Comparison of Two Neural Networks in MC-CDMA Multiuser Detection

MC CDMA is a thriving topic in recent years. Multiuser interference is also very severe as in DS CDMA. ML method is the best multiuser detection, but it has a computational complexity exponentially increased with the number of users. Mean field annealing and chaotic neural network are two promising optimum techniques. This paper applies them into the ML detection, comparison of the two methods is made.

NOVEL ADAPTIVE MULTIUSER DETECTIONALGORITHM BASED ON WAVELET TRANSFORM

The wavelet transform-based adaptive multiuser detection algorithm is presented. The novel adaptive multiuser detection algorithm uses the wavelet transform for the preprocessing, and wavelet-transformed signal uses LMS algorithm to implement the adaptive multiuser detection. The algorithm makes use of wavelet transform to divide the wavelet space, which shows that the wavelet transform has a better decorrelation ability and leads to better convergence. White noise can be wiped off under the wavelet transform according to different characteristics of signal and white noise under the wavelet transform. Theoretical analyses and simulations demonstrate that the algorithm converges faster than the conventional adaptive multiuser detection algorithm, and has the better performance. Simulation results reveal that the algorithm convergence relates to the wavelet base, and show that the algorithm convergence gets better with the increasing of regularity for the same series of the wavelet base. Finally the algorithm shows that it can be easily implemented.

Low Complexity Multiuser Detection with Recursively Successive Zero-Forcing and SIC Based on Nullspace for Multiuser MIMO-OFDM System

To improve the spectrum efficiency, this paper considers the multiuser detection with the MU-MIMO technology for multiuser MIMO-OFDM system uplink with the same subcarrier shared by multiple users. A low complexity multiuser detection algorithm with recursively successive zero-forcing and successive interference cancellation(RSZF-SIC) based on nullspace is proposed. The RSZF process based on the block diagonalization(BD) technique eliminates the co-channel interference(CCI) by a recursive method based on the nullspace orthogonal theorem. The SIC process detects the user signals respectively with the reasonable user detection sequence based on the results of the RSZF process. The computational complexity of the proposed algorithm is effectively reduced by reducing the total number of singular value decomposition(SVD) operations and the dimension of the SVD matrix in the recursive procedure. The performance of the proposed algorithm is improved in terms of bit error rate and sum capacity of the system, especially in the highSNR regime.

ANALYSIS OF GROUP MULTIUSER DETECTION BASED ON COALITION GAME THEORY

Coalition game theory is introduced to investigate the performance,fairness and stability of decorrelating group multiuser detection receiver,not only from the perspective of individual nodes,but also various coalitions and the whole system as well. Firstly,to derive how the system scale with coalition size,a stochastic model with transferable payoffs (stochastic TU-model) is provided. Secondly,to find the most preferred coalition structures from the view point of individual nodes,a model with Non-Transferable payoffs (NTU-model) is presented. Theoretical analysis and simulation results suggest that stochasticaly the grand coalition is payoff maximizing for the system as a whole,while individual nodes with good-conditioned channels may prefer local "win-win coalitions".

A novel constant modulus array for multiuser detection

This paper proposes a new multitarget constant modulus array structure for code division multiple access (CDMA) systems. The new algorithm for the structure is called pre-despreading and wavelet denoising constant modulus algorithm (D-WD-CMA). In the new algorithm, the pre-despreading is applied to multitarget arrays to remove some multiple access inter- ferences. After that the received signal is subjected to wavelet de-noising to reduce some noise, and used in CMA adaptive iteration for signal separation. Simulation results showed that the proposed algorithm performed better than the traditional CMA algorithm.

