共查询到20条相似文献,搜索用时 31 毫秒
1.
Vyacheslav Tuzlukov 《Circuits, Systems, and Signal Processing》2011,30(6):1197-1230
The generalized receiver (GR) based on a generalized approach to signal processing (GASP) in noise is investigated in a direct-sequence
code-division multiple access (DS-CDMA) wireless communication system with frequency-selective channels. We consider four
avenues: linear equalization with finite impulse response (FIR) beamforming filters; channel estimation and spatially correlation;
optimal combining; and partial cancellation. We investigate the GR with simple linear equalization and FIR beamforming filters.
Numerical results and simulation show that the GR with FIR beamforming filters surpasses in performance the optimum infinite
impulse response beamforming filters with conventional receivers, and can closely approach the performance of GR with infinite
impulse response beamforming filters. Channel estimation errors are taken into consideration so that DS-CDMA wireless communication
system performance will not be degraded under practical channel estimation. GR takes an estimation error of a maximum likelihood
(ML) multiple-input multiple-output (MIMO) channel estimation and GR spatially correlation into account in computation of
minimum mean square error (MMSE) and log-likelihood ratio (LLR) of each coded bit. The symbol error rate (SER) performance
of DS-CDMA employing GR with a quadrature sub-branch hybrid selection/maximal-ratio combining (HS/MRC) scheme for 1-D modulations
in Rayleigh fading is obtained and compared with that of conventional HS/MRC receivers. Procedure of selecting a partial cancelation
factor (PCF) for the first stage of a hard-decision partial parallel interference cancellation (PPIC) of the GR employed in
DS-CDMA wireless communication system is proposed. A range of optimal PCFs is derived based on the Price’s theorem. Computer
simulation results show superiority in bit error rate (BER) performance that is very close to that potentially achieved and
surpasses the BER performance of the real PCF for DS-CDMA systems discussed in literature. 相似文献
2.
Multiuser receivers for CDMA systems in Rayleigh fading channels 总被引:2,自引:0,他引:2
Multiuser demodulation in relatively fast fading channels is analyzed. The optimal maximum likelihood sequence detection (MLSD) receiver is derived and a general suboptimal receiver to approximate the MLSD is proposed. The performance of the parallel interference cancellation (PIC) and decorrelating receivers is compared. The PIC receiver is demonstrated to achieve better performance in known channels than the decorrelating receiver, but it is observed to be more sensitive to the channel coefficient estimation errors than the decorrelator. At high channel loads the PIC receiver suffers from bit error rate (BER) saturation, whereas the decorrelating receiver does not. The performance of data-aided (DA) and decision-directed (DD) multiuser channel estimation is also compared. DA channel estimation is shown to be more robust than DD channel estimation, which may suffer from BER saturation caused by hangups at high signal-to-noise ratios (SNRs). The impact of channel estimation filter impulse response on the BER is studied by comparing optimal and suboptimal channel estimation filters. The implementation complexity of the decorrelating and PIC receivers is compared in terms of required floating point operations and clock cycles in a practical communication scenario. It is observed that the PIC receiver is only moderately more complex to implement than the conventional matched filter bank receiver, whereas the decorrelating receiver is significantly more complex 相似文献
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单载波频域均衡(SC-FDE)是宽带无线通信系统中一种具有竞争力的解决方案,获得了广泛的关注和研究。SC-FDE方案不仅抗多径能力出色、复杂度低,且具有比正交频分复用(OFDM)信号更低的峰均比值。在突发SC- FDE系统中,接收机需要利用训练序列快速获取信道的特征信息,以避免解调性能损失。传统的基于训练序列的信道估计方法并不适合宽带猝发SC-FDE系统,难以兼顾估计准确性和复杂度。该文提出一种基于时域训练序列的精细信道估计方法。该方法利用时域PN序列得到信道参数的最大似然估计值,并利用信道稀疏的特征,根据信道噪声强度对信道估计值进行噪声抑制处理。仿真表明:与传统信道估计方法相比,该信道估计方法能取得更高的估计精度,且具有较低的实现复杂度。 相似文献
5.
