Unsupervised receiver processing techniques for linear space-time equalization of wideband multiple input / multiple output channels

In this paper, we address the problem of unsupervised (blind) space-time equalization of frequency-selective multiple-input multiple-output (MIMO) channels. The motivation behind this work is that in order to provide the high transmission rates that data-demanding applications require, wireless multiple antenna (MIMO) systems will have to operate in wide bandwidths. In such scenarios, frequency selectivity may induce important intersymbol interference (ISI), in addition to the interuser interference (IUI) that each antenna's transmitted stream of data suffers from the other antennas. Under these conditions, channel estimation of the frequency-selective MIMO channel may become a daunting task that ultimately reduces the effective transmission rate. We present a family of globally convergent blind space-time equalization techniques, developed from multiuser kurtosis output-based criteria, which allow the recovery of the MIMO channel inputs without the training overhead that channel estimation typically requires, thus improving the MIMO channel's spectral efficiency.     

关于光信噪比检测量值偏差的分析及研究

本文针对OTN、DWDM系统存在光信噪比检测结果量值差异较大的问题,从技术原理、检测方式、计算方法、适用条件等方面分析产生该问题的原因,总结出具体解决方案及注意事项,可以为工程验收测试以及运行维护提供借鉴, 有助于减少或杜绝此类问题的影响。     

Low-complexity equalization of OFDM in doubly selective channels

Orthogonal frequency division multiplexing (OFDM) systems may experience significant inter-carrier interference (ICI) when used in time- and frequency-selective, or doubly selective, channels. In such cases, the classical symbol estimation schemes, e.g., minimum mean-squared error (MMSE) and zero-forcing (ZF) estimation, require matrix inversion that is prohibitively complex for large symbol lengths. An analysis of the ICI generation mechanism leads us to propose a novel two-stage equalizer whose complexity (apart from the FFT) is linear in the OFDM symbol length. The first stage applies optimal linear preprocessing to restrict ICI support, and the second stage uses iterative MMSE estimation to estimate finite-alphabet frequency-domain symbols. Simulation results indicate that our equalizer has significant performance and complexity advantages over the classical linear MMSE estimator in doubly selective channels.     

Simple equalization of time-varying channels for OFDM

We present a block minimum mean-squared error (MMSE) equalizer for orthogonal frequency-division multiplexing (OFDM) systems over time-varying multipath channels. The equalization algorithm exploits the band structure of the frequency-domain channel matrix by means of a band LDL/sup H/ factorization. The complexity of the proposed algorithm is linear in the number of subcarriers and turns out to be smaller with respect to a serial MMSE equalizer characterized by a similar performance.     

温度检测实现最大功率控制装置

介绍一种新型的功率控制装置,详细描述硬件设计和软件控制方法,并给出实际验证和分析结果。该装置由带热敏电阻的温度检测模块、功率温度补偿数据表和功率控制模块组成,具有降低手机硬件成本,减少器件电路板空间和缩短校准时间等优势。     

Diversity analysis of space-time coding in cascaded Rayleigh fading channels

Cascaded Rayleigh distribution is used to model multipath fading in mobile-to-mobile communication scenarios and provides a better fit to experimental data in such scenarios compared to the conventional Rayleigh channel model. In this letter, we derive an exact expression for the pairwise error probability (PEP) of space-time trellis codes over the cascaded Rayleigh fading channel, which is in the form of a simple single finite-range integral. Through the derived PEP expression, we present the maximum diversity order achievable over such channels and demonstrate the performance degradation in comparison to conventional Rayleigh channels. Monte-Carlo simulations are further demonstrated to confirm the analytical results.     

Application of filter sharpening to cascaded integrator-combdecimation filters

A new architecture for the implementation of high-order decimation filters is described. It combines the cascaded integrator-comb (CIC) multirate filter structure with filter sharpening techniques to improve the filter's passband response. This allows the first-stage CIC decimation filter to be followed by a fixed-coefficient second-stage filter, rather than a programmable filter, thereby achieving a significant hardware reduction over existing approaches. Furthermore, the use of fixed-coefficient filters in place of programmable-coefficient filters improves the overall throughput rate. The resulting architecture is well suited for single-chip VLSI implementation with very high data-sample rates. We discuss an example with specifications suitable for use in a wideband satellite communication subband tuner system and for signal analysis     

