The Effect of Decision Delay in MMSE-THP Systems

In this paper, the effect of decision delay in minimum mean square error Tomlinson-Harashima precoding systems is investigated. The optimal decision delays are partly solved under three cases that are divided by comparing the feedback filter order with channel order. The mean square error and the bit error rate of the system under different decision delays have been thoroughly examined. Simulation results verify the validity of the derived optimal decision delay.     

Effect of Phase Ripple on Class 4 Partial Response Data Signals

An expression is derived for the mean square error of a SSBAM or a baseband multilevel class 4 partial response data signal when distorted by a channel which has a sinusoidal phase ripple. Such characteristics are approximated when the channel has been equalized by so called "bump" group delay equalizers. Included are the expressions for the optimum carrier phase and sampling time. For a low frequency group delay ripple, it is shown that the error can vary by a factor of seven for differing frequency and phasing of the ripple with the same peak group delay variation.     

Analysis and optimization of pilot symbol-assisted Rake receivers for DS-CDMA systems

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.     

基于最低误码率准则的奇次三阶Volterra均衡器用于干扰抑制

该文针对通信系统中的干扰抑制问题,提出一种基于最低误码率准则的Volterra均衡器.区别于以往研究中采用最小均方误差准则估计Volterra核,本文采用最低误码率准则.仿真表明:对于扩展的二元相移键控信号,在相对强的窄带干扰下,匹配滤波器和基于最小均方误差准则的线性均衡器已失效,而基于最低误码率准则的Volterra均衡器仍能表现出良好的性能,也大大优于最小均方误差准则的Volterra均衡器;并且在计算复杂度与误码率性能的权衡中,奇次三阶Volterra均衡器更有实用价值.     

Performance analysis for relay networks with hierarchical support vector machines

In this paper, we consider a cooperative relay scheme for a mobile network with MIMO technology. The channel capacity for two well‐known relaying schemes are investigated: analogue relaying (amplify and forward) and digital relaying (decode and forward) from a mobile device to the base station through a relay node. In order to further increase the channel capacity, we propose an efficient hierarchical procedure based on support vector machine, namely hierarchical support vector machines (HSVM), to estimate the wireless networks condition approximately and design two ways (matched filter and minimum mean square error filter) of increasing the channel capacity according to the estimated wireless network condition. The proposed HSVM can estimate the wireless networks condition in much shorter time compared with the traditional minimum mean square error scheme without incurring much estimation error, which is spatial, useful for delay sensitive communication. For digital relaying, the effect of imperfect channel decode is also addressed. Our numerical results demonstrate the reduction of estimation complexity by adopting HSVM and the significant improvement of network capacity by applying the matched filter weight at relay nodes according to the network estimation. Copyright © 2011 John Wiley & Sons, Ltd.     

信道反馈延迟时MIMO中继系统的线性预编码算法

针对采用放大转发(Amplify and Forward, AF)中继技术的多入多出(Multiple Input Multiple Output, MIMO)系统, 考虑信道估计误差及反馈存在延迟的情况, 提出一种基于最小均方误差(Minimum Mean Squared Error, MMSE)准则的预编码设计方案.假设基站-中继端及中继端-终端的信道均存在估计误差与反馈延迟, 在基站和中继端功率都受限条件下, 以MMSE为准则, 推导得到了基站预编码矩阵、中继转发矩阵和终端解码矩阵的闭式解.数值仿真结果表明, 该方案所提出的预编码算法能有效地改善系统的误比特率与均方误差.     

Simulation of digital transmission over mobile channels at 300 kb/s

Studies of digital transmission over typical urban and suburban mobile channels using simulations that employ a local area model for the time varying mobile channel impulse response are discussed. The digital transmission techniques of coherently detected and differentially coherent detected versions of quadrature phase-shift keying (QPSK), Gaussian minimum shift keying (GMSK), and coherently detected binary phase-shift keying (BPSK) over example mobile channels are presented. Two measures of performance are considered; the mean bit error ratio (and irreducible bit error ratio), which is used to compare the robustness of the various modulation methods to delay spread, and the outage probability, which provides a measure of the overall transmission quality as would be perceived by a user. Emphasis is placed on results obtained for GMSK, which is the modulation scheme to be employed in the Pan-European digital cellular mobile system. The effects of RMS delay spread on the mean bit error ratio, mean irreducible bit error ratio, and probability of outage are considered for different channel types     

Adaptive joint beamforming and B‐MMSE detection for CDMA signal reception under multipath interference

