STBC-Based (Turbo) STTC Codes Built by Set Partitioning for Three Transmit Antennas: Construction and Performances

Simulating wideband fading channels, multiple-input multiple-output (MIMO) channels, and diversity-combined fading channels often demands the generation of multiple uncorrelated Rayleigh fading waveforms. In this letter, two appropriate parameter computation methods, namely the method of exact Doppler spread (MEDS) and L_p -norm method (LPNM), for deterministic sum-of-sinusoids (SoS) channel simulators are investigated to guarantee the uncorrelatedness between different simulated Rayleigh fading processes. Numerical and simulation results show that the resulting deterministic SoS channel simulator can accurately and efficiently reproduce all the desired statistical properties of the reference model     

一种新的Jakes模型参数计算方法

本文分析了小尺度无线衰落信道的理论参考模型—Clark模型,比较了两种较为重要的确定性仿真模型的参数计算方法—精确多普勒扩展法（MEDS）和随机精确多普勒扩展法（R_MEDS）,提出了一种新的用于仿真平坦衰落信道Jakes模型的参数计算方法,即在MEDS的基础上对离散多普勒频率引入随机抖动。仿真数据和图形表明,在模型复杂度较低的情况下,新的信道模型的自相关和互相关特性较R_MEDS有很大改善,而且与原始MEDS相比,新模型多普勒频率为随机变量,可以有效仿真瑞利衰落、多个不相关的瑞利衰落和频率选择性衰落信道等,并且可以结合工程需要设定随机抖动幅度,保证了衰落信道的不相关性和遍历性的有机统一。      

A New Design Concept for High-Performance Fading Channel Simulators Using Set Partitioning

In this paper, we introduce a new technique for the design of high-performance Rayleigh fading channel simulators. The proposed design method uses set partitioning – a technique, which plays a key role in the design of trellis-coded modulation schemes. We show how set partitioning can be used to design multiple uncorrelated fading waveforms enabling the simulation of Rayleigh fading channels. For the important case of isotropic scattering, we show that the sample average of the generated waveforms results in a deterministic process, the autocorrelation function (ACF) of which tends to the zeroth-order Bessel function of the first kind as the number of sample functions increases. The proposed procedure is completely deterministic. The comparison with a stochastic procedure using Monte Carlo techniques will be made. A study of the performance shows clearly that the new technique using set partitioning outperforms by far existing Monte Carlo methods.     

多径非相关瑞利信道生成的改进

提出一种多径非相关瑞利信道生成改进方法。和目前其他瑞利信道生成方法相比，该方法不仅能满足瑞利信道所具备的统计特性，而且保证信号多径传播中各径信号不相关特性。通过仿真可以看出该方法的单径信道二阶特性和现有模型统计特性相仿，而多径非相关性明显较好。     

Direct-sequence spread-spectrum parallel acquisition innonselective and frequency-selective Rician fading channels

This work presents the performance of the direct-sequence spread-spectrum (DS-SS) parallel acquisition system, previously proposed by the authors (1989, 1990), for nonselective and frequency-selective Rician (i.e. specular plus Rayleigh) fading channels. The acquisition system utilizes a bank of parallel I-Q noncoherent matched filters for the search mode, and a coincidence detector for the verification mode. The probabilities of detection and false alarm are derived and the mean and variance of the acquisition time are evaluated as a measure of the system performance. The nonselective channel is a Rayleigh fast fading channel, while the frequency-selective channel model is the so-called wide sense stationary uncorrelated scattering (WSSUS), selective only on frequency. These channels are typical for aircraft-satellite and line-of-sight (LOS) communications     

Simplified eIRA code design and performance analysis for correlated Rayleigh fading channels

We present a simple design technique for extended irregular repeat-accumulate (eIRA) codes for flat Rayleigh fading channels, using simple channels as surrogates in the design. We show that eIRA codes designed for the burst-erasure channel (BuEC) or the burst-erasure channel with AWGN (BuEC-G) achieve essentially the same performance over Rayleigh fading channels as codes designed for the fading channel. Thus, to design good codes for Rayleigh fading channels, instead of implementing the complex design procedures targeted, specifically for this channel, we propose the simple approach of designing codes over surrogate channels, the BuEC or the BuEC-G. We also show that eIRA codes designed for the BuEC enjoy the advantage of efficient encodability and a lower error-rate floor. Finally, we demonstrate that it is the distribution of the number of faded bits per codeword which determines the difference between correlated and uncorrelated fading channel performance. Perfect channel state information is assumed in this paper.     