Novel space-time multiuser detection algorithm of WCDMA system

The structure and performance of space-time multiuser detection receiver at base stations of WCDMA system is analyzed, in which smart antenna is employed. WCDMA uplink signal model is established in this paper. Space-time multiuser receiver presented in this paper combines 2D-RAKE with parallel interference cancellation (PIC), and the improved parallel interference cancellation methods are given. A novel space-time multiuser detection scheme, 2DRAKE-GPPIC is proposed. This scheme employs smart antenna to suppress unexpected DOA (Direction Of Arrival) signal, uses RAKE receiver to combine different delays of expected signal, and utilizes grouped partial parallel interference cancellation (GPPIC) algorithm to suppress further the interference signal in the main lobe of array antennas. The simulation results reveal that the scheme of space-time multiuser detection presented in this paper has better performance for WCDMA system.

Algorithm and application of multiuser detection for CDMA-based MANET

Throughput of mobile ad hoc network （MANET） is limited by collision avoidance. In CDMA-based MANET, this limitation can be overcome by multiuser detection （MUD） because conventional colliding packets can be detached and detected by MUD so that multi-packet reception （MPR） is possible. This paper introduces the principles of MUD algorithm for MANET, and proposes an adaptive blind MUD algorithm. A special medium access control （MAC） protocol is designed to make MANET more efficient. This is achieved by sending more packets to a destination simultaneously. The proposed MUD algorithm and MAC protocol allow CDMA-based MANET to support MPR. Simulations show a remarkable improvement in the throughput performance of MANET.

Space-Time Multiuser Detection for DS-CDMA Communication in MIMO Systems

Space-time signal processing based on multiple-input multiple-output（MIMO） systems is an active research field in which interfering signals are cancelled and multiuser detection is achieved using space diversity. In a Rayleigh fading channel, space-time block cedes using multiple transmitting antennas can improve system performance and reduce bit-error-rate for multiuser detection. In this paper, several antenna configurations are designed for DS-CDMA communication in MIMO systems. Space-time linear multinser detection and space-time serial interference cancellation multiuser detection are simulated. Bit-error-rate and computation complexities of the two methods are compared. Conclusions are given in the end.

Improved Blind Multiuser Detection Algorithm Based on Minimum Output Energy

Based on minimum output energy,an improved blind multiuser detection algorithm is proposed by the use of Hopfield neural network.Compared with traditional algorithms,the proposed algorithm does not need the circuit for constraints.The resources are greatly saved and the complexity is reduced as well.The simulation results show that the performance of the improved algorithm is similar to that of the optimal multiuser detection algorithm which is not suitable for the mobile station.Compared with the traditional gradient blind multiuser detection algorithm,the convergence speed of the improved algorithm is quickened.

A new support vector machine based multiuser detection scheme

In order to suppress the multiple access interference (MAI) in 3G, which limits the capacity of a CDMA communication system, a fast relevance vector machine (FRVM) is employed in the multiuser detection (MUD) scheme. This method aims to overcome the shortcomings of many ordinary support vector machine (SVM) based MUD schemes, such as the long training time and the inaccuracy of the decision data, and enhance the performance of a CDMA communication system. Computer simulation results demonstrate that the proposed FRVM based multiuser detection has lower bit error rate, costs short training time, needs fewer kernel functions and possesses better near-far resistance.

A Particle Filter of Blind Equalization and Multiuser Detection in Asynchronous DS/CDMA Systems

The particle filter （PF） is proposed to be the asynchronous direct-sequence code-division multiple-access （DS/CDMA） multiuser detector without knowing the channel state information. The PF performs symbol detection according to the joint posterior density probability of simulated particles including relative delays, fading gains and symbols via sequential importance sample and resample. A simplified scheme is also proposed by separating the indepent relative delays and fading with symbols. These parameters are modeled as the extended aggressive processes and estimated by the Kalman filter, so as to provide their arbitrary distribution for symbol detection. Simulation results show that the bit error rate of the PF is less than conventional detectors. Moreover, the complexity of PF is moderate comparable to other nonlinear suboptimal approaches.