The effect of imperfect channel estimation (CE) on the performance of pilot-symbol-assisted modulation (PSAM) and MRC Rake reception over time- or frequency-selective fading channels with either a uniform power delay profile (UPDP) or a nonuniform power delay profile (NPDP) is investigated. For time-selective channels, a Wiener filter or linear minimum mean square error (LMMSE) filter for CE is considered, and a closed-form asymptotic expression for the mean square error (MSE) when the number of pilots used for CE approaches infinity is derived. In high signal-to-noise ratio (SNR), the MSE becomes independent of the channel Doppler spectrum. A characteristic function method is used to derive new closed-form expressions for the bit error rate (BER) of Rake receivers in UPDP and NPDP channels. The results are extended to two-dimensional (2-D) Rake receivers. The pilot-symbol spacing and pilot-to-data power ratio are optimized by minimizing the BER. For UPDP channels, elegant results are obtained in the asymptotic case. Furthermore, robust spacing design criteria are derived for the maximum Doppler frequency. 相似文献
6.
Jun Wang Hongyang Chen Shaoqian Li 《Wireless Communications and Mobile Computing》2012,12(15):1363-1370
For wireless multiple‐input multiple‐output (MIMO) communications systems, both channel estimation error and spatial channel correlation should be considered when designing an effective signal detection system. In this paper, we propose a new soft‐output MMSE based Vertical Bell Laboratories Layered Space‐Time (V‐BLAST) receiver for spatially‐correlated Rician fading MIMO channels. In this novel receiver, not only the channel estimation errors and channel correlation but also the residual interference cancellation errors are taken into consideration in the computation of the MMSE filter and the log‐likelihood ratio (LLR) of each coded bit. More importantly, our proposed receiver generalizes all existing soft‐output MMSE V‐BLAST receivers, in the sense that, previously proposed soft‐output MMSE V‐BLAST receivers can be derived as the reduced forms of our receiver when the above three considered factors are partially or fully simplified. Simulation results show that the proposed soft‐output MMSE V‐BLAST receiver outperforms the existing receivers with a considerable gain in terms of bit‐error‐rate (BER) performance. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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This paper develops a maximum likelihood sequence estimation (MLSE) receiver for the frequency-flat, fast-fading channel corrupted by additive Gaussian noise when linear modulations (M-ASK, M-PSK, and M-QAM) are employed. This paper extends Ungerboeck's derivation of the extended MLSE receiver for the purely frequency-selective channel to the time-selective channel. Although the new receiver's structure and metric assume ideal channel state information (CSI) at the receiver, the receiver structure can be used wherever high-quality CSI is available. The receiver is maximum likelihood for a variety of channels, including Ricean, Rayleigh, lognormal, and additive white Gaussian noise (AWGN) channels. Bounds on the receiver's bit error rate (BER) are deduced for ideal and pilot tone CSI for fast Rayleigh fading. A crude lower bound is developed on the BER of predictor-based receivers for the same channel. This paper offers insight into matched filtering and receiver processing for the fast-fading channel and shows how pilot symbols and tones should be exploited 相似文献
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Strohmer T与Beaver S于2003年提出了适用于时频散射信道的网格正交频分复用 (LOFDM, Lattice Orthogonal Frequency Division Multiplexing)系统,与传统OFDM系统相比该系统具有更高的频带利用率和更好的误码性能。LOFDM系统发送端需要自适应地调整信号的原形脉冲和其时频分布的参数,使之与信道保持匹配;而接收端则需要准确的信道估计以实现相干解调。本文针对LOFDM 系统由于其信号的时频交错特性接收端无法直接利用接收信号进行时域信道估计的问题,采用一种低复杂度的等效时频子空间投影方法有效分离奇偶子载波,并在此基础上提出了一种LOFDM系统频率选择性块衰落信道条件下的时域信道估计算法。同时还对系统存在的干扰进行了分析,推导得到LOFDM系统信道估计算法的Cramér-Rao理论下界。仿真表明:提出的LOFDM信道估计算法不仅具有较好的均方误差性能,而且近似达到理想信道估计的误符号率性能。 相似文献
10.
