Doubly iterative receiver for block transmissions with EM-based channel estimation

Cyclic-prefix code division multiple access (CP-CDMA), multicarrier CDMA (MC-CDMA) and single carrier cyclic-prefix (SCCP) transmission are some schemes that could support the increasing demand of future high data rate applications. The linear and nonlinear equalizers used to detect the transmitted signal are always far from the Maximum-Likelihood (ML) detection bound. The block iterative generalized decision feedback equalizer (BI-GDFE) is an iterative and effective interference cancelation scheme which could provide near-ML performance yet with very low complexity. In order to deploy this scheme, the channel state information (CSI) must be available at the receiver. In practice, this information has to be estimated by using pilot and data symbols. This paper investigates the problem of channel estimation using the Expectation Maximization (EM) algorithm. The BI-GDFE provides the soft information of the transmitted signals to the EM-based algorithm in the form a combination of hard decision and a coefficient so-called the input-decision correlation (IDC). The resultant receiver becomes a doubly iterative scheme. To evaluate the performance of the proposed estimation algorithm, the Cramér-Rao Lower Bound (CRLB) is also derived. Computer simulations show that the bit error rate (BER) performance of the proposed receiver for joint channel estimation and signal detection can reach the performance of the BI-GDFE with perfect CSI.     

宽带CDMA系统中的一种新的自适应信道估计方法

该文提出了采用实测的信道自相关系数作为权重的信道估计处理方法,并给出其误差性能的数学表达式,同时给出了经典的滑动平均信道估计方法的误差性能的数学表达式。理论分析及仿真结果表明所提的方法能自动适应移动信道的时变模型及衰落速率,具有有效地抑制噪声的优点;同时克服了滑动平均估计方法的估计长度对估计准确性影响较大的缺点,在移动速度固定及移动速度变化很大的环境下都具有稳定的误差性能;尤其在移动速度变化很大的环境下具有比滑动平均估计方法更低的估计方差,大大提高了RAKE接收机的性能。     

一种新的MIMO-OFDM系统自适应快时变信道估计算法

为了能够获得较精确的快时变信道估计,利用模糊模型拟合快时变信道,提出了一种新的信道估计算法。算法采用自适应技术进行导频子载波频域传输函数模型参数的识别,然后通过插值拟合全部信道的频域传输函数。仿真结果表明,在系统多普勒频移小于0.1的情况下,信道估计的MSE性能得到改善。     

Iterative rake receiver with map channel estimation for ds-cdma systems

We propose an iterative rake receiver structure using an optimum semi-blind channel estimation algorithm for ds-cdma mobile communication systems. This receiver performs an iterative estimation of the channel according to the maximum a posteriori criterion, using the expectation-maximization algorithm. This estimation process requires a convenient representation of the discrete multipath fading channel based on the Karhunen-Loève orthogonal expansion theorem. The rake receiver uses pilot as well as unknown control and data symbols optimally for improving channel estimation quality. Moreover, it can take into account the coded structure of all unknown transmitted symbols when channel estimation quality is poor or unsatisfactory. The validity of the proposed method is highlighted by simulation results obtained for the FDD mode of the umts interface.     

A novel adaptive receiver with enhanced channel tracking capabilityfor TDMA-based mobile radio communications

The paper presents a novel fast-adaptive nonlinear receiver which exploits soft statistics for tracking the random fluctuations experienced by time division multiple access (TDMA) mobile radio links impaired by frequency-selective time-variant multipath phenomena. The detection task is accomplished by an Abend-Fritchman-like symbol-by-symbol maximum likelihood (SbS-ML) detector which delivers both hard decisions and soft statistics in form of a posteriori probabilities (APPs) of the states of the intersymbol interference (ISI) channel. In the proposed adaptive receiver, these APPs are employed in place of the conventional hard-detected data to feed an ad hoc developed nonlinear recursive Kalman-type channel estimator. Extensive computer simulations show that the exploitation of soft statistics enhances the tracking capability of the channel estimator so that the proposed receiver generally outperforms the usual ones based on adaptive maximum likelihood sequence estimators (MLSEs) for signal-to-noise ratio (SNR) values over 12-13 dB. Furthermore, the experienced performance gap with respect to more complex per-survivor processing (PSP)-based multi-estimator detectors appears generally small on slowly and moderately fast time-varying channels characterized by values of the product Doppler bandwidth × signaling period B_DT_S below 5×10^-3     