FIXED-POINT BLIND ADAPTIVE MULTIUSER DETECTION ALGORITHM FOR IR UWB SYSTEMS IN MULTIPATH CHANNEL

Using the hypothesis that data transmitted by different users are statistically independent of each other,this paper proposes a fixed-point blind adaptive multiuser detection algorithm for Time-Hopping (TH) Impulse Radio (IR) Ultra Wide Band (UWB) systems in multipath channel,which is based on Independent Component Analysis (ICA) idea. The proposed algorithm employs maximizing negentropy criterion to separate the data packets of different users. Then the user characteristic se-quences are utilized to identify the data packet order of the desired user. This algorithm only needs the desired user’s characteristic sequence instead of channel information,power information and time-hoping code of any user. Due to using hypothesis of statistical independence among users,the proposed algorithm has the outstanding Bit Error Rate (BER) performance and the excellent ability of near-far resistance. Simulation results demonstrate that this algorithm has the performance close to that of Maximum-Likelihood (ML) algorithm and is a suboptimum blind adaptive multiuser detection algorithm of excellent near-far resistance and low complexity.

Soft-PIC multiuser detection in MC-CDMA uplink system

It is necessary for an MC-CDMA uplink receiver to employ MUD (multiuser detection) in a frequency selective fading channel. After analyzing the algorithm of PIC(parallel interference cancellation) MUD, a novel MUD scheme, Soft-PIC (soft parallel interference cancellation) is proposed. Based on the reliability of each detected user signal in the former stage, this Soft-PIC detection scheme substitutes a soft decision of the variable for the hard decision in PIC scheme. Compared with the PIC scheme, it can reconstruct the interference signals more accurately and eliminate MAI(multiple access interference) in a more efficient way.PIC is one of the most practical schemes in numerous multiuser detection technologies. However, Soft-PIC as an improved PIC scheme deserves further study.

NOVEL DECODING OF SQUARE QAM MODULATED MIMO SYSTEMS BASED ON TURBO MULTIUSER DETECTION

By introducing the bit-level multi-stream coded Layered Space-Time （LST） transmitter along with a novel iterative MultiStage Decoding （MSD） at the receiver, the paper shows how to achieve the near-capacity performance of the Multiple-Input Multiple-Output （MIMO） systems with square Quadrature Amplitude Modulation （QAM）. In the proposed iterative MSD scheme, the detection at each stage is equivalent to multiuser detection of synchronous Code Division Multiple Access （CDMA） multiuser systems with the aid of the binary representation of the transmitted symbols. Therefore, the optimal Soft-Input Soft-Output （SISO） multiuser detection and low-complexity SISO multiuser detection can be utilized herein. And the proposed scheme with low-complexity SISO multiuser detection has polynomial complexity in the number of transmit antennas M, the number of receive antennas N, and the number of bits per constellation point Me. Simulation results demonstrate that the proposed scheme has similar Bit Error Rate （BER） performance to that of the known Iterative Tree Search （ITS） detection.

HYBRID INTERFERENCE CANCELLATION SCHEME FOR BLIND MULTIUSER DETECTION IN MULTIPATH FADING CHANNELS

This paper introduces and analyzes a detection scheme for adaptive suppression of Multiuser Access Interference (MAI) and MultiPath Distortion (MPD) for mobile station of DS/CDMA system. The proposed detection scheme may amount to a RAKE receiver structure,wherein each branch is considered as a linear multiuser filter designed under a Linear Constrained Minimum Variance (LCMV) optimization strategy to suppress MAI, followed by a proper combining rule to suppress MPD. The adaptive blind multiuser detecting and optimum combining of the proposed receiver are realized, based on the Least-Mean-Square (LMS) algorithm and an adaptive vector tracking algorithm respectively. Finally, the feasibility of the above two algorithms is proved by the numerical results provided by computer simulation.