Turbo space-time equalization of TCM for broadband wireless channels

This paper presents a space-time turbo (iterative) equalization method for trellis-coded modulation (TCM) signals over broadband wireless channels. For fixed wireless systems operating at high data rates, the multipath delay spread becomes large, making it impossible to apply trellis-based equalization methods. The equalizer proposed here consists of a broadband beamformer which processes antenna array measurements to shorten the observed channel impulse response, followed by a conventional scalar turbo equalizer. Since the applicability of trellis-based equalizers is limited to additive white noise channels, the beamformer is required to preserve the whiteness of the noise at its output. This constraint is equivalent to requiring that the finite-impulse response (FIR) beamforming filters must have a power complementarity property. The power complementarity property imposes nonnegative definite quadratic constraints on the beamforming filters, so the beamformer design is expressed as a constrained quadratic optimization problem. The composite channel impulse response at the beamformer output is shortened significantly, making it possible to use a turbo equalizer for the joint equalization and decoding of trellis modulated signals. The proposed receiver structure is simulated for two-dimensional TCM signals such as 8-PSK and 16-QAM and the results indicate that the use of antenna arrays with only two or three elements allows a large decrease in the channel signal-to-noise ratio needed to achieve a 10/sup -4/ bit-error rate.     

Blind decision feedback equalization of time-varying channels withDPSK inputs

This paper presents a new method to the blind equalization of a class of linear time-varying mobile channels for differentially encoded channel input signals. Through reparameterization, the equivalent discrete system can be modeled as a single-input multiple-output system. Unlike some existing methods, this new algorithm does not require prior knowledge on the cyclic frequency of the channel response. The algorithm is simple and relies only on a decision feedback structure and the differential encoding nature of the channel input signals. The convergence analysis of the decision feedback system is presented along with simulation examples     

Novel spatiotemporal equalization based on cascaded connection of multibeam adaptive array and multi-input MLSE

This paper proposes a novel spatiotemporal equalizer using a cascaded connection of multibeam adaptive array and multi-input maximum likelihood sequence estimation (MLSE) based on single-user detection. The computational load for the proposed method is much lower than that of the optimal method, and computer simulations revealed that its bit-error-rate (BER) performance is identical to that of the optimal method. Theoretical analysis also supports equivalency between these methods.     

On adaptive decision-feedback equalization of intersymbolinterference channels in coded modulation systems

Recently, Eyuboglu (1988) has shown that adaptive noise-predictive decision-feedback equalization (DFE) can be combined with coded modulation to achieve high-speed data transmission by periodic interleaving. In this paper, we present a new method of adaptive DFE with periodic interleaving for coded modulation systems. The method is an improved version of that proposed by Eyuboglu, where the deinterleaving operation is performed on a vector-by-vector basis, instead of a sample-by-sample basis. Unlike the original system in which the linear equalizer's coefficients can be adjusted only with hard decisions from the threshold detector, the improved structure updates the coefficients of both the linear equalizer and the noise predictor based on soft decisions from the most likely path in the soft decoder. The improved system achieves better error-rate performance than the original with a little increase in hardware complexity. As compared to another improved design reported by Zhou et al. (1990), the new structure also gains advantages in error-rate performance, hardware complexity, and throughput delay     

Bayesian techniques for equalization of rapidly fading frequency selective channels

This paper applies the Bayesian conditional decision feedback estimator (BCDFE) to rapidly fading frequency selective channels. The BCDFE is a model-based deconvolution algorithm which jointly estimates the transmitted data and channel parameters. The BCDFE smoothly transitions between trained and blind operation and consequently provides robust performance in rapidly fading channels. We provide a brief derivation of the BCDFE and characterize the performance on the land mobile radio channel. We assess the BCDFE's principle design characteristics and the resulting performance in both transient and steady-state operation. The effects of delay spread, Doppler spread, and cochannel interference on the bit error probability performance are also presented. The BCDFE demonstrates many of the desirable characteristics of an equalizer for mobile radio.     

Blind equalization for an application of unitary space-time modulation in ISI channels

Transmit diversity schemes have gained attention due to the promise of increased capacity and improved performance. Among these schemes, unitary space-time modulation and differentially encoded unitary space-time modulation allow for simple noncoherent decoding for flat-fading channels. In this paper, a new blind equalization algorithm for these transmission schemes in intersymbol interference (ISI) channels is proposed. A matrix-type constant modulus algorithm that exploits the unitary structure of the space-time codes is developed. The equalizer is paired with a noncoherent decoder, resulting in a completely blind, low-complexity method for decoding in the presence of ISI. A noiseless convergence analysis is conducted and verified via simulation in both noiseless and noisy cases. The performance of the overall system is evaluated via simulation and semi-analytically, and the achieved performance is between that of the ideal zero-forcing and the minimum-mean squared-error equalizers.     