Blind adaptive channel estimation in ofdm systems

We consider the problem of blind channel estimation in zero padding OFDM systems, and propose blind adaptive algorithms in order to identify the impulse response of the multipath channel. In particular, we develop RLS and LMS schemes that exhibit rapid convergence combined with low computational complexity and numerical stability. Both versions are obtained by properly modifying the orthogonal iteration method used in numerical analysis for the computation of singular vectors. With a number of simulation experiments we demonstrate the satisfactory performance of our adaptive schemes under diverse signaling conditions     

Iterative receiver for OFDM systems based on semi-blind channel estimation

In this paper we propose two iterative algorithms of joint channel estimation and symbol detection for Orthogonal Frequency Division Multiplexing （OFDM） systems. In which, superimposed pilot scheme is adopted and an initial Channel State Information （CSI） is obtained by employing a first-order statistic. In each subsequent iteration, we propose two algorithms to update the CSI. The Mean Square Error （MSE） of channel estimation and Bit Error Rate （BER） performance are given and simulation results demonstrate that the iterative algorithm using method B has good performance approaching the ideal condition.     

A compact CPW fed slot antenna for ultra wide band applications

A printed compact coplanar waveguide fed triangular slot antenna for ultra wide band (UWB) communication systems is presented. The antenna comprises of a triangular slot loaded ground plane with a T shaped strip radiator to enhance the bandwidth and radiation. This compact antenna has a dimension of 26 mm × 26 mm when printed on a substrate of dielectric constant 4.4 and thickness 1.6 mm. Design equations are implemented and validated for different substrates. The pulse distortion is insignificant and is verified by the measured antenna performance with high signal fidelity and virtually steady group delay. The simulation and experiment reveal that the proposed antenna exhibits good impedance match, stable radiation patterns and constant gain and group delay over the entire operating band.     

A novel high speed multitap bus structure

Reducing reflections, noise, and settling time on a bus through unique selections of node terminations, bus characteristic impedance, and bus construction allows dramatically higher operating speed. The new structure is described, the theory discussed, and results from fully operational physical and electrical implementations are presented     

An adaptive receiver of joint data and channel estimation for meteor burst communications

In view of the characteristics of the meteor burst channel, the variable rate data transmission should be adopted to improve the system average throughput, which results in channel tracing and equalization problems at the receiver. Although the joint data and channel estimation of maximum likelihood sequence detection performing the principle of per‐survivor processing (PSP) is considered as an optimal detection scheme, its great computational complexity is a major problem and can hardly agree with the decreasing of the meteor channel. Based on the estimation of the system parameters, an adaptive state reduction of the PSP (ASRP) algorithm with only a few states in the trellis diagram is employed, while these states are chosen by the time‐varying threshold according to the exponential decay of meteor channels. It is shown that, ASRP can make a good tradeoff between the performance and the computational complexity, and provides reliable data transmission for adaptive modulation and coding of the meteor burst communication system. Computer simulation results and performance analysis are also included to support our developments. Copyright © 2010 John Wiley & Sons, Ltd.     

A high speed sampler for sub-sampling IR-UWB receiver

A high speed sampler for a sub-sampling impulse radio UWB receiver is presented. In this design, the sampler uses a time-interleaved topology with a single track and hold circuit, full custom clock generator, and offset cancelled comparator. These three main blocks are also discussed and analyzed. The circuit was fabricated in 0.13 μm CMOS technology. Measurement results indicate that the sampler achieves a maximum 3 GS/s sampling rate. The power consumption of the sampler is 27 mW under a supply voltage of 1.2 V. The total chip area including pads is 1.4 × 0.97 mm2.     