NEW LSCM BLIND MULTIUSER DETECTION ALGORITHM FOR ANTENNA ARRAY CDMA SYSTEM

Two blind multiuser detection algorithms for antenna array in Code Division Multiple Access （CDMA） system which apply the linearly constrained condition to the Least Squares Constant Modulus Algorithln （LSCMA） are proposed in this paper. One is the Linearly Constrained LSCMA （LC-LSCMA）, the other is the Preprocessing LC-LSCMA （PLC-LSCMA）. The two algorithms are compared with the conventional LSCMA. The results show that the two algorithms proposed in this paper are superior to the conventional LSCMA and the best one is PLC-LSCMA.

BLIND MULTIUSER DETECTION FOR V-BLAST CODED MULTICARRIER CDMA SYSTEM

Focusing on the space-time coded multiuser mobile communication systems in the frequency-selective fading environment, this paper proposes a Vertical Bell labs LAyered Space-Time (V-BLAST) coded Multicarrier Code-Division Multiple-Access (MC-CDMA) scheme and its blind channel identification algorithm. This algorithm employs an ESPRIT-like method and the singular value decomposition, and the channels between every transmit antenna of every user and every receive antenna of the base station are blindly estimated with a closed-form solution. Based on it, an equivalent Minimum Mean-Squared Error (MMSE) time-domain multiuser detector is derived. Moreover, the proposed scheme exploits the precoding in the transmitter in order to eliminate the constraint of more receive antennas than transmit ones, required by most conventional V-BLAST codec schemes. Computer simulation results demonstrate the validity of this proposed scheme.

ON THE PERFORMANCE OF ANALOG MULTIUSER DETECTION IN ULTRA-WIDEBAND TRANSMITTED-REFERENCE SYSTEM

The detection performance is evaluated for our proposed analog multiuser receiver in Ultra-WideBand (UWB) transmitted-reference system. In the presence of dense multipath and multi-access signals,the performance analysis is difficult due to the complicated waveform of received impulse. We develop an approach to analyze the steady-state Signal-to-Interference-plus-Noise (SINR) of the detector output. The multipath-spread impulse is fitted to an exponentially decaying profile in the analysis. A closed-form expression of steady-state SINR is further deduced for the proposed Least Minimum Square (LMS) detector. The analysis is validated by simulations in Line-Of-Sight (LOS) and Non-Line-Of-Sight (NLOS) channel respectively. Based on the theoretical results,the multipath delay spread is employed to determine the optimal width of the integration window of the detector.

AN IMPROVED SUBSPACE TRACKING ALGORITHM FOR BLIND ADAPTIVE MULTIUSER DETECTION

As the Projection Approximation Subspace Tracking with deflation(PASTd) algorithm is sensitive to impulsive noise, an improved subspace tracking algorithm is proposed and applied to blind adaptive multi-user detection. Simulation results show that the improved PASTd algorithm not only remains the properties of the conventional PASTdalgorithm, but also has good Bit Error Rate(BER) performance in impulsive noise environment, thus it can effectively improve the system performance.

SUCCESSIVE BEAMFORMING,MULTIUSER DETECTION AND DIVERSITY RECEPTION FOR MULTICARRIER DS-CDMA SYSTEM WITH ANTENNA ARRAY

Code-Division Multiple-Access (CDMA) systems are interference limited,and therefore efficient interference management is necessary to enhance the performance of a CDMA system.In this paper,a successive beamforming (spatial filtering),linear decorrelating MultiUser Detection (MUD, temporal filtering) and diversity reception structure for uplink multicarrier Direct Sequence CDMA (DS-CDMA) system with antenna array are proposed.By beamforming,the antenna array suppresses interference according to the distinct array signature.Subsequently,linear decorrelating MUD is ap- plied to separate the signals of different users and eliminate Multiple Access Interference (MAI).Finally, the decorrelated signals at different subcarriers that belong to the same user are combined to achieve frequency diversity.Simulation results show that the proposed structure offers significant Bit Error Rate (BER) performance improvement by successively exploiting the space-time-frequency processing.