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1.
1 IntroductionIthasbeenshownthatthecapacityofwirelesscommunicationsystemscanbeincreaseddramatical lybyemployingmultipletransmittingandreceivingantennas.Space timecodinghasbeenpaidmoreat tentionrecentlybecauseitisaneffectivewaytoex ploitspatialandtemporaldiversity[1~2 ] .Despitealossincodingadvantage,space timeblockcodingcanofferthemaximumdiversitygainbasedononlythelinearprocessingatthereceiver[3~ 4] andhasbeenproposedtobeusedin 3Gsystems.InterferencesuppressionismorechallenginginCDMAsyste… 相似文献
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Space-time multiuser detection in multipath CDMA channels 总被引:3,自引:0,他引:3
The problem of multiuser detection in multipath CDMA channels with receiver antenna array is considered. The optimal space-time multiuser receiver structure is first derived, followed by linear space-time multiuser detection methods based on iterative interference cancellation. Blind adaptive space-time multiuser detection techniques are then proposed, which require prior knowledge of only the spreading waveform and the timing of the desired user's signal. Single-user-based space-time processing methods are also considered and are compared with the multiuser approach. It is seen that the proposed multiuser space-time processing techniques offer substantial performance gains over the single-user-based methods, especially in a near-far situation 相似文献
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Space-time processing and multiuser detection are two promising techniques for combating multipath distortion and multiple-access interference in code division multiple access (CDMA) systems. To overcome the computational burden that rises very quickly with increasing numbers of users and receive antennas in applying such techniques, iterative implementations of several space-time multiuser detection algorithms are considered here. These algorithms include iterative linear space-time multiuser detection, Cholesky iterative decorrelating decision-feedback space-time multiuser detection, multistage interference canceling space-time multiuser detection, and expectation-maximization (EM)-based iterative space-time multiuser detection. A new space-time multiuser receiver structure that allows for efficient implementation of iterative processing is also introduced. Fully exploiting various types of diversity through joint space-time processing and multiuser detection brings substantial gain over single-receiver-antenna or single-user-based methods. It is shown that iterative implementation of linear and nonlinear space-time multiuser detection schemes discussed in this paper realizes this substantial gain and approaches the optimum performance with reasonable complexity. Among the iterative space-time multiuser receivers considered in this paper, the EM-based (SAGE) iterative space-time multiuser receiver introduced here achieves the best performance with excellent convergence properties. 相似文献
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给出了一种新的线性空时多用户接收机的一般表达形式。对这种表达形式的分析表明,线性空时多用户接收机可以分解为4个级联部分,即匹配滤波、空域合并、多径合并和多用户检测器,并且前3个部分的运算仍是以单用户接收为基础的。仿真结果表明,这种结构分解可以有效降低线性空时多用户接收机的计算复杂度,加快自适应接收机的收敛速度,更利于实际系统应用。 相似文献
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The arrival of new data services for wireless mobile communications requires an efficient use of the available bandwidth. Interference-limited cellular systems based on code-division multiple access (CDMA) can benefit from multiuser detection (MUD) and beamforming with antenna array to reduce multiple-access interference. Group-based techniques have been proposed to reduce the complexity of space-time MUD and have been shown to provide a performance-complexity tradeoff between matched filtering and full MUD. In this paper, the intergroup interference, which is a limiting factor in group-based systems, is reduced using multistage parallel interference cancellation after group-based minimum mean square error (MMSE) linear filtering. In addition, the extra resources that are available at the receiver are exploited by sharing users among groups. The proposed receiver is shown to converge, as the number of stages increases, to the full space-time MMSE linear MUD filter. The results show that the new approach provides bit error rate (BER) performance close to the full MUD receiver at a fraction of the complexity. 相似文献
6.
Teng Joon Lim Rasmussen L.K. Sugimoto H. 《Selected Areas in Communications, IEEE Journal on》1998,16(9):1711-1722
We introduce a multiuser receiver based on the Kalman filter, which can be used for joint symbol detection and channel estimation. The proposed algorithm has the advantage of working even when the spreading codes used have a period larger than one symbol interval (“long codes”), unlike adaptive equalizer-type detectors. Simulation results which demonstrate the performance advantage of the proposed receiver over the conventional detector, the minimum mean squared error (MMSE) detector and a recursive least squares (RLS) multiuser detector are presented. A thorough comparison of the MMSE detector and the proposed detector is attempted because the Kalman filter also solves the MMSE parameter estimation problem, and it is concluded that, because the state space model assumed by the Kalman filter fits the code division multiple access (CDMA) system exactly, a multiuser detector based on the Kalman filter must necessarily perform better than a nonrecursive, finite-length MMSE detector. The computational complexity of the detector and its use in channel estimation are also studied 相似文献
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Turbo Interference Mitigation in Layered Space-Time MIMO DS-CDMA Uplink with TTCM(Turbo Trellis Coded Modulation) 总被引:1,自引:1,他引:0
In this paper we propose the use of a turbo receiver for the uplink of a MIMO CDMA system employing layered space-time transmission.