一种用于欠采样脉冲式超宽带接收机中的高速采样器

本文提出了一种用于欠采样脉冲式超宽带接收机中的高速采样器。该采样器采用时间交错拓扑结构,包含独立的采样保持电路、全定制时钟产生器和失调消除比较器三个主要模块。这三个模块在文中进行了具体的讨论和分析。该电路采用0.13um CMOS工艺制造。测试结果表明,采样器实现了最高3 GHz的采样速度。在1.2 V电源电压下,其功耗为27 mW。包含引脚的芯片总面积为1.4×0.97 mm2。     

A wide dynamic range receiver channel for a pulsed time-of-flightlaser radar

An integrated receiver channel for a pulsed time-of-flight (TOF) laser rangefinder has been designed and tested. The bandwidth of the receiver channel is 170 MHz, the transimpedance can be controlled in the range from 1.1 kΩ to 260 kΩ, and the input-referred noise is ~6 pA/√Hz. The distance measurement accuracy is ±4.7 mm (average of 10000 measurements), taking into account walk error (input signal amplitude varies in the range 1:624) and jitter. A considerable increase in the input dynamic range of the receiver has been achieved by placing an integrated current buffer with variable attenuation between the external photodetector and the transimpedance preamplifier. Integrated electronic gain control structures together with the small size and low power consumption achieved by the use of full custom integrated technology considerably simplifies rangefinding devices for many applications. The circuit was implemented in an 0.8-μm BiCMOS process     

A novel blind adaptive space-time receiver for multi-code DS-CDMA

Abstract-The capacity of conventional wireless communications systems based upon Direct-Sequence Code Division Multiple Access (DS-CDMA) schemes, is mainly limited by Multiple Access Interference (MAI). Therefore, methods aimed at reducing MAI are mandatory solutions to increase the capacity of such systems. Smart Antennas are a promising technology for improving the performance of high capacity mobile communications systems, because they are expected to be able to increase the Signal to Interference plus Noise power Ratio (SINR) of the received signals by dynamically adapting the equivalent array beam pattern in order to track the movements of the users within the cell. In this paper we propose a novel blind adaptive beamforming algorithm tailored for the up-link of multi-code multi-rate DS-CDMA wireless communications systems. Our proposal is based upon a modified Constant Modulus (CM) criterion, whose fundamental feature is the capability to overcome the main drawback of the classic CM algorithm, which lies in its difficulty of ensuring the convergence toward the desired user. The proposed algorithm exploits user-specific information intrinsically known at the receiver, which is the code uniquely associated to each user, without requiring the knowledge of the spatiotemporal propagation channel nor any specific training sequence. Within this paper we present a broadband solution, designed to temporally re-align uncorrelated clusters of multipaths, as well as spatially recombine correlated multipaths belonging to the same cluster. Computer simulations show that our proposed technique can effectively exploit path diversity and multipath correlation, also in the presence of Doppler effect and time-variable propagation conditions.     

非理想信道估计下迫零接收的空间相关多输入多输出空分复用系统的误码率分析

分析了非理想信道估计和发射空间相关信道下,采用迫零接收的多输入多输出空分复用无线通信系统的误码率性能.基于随机矩阵理论,导出了闭合形式的M-PSK和M-QAM误码率近似解析表达式,并通过仿真验证了表达式的有效性.所获得的表达式形式简单、便于数值计算,可以用于系统性能评估.     

SAGE based iterative receiver for joint synchronization and channel estimation in uplink MIMO-OFDMA systems

A new Turbo iterative receiver structure is proposed for the uplink multiple-input multiple-output orthogonal frequency division multiple access （MIMO-OFDMA） systems. The space-alternating generalized expectation-maximization （SAGE） algorithm is naturally embedded in the framework of iterative receiver to perform synchronization and detection usin~ the Turbo detector outputs. In each iteration, the expectation step intends to remove the multiple access interference （MAI） caused by other asynchronous users, and the maximization step is utilized to estimate the required parameters （i.e., timing offset, carrier frequency offset, channel state information, etc.） sequentially for each user. Simulation results show that the proposed algorithm can approach the performance of ideal receiver closely, while the processing complexity is rather lower than the conventional detectors.     

OFDM系统信道估计和自适应分配算法的研究

在多径衰落的信道中,用固定调制方式的分配技术可能会造成OFDM系统资源浪费,考虑如何将自适应分配技术与OFDM相结合成为提高移动通信性能的关键技术。本文中提出一种基于动态信噪比SNR切换门限的自适应算法,该算法在保证通信质量所需BER的前提下,结合OFDM和PSK/QAM调制方式的优势,按照各个子信道的状态分配比特信息量和功率大小,使所需要的发射功率达到最优化。本算法能提高OFDM的频谱利用率,也能使系统获得更优的性能。