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1.
Two reduced-complexity soft-input soft-output trellis decoding techniques are presented in this paper for equalizing single-input single-output intersymbol interference (ISI) channels and multiple-input multiple-output (MIMO) frequency selective fading channels. Given a trellis representing an ISI channel, the soft-output M-algorithm (SOMA) reduces the complexity of equalization by retaining only the best M survivors at each trellis interval. The remaining survivors are discarded. The novelty of the SOMA is the use of discarded paths to obtain soft-information. Through a simple update-and-discard procedure, the SOMA extracts reliable soft-information from discarded paths which enables a large trellis to be successfully decoded with a relatively small value of M. To decode a trellis representing a MIMO frequency selective fading channel, two challenges are faced. Not only that the trellis has a large number of states, the number of branches per trellis interval is also enormous. The soft-output trellis/tree M-algorithm (SOTTMA) expands each trellis interval into a tree-like structure and performs the M-algorithm twice: once at each trellis interval to reduce the number of states and the other at each tree sub-level to remove unwanted branches. With the proposed technique, high-order trellises with million of branches per interval can be decoded with modest complexity.  相似文献   

2.
针对多输入多输出(MIMO)系统,当发射端已知信道状态信息时,提出基于信道矩阵奇异值分解(SVD)的空时编码(STC)传输方案SVD-STC,并推导出相应的群检测算法.SVD-STC是分层空时(LST)码和空时网格码(STTC)的混合形式,在传输率和分集之间取得折衷.由于采用奇异值分解,SVD-STC具有不等保护特性,可以与信源编码结合,实现图像分等级传输,显著提高重建图像的质量,同时具有较高的传输率,适用于固定无线通信系统中的多媒体传输.  相似文献   

3.
单载波宽带MIMO系统广义近似消息传递Turbo频域均衡   总被引:1,自引:0,他引:1  
针对编码单载波循环前缀(SC-CP)多输入多输出(MIMO)系统,该文采用消息传递算法研究软输入软输出MIMO频域均衡器(FDE)的设计问题。基于广义近似消息传递(GAMP)算法,该文提出一种新的低复杂度MIMO频域均衡方法。这种消息传递MIMO均衡方法的显著特点是既保留了SC-CP传输所产生的频域均衡的优点,同时又避免了传统MIMO FDE中逐频点MIMO矩阵求逆运算,所以具有随MIMO系统接收天线数增加而线性增长的计算复杂度。计算机仿真结果表明,与传统方案相比,该文提出的MIMO频域均衡算法具有明显的误码率(BER)性能优势。  相似文献   

4.
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).  相似文献   

5.
在多输入多输出(Multiple-Input Multiple-Output, MIMO)无线通信中,信道衰落、随机噪声、空间多径效应和共信道干扰等因素会产生符号间干扰,造成接收端信号严重失真。为提高MIMO系统传输性能,有效减少信道中相位失真,提出了一种改进的非常数模半盲均衡方案(Non-constant Modulus Algorithm, NCMA)。该方案结合了MIMO信道先验知识对半盲均衡器的初始值进行预设,采用变步长迭代更新均衡器权系数,寻找到最小目标函数值。仿真结果表明,改进后的算法能通过控制变步长减小剩余稳态误差,加快收敛速度,改善信道均衡效果。  相似文献   

6.
基于对线性多输入多输出(MIMO)系统的自适应盲源分离和盲均衡的研究,为了能够有效恢复输入信号,提出了一种在MIMO系统中引入抖动处理技术的修正抖动符号误差恒模算法.仿真结果表明,该算法可以在仅已知输入信号统计量的情况下跟踪信道变化,并且有效克服多个均衡器的输出可能锁定到相同的源信号问题,抑制ISI和MUI,恢复所有发射天线的发送信息.  相似文献   