相关瑞利信道仿真方法的研究

在无线通信系统的仿真中,相关瑞利衰落信道扮演着重要的作用。一种基于对一系列统计独立的标准高斯随机过程进行线性变换,得到具有一定相关特性的瑞利衰落信道的仿真模型被提出。仿真结果及复杂度分析表明,由于本文提出的仿真模型采用了迭代算法,因此相对于传统的相关瑞利信道仿真模型,该模型具有准确,复杂度低,易实现等优点。     

Jakes fading model revisited

The Jakes fading model is a deterministic method for simulating time-correlated Rayleigh fading waveforms and is still widely used today. However, since it is difficult to create multiple uncorrelated fading waveforms with this model, the authors propose modifications to the model which solve this problem.<>     

Multiple Rayleigh fading channels modeling based on sum‐of‐sinusoids model

Assessing the performance of communication system is critical in system design in mobile communication study. Numerous methodologies have been employed to facilitate the assessment, amongst which generation of multiple fading channels is widely used and thus of great interest to us. Specifically, multiple Rayleigh fading channels are extensively utilized in simulation of the following: MIMO channels, amplify‐and‐forward fading channels, frequency‐selective channels, etc. The existing model to generate Rayleigh fading channels is the sum of sinusoids (SOS). However, the SOS model is flawed, as it sometimes generates impure correlated channels. That is, a small fraction of correlated channels are generated when we anticipate uncorrelated or vice versa. In this paper, on the basis of the concept of SOS, we introduce a new computational model to generate Rayleigh channels that completely match our anticipation—fully uncorrelated or fully correlated channels. Additionally, we also propose a design method to reduce the number of sinusoids, thus we achieve reduced computational cost of the system. Simulation results and comparison analysis indicate that, with reduced computational cost, our method is able to produce pure Rayleigh fading channels— 100% uncorrelated or the opposite.Copyright © 2013 John Wiley & Sons, Ltd.     

An Improved Simulator for the Correlation-Based MIMO Channel in Multiple Cluster Scattering Environments

An improved MIMO radio channel simulator is proposed, based on the most popular correlation-based MIMO channel model called Kronecker model and the sum-of-sinusoids (SoS) method which is widely used to generate Rayleigh fading waveforms with temporal correlation. Firstly, a simplified simulation model for generating multiple independent Rayleigh fading waveforms is presented, which employs only one random variable to set all Doppler frequency components in all waveforms. Next, a fast spatial correlation calculation technique, in a closed-form expression implemented by the Fourier Transform both for outdoor and indoor multiple cluster scattering environments, is introduced, which accurately reproduces the desired spatial correlation properties and indicates a direct dependence between spatial correlation and channel physical parameters. The ergodic and outage capacity of the simulated channel are also evaluated with respect to different azimuth of arrival and azimuth of departure (AoA/AoD) under the condition of 3GPP SCM (3rd Generation Partnership Project Spatial channel model) [23]. The presented simulator is therefore suitable for the theoretical analysis of MIMO radio systems, including dynamic system simulation.     

Improved models for the generation of multiple uncorrelatedRayleigh fading waveforms

An improved sum-of-sinusoids simulation model is proposed for Rayleigh fading channels. The new model employs random initial phase, and conditional random Doppler frequency for all individual sinusoids. The second-order statistics of the new simulator match the desired ones exactly even if the number of sinusoids is a single-digit integer. Other key statistics of the new simulator approach the desired ones of Clarke's (1968) reference model as the number of sinusoids approaches infinity, while good convergence is achieved when the number of sinusoids is small. Moreover, the new simulator can be directly used to generate multiple uncorrelated fading waveforms; it is also pointed out that a class of 16 different simulators, which have identical statistical properties, can be developed for Rayleigh fading channels     

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).     

