频率选择性信道下单载波空时分组编码传输系统中的信道估计技术

在频率选择性信道下给出了单载波频域均衡系统结合空时分组编码传输基于训练序列的最优信道估计算法。由于选取具有恒幅特性的Chu序列作为训练序列,因此这一算法能够实现信道估计的最小均方误差,并作了理论证明。最后,对本方案的性能进行了仿真比较,仿真的结果证实了本方案的优点。     

空时编码多载波码分多址MIMO系统下行频率选择性信道盲估计

基于子空间方法的无线信道盲估计由于其算法的固有特性,使得估计结果与实际信道之间存在一个不确定复系数,无法得到无线信道的精确估计。在利用子空间分解方法对空时编码多输入多输出MC-CDMA系统下行频率选择性信道盲估计的基础上,利用发射符号的有限码集特性,将单载波系统下的模糊复系数盲辨识方法推广到多载波多输入多输出系统,从而得到信道的精确估计。Monte-Carlo仿真表明,在信噪比较低的情况下,本方法的信道估计误差仍然较小。     

Iterative EM receiver for space-time coded systems in MIMO frequency-selective fading channels with channel gain and order estimation

An iterative receiver for a space-time trellis coded system in frequency-selective fading channel is proposed. It performs channel gain estimation and sequence detection by using the expectation-maximization (EM) algorithm. Channel order estimation is included in the receiver to avoid unnecessary trellis computations by using the conditional model order estimator (CME). In addition, three modifications to the original CME criterion are proposed to improve the estimation accuracy. Simulation results show that the proposed receiver has a slight degradation in frame error rate performance to the known channel maximum likelihood receiver. Moreover, it outperforms the conventional fixed long-tap length EM receiver with a lesser complexity. Furthermore, the proposed modifications to the CME criterion improve the channel order estimation accuracy, thus minimizing unnecessary computations.     

多输入多输出系统中空时分组码的盲信道估计

在空时系统设计中，信道估计是一个关键技术。对一种基于空时分组码的盲信道估计算法进行了研究。在信道输出端进行子空间分解，如果信号子空间是由信道唯一决定的，那么信道参数可被唯一估计为一个常数。提出的算法是基于空时分组码的普通形式，因此可被应用于任何分组码。最后，仿真结果显示了一些特定码字的估计效果。     

Iterative decoding and channel estimation for space-time BICM over MIMO block fading multipath AWGN channel

In this paper, we consider a generic model of space-time bit-interleaved coded modulation (ST-BICM) on a multiple-input multiple-output (MIMO) Rayleigh fading multipath channel. A practical low-complexity receiver structure performing iteratively MIMO data detection, channel decoding and channel estimation, is presented. The MIMO data detection, employing a reduced-state list-type soft output Viterbi algorithm enables to cope with severe channel intersymbol interference (ISI) without MIMO prefiltering. Among other results, simulations show that our approach can dramatically improve the downlink performance of time-division multiple access (TDMA) systems with high order modulation, keeping a reasonable complexity at the receiver side.     

Subspace approach to blind and semi-blind channel estimation for space-time block codes

A new approach to blind and semi-blind channel estimation for space-time block codes (STBCs) is presented. By exploiting the recently proposed generalized space-time block code framework, an STBC system is reduced from multiple-input multiple-output to a single-input multiple-output system. A conventional blind algorithm based on the subspace algorithm is then used to identify the channel impulse responses and achieve equalization. Simulation results demonstrate the performance of the proposed algorithm and a comparable scheme.     

Space-time-frequency coded OFDM over frequency-selective fading channels

This paper proposes novel space-time-frequency (STF) coding for multi-antenna orthogonal frequency-division multiplexing (OFDM) transmissions over frequency-selective Rayleigh fading channels. Incorporating subchannel grouping and choosing appropriate system parameters, we first convert our system into a set of group STF (GSTF) systems. This enables simplification of STF coding within each GSTF system. We derive design criteria for STF coding and exploit existing ST coding techniques to construct both STF block and trellis codes. The resulting codes are shown to be capable of achieving maximum diversity and coding gains, while affording low-complexity decoding. The performance merits of our design are confirmed by corroborating simulations and compared with existing alternatives.     

