Asymptotic Performance Analysis of Blind Minimum Output Energy Receivers for Large DS-CDMA Systems

The random matrix theory is used to analyze the asymptotic performance of the blind minimum output energy (MOE) receiver in direct-sequence code division multiple-access (DS-CDMA) systems in the presence of unknown multipath channel under the condition that the spreading factor and the number of users go to infinity with the same rate. As a special case, the asymptotic properties of the blind Capon receiver are also studied and the conditions of convergence of the signal-to-interference-plus-noise ratio (SINR) of this receiver to that of the optimal minimum-mean-square error (MMSE) receiver are discussed. In particular, it is shown that the SINR performances of the Capon and MMSE receivers are nearly identical in the uplink scenario, while the performance of the Capon receiver may be considerably inferior to that of the MMSE receiver in the downlink transmission case. As the performance of the Capon receiver is closely related to the performance of the Capon channel estimator, the asymptotic properties of the latter estimator are also studied and the conditions of convergence of the Capon channel estimate to a scaled version of the channel vector of the user-of-interest are obtained.     

Blind adaptive space-time multiuser detection with multipletransmitter and receiver antennas

The demand for performance and capacity in cellular systems has generated a great deal of interest in the development of advanced signal processing techniques to optimize the use of system resources. In particular, much work has been done on space-time processing in which multiple transmit/receive antennas are used in conjunction with coding to exploit spatial diversity. We consider space-time multiuser detection using multiple transmit and receive antennas for code-division multiple-access (CDMA) communications. We compare, via analytical bit-error-probability calculations, user capacity, and complexity, two linear receiver structures for different antenna configurations. Motivated by its appearance in a number of third-generation (3G) wideband CDMA standards, we use the Alamouti (see IEEE J. Select. Areas Commun., vol.16, p.1451-58, Oct. 1998) space-time block code for two-transmit-antenna configurations. We also develop blind adaptive implementations for the two transmit/two receive antenna case for synchronous CDMA in flat-fading channels and for asynchronous CDMA, in fading multipath channels. Finally, we present simulation results for the blind adaptive implementations     

Adaptive transmitter optimization for blind and group-blind multiuser detection

The linear subspace-based blind and group-blind multiuser detectors recently developed represent a robust and efficient adaptive multiuser detection technique for code-division multiple-access (CDMA) systems. In this paper, we consider adaptive transmitter optimization strategies for CDMA systems operating in fading multipath environments in which these detectors are employed. We make use of more recent results on the analytical performance of these blind and group-blind receivers in the design and analysis of the transmitter optimization techniques. In particular, we develop a maximum-eigenvector-based method of optimizing spreading codes for given channel conditions and a utility-based power control algorithm for CDMA systems with blind or group-blind multiuser detection. We also design a receiver incorporating joint optimization of spreading codes and transmitter power by combining these algorithms in an iterative configuration. We will see that the utility-based power control algorithm allows us to efficiently set performance goals through utility functions for users in heterogeneous traffic environments and that spreading code optimization allows us to achieve these goals with lower transmit power. The signal processing algorithms presented here maintain the blind (or group-blind) nature of the receiver and are distributed, i.e., all power and spreading code adjustments can be made using only locally available information.     

CMA Performance in CDMA Transmit Diversity System

1IntroductionThe capacity and performance of CDMAare largelyaffected by disturbances ,and Multi-Access Interference( MAI) is the main disturbance factor whenthe numberof user is large . Blind adaptive Multi-User Detection(B-MUD)is aneffectivetechniquetoreduce MAI[1 ~2].In many advanced and convergence faster algorithms ,Constant Mode Algorithm ( CMA) is an efficient B-MUDand has better systemperformance .Refs .[3 ~6]depict the CMAin details .The channel of mobile communications p…     

Robust blind multiuser detection against signature waveform mismatch based on second-order cone programming

Blind signal detection in multiuser code division multiple access (CDMA) system is particularly attractive when only the desired user signature is known to a given receiver. A problem common to several existing blind multiuser CDMA detectors is that the detection performance is very sensitive to the signature waveform mismatch (SWM) which may be caused by channel distortion. In this paper, we consider the design of a blind multiuser CDMA detector that is robust to the SWM. We present a convex formulation for this problem by using the second-order cone (SOC) programming. The resulting SOC problem can be solved efficiently using the recently developed interior point methods. Computer simulations indicate that the performance of our new robust blind multiuser detector is superior to those of many existing methods.     