The proposed receiver consists of a low complexity layered space-time multi-user detector using minimum mean squared error
(MMSE) filtering with a-priori information and a bank of MAP SISO decoders. Using the soft estimates from a bank of MAP decoders we obtain soft values of
the interfering symbols. The SISO multiuser detector subtracts the vector of the interfering symbols from the incoming signal.
The resulting vector is then filtered by an adaptive MMSE filter to reduce the residual MAI. This process iterates by exchanging
extrinsic informations between the bank of MAP decoders and the SISO multiuser detector. Turbo Trellis Coded Modulation (TTCM)
is used as Forward Error Correcting (FEC) code due to its high bandwidth efficiency. Our computer simulations show that the
proposed structure outperforms a classical iterative receiver based on parallel interference cancellation (PIC) as well as
a non-iterative MMSE receiver. Furthermore, in a multiuser context, the proposed receiver offers an error performance similar
to that of single-user case at high SNR.
Jean-Pierre Cances graduated in electrical engineering from ENST Bretagne in 1990. He received his Ph.D degree from Télécom Paris in satellite
communication engineering in 1993. He is now an assistant Professor at the Ecole Nationale Supérieure d'Ingénieurs de Limoges
(ENSIL). His current research interests include satellite communication systems, multicarrier detection and synchronization
algorithms, MIMO communication systems.
Gholam Reza Mohammad-khani received his BSc. and MSc. degrees in communication engineering from Sharif University of Technology, Tehran, Iran, respectively
in 1992 and 1994. He worked as a lecturer in Mashhad University in 1997. His current research interests include satellite
communication systems, multiuser detection and synchronization algorithms.
Vahid Meghdadi received his BSc. and MSc. degrees in communication engineering from Sharif University of Technology, Tehran, Iran, respectively
in 1989 and 1992. He worked as a lecturer in Mashhad University in 1993. Since 1994, he has been a Ph.D. student inEcole nationale
Supérieure d'Ingenieurs de Limoges (ENSIL) where he is now an assistant professor. His current research interests include
satellite communication systems, multiuserdetection and synchronization algorithms, MIMO communication systems. 相似文献
10.
By combining multipath processing, differential signal detection, and multiuser detection techniques, we develop a class of near-far resistant linear detectors for differentially coherent multipath signals. We derive and establish performance relationships among the following detectors: an optimally near-far resistant detector, a suboptimum detector which does not require knowledge of the signal coordinates, and a minimum mean square error (MMSE) detector which achieves near-optimum asymptotic efficiency. We present an adaptive multiuser detector which converges to the MMSE detector without training sequences and which requires less information than the conventional single user rake receiver. 相似文献
11.
Blind adaptive multiuser detection 总被引:26,自引:0,他引:26
Honig M. Madhow U. Verdu S. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1995,41(4):944-960
The decorrelating detector and the linear minimum mean-square error (MMSE) detector are known to be effective strategies to counter the presence of multiuser interference in code-division multiple-access channels; in particular, those multiuser detectors provide optimum near-far resistance. When training data sequences are available, the MMSE multiuser detector can be implemented adaptively without knowledge of signature waveforms or received amplitudes. This paper introduces an adaptive multiuser detector which converges (for any initialization) to the MMSE detector without requiring training sequences. This blind multiuser detector requires no more knowledge than does the conventional single-user receiver: the desired user's signature waveform and its timing. The proposed blind multiuser detector is made robust with respect to imprecise knowledge of the received signature waveform of the user of interest 相似文献
12.
We propose a modified linear parallel interference cancelation (PIC) structure using the adaptive minimum mean output-energy
(MMOE) algorithm for direct-sequence code-division multiple-access (DS-CDMA) systems. The complexity of the proposed receiver
structure is shown to be linear in the number of users and hence, lower complexity than the centralized minimum mean-squared
error (MMSE) multiuser detector. It is demonstrated that the proposed receiver structure can significantly reduce the long
training period required by the standard adaptive MMOE receiver in near-far environments. Both numerical and theoretical results
show that the proposed receiver performs close to the optimum MMSE receiver whereas the conventional adaptive MMOE detector
suffers from high BER’s due to the imperfect filter coefficients. Also our results show a three fold increase in the number
of users when the MMOE-PIC is used relative to the conventional MMOE receiver. Furthermore, the transient behavior of the
proposed MMOE-PIC receiver due to abrupt changes in the interference level is examined. It is shown that the proposed adaptive
receiver offers much faster self recovery, with less signal-to-interference ratio (SIR) degradation, than the standard MMOE
in sever near-far scenarios. 相似文献
13.