Blind estimation and detection of space-time trellis coded transmissions over the Rayleigh fading MIMO channel

We present a joint channel estimation and detection method of space-time trellis codes (STTC) in the context of an unknown flat fading multiple-input multiple-output (MIMO) channel. A combined state-space model for the space-time code and the Rayleigh fading MIMO channel is introduced, in order to use deterministic particle filtering at the receiver side. An important feature of the proposed method is that the fading rate need not be known to the receiver. Monte-Carlo simulations show that the performances of the proposed scheme are close to decoding with perfect channel state information (CSI) using the Viterbi algorithm (VA).     

A symbol-by-symbol channel estimation receiver for space-time block coded systems and its performance analysis on the nonselective rayleigh fading channel

We present a symbol-by-symbol channel estimation receiver for an orthogonal space-time block coded system, and derive its analytical performance on a slow, nonselective, Rayleigh fading channel. Exact, closed-form expressions for its bit error probability (BEP) performance for M-ary phase shift-keying modulations are obtained, which enable us to theoretically predict the actual performance achievable under practical conditions with channel estimation error. Our BEP expressions show explicitly the dependence of BEP on the mean square error of the channel estimates, which in turn depend on the channel fading model and the channel estimator used. Tight upper bounds are presented that show more clearly the dependence of the BEP on various system parameters. Simulation results using various fading models are obtained to demonstrate the validity of the analysis.     

频率选择性衰落信道下一种空时分组码的直接解码

该文针对 3个发射天线,1个接收天线的空时分组码系统,提出了频率选择性衰落信道下,无需信道估计,直接对空时分组码进行解码的方法,把子空间方法应用于空时编码当中,从信号处理和空时编码两个方面考虑空时分组码的直接解码问题,利用空时分组码所特有的正交设计,较为方便地从子空间中解出信号信息,从单载波的角度,解决了频率选择性衰落下空时分组码的解码问题。Monte-Carlo仿真给出了直接解码算法的性能,并与使用准确信道信息的解码算法做了性能比较。     

Novel semi-blind channel estimation schemes for Rician fading MIMO channel

In this paper, we propose two novel semi-blind channel estimation techniques based on QR decomposition for Rician fading Multiple Input Multiple Output (MIMO) channel. In the first technique, the MIMO channel matrix H can be decomposed as an upper triangular matrix R and unitary rotation matrix Q as H = RQ. The matrix R is estimated blindly from only received data by using the orthogonal matrix triangularization based Householder QR decomposition, while the optimum rotation matrix Q is estimated exclusively from the algorithm of Orthogonal Pilot Maximum Likelihood Estimator (OPML) based on pilot information. In the second technique, the joint semi-blind channel and data estimation is performed by using the Least Square (LS) algorithm based on QR decomposition. The simulation results obtained for 4-PSK data modulation scheme using two transmitters and six receiver antennas for different Rice factor (K) have shown that the BER performance increases with an increase in the Rice factor. Finally, we compare these two new techniques with the conventional semi-blind channel estimation technique based on Whitening Rotation (WR), and the results show that the first proposed technique outperforms and the second technique achieves a very nearby performance as compared to the technique based on whitening rotation.     

Orthogonal procrustes based semi-blind MIMO channel estimation under space-time block code transmissions

This work investigates a novel semi-blind channel estimation for multiple-input multiple-output(MIMO)space-time block coding(STBC)systems.Algorithms for channel estimation based on whitening-rotation(WR)decomposition that provides a combined quality and spatial scalability is utilized.Using a space-time code-constrained input design,our approach exploits the orthogonality of the signal and noise subspaces in conjunction with orthogonal procrustes(OP)technique to obtain an accurate estimate of the unitary ro...     

Single-carrier space-time block-coded transmissions over frequency-selective fading channels

We study space-time block coding for single-carrier block transmissions over frequency-selective multipath fading channels. We propose novel transmission schemes that achieve a maximum diversity of order N/sub t/N/sub r/(L+1) in rich scattering environments, where N/sub t/ (N/sub r/) is the number of transmit (receive) antennas, and L is the order of the finite impulse response (FIR) channels. We show that linear receiver processing collects full antenna diversity, while the overall complexity remains comparable to that of single-antenna transmissions over frequency-selective channels. We develop transmissions enabling maximum-likelihood optimal decoding based on Viterbi's ( 1998) algorithm, as well as turbo decoding. With single receive and two transmit antennas, the proposed transmission format is capacity achieving. Simulation results demonstrate that joint exploitation of space-multipath diversity leads to significantly improved performance in the presence of frequency-selective fading channels.     

