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1.
Group-blind multiuser detection for uplink CDMA 总被引:16,自引:0,他引:16
Xiaodong Wang Host-Madsen A. 《Selected Areas in Communications, IEEE Journal on》1999,17(11):1971-1984
Previously developed blind techniques for multiuser detection in code division multiple access (CDMA) systems lead to several near-far resistant adaptive receivers for demodulating a given user's data with the prior knowledge of only the spreading sequence of that user. In the CDMA uplink, however, typically the base station receiver has the knowledge of the spreading sequences of all the users within the cell, but not that of the users from other cells. In this paper, group-blind techniques are developed for multiuser detection in such scenarios. These new techniques make use of the spreading sequences and the estimated multipath channels of all known users to suppress the intracell interference, while blindly suppressing the intercell interference. Several forms of group-blind linear detectors are developed based on different criteria. Moreover, group-blind multiuser detection in the presence of correlated noise is also considered. In this case, two receiving antennas are needed for channel estimation and signal separation. Simulation results demonstrate that the proposed group-blind linear multiuser detection techniques offer substantial performance gains over the blind linear multiuser detection methods in a CDMA uplink environment 相似文献
2.
Group-blind multiuser detectors for uplink code-division multiple-access (CDMA) were recently developed by Wang and Host-Madsen. These detectors make use of the spreading sequences of known users to construct a group constraint to suppress the intracell interference. However, such techniques demand the estimation of the multipath channels and the delays of the known users. In this paper, several improved blind linear detectors are developed for CDMA in fading multipath channels. The proposed detectors utilize the correlation information between consecutively received signals to generate the corresponding group constraint. It is shown that by incorporating this group constraint, the proposed detectors can provide different performance gains in both uplink and downlink environments. Compared with the previously reported group-blind detectors, our new methods only need to estimate the multipath channel of the desired user and do not require the channel estimation of other users. Simulation results demonstrate that the proposed detectors outperform the conventional blind linear multiuser detectors. 相似文献
3.
Zoran Zvonar 《Wireless Personal Communications》1995,2(4):373-392
Multipath fading severely limits the performances of conventional code division multiple-access (CDMA) systems. Since every signal passes through an independent frequency-selective fading channel, even modest cross-correlations among signature sequences may induce severe near-far effects in a central multiuser receiver. This paper presents a systematic approach to the detection problem in CDMA frequency-selective fading channels and proposes a low complexity linear multiuser receiver, which eliminates fading induced near-far problem.We initially analyze an optimal multiuser detector, consisting of a bank of RAKE filters followed by a dynamic programming algorithm and evaluate its performance through error probability bounds. The concepts of error sequence decomposition and asymptotic multiuser efficiency, used to characterize the optimal receiver performance, are extended to multipath fading channels.The complexity of the optimal detector motivates the work on a near-far resistant, low complexity decorrelating multiuser detector, which exploits multipath diversity by using a multipath decorrelating filter followed by maximal-ratio combining. Analytic expressions for error probability and asymptotic multiuser efficiency of the suboptimal receiver are derived that include the effects of multipath fading, multiple-access interference and signature sequences correlation on the receiver's performance.The results indicate that multiuser detectors not only alleviate the near-far problem but approach single-user RAKE performance, while preserving the multipath diversity gain. In interference-limited scenarios multiuser receivers significantly outperform the RAKE receiver.This paper was presented in part at the Twenty-Sixth Annual Conference on Information Sciences and Systems, Princeton, NJ, March 1992 and MILCOM'92, San Diego, CA, October 1992. This work was performed while author was with the Department of Electrical and Computer Engineering, Northeastern University, Boston, USA. 相似文献
4.
Wang and Host-Madsen (see IEEE J. Select. Areas Commun., vol.17, p.1971-84, 1999) developed group-blind multiuser detectors for use in code-division multiple-access (CDMA) uplink environments in which the base station receiver has the knowledge of the spreading sequences of all the users within the cell, but not that of the users from other cells. Yu and Host-Madsen (see Proc. IEEE Vehicular Technology Conf. (VTC99), Houston, TX, p.1042-46, 1999) later developed an adaptive version of this detector for synchronous CDMA channels. We develop a new low-complexity, high-performance subspace tracking algorithm and apply it to adaptive group-blind multiuser detection in asynchronous multipath CDMA channels. The detector can track changes in the number of users and their composite signature waveforms. We present steady-state performance as well as the ability of the receiver to track changes in the signal subspace. We also address the performance gain of the group-blind detector over its blind counterpart for this application 相似文献
5.
Proposes a suboptimal low-complexity multiuser receiver for synchronous CDMA frequency-selective Rayleigh fading channels. In contrast to the conventional RAKE receiver, which suffers from near-far effects due to channel fading, the proposed multiuser receiver is shown to alleviate the near-far problem while preserving multipath diversity gain. This is demonstrated by comparing the symbol error probability and asymptotic multiuser efficiency of the proposed multiuser detector and RAKE receiver 相似文献
6.
