Decorrelating detector with diversity combining for single user frequency-selective rayleigh fading multipath channels

Diversity combining techniques are applied in mobile radio communications as a means of performance improvement in a fading multipath environment. Adaptive equalizers which incorporate diversity combining were shown to combat intersymbol interference (ISI) caused by multipath provided that the fading is sufficiently slow. However, for fast fading rates, noncoherent techniques are often desirable. In this paper, we examine the performance of several coherent and noncoherent detectors that make use of diversity combining. In particular, the decorrelating filter is shown to provide reliable performance for a frequency-selective Rayleigh fading multipath channel with ISI. Numerical and simulation results are presented for a channel with two independent Rayleigh fading paths. Signal design issues which arise in the implementation of the decorrelating detector and the zero-forcing equalizer are discussed.     

Suboptimal maximum-likelihood multiuser detection of synchronousCDMA on frequency-selective multipath channels

We propose a signal processing technique, based on the estimate-maximize algorithm, in order to perform multiuser code-division multiple-access (CDMA) detection. This algorithm iteratively seeks for the maximum-likelihood solution. The resulting structure is a successive interference cancellation scheme which can be applied to both synchronous and asynchronous CDMA. Higher performance than similar methods is obtained from using deterministic annealing and multiple stages. A soft output is defined, and the signal-to-noise ratio in the soft output of the detector is measured for predicting performance with an outer code with soft input decoder. The new receiver is applied to the problem whereby in a synchronous CDMA system the orthogonality of the codes is destroyed by a frequency-selective channel, caused by multipath fading. This nonlinear technique is shown to perform much better than the minimum mean-square-error linear solution and several other algorithms. The algorithm lends itself to an efficient DSP or VLSI implementation. We evaluate the performance by simulations with coherent quadrature phase-shift keying modulation, known channel and long random Rayleigh multipath. In most cases, we set the number of users equal to the processing gain for maximal throughput. The results are also presented in the form of outage probabilities for random Rayleigh multipath against required fading margin     

Space diversity in presence of discrete multipath fading channel

Most analytical studies of the performance of space diversity systems on fading channels assume a very rich multipath environment. In certain wireless applications, however, the number of significant multipath components can be small. In this letter, we consider a multipath channel in which the signal propagates from the transmitter to the receiver via L discrete paths which are uniformly distributed about the transmitter and receiver. For this channel, we study the effects of the number of multipath components and antenna array size on the error probability and outage capacity of space diversity systems. We observe that performance is significantly influenced by the presence of a channel with few multipath components.     

The effect of sample timing on bit error rate performance in a multipath fading channel

Digital mobile radio often suffers from fatal effects caused by frequency-selective fading, resulting in severe bit error rate (BER) degradation. The feasibility of digital mobile radio largely depends on the multipath-distortion tolerant capability of modulation technique. The BER performance is compared among four digital modulation techniques in a frequency selective fading channel with large multipath delay spread. In particular, taking the timing fluctuation of eye patterns due to delay distortion of a fading channel into account, the effect of sample timing on BER is analyzed. The analyses have revealed that BER performance markedly depends on the choice of sample timing, and also an interesting fact that BPSK is outstanding in the multipath-distortion tolerance, if coupled with adaptive sampling, and its BER curves remain almost the same as that of frequency-flat fading as long as multipath delay difference is less than a bit interval.     

Hybrid diversity combining techniques for DS‐CDMA over a multipath fading channel

The combined effect of antenna diversity and spread spectrum (SS) diversity for a direct sequence code division multiple access (DS‐CDMA) system using differential binary phase‐shift keying (DBPSK) modulation is evaluated. Both maximal ratio combining (MRC) and selection diversity (SD) are considered and the bit error rate (BER) performance for four following diversity schemes are compared: (1) SS diversity with MRC and antenna diversity with SD; (2) SS diversity with SD and antenna diversity with MRC; (3) MRC of both SS diversity and antenna diversity; (4) SD of both SS diversity and antenna diversity. It is shown that antenna diversity with MRC and SS diversity with selection has a performance very close to that of antenna diversity and SS diversity both with MRC. This revised version was published online in July 2006 with corrections to the Cover Date.     

Statistical modeling of W-CDMA signals for use over frequency-selective multipath channels

This letter presents a mathematical model for the statistics of wideband code-division multiple-access signals which experience multipath fading. The statistics are obtained from numerically generated signals, and are then modeled with an offset noncentral chi distribution with three degrees of freedom. The mathematical model is tested against the numerically generated data by the use of a chi-square goodness-of-fit test.     

