Perfect Blind-Channel Shortening for Multicarrier Systems

In multicarrier systems, when the order of a channel impulse response is larger than the length of the cyclic prefix (CP), there is a significant performance degradation due to interblock interference (IBI). This paper proposes a blind-channel shortening method in which the equalizer parameter vector is formed by the noise subspace of the received signal correlation matrix so that the output power is maximized. The proposed method can not only shorten the effective channel impulse response to within the CP length but also maximize the output signal-to-interference-and-noise ratio while eliminating the IBI. We point out that the performance depends on the choice of a decision delay and propose a simple method for determining the appropriate delay. We propose both a batch algorithm and an adaptive algorithm and show by simulation that they are superior to the conventional algorithms.     

Blind-Channel Identification for MIMO Single-Carrier Zero-Padding Block-Transmission Systems

We propose a blind identification method for multiple-input multiple-output (MIMO) single-carrier zero-padding block-transmission systems. The method uses periodic precoding on the source signal before transmission. The estimation of the channel impulse response matrix consists of two steps: 1) obtain the channel product matrix by solving a lower-triangular linear system; 2) obtain the channel impulse response matrix by computing the positive eigenvalues and eigenvectors of a Hermitian matrix formed from the channel product matrix. The method is applicable to MIMO channels with more transmitters or more receivers. A sufficient condition for identifiability is simply that the channel impulse response matrix is full column rank. The design of the precoding sequence which minimizes the noise effect in covariance matrix estimation is proposed and the effect of the optimal precoding sequence on channel equalization is discussed. Simulations are used to demonstrate the performance of the method.      

利用补零信息的单载波块传输盲信道估计方法

该文提出了一种针对单载波块传输(SCBT)系统的信道估计方法.该方法利用单载波块传输系统中的补零(ZP)信息,在频域实现了频率选择性信道基于子空间的盲估计.文中同时给出了所提方法的辨识条件.该方法性能优于过采样信道估计方法,且对信道阶数过估计不敏感.计算机仿真和分析验证了所提方法的有效性.     

5G多载波通信中信道估计干扰抑制均衡算法

传统5G多载波通信中信道估计干扰抑制算法存在着均衡性能较差的问题,表现为误码元数与误码率偏高,因此文章提出5G多载波通信中信道估计干扰抑制均衡算法.该算法首先对干扰项进行过采样处理,引入预处理矩阵以减小模损失的影响,对信道估计干扰进行均衡抑制.仿真实验结果表明,在信噪比相同的情况下,5G多载波通信中信道估计干扰抑制均衡...     

Semi-Blind Layered Space-Frequency Equalization for Single-Carrier MIMO Systems with Block Transmission

This letter proposes a novel semi-blind layered space-frequency equalization (LSFE) receiver for single- carrier cyclic-prefix (SC-CP) multiple-input multiple-output (MIMO) systems with block transmission, based on independent component analysis (ICA). Simulation results show that semi- blind LSFE with various Doppler shifts can provide performance close to the case with perfect channel state information (CSI), using a training overhead of only 0.05%. It also significantly outperforms its orthogonal frequency division multiplexing (OFDM) counterpart with perfect CSI and semi-blind linear SC frequency domain equalization (SC-FDE) over a wide range of signal to noise ratios (SNRs).     

Efficient Channel Estimation for MIMO Single-Carrier Block Transmission With Dual Cyclic Timeslot Structure

We investigate channel estimation for timeslot-structured single-carrier block transmission (SCBT) over space-, time-, and frequency-selective fading multiple-input multiple-output (MIMO) channels. A MIMO-SCBT with a dual cyclic timeslot structure is presented first. Then, an optimal channel estimation in the minimal mean square error (MMSE) sense on the timeslot basis is investigated. It is shown that the optimal pilots for the timeslot-based MMSE channel estimation are related to the statistical channel state information in eigenmode. Under the assumption that the transmit correlation is unknown at the transmitter, the optimal pilots satisfy the same condition as reported for the block-based least-square (LS) channel estimation in literature, and the channel estimation can be simplified to initial block-based LS channel estimation followed by space-time postprocessing. Particularly, for spatially uncorrelated channels, the space-time postprocessing can be reduced to pathwise processing. A new design of the pilot sequences is given, which leads to an efficient implementation of the channel estimation. Later on, a more efficient implementation for the initial channel estimation is obtained by using the structure of the pilot sequences, and discrete cosine transform (DCT)-based implementation is developed for the space-time postprocessing to approximate the optimal solution with low implementation complexity. Finally, the performance of the proposed channel estimation is verified via simulations.     

