algorithm for the step size. It adjusts the step-size according to the minimum output-energy principle within a specified range, thus overcomes the problems of bad effect of fixed step-size LMS algorithm. Compared with Adaptive Step-size LMS (AS-LMS) algorithm, through simulations, this algorithm can adapt the changes of the environment, suppress multiple access interference in the dynamic environment and the stability of Signal to Interference Ratio (SIR) is superior to that of AS-LMS.

Asymptotic eigenvalue moments for linear multiuser detection

Using the theory of lattices of non-crossing partitions, an explicit expression is obtained for the asymptotic moments of certain infinite random matrices that arise in multiuser detection in DS-CDMA systems with random spreading. By using this explicit expression, we obtain a self-contained proof of the Tse-Hanly formula for the output signal-to-interference-plus-noise ratio of a MMSE multiuser detector. The asymptotic moment results are used to design a low-complexity polynomial approximation of a linear multiuser detector. Analytical and numerical results of their performance analysis are also given.

Adaptive implementation of polynomial expansion detector for multi-user detection in DS-CDMA systems

The polynomial expansion (PE) multi-user detector was proposed to eliminate the computational complexity of matrix inversion involved in the decorrelating detector and the MMSE detector. Computation of the polynomial coefficients in a PE detector is, however, a complex task. A fast converging adaptive algorithm based on the Davidon-Fletcher-Powell (DFP) method is proposed for computing polynomial weights for a PE detector.

Subspace-based multiuser detection for DS-CDMA systems with correlated noise

Two subspace-based multiuser detectors are presented for a synchronous DS-CDMA system operating over a multipath fading channel with correlated noise. Based on the training sequence transmitted by the desired user and employing a noise whitening process, a linear MMSE detector is obtained which does not require knowledge of the code sequences and the propagation channel response. When the training sequence is not available, a matrix decomposition method is adopted to estimate the channel response. Through signature waveform estimation, a linear MMSE detector can be obtained blindly. Simulation results show that these two methods are robust against the near–far problem and the correlated noise.