共查询到20条相似文献,搜索用时 31 毫秒
1.
Sohn Insoo Gupta Someshwar C. 《International Journal of Wireless Information Networks》1999,6(2):59-66
With increasing need for capacity in mobilecellular communications, code division multiple accesshas been viewed as the technique to meet this goal.However, the conventional receiver suffers frommultiuser interference and the near-far effect. Toalleviate this problem, various multiuser receivers havebeen proposed. They have been shown to enhance theperformance of the conventional receiver with respect to capacity and interference rejection. Butthese receivers, intended for Gaussian noise channels,can fail in other environments such as impulsive noiseconditions. A possible solution is to exploit the advantages of neural networks. A neuralnetwork's ability to reject non-Gaussian noise can beutilized to implement multiuser receivers that rejectboth impulsive noise and multiuser interference.Following this logic, this paper considers nonadaptivemultiuser receiver and adaptive multiuser receiver basedon radial basis function neural networks. Simulations ofthese receivers show results that are superior to previously studied multiuser receivers, withrespect to practicality and performance. 相似文献
2.
1 IntroductionMultipleaccessinginthecodedomainisachievedbyspreadingthespectrumofthetransmit tedsignalsusingpreassignedcodeinformation .Sinceitisnotpossibletodesignsignaturesequenceforanypairofusersthatareideallyorthogonal,theinter ferencefromtheotheruse… 相似文献
3.
A soft iterative multisensor array receiver for coded multiuser wideband code-division multiple-access wireless uplink channels is proposed, such channels are typically both frequency- and time-selective. A new equivalent discrete-time synchronous representation is used to model asynchronous multiuser dispersive channels that employ, in general, random spreading. The proposed scheme suppresses multiuser interference over a wide range of user signal powers, by iteratively exchanging soft information between a minimum mean-square-error (MMSE) multiuser demodulator and a bank of single-user decoders, feeding back the outputs of the latter to aid in soft multiuser multisensor MMSE-RAKE demodulation and subtractive interference cancellation, in the second and subsequent iterations. It displays near-far resistance since it behaves like a successive interference subtracter across iterations. The array responses are obtained via a multipass estimation scheme that uses both (temporal) pilot symbols and soft estimates fed back from the decoders to effectively provide multisymbol pilot signals and thence successively refined estimates with increasing iterations, while seeking neither to rely on the array geometry nor to estimate the directions from which users' signals arrive at the receiver. Simulation studies indicate that this scheme performs close to the single-user case with a two-sensor receiver array, and perfect channel state information, after four iterations; alternatively, it allows significantly increased user capacity compared with conventional receivers, and suffers only a modest loss with estimated array responses 相似文献
4.
Meshkati F. Dongning Guo Poor H.V. Schwartz S.C. 《Wireless Communications, IEEE Transactions on》2008,7(4):1208-1216
A unified approach to power control is proposed for maximizing utility in terms of energy efficiency in code-division multiple access (CDMA) networks. The approach is applicable to a large family of multiuser receivers including the matched filter, the decorrelator, the linear minimum mean-square error (MMSE) receiver, and the (nonlinear) optimal detectors. It exploits the linear relationship between the transmit power and the output signal-to-interference-plus-noise ratio (SIR) for each user in the large-system limit. Suppose that each user seeks to selfishly maximize its own energy efficiency, a unique Nash equilibrium is shown to exist and be SIR-balanced, thus extending a previous result on linear receivers. A unified power control algorithm for reaching the Nash equilibrium is proposed, which adjusts transmit powers iteratively by computing the large-system multiuser efficiency, which is independent of instantaneous spreading sequences. The convergence of the algorithm is proved for linear receivers, and is demonstrated via simulation for the multiuser maximum likelihood detector. Moreover, the performance of the algorithm in finite-size systems is studied and compared with that of a conventional power control scheme, in which user powers depend on the instantaneous spreading sequences. 相似文献
5.