通用滤波多载波通信系统中干扰抑制均衡算法

作为5G多载波技术强有力的候选对象,通用滤波多载波利用子带滤波技术抑制带外功率泄露,进而降低同步要求和获得更高的频谱效率。本文首先针对通用滤波多载波在慢时变多径信道下的性能进行了分析和研究;其次为消除多径信道所带来的干扰,提出了适用于该多载波系统的信道估计方案,该方案设计了具有重复样式的导频结构进行信道估计,复杂度低;最后针对通用滤波多载波在多径信道下容易遭受符号间干扰的问题,提出了基于干扰消除的Zero-Forcing均衡算法和基于迭代干扰消除的均衡算法,两种算法均能够在消除ISI的基础上进一步地消除ICI和IBI。仿真结果表明,本文提出的信道估计和均衡算法能有效消除通用滤波多载波技术在多径信道下所经受的ISI、ICI和IBI。      

A Hybrid Domain Block Equalizer for Single-Carrier Modulated Systems

Poor performance in the presence of multipath with long delay spread has been considered as one of the main weaknesses of most single carrier modulated systems, including ATSC (advanced television systems committee) system. The introduction of distributed transmission network and single frequency network brings new challenges for the ATSC equalizer design, since the delay spread of a multipath channel under such scenarios becomes significantly longer than the traditional broadcasting practice of using one high power transmitter to cover a wide area, where the multipath distortion is mainly from reflected echoes. An iterative hybrid frequency-time domain equalizer for ATSC system is proposed in this paper based on our block-based interference analysis. The multipath distortion in the received ATSC signal is first tentatively removed with a frequency domain equalizer on a block-by-block basis. However, inter-block and intra-block interferences still exist due to the lack of cyclic structure in the received ATSC signal. A time domain interference cancellation algorithm is then used to cancel the inter-block interference and intra-carrier interference, based on the tentative decisions in time domain after the frequency domain equalization. These two steps are iterated until desired receiver performance is achieved. The proposed equalizer and the subsequent analysis are verified through numerical simulations.     

CMA-Based Channel Estimation for Space-Time Block Coding Transmission Systems

In this paper, we present channel estimation methods for space-time block coding (STBC) transmissions using constant modulus algorithm (CMA). The channel estimates are directly calculated from the convergence value of the CMA. Two algorithms using the channel-vector-based and channel-gain-based constant modulus (CM) criteria are proposed. An approximation of the CM cost function is introduced to allow the use of the recursive least-square (RLS) technique in designing fast RLS-CMA's. Performance of the proposed schemes is evaluated and compared with others using simulation. Illustrative results show that the proposed scheme outperforms the cross-correlated method and can approach the performance of the training-based method.     

Receiver Design for Single-Carrier Block Transmission Over Doubly Selective Channels

Single-carrier block transmission is an alternative scheme to orthogonal frequency-division multiplexing (OFDM) for wireless broadband communications. In this paper, a receiver is designed for single-carrier block transmission with cyclic prefix for mobile broadband communications. As the wireless transmission is over doubly selective channels, a basis expansion model is used to capture both the time- and frequency-selectivity of the channel and is parameterized for the receiver design. The receiver estimates the channel model coefficients in the time domain and uses these coefficients for equalization in the frequency domain. The channel estimation is assisted by time-domain pilot insertion. The structure of the frequency-domain channel matrix is exploited and a linear minimum mean-square error equalizer is used for the equalization. When the basis expansion model well matches the physical channel, simulation results show superior receiving performance of the proposed system compared with the OFDM system with a similar complexity.     

Blind-Channel Estimation for MIMO Systems With Structured Transmit Delay Scheme

This paper considers blind-channel estimation for multiple-input multiple-output (MIMO) systems with structured transmitter design. First, a structured transmit delay (STD) scheme is proposed for MIMO systems. Unlike existing transmit diversity approaches, in which different antennas transmit delayed, zero padded, or time-reversed versions of the same signal, in the proposed scheme, each antenna transmits an independent data stream, therefore promises higher data rate and more flexibility to transmitter design. Second, second-order statistics based blind-channel estimation algorithms are developed for MIMO systems with STD scheme. Channel identifiability is addressed for both correlation-based and subspace-based approaches. The proposed approaches involve no pre-equalization, have no limitations on channel zero locations, and do not rely on nonconstant modulus precoding. Third, when channel coding is employed, estimation accuracy can be further enhanced through “postprocessing”, in which channel estimation is refined by taking the tentative decisions from the channel decoder as pseudo-training symbols. Simulation examples are provided to demonstrate the robustness and effectiveness of the proposed approaches.      

