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1.
Modified linearly constrained CMA for blind adaptive multiuser detector in DS/CDMA systems 总被引:1,自引:0,他引:1
A modified linearly constrained constant modulus algorithm for blind adaptive multiuser detection in DS/CDMA systems is presented. By selecting a suitable linearly constrained cost function, the performance of the proposed algorithm is improved in terms of the capability of suppressing multiple access interference. Simulation results indicate that the proposed algorithm provides a faster convergence and steady-state performance. 相似文献
2.
Code-aided blind adaptive new user detection in DS/CDMA systems with fading time-dispersive channels 总被引:2,自引:0,他引:2
We consider the problem of detecting the entrance of a new-user in a direct-sequence code division multiple access (DS/CDMA) system operating over a fading dispersive channel. This problem has received considerable attention in the recent past in that it arises in a number of different contexts, such as decentralized user acquisition and data detection, handoff algorithms, soft handover procedures, and cell-search in wideband-CDMA systems. The detection algorithms that we propose in this paper are based on the application of the generalized-likelihood-ratio-test (GLRT) and can be implemented based on the knowledge of the spreading code of the user to be detected. In particular, the proposed procedures do not require any prior knowledge of either the propagation channel impulse response or the timing offset of the user to be detected. We consider both the cases of user detection in the reverse link of a cellular system, wherein it is assumed that the subspace spanned by the signals of the existing previous users is known to the receiver and that of user detection in the forward link, wherein the mobile receiver has no prior knowledge on the multiaccess interference. With regard to the latter situation, we develop a detection algorithm that ensures a constant false-alarm rate with respect to the second-order statistics of the overall disturbance. The performance of the proposed detection structures is finally assessed through closed-form formulas and through some sample plots, showing, for a given probability of false alarm, the probability that the new user is detected. 相似文献
3.
Seunghyun Min Kwang Bok Lee 《Electronics letters》1999,35(6):457-459
A channel estimation scheme, based on both pilot and traffic channels, is proposed for next generation DS/CDMA systems. This scheme has no channel estimation delay, and is found to perform significantly better than a scheme based on only the pilot channel 相似文献
4.
Lei Huang Fu-Chun Zheng 《Vehicular Technology, IEEE Transactions on》2004,53(6):1746-1755
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. 相似文献
5.
The problem of blind adaptive channel estimation in code-division multiple access (CDMA) systems is considered. Motivated by the iterative power method, which is used in numerical analysis for estimating singular values and singular vectors, we develop recursive least squares (RLS) and least mean squares (LMS) subspace-based adaptive algorithms in order to identify the impulse response of the multipath channel. The schemes proposed in this paper use only the spreading code of the user of interest and the received data and are therefore blind. Both versions (RLS and LMS) exhibit rapid convergence combined with low computational complexity. With the help of simulations, we demonstrate the improved performance of our methods as compared with the already-existing techniques in the literature. 相似文献
6.
A new blind adaptive multiuser detector for synchronous DS/CDMA systems based on a modified constant modulus algorithm is proposed. This detector is shown to outperform the minimum output energy detector in a downlink channel occupied by a large number of users. This blind detector is a good candidate for downlink receivers 相似文献
7.
A fresh look on the design of practical low-complexity direct-sequence code-division multiple-access (DS/CDMA) receivers is proposed from the Wiener reconstruction-filter point of view. The natural outcome is the emergence of a new class of linear scalar-parameterized auxiliary-vector receivers (filters). Then, the blind optimization of these receivers in the maximum signal-to-interference-plus-noise-ratio (SINR) sense becomes a straightforward procedure. The conceptual and computational simplicity of this general approach promises immediate practical utility. This new generation of receivers exhibits minimal optimization requirements and near-matched-filter (MF) operational complexity. Yet, theoretical arguments supported by numerical and simulation results included in this work suggest that the blind auxiliary-vector receiver compares favorably, both complexity-wise and performance-wise, to multiuser (MU) detectors such as the minimum output energy (MOE) and the decorrelating receiver (although the latter utilizes the assumed known spreading codes of all interfering users) 相似文献
8.
Ming Chen 《Electronics letters》2002,38(11):525-526
The optimal multiuser detector (MUD) in DS/CDMA systems requires the solution of a NP-hard combinatorial optimisation problem (COP). A near optimal MUD based on solving the COP with memory search method is proposed. With almost the same computational complexity as the parallel interference cancellation (PIC) MUD, it produces a better performance gain than PIC-MUD 相似文献
9.
This paper proposes a new linear blind multiuser detection based on widely linear (WL) signal processing. The received signal and its complex conjugate are separately filtered and the results are linearly combined. The WL maximum/minimum (max/min) mean-output-energy (MOE) receiver is derived by applying the modified cost function. It is shown that a performance gain can be attained for the improper direct-sequence code division multiple access (DS/CDMA) signal, due to the additional information contained in pseudocovariance matrix of observations. The adaptive implementation with acceptable complexity is also developed. Computer-simulation results show that a significant performance gain is obtained over the other classical methods. 相似文献
10.