K. Ghanem P. S. Hall R. Langley 《International Journal of Wireless Information Networks》2010,17(3-4):126-136
The problem of interference cancellation may arise in the nearest future for body-area networks (BANs) whenever a certain number of BANs are led to operate in the vicinity of each other under the same spectrum band. In this paper, using the data obtained from the measurements, the performance in terms of bit error rate (BER) of three linear CDMA receiver structures is investigated for BANs: the conventional receiver, the minimum mean square error receiver, and the decorrelator receiver. We show that in synchronous scenario, the three receivers exhibit the same performance regardless of the number of supported users and SNR level. The BER performance of the linear receivers in on-body channels is better than in Rayleigh channel with the belt-chest channel exhibiting the best gain due to the presence of a stronger LOS component. Furthermore, with orthogonal codes, these receivers are shown to be robust to the MAI level increase and do not require a perfect power control. 相似文献
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Omidi M.J. Gulak P.G. Pasupathy S. 《Selected Areas in Communications, IEEE Journal on》1998,16(9):1616-1629
Joint data and channel estimation for mobile communication receivers can be realized by employing a Viterbi detector along with channel estimators which estimate the channel impulse response. The behavior of the channel estimator has a strong impact on the overall error rate performance of the receiver. Kalman filtering is an optimum channel estimation technique which can lead to significant improvement in the receiver bit error rate (BER) performance. However, a Kalman filter is a complex algorithm and is sensitive to roundoff errors. Square-root implementation methods are required for robustness against numerical errors. Real-time computation of the Kalman estimator in a mobile communication receiver calls for parallel and pipelined structures to take advantage of the inherent parallelism in the algorithm. In this paper different implementation methods are considered for measurement update and time update equations of the Kalman filter. The unit-lower-triangular-diagonal (LD) correction algorithm is used for the time update equations, and systolic array structures are proposed for its implementation. For the overall implementation of joint data and channel estimation, parallel structures are proposed to perform both the Viterbi algorithm and channel estimation. Simulation results show the numerical stability of different implementation techniques and the number of bits required in the digital computations with different estimators 相似文献
13.
We consider joint channel estimation and data detection in uplink asynchronous code-division multiple-access systems employing aperiodic (long) spreading sequences in the presence of unknown multipath fading. Since maximum-likelihood (ML) sequence estimation is too complex to perform, multiuser receivers are proposed based on the sequential expectation-maximization (EM) algorithm. With the prior knowledge of only the signature waveforms, the delays and the second-order statistics of the fading channel, the receivers sequentially estimate the channel using the sequential EM algorithm. Moreover, the snapshot estimates of each path are tracked by linear minimum mean-squared error filters. The user data are detected by a ML sequence detector, given the channel estimates. The proposed receivers that use the exact expressions have a computational complexity O(2/sup K/) per bit, where K is the number of users. Using the EM algorithm, we derive low-complexity approximations which have a computational complexity of O(K/sup 2/) per bit. Simulation results demonstrate that the proposed receivers offer substantial performance gains over conventional pilot-symbol-assisted techniques and achieve a performance close to the known channel bounds. Furthermore, the proposed receivers even outperform the single-user RAKE receiver with Nyquist pilot-insertion rate in a single-user environment. 相似文献
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首先介绍了基于WCDMA系统中RAKE接收机的信道估计方法,然后将Turbo原理引入信道估计,针对WCDMA系统提出两种迭代信道的估计方法。通过使用RAKE接收机或解码之后的软信息来改善整个WCDMA系统的性能,对WCDMA系统中联合运用信道估计与解码技术进行了研究。由于联合信道估计与解码技术可以利用通信系统不同模块之间的“软信息”交换,从而有效地提高了信道估计准确程度和解码器的性能。仿真结果表明,利用解码之后的软信息来修正信道估计的方法较传统的RAKE接收机中的信道估计方法性能有较大改善,在误码率为10^-2左右时,提高大约1dB。 相似文献
