Blind identification and equalization based on second-orderstatistics: a time domain approach

A new blind channel identification and equalization method is proposed that exploits the cyclostationarity of oversampled communication signals to achieve identification and equalization of possibly nonminimum phase (multipath) channels without using training signals. Unlike most adaptive blind equalization methods for which the convergence properties are often problematic, the channel estimation algorithm proposed here is asymptotically ex-set. Moreover, since it is based on second-order statistics, the new approach may achieve equalization with fewer symbols than most techniques based only on higher-order statistics. Simulations have demonstrated promising performance of the proposed algorithm for the blind equalization of a three-ray multipath channel     

多径衰落信道下的一种盲多用户检测方法

多径衰落信道下的盲自适应多用户检测算法的运算复杂度通常都比较大,提出了一种基于MSWF和CMA的盲自适应多用户检测方法,该方法避免了矩阵求逆和信道估计运算,具有相对较小的运算复杂度。通过模拟实验比较了几种算法的误码率性能,结果表明,所提方法具有明显的优势。     

发射分集MC-CDMA系统盲干扰抑制

研究了多载波码分多址(MC-CDMA)系统的盲干扰抑制,采用基于空时分组码的发射分集。考虑对应于子载波的衰落系数是信道冲激响应的离散傅里叶变换,通过研究多径信号频域码空间和数据矢量空间,采用噪声子空间技术进行盲信道估计。为了抑制多址干扰(MAI),提出一种基于投影的辅助矢量算法(PAV),该算法计算复杂度低,在低输入信号干扰噪声比(SINR)时能提供有效的干扰抑制,在高输入SINR时具有稳健的性能。     

A new approach based on “soft statistics” to thenonlinear blind-deconvolution of unknown data channels

In this paper, we present a new nonlinear receiver for the blind deconvolution of intersymbol interference (ISI) impaired data. The proposed receiver achieves fast identification of an unknown transmission channel using only one channel estimator and requiring the computation of only the second-order conditional statistics of the baud-rate sampled received signal and the knowledge of the transmitted constellation. The main novelty of the proposed approach is that the receiver accomplishes fast channel-identification by using soft-statistics. In particular, the receiver consists of a symbol-by-symbol maximum a posteriori (SbS-MAP) detector that feeds a nonlinear Kalman-like channel estimator with the soft statistics constituted by the a posteriori probabilities (APPs) of the state sequence of the ISI channel. Several numerical results confirm that the proposed blind detector achieves the identification of nonminimum phase channels with deep spectral notches within 300 symbols, even at low signal-to-noise ratios (SNRs). Furthermore, an attractive feature of the proposed blind channel estimator is that it directly estimates the discrete-time impulse response of the unknown channel so that, in principle, any equalization technique for known channels may be performed after channel identification has been achieved     

一种基于ML算法及盲信道识别的DWPM系统

该文提出了一种基于ML算法及盲信道估计的离散小波包调制(Discrete Wavelet Packet Modulation,DWPM)系统.本文通过基于导频信号的盲信道识别方法,获得信道的状态信息,并且利用基于ZF(Zero Forcing)算法的H矩阵消除码间干扰,最后,利用ML(Maximum Likelihood)算法检测解调后的码元,并且通过仿真分析了该系统在多径衰落信道下的性能.仿真结果表明,该系统的性能要比传统的OFDM系统的性能好.     