基于降维盲信道估计的空时分组码MC-CDMA系统信号检测

研究了空时分组码多载波码分多址(MC-CDMA)系统的信号检测。对接收数据矢量进行解相关滤波,得到对应于每个用户奇数和偶数时间的无多址干扰(MAI)的降维信号,由白化滤波后的降维数据组成的矩阵的秩1近似来得到盲信道估计,再利用用户发射信息符号的有限码集特性来确定复标量模糊。在估计出所有用户的信道响应的基础上,用最小二乘算法进行信号检测。仿真结果验证了所提算法的有效性。     

空时编码OFDM系统中的一种简单信道估计算法

提出了一种适用于空时编码OFDM系统的简单信道估计算法。仿真结果表明:在2发2收空时编码 OFDM系统中该算法具有高的估计精度,且实现简单。     

Semiblind channel estimation and equalization for MIMO space-time coded OFDM

Based on the special features of space-time coding (STC) and orthogonal frequency-division multiplexing (OFDM), it is mathematically proved that all channel responses of a multiple-input-multiple-output STC-OFDM system can be identified blindly subject to two ambiguity matrices with a subspace-based method. A method is then presented to resolve the two ambiguity matrices by using few pilot symbols. With the estimated channels, a frequency domain approach is presented to recover the transmitted symbols. The presented semiblind algorithms are valid even if the channel transfer functions are not coprime and do not require precise channel order information (only an upper bound for the orders is required).     

地空衰落信道下JTIDS信号信噪比盲估计

针对地空衰落信道下联合战术信息分发系统（JTIDS）信号信噪比的估计问题,提出了一种适用于单脉冲和双脉冲时隙结构JTIDS信号的接收信噪比盲估计方法。首先,利用信道实时最大时延粗估计值确定无符号间干扰的数据区间;其次,基于JTIDS信号脉冲时隙结构中静默时间的保护间隔特性估计噪声功率;最后,根据选定区间数据的自相关函数估计接收信号的信号功率,从而估计出接收链路的信噪比。仿真实验结果表明,取单时隙样本长度时,在巡航、起降两种空中平台状态下,提出估计方法在较宽信噪比范围内具有良好的均方误差估计性能,可满足JTIDS系统的信噪比估计需求。     

频率选择信道下的空时分组码盲识别

在单接收天线下,针对频率选择性衰落信道下空时分组码( STBC)的盲识别问题,提出了一种基于Kolmogorov-Smirnov( K-S)检测的有效算法。该算法以经验累积分布函数作为特征函数,通过K-S检测经验累积分布函数之间的距离,达到识别空时分组码的目的。在不同调制方式、采样因子和置信区间的条件下分别对算法进行仿真并讨论其性能,结果表明,该算法性能较好,在信噪比大于6 dB时可达到90%以上的正确识别概率,在非合作通信方面具有一定的实用价值。     

Low complexity channel estimation for space-time coded wideband OFDM systems

In this article, channel estimation for space-time coded orthogonal-frequency division multiplexing (OFDM) systems is considered. By assuming that the channel frequency response is quasi-static over two consecutive OFDM symbols, we develop channel parameter estimators based on the use of space-time block coded (STBC) training blocks. Using an STBC training pattern, a low-rank Wiener filter-based channel estimator with a significant complexity reduction is proposed. A simplified approach for the optimal low-rank estimator is also proposed to further reduce the estimator complexity while retaining an accurate frequency domain channel estimation. Numerical results are provided to demonstrate the performance of the proposed low complexity channel estimators for space-time trellis coded OFDM systems.     

Concatenated space-time block coding with trellis coded modulation in fading channels

Trellis coded modulation (TCM) is a bandwidth efficient transmission scheme that can achieve high coding gain by integrating coding and modulation. This paper presents an analytical expression for the error event probability of concatenated space-time block coding with TCM which reveals some dominant factors affecting the system performance over slow fading channels when perfect interleavers are used. This leads to establishing the design criteria for constructing the optimal trellis codes of such a concatenated system over slow flat fading channels. Through simulation, significant performance improvement is shown to be obtained by concatenating the interleaved streams of these codes with space-time block codes over fading channels. Simulation results also demonstrate that these trellis codes have better error performance than traditional codes designed for single-antenna Gaussian or fading channels. Performance results over quasi-static fading channels without interleaving are also compared in this paper. Furthermore, it is shown that concatenated space-time block coding with TCM (with/without interleaving) outperforms space-time trellis codes under the same spectral efficiency, trellis complexity, and signal constellation.