Hüseyin Arslan 《Wireless Personal Communications》2007,42(4):479-490
In this paper, a low complexity coherent joint maximum-likelihood detection receiver is developed for canceling multi-access
interference in impulse radio (IR) based ultra wideband (UWB) wireless communication systems. Unlike previous joint demodulation
receivers, where the complexity is enormous and the other users’ codes are required, the proposed approach does not need to
know the time hopping (TH) codes of the other users which makes it a very attractive solution. The performance of joint demodulation
receiver depends on the ability to estimate the channel coefficients of desired and interfering users. A novel and practical
algorithm for estimating multiple users’ channel responses is developed. The performance of the proposed algorithms are tested
through computer simulations and the results are compared with the performance of the conventional single user UWB receiver.
It is observed that the proposed joint demodulation receiver provides significant performance gains with respect to conventional
single user receiver.
This paper is presented in part in IEEE International Conference on Communications (ICC) 2004, Paris, France. 相似文献
6.
Hui Liu Hujun Yin 《Communications, IEEE Transactions on》2001,49(8):1479-1487
Multicarrier direct-sequence code-division multiple access (MC-DS-CDMA) has emerged recently as a promising candidate for the next generation broad-band mobile networks. We consider the design of multiuser receivers for MC-DS-CDMA communications over fading channels. We present a class of spreading codes that enables the simple despreading-combining receiver to achieve the performance of the optimum multiuser linear receiver. These codes are shown to be optimum for independent fading channels under a code design criterion derived. Also derived are analytic solutions of optimum spreading codes for any given channel fading statistics. Simulation results are provided to demonstrate the significant gains in performance and simplicity due to the proposed techniques 相似文献
7.
The authors propose feedforward neural networks (NNs) as receivers for partial-response continuous-phase-modulation (CPM) systems. Their approach is to replace the entire receiver structure, excluding timing recovery, with a neural net unit whose inputs are time samples of the incoming baseband signals, and whose outputs are the decoded symbols. Simulation results for coherent and incoherent NN-based receivers are presented, and their performance is compared with that of the optimum maximum-likelihood receiver. The performance of NN-based receivers at large SNR is analyzed 相似文献
8.
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
9.
In this paper, we present a multiuser detection technique based on artificial neural network (NN) for synchronous multicarrier code division multiple access systems over Rayleigh fading channels. To test the robustness of the proposed receiver, also the effect of power control problem is studied with a comparative manner. Bit error rate (BER) performance of the NN based receiver is compared with the single user bound and conventional receivers. Although the BER performance of the conventional receiver degrades as the number of the users and power level differences among the users increase, as a decision structure, neural network based receiver gives closer BER performance to the single user bound. 相似文献
10.
Kashima T. Fukawa K. Suzuki H. 《Selected Areas in Communications, IEEE Journal on》2006,24(3):437-447
This paper proposes two new types of maximum a posteriori probability (MAP) receivers for multiple-input-multiple-output and orthogonal frequency-division multiplexing mobile communications with a channel coding such as the low-density parity-check code. One proposed receiver employs the expectation-maximization algorithm so as to improve performance of approximated MAP detection. Differently from a conventional receiver employing the minimum mean-square estimation (MMSE) algorithm, it applies the recursive least squares (RLS) algorithm to the channel estimation in order to track a fast fading channel. For the purpose of further improvement, the other proposed receiver applies a new adaptive algorithm that can be derived from the message passing on factor graphs. The algorithm exploits all detected signals but one of targeted time, and can gain a considerable advantage over the MMSE and RLS. Computer simulations show that the first proposed receiver is superior in channel-tracking ability to the conventional receiver employing the MMSE. Furthermore, it is demonstrated that the second proposed receiver remarkably outperforms both the conventional and the first proposed ones. 相似文献
11.
On the capacity of mobile ad hoc networks with delay constraints 总被引:4,自引:0,他引:4
Previous work on ad hoc network capacity has focused primarily on source-destination throughput requirements for different models and transmission scenarios, with an emphasis on delay tolerant applications. In such problems, network capacity enhancement is achieved as a tradeoff with transmission delay. In this paper, the capacity of ad hoc networks supporting delay sensitive traffic is studied. First, a general framework is . proposed for characterizing the interactions between the physical and the network layer in an ad hoc network. Then, CDMA ad hoc networks, in which advanced signal processing techniques such as multiuser detection are relied upon to enhance the user capacity, are analyzed. The network capacity is characterized using a combination of geometric arguments and large scale analysis, for several network scenarios employing matched filters, decorrelators and minimum-mean-square-error receivers. Insight into the network performance for finite systems is also provided by means of simulations. Both analysis and simulations show a significant network capacity gain for ad hoc networks employing multiuser detectors, compared with those using matched filter receivers, as well as very good performance even under tight delay and transmission power requirements. 相似文献
12.