Space-time blind multiuser detection for multirate DS/CDMA signals

Multiuser detection for multirate direct-sequence code-division multiple access (DS/CDMA) has been an active area of research. For example, nonblind low-rate (LR) and high-rate (HR) decorrelators have been proposed and analyzed in the literature for synchronous dual-rate systems with single receive antenna. Inspired by the subspace-based space-time (ST) blind linear detectors for synchronous single-rate systems, this paper extends the existing results and proposes the subspace-based ST-LR and ST-HR blind linear detectors, i.e., blind decorrelators and blind minimum mean-squared error (mmse) detectors, for synchronous dual-rate DS/CDMA. It is shown that: 1) ST-LR blind linear detectors can support no less users than ST-HR blind linear detectors as long as the desired spatial signature is identifiable (assuming that all the other system parameters are the same) and 2) the bit-error rate performance of ST-LR blind decorrelator is not inferior to that of its HR counterpart. The above conclusions are generalized to synchronous multirate systems. The extension to asynchronous systems is also described. Finally, the two-stage ST dual-rate blind detectors, which combine the adaptive purely temporal dual-rate blind mmse detectors with the nonadaptive beamformer, are presented.     

CDMA发射分集系统的多用户检测常模算法分析

空时分集技术的最大优点在于在不增加带宽的情况下可以提高系统的可靠性,是目前移动通信的研究热点.常模算法是一种性能优良的码分多址(CDMA)盲多用户检测技术,能确保判决信号与实际传送信号之间的差错较小,误码率性能良好.文中提出将标准线性受限常模算法(LCCMA)与空时分组码(STBC)相结合,设计出一种收敛快、能够改善系统性能的基于2-空时分组码的多用户接收机.     

基于差分空时分组码的卡尔曼盲多用户检测

对大容量、高性能蜂窝通信系统的需求引起了人们对先进信号处理技术的极大兴趣，尤其是使用多个发射／接收天线，利用空域分集的处理技术更是受到了广泛关注。使用多个发射天线及差分空时分组码，可用一种新的适用于频率平坦信道的盲自适应多用户接收机。新方法不需要信道估计，它首先利用卡尔曼(Kalman)自适应滤波器抑制多址干扰，然后完成差分空时解码获得分集增益。计算机仿真结果表明该方法具有较强的抗衰落和抑制多址干扰的能力，并能自适应地跟踪信号环境的变化。     

2-D rake receiver based on space-time channel parameter estimation

2-D RAKE receiver is an efficient way to realize the space-time processing for CDMA systems with aperiodic spreading codes. The Direction Of Arrival (DOA) and the relative time delay of every user's multipath must be known to realize the 2-D RAKE receiver. In the third generation CDMA mobile communication system, auxiliary pilot channel is used in the uplink channels. The different user's Vector Channel Impulse Response (VCIR) can be estimated from the pilot channel easily. The VCIR contains spatial and temporal information. In this paper, by utilizing the known pulse shape function, a parameter matrix method used to estimate the Spatial Signature Vector (SSV) and the relative time delay is proposed in frequency domain. The DOA can be estimated from the SSV. By reconstructing the SSV and utilizing approximate Capon space filter, the performance of the 2-D RAKE receiver with uniform circular array can be improved with a little additional computation work.     

Iterative receivers for multiuser space-time coding systems

Space-time coding (STC) techniques, which combine antenna array signal processing and channel coding techniques, are very promising approaches to substantial capacity increase in wireless channels. Multiuser detection techniques are powerful signal processing methodologies for interference suppression in CDMA systems. In this paper, by drawing analogies between a synchronous CDMA system and an STC multiuser system, we study the applications of some multiuser detection methods to STC multiuser systems. Specifically, we show that the so-called “turbo multiuser detection” technique, which performs soft interference cancellation and decoding iteratively, can be applied to STC multiuser systems in flat-fading channels. An iterative multiuser receiver and its projection-based variants are developed for both the space-time block coding (STBC) system and the space-time trellis coding (STTC) system. During iterations, extrinsic information is computed and exchanged between a soft multiuser demodulator and a bank of MAP decoders, to achieve successively refined estimates of the users' signals. Computer simulations demonstrate that the proposed iterative receiver techniques provide significant performance improvement over conventional noniterative methods in both single-user and multiuser STC systems. Furthermore, the performance of the proposed iterative multiuser receiver approaches that of the iterative single-user receiver in both STBC and STTC systems     

Blind zero forcing equalization of multichannel nonlinear CDMAsystems

Code division multiple access (CDMA) has emerged as a popular format for wireless communication systems. As a result of intersymbol interference (ISI) and nonlinearities, the performance of CDMA systems can suffer. In this paper, we propose a blind equalizer for CDMA systems with Volterra (nonlinear) channels. The equalizer requires multiple observations at the receiver, which are obtained through oversampling or an antenna array, and a knowledge of the code of the desired user. Zero forcing equalization is possible in the noise-free case. Simulations demonstrate the performance of the equalizer under a variety of operating conditions     