Frequency-Domain Block Turbo-Equalization for Single-Carrier Transmission Over MIMO Broadband Wireless Channel

This paper presents a new class of block turbo-equalizers for single-carrier transmission over multiple-input multiple-output (MIMO) broadband wireless channels. The key underlying idea consists in equalizing (nonoverlapping) groups of symbols and detecting their individual space-time components in a disjoint and iterative fashion. This functional split naturally induces new design options that have been accurately listed and described, i.e., choice of distinct criteria for intergroup interference (IGI) equalization and intragroup components detection, yielding hybrid structures, multiple iterative loops, and related scheduling variants. Selected algorithms in the proposed class are compared in terms of performance under various transmission scenarios. For all of them, minimum mean square error IGI equalization certainly occupies a central role (at least for the first iteration) and may be identified as the computational bottleneck. Fortunately, block spread transmission together with cyclic prefix operations make the channel matrix block circulant, thus allowing low-complexity inversion in the Fourier domain     

Iterative Overlap QRM-ML Block Detection for Single-Carrier MIMO Transmission Without CP Insertion

QR decomposition and M-algorithm based near maximum likelihood block detection (QRM-MLBD) significantly improves the single-carrier (SC) multiple-input multiple-output (SC-MIMO) transmission performance in a frequency-selective fading channel. In the conventional QRM-MLBD, the cyclic prefix (CP) is inserted in order to avoid the inter-block interference (IBI). However, CP insertion reduces the transmission efficiency. In this paper, an iterative overlap QRM-MLBD is proposed for SC-MIMO transmission with no CP insertion. It is confirmed by computer simulation that the iterative overlap QRM-MLBD with no CP insertion provides improved throughput performance while reducing the computational complexity over the conventional QRM-MLBD with CP insertion.     

码分双工系统中的干扰抑制技术

码分双工(CDD)是近年来新提出的一种双工方式,它支持上、下行信道同时使用同一频段。但是,由于上、下行信号可能存在较大的功率差异因而会导致较严重的相互干扰。该文针对这一问题提出了一套有效的干扰抑制和消除方案。首先,文中分析了CDD系统存在的几种干扰,在此基础上提出了基站端采用分布式天线和干扰消除器处理干扰的策略,移动台间的干扰则依靠定位技术和调度算法进行抑制。最后,计算及仿真结果证明了码分双工系统的可行性。     

分组衰落信道下OFDM系统载波干扰线性均衡技术研究

多普勒频移和接收载波频差使OFDM系统中各个子载波的正交性得到破坏,产生载波间干扰(IC I)。本文分析了分组衰落信道下OFDM系统各个子载波的信干比(SIR),得出载波间干扰主要集中在相邻的几个子载波上,由此提出了一种估计部分干扰系数来线性均衡OFDM符号中子信号的方法,从而改善接收信号的信干比,提高系统性能。仿真结果表明,使用相邻2个和4个子载波的干扰系数时,接收信号的信干比增益为6dB和10dB,较有效地克服了OFDM系统中载波间干扰。     

Interference Analysis of Multicarrier Systems Based on Affine Fourier Transform

Multicarrier techniques based on affine Fourier transform (AFT) have been recently proposed for transmission in the wireless channels. The AFT represents a generalization of the Fourier and fractional Fourier transform. We derive the exact and approximated interference power, upper bound and measure of applicability for the AFT based multicarrier (AFT-MC) system. It is demonstrated that the AFT-MC system effectively minimizes interference in time-varying multipath channels with line-of-sight component and narrow beamwidth of scattered components that often occurs in aeronautical and satellite communications.     

On the Capacity of Ultra Wideband Block Transmission Systems with Narrowband Interference Avoidance

In this letter, the theoretical capacities of single-carrier and multi-carrier block transmission systems that employ narrowband interference avoidance are derived. It is shown that the capacity of an OFDM system that implements active interference cancellation is degraded by approximately one bit per second per Hz at high SNR when 10% of the band is nulled. In contrast, the capacity of a single-carrier system that uses envelope scaling in the time domain to create deep frequency notches is not significantly affected by the nulling process.     

空时分组码MC-CDMA系统盲干扰抑制

该文考虑空时分组码多载波码分多址(MC-CDMA)系统的盲干扰抑制。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。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。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,用前一级滤波矢量的输出重构最大比合并(MRC)滤波矢量,将重构滤波矢量到由基本滤波矢量和前几级辅助矢量张成子空间上的正交投影作为辅助矢量,将前一级滤波矢量和新产生辅助矢量线性合并得到新的滤波矢量。仿真结果验证了该文算法的有效性。