Lampe A. Schober R. Gerstacker W. Huber J. 《Selected Areas in Communications, IEEE Journal on》2002,20(2):339-350
A novel multiuser detector for direct sequence code division multiple access is proposed. The receiver performs iterated soft decision interference cancellation (ISDIC) based on multiuser interference suppression filters designed for minimization of the mean-square error. Assuming a complex modulation format, we show that the multiuser interference becomes rotationally variant in the course of the iterations. Regarding this rotational variance in the design of the multiuser interference suppression filter, the presented iterative multiuser detector achieves significant performance gains compared with conventional ISDIC employing a standard minimum mean-squared error filter which is optimum only for rotationally invariant multiuser interference 相似文献
13.
This paper proposes a suboptimal receiver for joint spatial-temporal filtering and multiuser detection in mobile radio communications using single carrier signaling. The proposed receiver is a reasonable approximation of the maximum likelihood (ML) based optimal receiver described in the present paper. A cascaded connection of an adaptive array antenna and an ML multiuser sequence estimator is the basis of the proposed receiver. The major advantages of the proposed receiver over conventional adaptive array antennas are: (1) delayed path components of desired signals can be effectively combined; (2) interference signals exceeding the degree of freedom; and (3) those having the same incident angle as that of desired path components can both be suppressed. The proposed receiver does not require prohibitively large computational complexity. Results of computer simulations presented in this paper show that the proposed receiver exhibits excellent performance even in severe multipath fading environments 相似文献
14.
Caire G. Taricco G. Ventura-Traveset J. Biglieri E. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1997,43(5):1503-1517
We compare three receivers for coded narrowband transmission affected by fading and co-channel interference. The baseline receiver is based on conventional diversity reception with maximal-ratio combining. A multiuser approach allows us to derive a maximum-likelihood multiuser receiver and its reduced-complexity suboptimal version. Finally, a decorrelating diversity receiver, which seeks a tradeoff between performance and complexity, is studied. Closed-form performance parameters are derived for all the proposed receivers in the case of coded coherent PSK and independent frequency nonselective Rayleigh fading 相似文献
15.
Moshavi S. Yellin D. Sadowsky J.S. Perets Y. Pick K. 《Vehicular Technology, IEEE Transactions on》2005,54(5):1781-1792
This paper considers the link-level and network-level performance of code division multiple access (CDMA) pilot interference cancellation (pilot IC) technology, a low-complexity advanced receiver technology being considered for use in commercial third generation (3G) CDMA cellular systems. The concept behind this technology is to estimate and cancel at the handset receiver the interference effects associated with CDMA downlink pilot signals broadcast from the base stations of the network. The canceling of interference at the receiver improves the signal-to-interference/noise ratio (SINR), which enables increased cell capacity or throughput. In this paper, we derive SINR expressions for evaluating the probability of error performance of both the RAKE and pilot IC handset receivers, under conventional random spreading code assumptions. The approach can easily and accurately model a wide variety of transmitter, channel, and receiver conditions, including the effects of channel estimation. We also utilize radio network simulations to illustrate and quantify the capacity gains available for 3G CDMA networks through the use of pilot IC handsets. Network simulations are also used to examine the reduced level of soft-handoff found to be possible in pilot IC-based networks and the increased flexibility available in setting pilot power levels. We further consider the impact of using stronger pilot signals for improving the demodulation performance of sensitive higher-order modulation constellations that are needed to support spectrally efficient high-rate data services. 相似文献
16.
In this paper, the authors consider an asynchronous direct-sequence code division multiple access (DS/CDMA) system wherein users are allowed to transmit their symbols at one out of two available data rates. Three possible access schemes are considered, namely, the variable spreading length (VSL), the variable chip rate (VCR), and the variable chip rate with frequency shift (VCRFS) formats. Their performance is compared for the case that a linear one-shot multiuser receiver is employed. It is also shown that detection of the users transmitting at the higher rate requires a periodically time-varying processing of the observables. Moreover, the problem of blind adaptive receiver implementation is studied, and a cyclic blind recursive-least-squares (RLS) algorithm is provided which is capable of converging to the periodically time-varying high-rate users detection structure. Numerical results show that the proposed receivers are near-far resistant, and that the VCRFS access technique achieves the best performance. Finally as to the adaptive blind receiver implementation, computer simulations have revealed that the cyclic RLS algorithm for blind adaptive high-rate users demodulation outperforms the conventional RLS algorithm in most cases of primary importance 相似文献
17.