The combination of antenna array beamforming with multiuser detection can effectively improve the detection efficiency of a wireless system under multipath interference, especially in a fast‐fading channel. This paper studies the performance of an adaptive beamformer incorporated with a block‐wise minimum mean square error(B‐MMSE) detector, which works on a unique signal frame characterized by training sequence preamble and data blocks segmented by zero‐bits. Both beam‐former weights updating and B‐MMSE detection are carried out by either least mean square (LMS) or recursive least square (RLS) algorithm. The comparison of the two adaptive algorithms applied to both beamformer and B‐MMSE detector will be made in terms of convergence behaviour and estimation mean square error. Various multipath patterns are considered to test the receiver's responding rapidity to changing multipath interference. The performance of the adaptive B‐MMSE detector is also compared with that of non‐adaptive version (i.e. through direct matrix inversion). The final performance in error probability simulation reveals that the RLS/B‐MMSE scheme outperforms non‐adaptive B‐MMSE by 1–5 dB, depending on the multipath channel delay profiles of concern. The obtained results also suggest that adaptive beamformer should use RLS algorithm for its fast and robust convergence property; while the B‐MMSE filter can choose either LMS or RLS algorithm depending on antenna array size, multipath severity and implementation complexity. Copyright © 2004 John Wiley & Sons, Ltd.     

Recursive structures and finite impulse response implementations oflinear multiuser detectors for an asynchronous CDMA system

We present order-recursive structures for implementing the linear decorrelating and linear minimum mean square error (MMSE) detectors in a computationally efficient manner. These infinite memory length, linear time invariant, noncausal systems can be approximated by implementing them as K-input K-output finite impulse response (FIR) filters. We developed a linear multiuser receiver architecture called a recursive linear multiuser detector which has lower computational and memory requirements then an equivalent tap delay line FIR filter implementation. We establish the tradeoff between window length and bit error rate and find that relatively small window size yields performance indistinguishable from the ideal decorrelating detector and the ideal MMSE detector     

5G系统中基于解调参考信号的信道估计方法

5G系统使用解调参考信号(Demodulation Reference Signal,DMRS)用于下行信道估计,工程中通常采用插值法得到数据位置信道响应,考虑实际信道中噪声的影响,频域采用线性最小均方误差(Linear Minimum Mean Squared Error,LMMSE)插值算法。针对LMMSE需要获取信道先验统计特性以及存在矩阵求逆运算量大问题,利用信号时域内能量集中特点估计出信道均方根时延、信噪比和信道自相关矩阵,对于DMRS信号在频域上间隔较大、DMRS信号所在子载波相关性不强的问题,通过引入导频加密方法提升DMRS信号所在子载波间的相关性以提升信道估计性能,并通过滑动窗口插值方法进一步降低LMMSE算法求逆运算复杂度。仿真结果表明,所提算法均方误差和误码率总体均优于线性插值和基于矩阵奇异值分解的LMMSE算法,并与传统LMMSE算法相比性能极为接近,而且复杂度降低了99.85%,适合实际工程应用。     

均方误差短时反馈算法的残余频偏纠正及阈值选取的研究

介绍了一种在全数字接收机中基于最小均方误差的残余频偏矫正算法,目的是改善由于残余频偏累积引起的误码率的加剧,以及通过利用最小均方误差判定准则确定判决门限值的大小.此种算法通过均方误差准则探测分析有无残余频偏,再利用短时反馈算法进行残余频偏的矫正.重点介绍了残余频偏矫正的算法和判决门限值的选取.矫正后误码率明显下降,码元质量得到有效改善.     

A low‐complexity adaptive receiver for DS‐CDMA systems in unknown code delay environment

In direct‐sequence code division multiple access (DS/CDMA) multiuser communication systems in multipath channels, both intersymbol interference (ISI) and multiple‐access interference (MAI) must be considered. The multipath channel characterizes the propagation effects including the timing offset and delays, etc. Traditionally, we use the delay‐locked loop (DLL) code tracking loop to recover the timing delay. But DLL cannot work well in multipath environment. In this paper, we propose a low‐complexity adaptive receiver to suppress ISI/MAI and solve the timing offset problems without using conventional DLL code tracking loop. The proposed receiver employs an adaptive filter whose weights are adapted using a block least‐mean square error algorithm with fractional sampling. Simulations confirm the good performance, including learning curves and theoretical analysis of minimum mean‐square error, of the proposed receiver. Copyright © 2010 John Wiley & Sons, Ltd.     

Compact coder for component color television

A study of predictive coding of component TV signals for compression to transmit at rates that give good picture quality is reported. Designing predictors for minimum mean square prediction error is effective, both for luminance and chrominance signals. Predictors designed in this manner were found to be as good as or better than all other predictors tested. Quantizers designed for minimum mean square system error were primarily used in this study. A programmable testbed was built to permit quick comparisons. Predictors were compared on the testbed using a 2-b quantizer in order to have adequate system error to display visible differences. For simple intrafield coding, component signals compressed for transmission at 30 Mb/s gave about equivalent quality to an NTSC composite signal coded directly for transmission at 45 Mb/s. With 45-Mb/s transmission, component signal coding showed no detectable degradation on close inspection of real pictures. Maximum chrominance changes on test patterns yield visually detectable chrominance slope overload     

Delay detection method using cross-spectrum for multitransmitter simulcasting

The authors propose a precise delay detection method using cross-spectrum which can be adopted for phase synchronisation of high speed multitransmitter simulcasting mobile radio communication systems. It is also shown that the detection error of this method is improved by pseudorandom noise (PN) signals and the minimum square error estimation.<>     

WiMax SUI信道下DS-CDMA的性能分析

频域均衡直序码分多址(Ds-CDMA)系统基于最小均方误差(MMSE)准则有两种检测技术:传统的将MMSE运用于每个载波的检测技术(PC-MMSE)和新型线性将MMSE运用于每个用户的检测技术(PU-MMSE).文中在WiMax SUI信道下对使用这两种检测技术的DS-CDMA系统进行计算机仿真.仿真结果表明,使用新型检测技术的DS-CDMA系统能获得比传统检测技术更好的BER(误比特率)性能.     