A timing-free blind multiuser detection technique is proposed for differentially encoded direct-sequence/code division multiple access (DS/CDMA) networks. Unlike previously derived blind multiuser detectors, the proposed algorithm does not rely on any information beyond the spreading code of the desired user, namely neither the complex amplitude nor the symbol timing of the signal of interest is assumed to be known to the receiver. The proposed detector structure is immune to cochannel interferers with arbitrarily large powers, and, as computer simulation results show, compares favorably with competing alternatives. Moreover, the proposed detector achieves performance quite close to that of the ideal minimum mean square error (MMSE) multiuser receiver, which requires knowledge of the spreading codes, timing offsets, and received energies for the signals of all active users 相似文献
14.
Multiuser detection (MUD) and channel estimation techniques in space-division multiple-access aided orthogonal frequency-division multiplexing systems recently has received intensive interest in receiver design technologies. The maximum likelihood (ML) MUD that provides optimal performance has the cost of a dramatically increased computational complexity. The minimum mean-squared error (MMSE) MUD exhibits poor performance, although it achieves lower computational complexity. With almost the same complexity, an MMSE with successive interference cancellation (SIC) scheme achieves a better bit error rate performance than a linear MMSE multiuser detector. In this paper, hybrid ML-MMSE with SIC adaptive multiuser detection based on the joint channel estimation method is suggested for signal detection. The simulation results show that the proposed method achieves good performance close to the optimal ML performance at low SNR values and a low computational complexity at high SNR values. 相似文献
15.
Based on the minimum mean squared error (MMSE) between the data stream and the linear combiner output, a new multiuser detection
(MUD) algorithm that combines space–time (ST) processing and antenna array on direct-sequence CDMA signals is proposed. The
proposed ST-MUD algorithm is proved to be equivalent to two existing MMSE-based ST-MUD algorithms, and the theoretical BER
performances for all the three algorithms are the same. The most attractive feature of the new ST-MUD algorithm is based on
the fact that the new method does not require explicit estimation of channel and signaling information. This avoids any channel
estimation error, and the method is thus more robust and more accurate than the other two ST-MUD algorithms in practical implementation.
Adaptation of the proposed ST-MUD algorithm is implemented by using training sequences. Performance of this new multiuser
detector is compared with that of two existing MMSE multiuser detectors and the conventional single-user space–time rake receiver
through simulations. The proposed ST-MUD algorithm provides a performance better than existing algorithms and is especially
suitable for practical CDMA systems. 相似文献
16.
Linear space-time multiuser detection for multipath CDMA channels 总被引:10,自引:0,他引:10
We consider the problem of detecting synchronous code division multiple access (CDMA) signals in multipath channels that result in multiple access interference (MAI). It is well known that such challenging conditions may create severe near-far situations in which the standard techniques of combined power control and temporal single-user RAKE receivers provide poor performance. To address the shortcomings of the RAKE receiver, multiple antenna receivers combining space-time processing with multiuser detection have been proposed in the literature. Specifically, a space-time detector based on minimizing the mean-squared output between the data stream and the linear combiner output has shown great potential in achieving good near-far performance with much less complexity than the optimum space-time multiuser detector. Moreover, this space-time minimum mean-squared error (ST-MMSE) multiuser detector has the additional advantage of being well suited for adaptive implementation. We propose novel trained and blind adaptive algorithms based on stochastic gradient techniques, which are shown to approximate the ST-MMSE solution without requiring knowledge of the channel. We show that these linear space-time detectors can potentially provide significant capacity enhancements (up to one order of magnitude) over the conventional temporal single-user RAKE receiver 相似文献
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Morosi S. Fantacci R. Del Re E. Chiassai A. 《Wireless Communications, IEEE Transactions on》2007,6(10):3552-3557
This paper deals with a turbo multiuser detector suitable for applications in overloaded coded DS-CDMA systems. The turbo-MUD receiver is based on the use of a linear MMSE detector in the first iteration and a parallel interference cancellation scheme in the successive ones. The inputs of the interference cancellator are both the detector outputs and the soft information from a bank of turbo decoders. The performance of the proposed receiver has been derived by means of computer simulations and applications of the density evolution theory: in particular, this technique permits to properly evaluate the number of MMSE iterations, simplifying the overall receiver design. 相似文献
20.
《Vehicular Technology, IEEE Transactions on》2009,58(5):2299-2313