This letter proposes the subspace-based blind adaptive channel estimation algorithm for dual-rate quasi-synchronous DS/CDMA systems, which can operate at the low-rate (LR) or high-rate (HR) mode. Simulation results show that the proposed blind adaptive algorithm at the LR mode has a better performance than that at the HR mode, with the cost of an increasing computational complexity 相似文献
11.
天线阵CDMA系统中基于神经网络的盲空时信道估计 总被引:3,自引:3,他引:3
提出了天线阵CDMA系统中盲空时信道估计的约束优化神经网络模型,对其全局收敛性进行了分析,并对其性能进行了数值模拟。 相似文献
12.
This paper presents an improved two-stage decorrelating detection scheme for direct-sequence code-division multiple-access (DS-CDMA) systems. Decorrelator outputs corresponding to each user are tested to determine whether or not a final decision can be made with high reliability. For users with high reliability, a hard decision is made at this stage. For the remaining users, a conditional quantization algorithm is employed before a decision is made. Results indicate that significant performance enhancement can be achieved at the expense of a modest increase in computational complexity. The algorithm is also applied to synchronous as well as asynchronous multipath channels with excellent results. We also extend the two-stage decorrelating detection scheme to time-variant communication scenarios and present an adaptive version of the two-stage decorrelator 相似文献
13.
An effective multiuser receiver for DS/CDMA systems 总被引:2,自引:0,他引:2
Multiuser detection (MUD) is a key technique for combating multiple access interference (MAI) in CDMA systems. We propose a simple and effective multiuser receiver, which we refer to as the objective function based multiuser detector (OFMUD). This is a successive multistage joint detector based on the statistical optimization of an objective function. Two objective functions are considered in this paper. The first one is based on a maximum likelihood solution, and the second one is based on the least squared error solution. A key feature of the proposed detector is that among all the K user bits, we update the estimate of one and only one bit (the one that is most likely to be wrong) in every stage. Analytical and numerical results show that significant performance improvement can be achieved compared with the conventional DS/CDMA receiver. At the same time, the near-far problem is alleviated. In addition, it is shown that the proposed receiver can outperform the popular multiuser parallel interference cancellation receiver in most cases with a smaller computational cost 相似文献
14.
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16.
Performance of multicarrier DS CDMA systems 总被引:1,自引:0,他引:1
In this paper, we apply a multicarrier signaling technique to a direct-sequence CDMA system, where a data sequence multiplied by a spreading sequence modulates multiple carriers, rather than a single carrier. The receiver provides a correlator for each carrier, and the outputs of the correlators are combined with a maximal-ratio combiner. This type of signaling has the desirable properties of exhibiting a narrowband interference suppression effect, along with robustness to fading, without requiring the use of either an explicit RAKE structure or an interference suppression filter. We use bandlimited spreading waveforms to prevent self-interference, and we evaluate system performance over a frequency selective Rayleigh channel in the presence of partial band interference; we also compare system performance with that of a single-carrier RAKE system 相似文献
17.
Recently developed subspace techniques for blind adaptive multiuser detection are briefly reviewed first. In particular, blind
methods based on signal subspace tracking for adapting linear multiuser detectors in AWGN CDMA channels are considered, as
well as extensions of these techniques to frequency selective fading channels, dispersive channels, and antenna array spatial
processing. In addition, subspace‐based nonlinear adaptive techniques for robust blind multiuser detection in non‐Gaussian
ambient noise channels are also described. Several new techniques are then developed within the subspace framework for blind
joint channel estimation and multiuser detection, under some specific channel conditions. These include (1) an adaptive receiver
structure for joint multiuser detection and equalization in dispersive CDMA channels, (2) a subspace method for joint multiuser
detection and equalization in unknown correlated noise, and (3) a method for joint interference suppression and channel tracking
in time‐varying fading channels.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
18.
Seskar Ivan Pedersen Klaus I. Kolding Troels E. Holtzman Jack M. 《Wireless Networks》1998,4(6):447-452
This paper addresses the practical implementation of Successive Interference Cancellation (SIC) for DS/CDMA systems. The practical
aspects of such an implementation are discussed and a convenient pipelined architecture is presented. An important aspect
is the integration of power control (PC) and interference cancellation which has synergistic effects of optimizing the SIC,
reducing intercell interference, and facilitating the implementation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
Jin Hee Han Sang Wu Kim 《Communications Letters, IEEE》1998,2(11):298-300
We consider frequency overlapped DS/CDMA (FO/CDMA) communication systems where a number of DS/CDMA systems share frequency bands with adjacent systems. We analyze the multiple-access interference from adjacent systems with arbitrary amount of frequency overlap and compare the capacity of FO/CDMA with that of single wideband CDMA (WCDMA). The optimum amount of overlap increases with the number of overlapped systems. However the maximum capacity is obtained when the optimum number of systems are overlapped by half null-to-null bandwidth. It is shown that the FO/CDMA yields higher capacity in the case of relaxed bit error rate requirement and low decay rate of multipath intensity profile. Otherwise, WCDMA is superior 相似文献