Estimation of the parameters of a multipath channel usingset-theoretic deconvolution

A method for the estimation of the parameters of multipath communication channels is developed. The method makes use of matched filtering, set-theoretic deconvolution and autoregressive modeling. Pulse compression waveforms are used as channel probing signals. The results of a feasibility study in which the proposed method is applied to specular multipath channels to estimate the multipath parameters at a number of different signal-to-noise ratios (SNR) are presented     

一种基于DFT变换的多径信道估计改进算法

根据LTE(长期演进)系统下行链路的要求,结合硬件实现的实用性分析传统的信道估计算法,对信道估计中噪声区间不连续的情况、DFT(离散傅里叶变换)运算造成的频谱泄露问题、循环前缀长度内噪声不易消除等提出一种通过频域加窗,对噪声进行估计修正和对循环前缀内的信号进行滤波的方法对算法进行改进。通过对算法进行仿真,结果表明在增加少量算法复杂度上,提高了算法的准确性,提高系统的性能,适合于硬件的实现。     

On channel parameter estimation in a space-time bit-interleaved-coded modulation system for multipath DS-CDMA uplink with receive diversity

In this paper, we consider iterative space-time multiuser detection and channel parameter estimation in a bit-interleaved coded modulation scheme for asynchronous direct-sequence code division multiple access (DS-CDMA) transmission over frequency selective, slowly fading channels. Accurate estimation of the channel parameters is critical as it has great impact on the overall BER performance. We present an iterative space-time multiuser (STMU) turbo detection and estimation scheme, based on space alternating generalized expectation maximization (SAGE) algorithm. This algorithm operates on the coded symbols by exchanging soft information between the detector and the estimator. We show through computer simulations that the proposed low complexity STMU receiver considerably outperforms conventional estimation schemes and achieves excellent performance, both in terms of BER and estimation error variance. Finally, we will consider different mapping strategies and investigate their impact on the performance and complexity of the estimator.     

Note on the optimal transversal equalizer for a dual multipath noiseless channel

Optimal transversal equalization is considered for a noiseless multipath channel comprising a main signal followed by a larger magnitude ghost. It is shown that for the optimal transversal equalizer, the output residual intersymbol variance decreases with increase of processing delay. For the same processing delay, the optimal transversal equalizer intersymbol variance is always larger than that of the finite optimal Wiener equalizer, especially as the magnitudes of the main signal and ghost approach equality.     

Theory of the performance of a DECT receiver in a multipath channel

The performance of a digital enhanced cordless telecommunications (DECT) receiver in a multipath channel is studied. The following issues were investigated: irreducible bit-error rate (BER) performance of the differentially coherent detector in Rayleigh and Rician channels; BER performance in the presence of both the noise in the receiver and a multipath interference. The theoretical estimates of the irreducible error rate developed in the paper showed reasonable agreement with the data obtained from computer-based simulation of the DECT link through a Rayleigh multipath channel. The combined effect from receiver noise and multipath interference has been studied, and asymptotic formulas for the total error probability have been developed. The results of calculating the error probabilities using these asymptotics demonstrate good agreement with measured data     

The effect of multipath interference on the performance of packetradios

The effect of multipath interference on the performance of packet radios is investigated. The protocols considered include pure ALOHA and slotted ALOHA. Signal reception with and without capture effect is considered in the analysis. Mathematical expressions of system throughput and packet delay have been successfully obtained for each protocol. Numerical calculations are used to demonstrate when the multipath interference can be ignored and when it can be disastrous     

Effects of Doppler spread on adaptive orthogonal frequency division multiplexing channel capacity employing diversity in multipath environments

This paper derives the capacity of a fading channel with orthogonal frequency division multiplexing transmission employing diversity techniques and adaptive policies in Rayleigh fading environments. The effects of Doppler shift f_d on channel capacity are analysed. The main contribution of this work is to model intercarrier interference as a function of f_d and symbol duration T_s. Two diversity techniques are considered (i) maximal ratio combining (MRC) and (ii) selective combining (SC). Three adaptive policies are combined with MRC and SC to estimate the following channel capacity: (i) optimal rate adaptive; (ii) optimal power and rate adaptive; and (iii) channel inversion with fixed rate adaptive. Closed‐form expressions and bounds on channel capacity employing different diversity techniques are derived. Simulation results are given. Copyright © 2011 John Wiley & Sons, Ltd.     