Maximum-likelihood estimation of FIR channels excited byconvolutionally encoded inputs

If error correcting coding is present in the information symbols, the channel estimation procedure may be further complicated, since the encoder introduces a nonlinear operation on the information symbols (in the field of reals). Moreover, because of the encoder's memory, the input to the channel may not be i.i.d. Therefore classical blind channel equalization methods may not be suitable for systems with coding. A blind stochastic maximum-likelihood channel estimation algorithm is proposed for convolutionally coded signals transmitted through a multipath channel. The performance of the estimator is explored, based on the evaluation of approximate Cramer-Rao bounds. The CRBs are used in turn to obtain approximate expressions for the probability of error. Finally, some illustrative simulations are presented     

基于稀疏超指数盲均衡的高频外辐射源雷达发射信号提取

基于天波雷达发射信号的外辐射源雷达需要在接收站提取发射信号用于匹配滤波处理, 而到达接收站的发射信号往往受到电离层反射与折射多径污染的问题, 提出了一种基于超指数与常数模盲均衡算法的发射信号混合盲反卷积方法.利用电离层折射与反射等多径杂波的稀疏性, 采用稀疏处理降低混合算法中超指数盲均衡算法的计算量, 从而实现发射信号的恢复.针对发射信号恢复质量对检测性能的影响进行了分析评估.计算机仿真表明, 所提出的盲均衡算法保持了超指数算法快速收敛的优点, 同时, 在性能损失很小的情况下计算量显著下降, 具有良好的工程应用前景.     

Blind MAI and ISI suppression for DS/CDMA systems using HOS-basedinverse filter criteria

Cumulant-based inverse filter criteria (IFC) using second-and higher order statistics (HOS) proposed by Tugnait et al. (1993) have been widely used for blind deconvolution of discrete-time multi-input multi-output (MIMO) linear time-invariant systems with non-Gaussian measurements through a multistage successive cancellation procedure, but the deconvolved signals turn out to be an unknown permutation of the driving inputs. A multistage blind equalization algorithm (MBEA) is proposed for multiple access interference (MAI) and intersymbol interference (ISI) suppression of multiuser direct sequence/code division multiple access (DS/CDMA) systems in the presence of multipath. The proposed MBEA, which processes the chip waveform matched filter output signal without requiring any path delay information, includes blind deconvolution processing using IFC followed by identification of the estimated symbol sequence with the associated user through a user identification algorithm (UIA). Then, some simulation results are presented to support the proposed MBEA and UIA. Finally, some conclusions are drawn     

Instantaneous Mixture Channel Selection for Blind Equalization Using Cumulant Features in MIMO Systems

Cognitive radio combined with multiple-input multiple-output (MIMO) communications provides high data rate, efficiency and high reliability. One of the most important challenges in MIMO communication is combating MIMO multipath channel. MIMO blind equalizers and channel estimators combat MIMO multipath channels without the use of training or pilot sequences. First, the multipath channel is converted into instantaneous mixture channel (IMC), using second-order statistics of the data. Then using higher-order statistics, these mixtures are separated. However, proper selection of IMC is a major challenge. In this paper, a novel blind algorithm for choosing the best IMC is proposed. The proposed algorithm is based on the cumulant value of the received signal.     

Blind Spectrum Sensing Algorithms for Cognitive Radio Networks

In a cognitive radio network, the spectrum that is allocated to primary users can be used by secondary users if the spectrum is not being used by the primary user at the current time and location. The only consideration is that the secondary users have to vacate the channel within a certain amount of time whenever the primary user becomes active. Thus, the cognitive radio faces the difficult challenge of detecting (sensing) the presence of the primary user, particularly in a low signal-to-noise ratio region, since the signal of the primary user might be severely attenuated due to multipath and shadowing before reaching the secondary user. In this paper, a blind sensing algorithm is derived, which is based on oversampling the received signal or by employing multiple receive antennas. The proposed method combines linear prediction and QR decomposition of the received signal matrix. Then, two signal statistics are computed from the oversampled received signal. The ratio of these two statistics is an indicator of the presence/absence of the primary signal in the received signal. Our algorithm does not require the knowledge of the signal or of the noise power. Moreover, the proposed detection algorithm in this paper is blind in the sense that it does not require information about the multipath channel distortions the primary signal has undergone on its way to reaching the secondary user. Simulations have shown that our algorithm performs much better than the commonly used energy detector, which usually suffers from the noise uncertainty problem.      