In this paper we analyze the effects of antenna array (AA) and imperfect power control on the performance of the uplink synchronous and/or asynchronous orthogonal multicarrier (MC) direct sequence‐code division multiple access (DS‐CDMA) system in multipath Rayleigh fading channels. Bit error rate (BER) performance is evaluated in terms of the number of antennas, the number of total subcarriers, power control error (PCE), and the number of users. Our numerical results show that the available user capacity of synchronous uplink is more than 1.5 times higher than that of asynchronous uplink, even though PCE increases. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
7.
YangWei ChenJunshi TanZhenhui TakisMathiopoulos 《电子科学学刊(英文版)》2005,22(3):220-228
In this paper, a Direction Of Arrival (DOA) estimation algorithm is proposed for multiuser signals through uplink asynchronous multipath Code Division Multiple Access (CDMA) channels. The algorithm is based directly on the correlation matrices of matched filter bank outputs of desired user‘s multipath signals and it does not require that the elements of base station antenna array outnumber the multipath signals, which is necessary for the conventional sub-space based direction-finding algorithm. Simulation results show that the proposed algorithm estimates the DOA of multipath signals effectively and acceptably. The proposed algorithm has the prominent advantages of low complexity, simpleness and practicality, which make it much more suitable for practical application. 相似文献
8.
Zi-Wei Zheng 《Wireless Personal Communications》2010,53(1):67-79
In this paper, we consider the receiver design problem for the uplink multiuser code division multiple access (CDMA) communication
system based on the neural network technique. The uplink multiuser CDMA communication system model is described in the form
of space–time domain through antenna array and multipath fading expression. Novel suitable neural network technique is proposed
as an effective signal processing method for the receiver of such an uplink multiuser CDMA system. By the appropriate choice
of the channel state information for the neural network parameters, the neural network can collectively resolve the effects
of both the inter-symbol interference due to the multipath fading channel and the multiple access interference in the receiver
of the uplink multiuser CDMA communication system. The dynamics of the proposed neural network receiver for the uplink multiuser
CDMA communication system is also studied. 相似文献
9.
There has been an increasing interest in the use of code-division multiple access (CDMA) in cellular mobile and wireless personal communications. The choice of such multiaccess technique is attractive because of its potential capacity increases and other technical factors such as privacy and multipath rejection capabilities. However, it is well known that the performance of CDMA can be significantly degraded due to cochannel interference (CI) and the near-far effects. We consider the performance of direct-sequence (DS)-based CDMA over fading channels that are modeled as slowly varying Rayleigh-fading discrete multipath channels. Specifically, we propose and analyze an adaptive multistage interference cancellation strategy for the demodulation of asynchronous DS spread-spectrum multiple-access signals. Numerical results show that the proposed multistage detector, which alleviates the detrimental effects of the near-far problem, can significantly improve the system performance 相似文献
10.
Code division multiple access (CDMA) schemes allow a number of asynchronous users to share a transmission medium with minimum cooperation among them. However, sophisticated signal processing algorithms are needed at the receiver to combat interference from other users and multipath effects. A discrete-time multirate formulation is introduced for asynchronous CDMA systems, which can incorporate multipath effects. This formulation reveals interesting links between CDMA receivers and array processing problems. In this framework, linear receivers are derived that can completely suppress multiuser interference (decorrelating receivers). A criterion is introduced, which guarantees the decorrelating property, while providing optimal solutions in the presence of noise. Parametric FIR designs as well as nonparametric solutions are delineated, and their performance is analyzed. The proposed receivers are resistant to near-far effects and do not require the estimation of the users' and noise powers 相似文献
11.
《Vehicular Technology, IEEE Transactions on》2008,57(6):3563-3577
12.
Madhow U. Honig M.L. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1999,45(6):2039-2045
The performance of a near-far-resistant, finite-complexity, minimum mean squared error (MMSE) linear detector for demodulating direct sequence (DS) code-division multiple access (CDMA) signals is studied, assuming that the users are assigned random signature sequences. We obtain tight upper and lower bounds on the expected near-far resistance of the MMSE detector, averaged over signature sequences and delays, as a function of the processing gain and the number of users. Since the MMSE detector is optimally near-far-resistant, these bounds apply to any multiuser detector that uses the same observation interval and sampling rate. The lower bound on near-far resistance implies that, even without power control, linear multiuser detection provides near-far-resistant performance for a number of users that grows linearly with the processing gain 相似文献
13.
He-Chi Hwang Che-Ho Wei 《Vehicular Technology, IEEE Transactions on》2000,49(3):875-884
We present an efficient blind algorithm for estimating the code timing of a desired user in an asynchronous direct-sequence code-division multiple-access (DS/CDMA) system over frequency-nonselective-fading channels. The proposed algorithm acquires the code timing explicitly and results in a near-far resistant minimum mean-squared error (MMSE) demodulation without requiring the knowledge of the timing information, amplitudes, and transmitted symbols of all transmissions. The only required knowledge is the information of the signature sequence used by the desired transmission. Several computer simulations are done for additive white Gaussian channels, Rayleigh fading channels, and two-ray Rayleigh fading multipath channels, respectively. Numerical results show that the new algorithm is near-far resistant to the multiple-access interference (MAI) in the DS/CDMA system 相似文献
14.