18.
Bit-error probability (BEP) analysis for linear multiuser receivers with multiple sensors in frequency selective Rayleigh fading channels is presented. The analysis is applied to evaluate the BEP in antenna diversity reception and in a cellular CDMA system. Diversity and multiuser receivers are compared based on the examples. It is observed that adding new diversity antenna elements improves performance even if the correlation between the antenna elements is relatively large (up to 0.7). However, the large correlation values pose a significant reduction in the diversity gain in comparison to the zero correlation. It is also seen that the macroscopic diversity improves the performance of receivers significantly in cellular CDMA networks. When comparing diversity and multiuser receivers it is concluded that multiuser receivers are necessary to provide low BEPs. It is also highly beneficial to have at least two diversity antennas available, in particular, if there is no multipath diversity provided by the channel. The results also show that the reduction of intercell multiple-access interference yields a significant performance advantage in cellular networks. It is also demonstrated that the combination of spatial diversity and a multiuser receiver provides a significant receiver performance or system capacity gain in comparison to implementing only one of them 相似文献
19.
A covariance shaping framework for linear multiuser detection 总被引:1,自引:0,他引:1
Eldar Y.C. Shamai S. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2005,51(7):2426-2446
A new class of linear multiuser receivers, referred to as the covariance shaping multiuser (CSMU) receiver, is proposed, for suppression of interference in multiuser wireless communication systems. This class of receivers is based on the recently proposed covariance shaping least-squares estimator, and is designed to minimize the total variance of the weighted error between the receiver output and the observed signal, subject to the constraint that the covariance of the noise component in the receiver output is proportional to a given covariance matrix, so that we control the dynamic range and spectral shape of the output noise. Some of the well-known linear multiuser receivers are shown to be special cases of the CSMU receiver. This allows us to interpret these receivers as the receivers that minimize the total error variance in the observations, among all linear receivers with the same output noise covariance, and to analyze their performance in a unified way. We derive exact and approximate expressions for the probability of bit error, as well as the asymptotic signal-to-interference+noise ratio in the large system limit. We also characterize the spectral efficiency versus energy-per-information bit of the CSMU receiver in the wideband regime. Finally, we consider a special case of the CSMU receiver, equivalent to a mismatched minimum mean-squared error (MMSE) receiver, in which the channel signal-to-noise ratio (SNR) is not known precisely. Using our general performance analysis results, we characterize the performance of the mismatched MMSE receiver. We then treat the case in which the SNR is known to lie in a given uncertainty range, and develop a robust mismatched MMSE receiver whose performance is very close to that of the MMSE receiver over the entire uncertainty range. 相似文献
20.
Po-An Sung Kwang-Cheng Chen 《Selected Areas in Communications, IEEE Journal on》1996,14(8):1583-1594
We generalize the multiuser (CDMA spread spectrum) communication systems to the fading environments. We first extend Verdu's (1986) conventional optimum receiver to Rayleigh-fading environments and then evaluate its performance. Having no knowledge of the received power at the receiving end, we therefore need an estimator to efficiently estimate the received signal strength of each user in fading environments. A linear minimum mean square error (LMMSE) unbiased estimator is proposed to attain this goal. By using the minimum mean square error (MMSE) Bayesian estimation, we further propose the LMMSE bit estimator for efficient demodulation. Its performance is close to the optimum multiuser receiver but with a much simpler polynomial complexity. To further reduce the complexity, we extend the LMMSE estimator to the sequential LMMSE estimator. In sequential estimation, we do not need to implement the matched filter banks and to perform the matrix inversion when estimating. In addition, it converges after approximately 2k iterations, where k is the number of users. With this fast convergence property and the simple structure, the sequential LMMSE estimator provides an attractive alternative to the implementation of a multiuser system 相似文献