基于分数阶域最优滤波的语音增强算法

本文介绍了一种基于分数阶域最优滤波的语音增强新算法.当存在畸变系统对信号造成畸变或者不能通过坐标轴旋转来完全解除信号和噪声的时频耦合时,本文将利用一种更具普适性的滤波方法,即采用最小均方误差准则下的分数阶最优滤波消除畸变和噪声的影响.仿真表明,在最小均方误差准则下求得的最优滤波算子并不一定是全局最小的,但是在不增加额外...     

Layered space-frequency equalization in a single-carrier MIMO system for frequency-selective channels

Frequency-domain equalization (FDE) has been shown to be an effective approach to combat frequency-selective wireless channels. In this letter, we propose a layered space-frequency equalization (LSFE) architecture for a single-carrier (SC) multiple-input multiple-output (MIMO) system, where MIMO FDE is employed at each stage or (layer) of detection. At a particular stage, a group of the best data streams in the minimum mean square error sense are detected and are canceled from the received signals. Simulation results show that our proposed LSFE structures can outperform layered space-time equalization (LSTE) structures and uncoded orthogonal frequency division multiplex (OFDM), especially at a higher delay spread. Performance is enhanced further, by incorporating the FDE with time-domain decision feedback at each stage of LSFE. We also provide performance analysis for LSFE, in comparison with OFDM.     

On the error floor of MSK signal transmission over a multipathchannel with small time dispersion

The error floor of minimum shift keying (MSK) signal transmission over a mobile radio channel with small time dispersion is analyzed. In contrast to previous investigations, no restrictive assumptions about the impulse response of the channel and/or sampling time are made, and closed-form analytical expressions for the error floor and optimum sampling time are derived. It is found that, generally, the error probability depends on the variance of relative delay (which conforms to the conventional RMS delay spread) as well as on the product of mean relative delays of echoes advancing and succeeding the chosen sampling time, weighted by corresponding mean powers. This implies that (elsewhere widely accepted) simple determination of the error floor by RMS delay spread only can now be seen as a special case when sampling is at mean delay and distribution of the delay profile's power around it is balanced. Furthermore, it is shown that the novel formula reflects the impact of delay profile shape on the error performance (that has been usually neglected, although not always justifiably), and that in general case, the optimum sampling instant is not at the mean delay. The theoretical results are verified by comparison with Monte Carlo (MC) simulations' results; achieved agreement lies within the accuracy of the simulations     

Polynomial spline-approximation of Clarke's model

We investigate polynomial spline approximation of stationary random processes on a uniform grid applied to Clarke's model of time variations of path amplitudes in multipath fading channels with Doppler scattering. The integral mean square error (MSE) for optimal and interpolation splines is presented as a series of spectral moments. The optimal splines outperform the interpolation splines; however, as the sampling factor increases, the optimal and interpolation splines of even order tend to provide the same accuracy. To build such splines, the process to be approximated needs to be known for all time, which is impractical. Local splines, on the other hand, may be used where the process is known only over a finite interval. We first consider local splines with quasioptimal spline coefficients. Then, we derive optimal spline coefficients and investigate the error for different sets of samples used for calculating the spline coefficients. In practice, approximation with a low processing delay is of interest; we investigate local spline extrapolation with a zero-processing delay. The results of our investigation show that local spline approximation is attractive for implementation from viewpoints of both low processing delay and small approximation error; the error can be very close to the minimum error provided by optimal splines. Thus, local splines can be effectively used for channel estimation in multipath fast fading channels.     

Intersymbol interference and error probability

Using a criterion of minimum average error probability we derive a method for specifying an optimum linear, time invariant receiving filter for a digital data transmission system. The transmitted data are binary and coded into pulses of shapepm s(t). The linear transmission medium introduces intersymbol interference and additive Gaussian noise. Because the intersymbol interference is not Gaussian and can be correlated with the binary digit being detected, our problem is one of deciding which of two waveforms is present in a special type of correlated, non-Gaussian noise. For signal-to-noise ratios in a range of practical interest, the optimum filter is found to be representable as a matched filter followed by a tapped delay line--the same form as that of the least mean square estimator of the pulse amplitude. The performance (error probability vs.S/N) of the optimum filter is compared with that of a matched-filter receiver in an example.