Second-order statistics-based blind equalization of IIRsingle-input multiple-output channels with common zeros

The problem of blind equalization of single-input multiple-output (SIMO) communications channels is considered using only the second-order statistics of the data. Such models arise when a single receiver data is fractionally sampled (assuming that there is excess bandwidth) or when an antenna array is used with or without fractional sampling. We focus on direct design of finite-length minimum mean-square error (MMSE) blind equalizers. Unlike the past work on this problem, we allow infinite impulse response (IIR) channels. Our approaches also work when the “subchannel” transfer functions have common zeros as long as the common zeros are minimum-phase zeros. Illustrative simulation examples are provided     

Estimation and equalization of doubly selective channels using known symbol padding

This paper considers the situation where users that experience high-mobility transmit data over frequency-selective channels, resulting in a doubly selective channel model (i.e., time- and frequency-selective channels) and this within the framework of Known Symbol Padding (KSP) transmission. KSP is a recently proposed block transmission technique where short sequences of known symbols acting as guard bands are inserted between successive blocks of data symbols. This paper proposes three novel channel estimation methods that allow for an accurate estimation of the time-varying transmission channel solely relying on the knowledge of the redundant symbols introduced by the KSP transmission scheme. The first method is a direct adaptive one while the others rely on a recently proposed model, the Basis Expansion Model (BEM), where the doubly selective channel is approximated with high accuracy using a limited number of complex exponentials. An important characteristic of the proposed methods is that they exploit all the received symbols that contain contributions from the training sequences and blindly filter out the contribution of the unknown surrounding data symbols. Besides these channel identification methods, the classical KSP equalizers are adapted to the context of doubly selective channels, which allows evaluation of the bit-error-rate (BER) performance of a KSP transmission system relying on the proposed channel estimation methods in the context of doubly selective channels. Simulation results show that KSP transmission is indeed a suitable transmission technique toward the delivery of high data rates to users experiencing a high mobility, when adapted KSP equalizers are used in combination with the proposed channel estimation methods.     

Reduced-complexity equalization techniques for ISI and MIMO wireless channels in iterative decoding

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.     

WATER—FILLING SPACE—TIME GODE IN CORRELATED FLAT RAYLEIGH FADING MISO CHANNELS

In this paper,STC with water-filling transmit power distribution in MISO system is proposed when the partial channel information feedback is possible,for example,at slow fading scenarion.The performances of the water-filling STC including water-filling STTC and waterfilling STBC are analyzed.Performance comparison of the Ungerboeck‘s2/3 trellis coded 8PSK modulated 2-STBC and 2-STTCs with QPSK is given out different channel correlation.     

Soft-output detection of CPM signals in frequency flat, Rayleighfading channels

Symbol-by-symbol detection algorithms are useful in systems in which soft-decision metrics are important, e.g., systems with interleaved coded modulation. A soft-output algorithm for the detection of continuous phase modulated (CPM) signals transmitted over frequency flat, Rayleigh fading channels is developed. Since the optimum detector is computationally too complex for any practical implementation, some suboptimal detectors which give near optimal performance are proposed. Some theoretical approximations for the performance of the interleaved coded system are given. The performance of the soft-output algorithms is also extensively characterized by means of Monte-Carlo simulations     

Turbo均衡在Non-CP SC-FDE系统中的应用

针对无循环前缀的单载波频域均衡(Non-CP SC-FDE)系统中的符号间干扰(ISI),提出了一种Turbo均衡与循环重构联合迭代算法。通过循环重构技术消除ISI,并采用频域均衡频域判决反馈(FDE-FDDF)方式,将Turbo均衡算法与循环重构算法结合在一起进行迭代。仿真结果表明,Non-CP SC-FDE系统使用该算法能实现与传统有CP系统近似的误码性能,在大幅提高传输效率的同时能够有效消除多径干扰。     

Blind equalization of IIR channels using hidden Markov models andextended least squares

In this paper, we present a blind equalization algorithm for noisy IIR channels when the channel input is a finite state Markov chain. The algorithm yields estimates of the IIR channel coefficients, channel noise variance, transition probabilities, and state of the Markov chain. Unlike the optimal maximum likelihood estimator which is computationally infeasible since the computing cost increases exponentially with data length, our algorithm is computationally inexpensive. Our algorithm is based on combining a recursive hidden Markov model (HMM) estimator with a relaxed SPR (strictly positive real) extended least squares (ELS) scheme. In simulation studies we show that the algorithm yields satisfactory estimates even in low SNR. We also compare the performance of our scheme with a truncated FIR scheme and the constant modulus algorithm (CMA) which is currently a popular algorithm in blind equalization