Blind turbo multiuser detection for long-code multipath CDMA

We consider the problem of demodulating and decoding multiuser information symbols in an uplink asynchronous coded code-division multiple-access (CDMA) system employing long (aperiodic) spreading sequences, in the presence of unknown multipath channels, out-cell multiple-access interference (OMAI), and narrow-band interference (NBI). A blind turbo multiuser receiver, consisting of a novel blind Bayesian multiuser detector and a bank of MAP decoders, is developed for such a system. The effect of OMAI and NBI is modeled as colored Gaussian noise with some unknown covariance matrix. The main contribution of this paper is to develop blind Bayesian multiuser detectors for long-code multipath CDMA systems under both white and colored Gaussian noise. Such detectors are based on the Bayesian inference of all unknown quantities. The Gibbs sampler, a Markov chain Monte Carlo procedure, is then used to calculate the Bayesian estimates of the unknowns. The blind Bayesian multiuser detector computes the a posteriori probabilities of the channel coded symbols, which are differentially encoded before being sent to the channel. Being soft-input soft-output in nature, the proposed blind Bayesian multiuser detectors and the MAP decoders can iteratively exchange the extrinsic information to successively refine the performance, leading to the so-called blind turbo multiuser receiver     

Blind multiuser detection for code-hopping DS-CDMA signals in asynchronous multipath channels

Blind detection of a desired user's signal in a code-hopping (CH) direct sequence code-division multiple access (CDMA) system is considered. In CH CDMA systems each user switches between a predetermined set of short-code sequences. A user signal in such systems may be treated as the superposition of several virtual short-code signals. A code-constrained inverse filter criterion (IFC)-based blind detector for short-code CDMA signals in asynchronous multipath channels to detect a desired user's signal was recently presented by Tugnait and Li (2001). A novel approach combining the code-constrained IFC and a penalty function is proposed to simultaneously extract all virtual users associated with a given CH user. Global minima of the proposed cost function are analyzed. An extension of an existing subspace-based approach is also investigated. An illustrative simulation example is provided where the proposed algorithm is compared with a clairvoyant matched filter receiver, two linear minimum mean-square error (MMSE) receivers with channels known, and the subspace-based approach.     

A Cyclodespreader Architecture for Detecting Multiple Downlink Aperiodic CDMA Signals

Although a code-division multiple-access (CDMA) system is spectrally efficient and has some immunity against intentional reception, its capacity and performance are generally limited by multiple access interference (MAI) caused by other users. For an aperiodic CDMA system, the spreading sequences span multiple symbol intervals, and the cross-correlations between these sequences, which are a measure of the MAI, are periodic over multiple symbols. In this paper, we present a receiver with a parallel architecture that converts an aperiodic CDMA sequence into a piecewise periodic sequence in each arm. We refer to this receiver as a cyclodespreader because the despreader exploits the cyclostationary property of an aperiodic signal. As a result, the transmitted data can be detected separately in each arm of the receiver using low-complexity conventional algorithms proposed for periodic CDMA systems. The goal of the receiver is to decode several signals received from different cochannel base stations. The performance of the system is evaluated using real aperiodic CDMA signals, and it is compared to that of a conventional matched filter (MF) receiver using the number of correctly decoded messages as the performance measure.     

Blind Multiuser Detection with Array Observations

Cochannel interference is usually a major limitation to the performance of mobile wireless systems. Examples of different forms of cochannel interference include multi-access interference in CDMA systems and cochannel interference resulting from frequency reuse in TDMA systems. In order to mitigate the interference from other users we present a blind multiuser receiver which utilizes array observations and performs both spatial and temporal processing of the received signal. The presented technique is completely blind in the sense that no signature sequences, channel state or spatial location needs to be known a priori, nor use of a training sequences, channel state or spatial location needs to be known a priori, nor use of a training sequence is required for the adaptation. The diversity introduced by the array observations can be efficiently combined with the use of CDMA signature sequences. After initial convergence, a reliable estimate of the combined temporal and spatial signature for each user is provided that can be employed by a multiuser receiver of lower complexity.     