7.
We consider the Kalman filter for equalization of a multiple-input multiple-output (MIMO), frequency selective, quasi-static fading channel. More specifically, we consider a coded system, where the incoming bit stream is convolutionally encoded, interleaved and then spatially multiplexed across the transmit antennas. Each substream is modulated into M-ary symbols before being transmitted over a frequency selective channel. At the receiver, we propose to use the Kalman filter as a low complexity MIMO equalizer, as opposed to the trellis based maximum a-posteriori (MAP) equalizer whose computational complexity grows exponentially with the channel memory, the number of transmit antennas and the spectral efficiency (bits/s/Hz) of the system. We modify the structure of the Kalman filter and enable it to process the a-priori (soft) information provided by the channel decoder, thereby allowing us to perform iterative (turbo) equalization on the received sequence. The iterative equalizer structure is designed for general M-ary constellations. We also propose a low complexity version of the above algorithm whose performance is comparable to its full complexity counterpart, but which achieves a significant complexity reduction. We demonstrate via simulations that for higher order constellations, when sufficient number of receive antennas are available (e.g. for a 2 transmitter, 3 receiver system, QPSK), the performance of the proposed algorithms after 4 iterations is within 1.5 dB of the non-iterative MAP algorithm with close to an order of magnitude complexity reduction. By objectively quantifying the complexity of all the considered algorithms we show that the complexity reduction for the proposed schemes becomes increasingly significant for practical systems with moderate to large constellation sizes and a large number of transmit antennas  相似文献   

8.
Space-time turbo equalization in frequency-selective MIMO channels   总被引:11,自引:0,他引:11  
A computationally efficient space-time turbo equalization algorithm is derived for frequency-selective multiple-input-multiple-output (MIMO) channels. The algorithm is an extension of the iterative equalization algorithm by Reynolds and Wang (see Signal Processing, vol.81, no.5, p.989-995, 2001) for frequency-selective fading channels and of iterative multiuser detection for code-division multiple-access (CDMA) systems by Wang and Poor (see IEEE Trans. Commun., vol.47, p.1046-1061, 1999). The proposed algorithm is implemented as a MIMO detector consisting of a soft-input-soft-output (SISO) linear MMSE detector followed by SISO channel decoders for the multiple users. The detector first forms a soft replica of each composite interfering signal using the log likelihood ratio (LLR), fed back from the SISO channel decoders, of the transmitted coded symbols and subtracts it from the received signal vector. Linear adaptive filtering then takes place to suppress the interference residuals: filter taps are adjusted based on the minimum mean square error (MMSE) criterion. The LLR is then calculated for adaptive filter output. This process is repeated in an iterative fashion to enhance signal-detection performance. This paper also discusses the performance sensitivity of the proposed algorithm to channel-estimation error. A channel-estimation scheme is introduced that works with the iterative MIMO equalization process to reduce estimation errors.  相似文献   

9.
Sampling-based soft equalization for frequency-selective MIMO channels   总被引:1,自引:0,他引:1  
We consider the problem of channel equalization in broadband wireless multiple-input multiple-output (MIMO) systems over frequency-selective fading channels, based on the sequential Monte Carlo (SMC) sampling techniques for Bayesian inference. Built on the technique of importance sampling, the stochastic sampler generates weighted random MIMO symbol samples and uses resampling to rejuvenate the sample streams; whereas the deterministic sampler, a heuristic modification of the stochastic counterpart, recursively performs exploration and selection steps in a greedy manner in both space and time domains. Such a space-time sampling scheme is very effective in combating both intersymbol interference and cochannel interference caused by frequency-selective channel and multiple transmit and receiver antennas. The proposed sampling-based MIMO equalizers significantly outperform the decision-feedback MIMO equalizers with comparable computational complexity. More importantly, being soft-input soft-output in nature, these sampling-based MIMO equalizers can be employed as the first-stage soft demodulator in a turbo receiver for coded broadband MIMO systems. Such a turbo receiver successively improves the receiver performance through iterative equalization, channel re-estimation, and channel decoding. Finally, computer simulation results are provided to demonstrate the performance of the proposed sampling-based soft MIMO equalizers in both uncoded and turbo coded systems.  相似文献   