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Several receiver structures for linearly modulated signals are proposed for time-varying frequency-selective channels. Their channel estimators explicitly model the time variation of the channel taps via polynomials. These structures are constructed from the following building blocks: (i) sliding or fixed block channel estimators; (ii) maximum likelihood sequence detectors (MLSDs) or decision feedback equalizers (DFEs); and (iii) single or multiple passes. A sliding window channel estimator uses a window of received samples to estimate the channel taps within or at the end of the window. Every symbol period, the window of samples is slid along another symbol period, and a new estimate is calculated. A fixed block channel estimator uses all received samples to estimate the channel taps throughout the packet, all at once. A single pass receiver estimates the channel and detects data once only. A multipass receiver performs channel estimation and data detection repetitively. The effect of the training symbol positions on the performance of the block multipass approach is studied. The bit error rate (BER) performance of the MLSD structures is characterized through simulation and analysis. The proposed receivers offer a range of performance/complexity tradeoffs, but all are well suited to time-varying channels. In fast fading channels, as the signal-to-noise ratio (SNR) increases, they begin to significantly outperform the per-survivor processing-based MLSD receivers which employ the least mean-squares (LMS) algorithm for channel estimation 相似文献
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两种插值信道估计方法的比较 总被引:1,自引:0,他引:1
在瑞利衰落信道中,使用时分复用的导频信号辅助的信道估计方案时,提出了在使用极大似然方法估计出导频符号的信道参数之后,再利用一个时隙上所有导频符号的Chebyshev多项式的数学插值估计数据符号信道参数的方法。同时比较了分段线性插值加递归的信道估计方法。仿真结果表明,使用Chebyshev多项式的数学插值估计信道参数的方法比使用线性插值加线性递归的信道估计方法能更好的改善系统的性能。 相似文献
18.
The orthogonal frequency division multiplexing (OFDM) transmission scheme is currently experiencing increased popularity due
to advances in very large scale integration technology. It is used for a variety of broadband systems such as asymmetric digital
subscriber lines, very-high-speed digital subscriber lines, digital video, and audio broadcasting, and wide local area network
standards such as IEEE 802.11a, IEEE 802.11 g, and ETSI Hiperlan/2. However, propagation impairments can cause severe degradation
in bit error rates (BER) for coherent detection. We derive a semi-analytical method to evaluate BER of a quadrature phase
shift keying (QPSK)-OFDM system in Nakagami, m < 1 fading and additive noise where pilot-assisted linear channel estimation and channel equalization are used. This allows
modeling of more severe fading environments than can be depicted by a Rayleigh distribution. Numerical simulations are used
to validate the proposed methods. The techniques developed can be applied to other channel estimation techniques, modulation
schemes and the performance evaluation of equalized single carrier narrowband systems. 相似文献
19.
信道估计技术是正交频分复用(OFDM)系统中的关键技术。其中直接判决信道估计算法在减少均方误差(MSE)和误码率(BER)等方面具有优越性而备受关注。提出了一种基于循环线性最小均方误差(LMMSE)的直接判决信道估计算法,并且在高斯白噪声信道和多径瑞利信道下进行了仿真。实验结果表明,该算法与其他的算法相比,在减少MSE和BER等方面具有明显的优势。 相似文献
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Wonjin Sung In-Kyung Kim 《Selected Areas in Communications, IEEE Journal on》2000,18(11):2336-2344
We propose a channel classification method that identifies the delay path profile of Rayleigh fading channels, which can be used in conjunction with conventional maximum-likelihood sequence estimation (MLSE) receivers. The proposed method determines the appropriate number of delay taps for the MLSE trellis, based on a decision variable obtained from multiple traffic bursts. By formulating the decision variable using the F-distribution, we derive exact expressions for misclassification probability. A new MLSE receiver structure that utilizes the channel classification method is described, and bit error rate (BER) simulation results are presented to demonstrate the performance improvement. The particular application which is discussed is the IS-136 TDMA standard 相似文献