码分多址系统中抗远近效应的多用户盲均衡接收方案 总被引:1,自引:1,他引:0
针对码多址系统中多径瑞利衰落信息的远近效应,我们提出了用户盲均衡检测方案,并与多极检测法进行了比较研究,数值模拟表明,多用户盲均衡检测方案的抗远近效应能力优于无信道估计误差的二级检测。 相似文献
15.
If transmission power is increased in a direct-sequence code-division multiple-access network, interference increases, thus reducing network capacity. In this paper, we address these opposite goals of reducing transmission power and increased network capacity by jointly considering power control and multiuser detection. Since propagation delay occurs inevitably during data communication, we present an analysis by considering also that the interference measurement is not available at the transmitter instantaneously but with some time-delay, something that is generally neglected in the literature. This framework is used to investigate the design of a distributed power control strategy enhanced with linear multiuser receivers in an asynchronous uplink channel, subject to multipath and quality of service constraints. Thus, a cross-layer solution that combines a Linear-Quadratic-Gaussian power control scheme with a linear multiuser receiver is proposed to compensate for the round-trip delay and the time-varying channel characteristics in the communication link. Simulation results are used to show the advantages of such scheme in terms of saving energy, increasing network capacity and robustness against propagation delays. 相似文献
16.
This paper presents blind channel estimation for downlink W-CDMA system that employs chaotic codes and Walsh codes for spreading information bits of the multiple users. In a W-CDMA system, while transmitting over multipath channels, both intersymbol interference (ISI) as a result of Inter Chip Interference and multiple access interference (MAI) cannot be easily eliminated. Although it is possible to design multiuser detectors that suppress MAI and ISI, these detectors often require explicit knowledge of at least the desired users’ signature waveform. Earlier work focused on a subspace based channel estimation algorithm for asynchronous CDMA systems to estimate the multiple users’ symbols, where only AWGN channel was considered. In our work, we study a similar subspace-based signature waveform estimation algorithm for downlink W-CDMA systems, which use chaotic codes instead of pseudo random codes, that provide estimates of the multiuser channel by exploiting structural information of the data output at the base station. In particular, we show that the subspace of the (data+noise) matrix contains sufficient information for unique determination of channels, and hence, the signature waveforms and signal constellation. We consider Rayleigh and Rician fading channel model to quantify the multipath channel effects. Performance measures like bit error rate and root mean square error are plotted for both chaotic codes and Walsh codes under Rayleigh and Rician fading channels. 相似文献
17.
Li Ping 《Communications Magazine, IEEE》2005,43(6):S19-S23
This article outlines a multiple access scheme in which interleaving is the only means of user separation. As a special form of CDMA, the new scheme inherits many advantages of CDMA, such as dynamic channel sharing, mitigation of cross-cell interference, asynchronous transmission, ease of cell planning, and robustness against fading. Furthermore, it allows a low-cost interference cancellation technique applicable to systems with large numbers of users in multipath channels. Performance close to theoretical limits has been observed based on an unequal power control strategy. 相似文献
18.
Jin-Il Kim Suk-Hyon Yoon Sung-Jin Kang Chang-Eon Kang 《Electronics letters》1998,34(12):1194-1195
A channel estimation technique in the uplink of a noncoherent DS/CDMA system with M-ary orthogonal signalling over multipath fading channels is considered. This method is used for the multiuser interference cancellation with coherent detection. The performance of the proposed multiuser detector is compared with that of a conventional detector and a significant improvement of performance is shown 相似文献
19.
OptimumMultiuserDetectorforMultipathSlowFadingAsynchronousCDMAChannelsWangZhaocheng;YangZhixing;YaoYan(TsinghuaUniversity,Bei... 相似文献
20.
Population Declining Ant Colony Optimization Multiuser Detection in Asynchronous CDMA Communications 总被引:1,自引:1,他引:0
In this paper we present a population declining ant colony optimization (PDACO) multiuser detector for asynchronous CDMA communications.
Ant colony optimization (ACO) algorithms have already been used in multiuser detection in CDMA systems; however, as the pheromone
accumulates, we may not get a global optimum because it stops searching early. PDACO can enlarge searching range through increasing
the initial population of the ant colony, and the population declines in successive iterations. So, the performance of PDACO
is superior with the same computational complexity. PDACO is applied to multiuser detection in asynchronous CDMA systems over
slowly multipath Rayleigh-fading channels in this paper. Via computer simulations it is shown that the performance of PDACO
detector is much better in bit-error rate and near-far effect resistance than conventional detector, ACO detector and genetic
algorithm detector, and is close the optimal multiuser detector. 相似文献