10.
In this letter, an ordered successive interference cancellation (OSIC) scheme is applied for multiple‐input multiple‐output (MIMO) detection in ultra‐wideband (UWB) communication systems. The error rate expression of an OSIC receiver on a log‐normal multipath fading channel is theoretically derived in a closed form solution. Its bit error rate performance is analytically compared with that of a zero forcing receiver in the UWB MIMO detection scheme followed by RAKE combining.  相似文献   

11.
多输入多输出(Multiple-Input Multiple Output,MIMO)技术已被广泛应用于无线通信系统。由于信道中均衡、预编码、空间模式、调制和编码方案(Modulation and Coding Scheme,MCS)之间耦合的复杂性,在MIMO系统中执行链路自适应仍十分困难。通过实数分类器提出MIMO系统中的链路自适应方案来最大化频谱效率,并保持传输的可靠性。从信道状态信息(Channel State Information,CSI)中提取特征,并结合特定的代价函数选择调制和编码方案,基于最大化频谱效率的目标来选择空间模式。  相似文献   

12.
In this paper a novel algorithm based on subspace projections is developed for the blind kernel identification of LTI FIR multiple input multiple output (MIMO) systems, as well as blind equalization of finite memory SIMO Volterra systems. In addition, for Volterra systems, the algorithm computes the memory lengths of the nonlinearities involved. Simulations in the context of blind channel equalization and identification demonstrate good performance in comparison to existing schemes.  相似文献   

13.
In this correspondence, we present a new method for the iterative equalization and decoding of multilevel trellis coded modulation (TCM) signals over frequency selective channels. Results show that the proposed algorithm achieves better performance compared to the previous work on the MMSE filter- based turbo equalization for a non-binary coded modulation scheme. The performance gain is accomplished by utilizing the combined modulation and coding nature of TCM and passing the refined signal obtained from different paths to the TCM decoder as the channel value in addition to the a priori probabilities.  相似文献   

14.
Modern wireless communications require an efficient spectrum usage and high channel capacity and throughput. Multiple-input and multiple-output (MIMO), Linear equalizers, multi-user detection and multicarrier code-division multiple access (MC-CDMA) are possible solutions to achieve spectral efficiency, high channel capacity, eliminate multiple access interference (MAI), eliminate Inter symbol interference (ISI) and robustness against frequency selective fading. In this paper, we combine all these techniques and investigate BER performance. We propose a low complexity receiver structure for Single-input Multiple-output (SIMO) downlink MC-CDMA systems. It employs an interference cancellation scheme to suppress the interference caused by the multipath fading channel. Also, the proposed scheme is developed for MIMO MC-CDMA system. The performance analysis of Downlink MIMO MC-CDMA systems with V-BLAST over frequency selective fading channel is investigated under various number of transmit and receive antennas. The simulation results show proposed SIMO equalization with parallel interference cancellation scheme is effective in reducing the ISI and the MAI. It improves the performance significantly and the simulation results show that MIMO MC-CDMA with V-BLAST multi-user detection provides high data rate and the BER significant improvement.  相似文献   

15.
In this paper, we propose an efficient frequency domain equalization scheme for Multiple Input Multiple Output (MIMO) Single-Carrier Frequency-Division Multiple Access (SC-FDMA) systems. The proposed scheme avoids the complexity problem associated with the conventional MIMO Zero-Forcing (ZF) equalizer as well as the noise enhancement problem. The matrix inversion process associated with the proposed equalization scheme is performed in two steps to reduce complexity. A regularization term is added in the second step of the matrix inversion to avoid the noise enhancement. Simulation experiments on uplink MIMO SC-FDMA systems show that the proposed equalization scheme provides better performance than that of the ZF equalizer and its complexity is far less than that of the ZF equalizer.  相似文献   

16.
In this paper, a novel trellis source encoding scheme based on punctured ring convolutional codes is presented. Joint source and channel coding (JSCC) using trellis coded continuous phase modulation (CPM) with punctured convolutional codes over rings is investigated. The channels considered are the additive white gaussian noise (AWGN) channel and the Rayleigh fading channel. Optimal soft decoding for the proposed JSCC scheme is studied. The soft decoder is based on the a posteriori probability (APP) algorithm for trellis coded CPM with punctured ring convolutional codes. It is shown that these systems with soft decoding outperform the same systems with hard decoding especially when the systems operate at low to medium signal-to-noise ratio (SNR). Furthermore, adaptive JSCC approaches based on the proposed source coding scheme are investigated. Compared with JSCC schemes with fixed source coding rates, the proposed adaptive approaches can achieve much better performance in the high SNR region. The novelties of this work are the development of a trellis source encoding method based on punctured ring convolutional codes, the use of a soft decoder, the APP algorithm for the combined systems and the adaptive approaches to the JSCC problem.  相似文献   