Blind identification of multipath channels: a parametric subspaceapproach

In this paper, blind identification of single-input multiple-output (SIMO) systems using second-order statistics (SOS) only is considered. Using the assumption of a specular multipath channel, we investigate a parametric variant of the so-called subspace method. Nonparametric subspace-based methods require precise estimation of the model order; overestimation of the model order leads to inconsistent channel estimates. We show that the parametric subspace method gives consistent channel estimates when only an upper bound of the channel order is known. A new algorithm, which exploits parametric information on the channel structure, is presented. A statistical performance analysis of the proposed parametric subspace criterion is presented; limited Monte Carlo experiments show that the proposed algorithm is second-order optimal for a large class of channels     

一种新的抗远近效应的盲DS-CDMA接收机

本文研究多径频率选择性衰落信道下直接序列扩频码分多址(DS-CDMA)信号的处理问题,提出了一种新型的盲接收机.该接收机不需预知多址干扰用户的扩频码,不需预知信道参数,只需已知期望用户的扩频码和粗略的定时,就可以完成用户的盲检测.同时,该接收机通过降维自适应去相关滤波和基于判决指导的自适应多径合并,来获得低成本和良好的抗衰落、抗远近效应性能.仿真结果验证了本文提出的接收机的优良性能.     

Fixed-point blind adaptive multiuser detection algorithm for IR UWB systems in multipath channel

Using the hypothesis that data transmitted by different users are statistically independent of each other, this paper proposes a fixed-point blind adaptive multiuser detection algorithm for Time-Hopping (TH) Impulse Radio (IR) Ultra Wide Band (UWB) systems in multipath channel, which is based on Inde-pendent Component Analysis (ICA) idea. The proposed algorithm employs maximizing negentropy criterion to separate the data packets of different users. Then the user characteristic sequences are utilized to identify the data packet order of the desired user. This algorithm only needs the desired user’s characteristic se-quence instead of channel information, power information and time-hoping code of any user. Due to using hypothesis of statistical independence among users, the proposed algorithm has the outstanding Bit Error Rate (BER) performance and the excellent ability of near-far resistance. Simulation results demonstrate that this algorithm has the performance close to that of Maximum-Likelihood (ML) algorithm and is a subopti-mum blind adaptive multiuser detection algorithm of excellent near-far resistance and low complexity.     

Suboptimum Viterbi algorithm for trellis-coded QAM scheme inmultipath Rayleigh fading channels

A new suboptimum Viterbi algorithm for trellis-coded quadrature amplitude modulation based on the channel state information of the multipath Rayleigh fading channel is proposed. Simulation results show that the proposed algorithm has merits for applications that require low bit energy-to-noise ratio     

异步DS-CDMA盲多用户检测

该文研究了频率选择性瑞利衰落信道中的异步DS-CDMA系统盲多用户检测。提出一种期望信号矢量估计方法,该方法同时利用了多径传播和接收机同步失调的特性,以利于把盲线性滤波优化技术应用于稳健的干扰抑制。为了抑制多址干扰(MAI),提出一种基于投影的辅助矢量(PAV)算法。该算法计算复杂度低,特别适用于短数据采样时滤波矢量的快速优化,仿真结果表明在低输入信号干扰噪声比(SINR)时能提供有效的干扰抑制,在高输入SINR时具有稳健的性能。     

异步DS-CDMA系统盲空时信道估计及多用户检测

该文提出了适用于频率选择性瑞利衰落信道中的异步DS-CDMA系统盲空时信道估计及多用户检测算法。通过研究多径信号码空间和数据矢量空间,采用噪声子空间技术进行异步DS-CDMA系统盲空时信道参数估计,同时利用了多径传播和接收机同步失调的特性,以利于把盲线性滤波优化技术应用于稳健的干扰抑制。使用一种修改的ULV更新算法进行噪声子空间跟踪,该算法不需要相关矩阵的秩估计,直接估计噪声子空间,不进行信号子空间跟踪。并且研究了线性约束最小方差(LCMV)盲空时多用户检测及其基于Householder变换约束最小均方算法(HCLMS)的自适应实现。仿真结果验证了该文算法的有效性。     