Rate-Distortion Optimized Video Transmission Over DS-CDMA Channels with Auxiliary Vector Filter Single-User Multirate Detection

In this paper, we consider the rate-distortion optimized resource allocation for video transmission over multi-rate wireless direct-sequence code-division-multiple-access (DS-CDMA) channels. We consider the performance of transmitting scalable video over a multipath Rayleigh fading channel via a combination of multi-code multirate CDMA and variable sequence length multirate CDMA channel system. At the receiver, despreading is done using adaptive space-time auxiliary-vector (AV) filters. We propose a new interference cancelling design that uses just a single AV filter for single-user mutirate despreading. Our experimental results show that the proposed interference cancelling design has excellent performance in scalable video transmission over DS-CDMA systems that use a combination of multicode multirate and variable processing gain multirate CDMA. The proposed design takes advantage of the fact that single user's video data is transmitted using two spreading codes, one for the base layer and one for the enhancement layers, and of the fact that these spreading codes can have different processing gains. The proposed interference cancelling design is compared with two conventional single-user multirate CDMA receiver configurations, however now we use an AV filter rather than a simple matched filter. We also propose a resource allocation algorithm for the optimal determination of source coding rate, channel coding rate and processing gain for each scalable layer, in order to minimize the expected distortion at the receiver.     

Iterative multiuser interference reduction: turbo CDMA

We view the asynchronous random code division multiple-access (CDMA) channel as a time-varying convolutional code. We study the case where the users encode their data, and, therefore, the single user transmitters and the CDMA channel appear as the concatenation of two coding systems. At the receiver we employ serial turbo decoding strategies. Unlike conventional turbo codes where both the inner and outer code may be selected, in our case, the inner code is due to the CDMA channel which we assume to be random. Nevertheless, the decoding system resembles the decoder of a serial turbo code and single-user performance is obtained even for numbers of users approaching the spreading code length     

Low-rate super-orthogonal channel coding for fiber-optic CDMAcommunication systems

In this paper, we consider using practical low-rate error correcting codes in fiber-optic code division multiple-access (CDMA) communication systems. To this end, a different method of low-rate channel coding is proposed. As opposed to the conventional coding schemes, this method does not require any further bandwidth expansion for error correction in fiber-optic CDMA communication systems. The low-rate channel codes that are used for demonstrating the capabilities of the proposed method are super-orthogonal codes. These codes are near optimal and have a relatively low complexity. We evaluate the upper bounds on the bit-error probability of the proposed coded fiber-optic CDMA system assuming both on-off keying and binary pulse position modulation schemes. It is shown that the proposed method significantly outperforms the uncoded systems for various receiver structures such as a correlator with and without hard-limiter and chip-level detector. Furthermore, the performance of the proposed coded fiber-optic CDMA system is also evaluated in the presence of different values of dark current     

盲速率判决技术在OFDM系统中的应用

该文借助CDMA系统中的盲速率判决技术解决交织与相位旋转(IPR-OFDM)( IPR:Interleaving and Phase Rotation),系统中接收端恢复交织序号,对接收信号进行检测的问题。IPR-OFDM系统在发送端使用了V 个交织器,接收端为了恢复数据需要知道发送端使用的交织器序号进行解交织。一种解决方法是发送辅助信息(SI:Side Information),这需要占用信道容量;该文借助于CDMA系统中速率判决的思想提出一种在接收端进行盲判的方法,它通过检测CRC(循环冗余校验码)和反转误码率(SER)信息等来获得所需要的交织序号,这种方法相对于前者提高了信道利用率。     

Joint-detection and interference cancellation based burst-by-burst adaptive CDMA schemes

Spread adaptive quadrature amplitude modulated (AQAM) code-division multiple access (CDMA) is proposed as a powerful means of exploiting the time-variant channel capacity fluctuations of wireless channels. It is studied in comparison to variable spreading factor (VSF)-based techniques. These adaptive-rate transmission methods are compared in the context of joint detection and interference cancellation assisted adaptive CDMA (ACDMA) systems. More explicitly, we exploit the time-variant channel quality of mobile channels by switching either the modulation mode (AQAM) or the spreading factor (VSF) on a burst-by-burst basis. The most appropriate modulation mode or spreading factor is chosen based on the instantaneous channel quality estimated. The chosen modem mode or spreading factor is communicated to the remote communicator either through explicit signalling or extracted at the receiver using blind detection techniques. The multiuser joint detector (JD) and the successive interference cancellation (SIC) receiver are compared in the context of these adaptive schemes, with the conclusion that the JD outperformed the SIC receiver in the ACDMA schemes at the cost of increased complexity. Finally, the performance of the uncoded AQAM JD-CDMA scheme is also compared to that of adaptive trellis coded modulation (TCM) assisted AQAM JD-CDMA, which allows us to incorporate adaptive channel coding without any bandwidth expansion. We also show that in the particular scenario studied, adaptive TCM outperformed adaptive turbo TCM since the system was designed for maintaining a low turbo-interleaver delay.