17.
Per-tone equalization for MIMO OFDM systems   总被引:5,自引:0,他引:5  
This paper focuses on multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems with channel order larger than the cyclic prefix (CP) length. Writing the demodulating fast Fourier transform (FFT) as a sliding FFT followed by a downsampling operation, we show in this paper that by swapping the filtering operations of the MIMO channel and the sliding FFT, the data model for the temporally smoothened received signal of each individual tone of the MIMO OFDM system is very similar to the data model for the temporally smoothened received signal of a MIMO single-carrier (SC) system. As a result, to recover the data symbol vectors, the conventional equalization approach for MIMO SC systems can be applied to each individual tone of the MIMO OFDM system. This so-called per-tone equalization (PTEQ) approach for MIMO OFDM systems is an attractive alternative to the recently developed time-domain equalization (TEQ) approach for MIMO OFDM systems. In the second part of this paper, we focus on direct per-tone equalizer design and adapt an existing semi-blind equalizer design method for space-time block coding (STBC) SC systems to the corresponding semi-blind per-tone equalizer design method for STBC OFDM systems.  相似文献   

18.
19.
In this paper, we investigate adaptive blind source separation and equalization for multiple-input/multiple-output (MIMO) systems. We first analyze the convergence of the constant modulus algorithm (CMA) used in MIMO systems (MIMO-CMA). Our analysis reveals that the MIMO-CMA equalizer is able to recover one of the input signals, remove the intersymbol interference (ISI), and suppress the other input signals. Furthermore, for the MIMO finite impulse response (FIR) systems satisfying certain conditions, the MIMO-CMA FIR equalizers are able to perfectly recover one of the system inputs regardless of the initial settings. We then propose a novel algorithm for blind source separation and equalization for MIMO systems. Our theoretical analysis proves that the new blind algorithm is able to recover all system inputs simultaneously regardless of the initial settings. Finally, computer simulation examples are presented to confirm our analysis and illustrate the effectiveness of blind source separation and equalization for MIMO systems  相似文献   

20.
Near-optimum soft decision equalization for frequency selective MIMO channels   总被引:11,自引:0,他引:11  
In this paper, we develop soft decision equalization (SDE) techniques for frequency selective multiple-input multiple-output (MIMO) channels in the quest for low-complexity equalizers with error performance competitive to that of maximum likelihood (ML) sequence detection. We demonstrate that decision feedback equalization (DFE) based on soft-decisions, expressed via the posterior probabilities associated with feedback symbols, is able to outperform hard-decision DFE, with a low computational cost that is polynomial in the number of symbols to be recovered and linear in the signal constellation size. Building on the probabilistic data association (PDA) multiuser detector, we present two new MIMO equalization solutions to handle the distinctive channel memory. The first SDE algorithm adopts a zero-padded transmission structure to convert the challenging sequence detection problem into a block-by-block least-square formulation. It introduces key enhancement to the original PDA to enable applications in rank-deficient channels and for higher level modulations. The second SDE algorithm takes advantage of the Toeplitz channel matrix structure embodied in an equalization problem. It processes the data samples through a series of overlapping sliding windows to reduce complexity and, at the same time, performs implicit noise tracking to maintain near-optimum performance. With their low complexity, simple implementations, and impressive near-optimum performance offered by iterative soft-decision processing, the proposed SDE methods are attractive candidates to deliver efficient reception solutions to practical high-capacity MIMO systems. Simulation comparisons of our SDE methods with minimum-mean-square error (MMSE)-based MIMO DFE and sphere decoded quasi-ML detection are presented.  相似文献   

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