基于盲源分离的水声信道盲均衡处理方法

提出了一种基于盲源分离的水声信道讯均衡处理方法,通过对接收信号过采样构成源信号,采用了基于信息最大化原理(Infomax)在线分离算法进行了水声信道的盲均衡,并研究了时变水声信道条件下算法的均衡情况,仿真实验结果表明,该处理方法对多径水声信道具有较好的均衡效果,同时不受最小相位的条件限制。     

Blind turbo multiuser detection for long-code multipath CDMA

We consider the problem of demodulating and decoding multiuser information symbols in an uplink asynchronous coded code-division multiple-access (CDMA) system employing long (aperiodic) spreading sequences, in the presence of unknown multipath channels, out-cell multiple-access interference (OMAI), and narrow-band interference (NBI). A blind turbo multiuser receiver, consisting of a novel blind Bayesian multiuser detector and a bank of MAP decoders, is developed for such a system. The effect of OMAI and NBI is modeled as colored Gaussian noise with some unknown covariance matrix. The main contribution of this paper is to develop blind Bayesian multiuser detectors for long-code multipath CDMA systems under both white and colored Gaussian noise. Such detectors are based on the Bayesian inference of all unknown quantities. The Gibbs sampler, a Markov chain Monte Carlo procedure, is then used to calculate the Bayesian estimates of the unknowns. The blind Bayesian multiuser detector computes the a posteriori probabilities of the channel coded symbols, which are differentially encoded before being sent to the channel. Being soft-input soft-output in nature, the proposed blind Bayesian multiuser detectors and the MAP decoders can iteratively exchange the extrinsic information to successively refine the performance, leading to the so-called blind turbo multiuser receiver     

一种新的适用于多径信道的基于LMK准则的盲自适应多用户检测及其收敛性分析

基于最小平均峰度(Least MeanKurtosis,LMK)准则],该文提出了一种适用于同步直扩码分多址(DS/CDMA)系统多径慢衰落信道中的线性盲自适应多用户检测算法。这种算法基于高阶统计量(High Order Statistics,HOS)特性,算法复杂度相对较低。文中分析了算法在多径信道中无噪声情况下的收敛特性,指出在这种情况下,算法具有全局最小点,此时算法满足解相关条件。仿真结果表明,文中给出的检测器具有较强的多址干扰抑制性能。     

A Low-PAPR Differential Frequency Shift Orthogonal Keying Transceiver for Multi-Carrier Spread Spectrum System over High Mobility Multipath Channels

A new differential transceiver with a frequency-shift orthogonal keying (FSOK) technique is proposed for the multi-carrier spread spectrum (MC-SS) system over high mobility multipath fading channels. The design of the transceiver involves the following stages. First, the data stream is mapped into MPSK-FSOK symbols and spreaded by the frequency-shift orthogonal sequences. Second, the differential block encoder is exploited to combat the mobile channels. The Chu sequence is adapted for initial differential encoding, making the post-IFFT transmit signals with a low peak-to-average power ratio. Next, for the receiver, the maximum ratio combining technique is used for the block-based differential frequency-domain equalizer, which can overcome the multipath fading channel effect without requiring channel estimation. Finally, an efficient maximum likelihood despreading and demapping scheme is used to detect the modulation symbols. Furthermore, the differential MC-SS transceiver can be easily re-configured for a MISO differential MC-SS system with high link quality. Simulation results show that, under high mobility multipath channels, the proposed SISO differential MC-SS system can outperform the conventional MC-SS system. The proposed MISO differential MC-SS system with space-time diversity gain and M-ary modulation gain also exhibits excellent performance.