A multipath model for the powerline channel

The development of powerline communication (PLC) systems for Internet, voice, and data services requires measurement-based models of the transfer characteristics of the mains network suitable for performance analysis by simulation. This paper presents an analytic model describing complex transfer functions of typical powerline networks using only a small set of parameters. The model is based on physical signal propagation effects in mains networks including numerous branches and impedance mismatching. Besides multipath propagation accompanied by frequency-selective fading, signal attenuation of typical power cables increasing with length and frequency is considered. A verification of the model at a test network, as well as its use for definition of attenuation profiles and reference channels, demonstrate the practical value of the proposed model     

32APSK调制在多径信道中的星座优化

为了提升APSK调制在多径信道中的使用性能,提出基于误码率分析的新星座构造方法,该方法通过星座点的旋转,能很好的对抗多径失真对信号的影响.本文以32APSK为例进行星座优化,通过计算机仿真搜索,得到32MAPSK调制星座的最优旋转角度.仿真表明,该方法不需要增加任何硬件设备,具有简便、性能提升明显的特点.     

MLSE receiver for direct-sequence spread-spectrum systems on a multipath fading channel

To accommodate high-speed data transmissions, it may be necessary to substantially reduce the processing gain of a direct-sequence spread-spectrum (DSSS) system. As a result, intersymbol interference effects may become more severe. In this paper, we present a new structure for maximum-likelihood sequence estimation equalization of DSSS signals on a multipath fading channel that performs the function of despreading and equalization simultaneously. Analytical upper bounds are derived for the bit-error probability when random spreading sequences are used, and comparisons to simulation results show that the bounds are quite accurate. The results also show that significant performance improvement over the conventional RAKE receiver is obtained.     

基于DMF捕获系统频率选择性信道下捕获性能的分析

对基于数字匹配滤波器(DMF)捕获系统在频率选择性信道下的捕获性能进行了深入讨论，利用状态转移图推导出单次驻留判决方式时平均捕获时间的表达式，对平均捕获时间与多径分量的关系进行了数字分析。得出的主要结论是：对于多径分量为非衰落信号时，多径分量之间的能量差别越大，系统捕获性能越好，多径分量的能量相等时，系统捕获性能最差，且随着可以分离的多径路数的增加下降；对于多径分量为慢衰落信号时，多径信道的捕获性能好于单径信道(非频率选择性衰落信道)，且多径分量之间的能量差别越大，系统捕获性能越差，当多径分量的能量相等时，捕获性能最好，这与非衰落信道的情形相反。因此在频率选择性衰落信道中，采用分集接收可以改善系统的捕获性能。     

On the bounds of frequency-selective channel capacity with doubly correlated geometrical MIMO channel model

The multi-input multi-output (MIMO) technology plays an important role in link transmissions. This article considers the general case for the ergodic capacity in doubly correlated frequency-selective MIMO channel. In the study, the geometrical MIMO channel model is presented. Based on the formula of MIMO ergodic capacity, the capacity limits are studied with arbitrary finite number of antennas in the frequency-selective MIMO channel. It first derives the exact expressions for the upper bound and lower bound in doubly correlated MIMO channel. The results for the single-ended correlation and independent identically distributed (i.i.d.) MIMO channel are also obtained as special cases. Then the simple expressions of the capacity bounds are attained at high SNR. Finally, results are provided by Monte Carlo simulations to verify the tightness of the derived bounds.     

Equalization and semi-blind channel estimation for space-time block coded signals over a frequency-selective fading channel

In this paper, we investigate the equalization and channel identification for space-time block coded signals over a frequency-selective multiple-input multiple-output (MIMO) channel. The equalization has been considered by taking into account the cyclostationarity of space-time block coded signals. The minimum mean square error (MMSE) solutions have been derived for the linear and decision feedback (DF) equalizers. The channel estimation is required for the equalization. With known symbols (as pilot symbols), MIMO channels can be estimated. In addition, due to the redundancy induced by space-time block code, it is possible to identify MIMO channels blindly using the subspace method. We consider both blind and semi-blind channel estimation for MIMO channels. It is shown that the semi-blind channel estimate has fewer estimation errors, and it results in less (bit error rate) performance degradation of the MMSE linear and DF equalizers.