Design of high-speed simulation models for mobile fading channelsby using table look-up techniques

This paper describes a procedure for the design of fast simulation models for Rayleigh fading channels. The presented method is based on an efficient implementation of Rice's sum of sinusoids by using table look-up techniques. The proposed channel simulator is composed of a few numbers of adders, storage elements, and simple modulo operators, whereas time-consuming operations like multiplications and trigonometric operations are not required. Such a multiplier-free simulation model is introduced as a high-speed channel simulator. It is shown that the high-speed channel simulator can be interpreted as a finite state machine which generates deterministic output envelope sequences with approximately Rayleigh distribution. The statistical properties of the designed high-speed channel simulator are investigated analytically and compared with the statistics of the underlying Rayleigh reference model. Results of experiments for measuring the speed of the presented and other types of channel simulators are also presented     

Closed-form approximation for the outage capacity of orthogonal STBC

In this letter we derive a tight analytical approximation for the outage capacity of orthogonal space-time block codes (STBC's). The proposed expression is a simple closed-form function of the power covariance matrix of the channel. In the case of uncorrelated channels, the expression only depends on the variances of the channel power gains that can be expressed analytically for the most common fading distributions: Rayleigh, Rice, Nakagami, Weibull, etc. Furthermore, the approximation encompasses different fading distributions and gains between different pairs of transmit and receive antennas, which can occur in distributed STBC networks.     

Improved Frequency Domain Channel Estimation and Equalization for MIMO Wireless Communications

This paper introduces an improved frequency domain channel estimation method based on interpolation vectors for single carrier frequency domain equalization (SC-FDE) with the multiple-input multiple-output (MIMO) scheme. The proposed algorithm is derived by employing the least squares (LS) criterion, and a specified application for the wide sense stationary uncorrelated scattering (WSSUS) Rayleigh fading channel is presented. The channel frequency domain responses estimated at two adjacent pilot blocks are used to track the time-variant channel information, which can effectively improve the accuracy of channel estimation without significantly increasing complexity. Maximum mean square error (MMSE) frequency domain equalization based on the estimated channel is employed in the receiver to recover transmitted signals. This paper also investigates a training sequence design method for multiple transmit antennas and a noise variance estimation method. Numerical simulation results show that the proposed methods can perform very well for fading channels with long multipath delay and high Doppler spread.     

Linear expansions for frequency selective channels in OFDM

Modeling the frequency selective fading channels as random processes, we employ a linear expansion based on the Karhunen–Loeve (KL) series representation involving a complete set of orthogonal deterministic vectors with a corresponding uncorrelated random coefficients. Focusing on OFDM transmissions through frequency selective fading, this paper pursues a computationally efficient, pilot-aided linear minimum mean square error (MMSE) uncorrelated KL series expansion coefficients estimation algorithm. Based on such an expansion, no matrix inversion is required in the proposed MMSE estimator. Moreover, truncation in the linear expansion of channel is achieved by exploiting the optimal truncation property of the KL expansion resulting in a smaller computational load on the estimation algorithm. The performance of the proposed approach is studied through analytical and experimental results. We first exploit the performance of the MMSE channel estimator based on the evaluation of minimum Bayesian MSE. We also provide performance analysis results studying the influence of the effect of SNR and correlation mismatch on the estimator performance. Simulation results confirm our theoretical results and illustrate that the proposed algorithm is capable of tracking fast fading and improving performance.     

Analysis and Simulation of Second-Order Statistics with Modified Characteristic Function Parameters in a Multipath Fading Environment

In this paper, we analyse and implement a modified low pass filtering based characteristic function for a multipath Rayleigh fading channel. A new class of this modified filtering sequence based statistical simulation model is proposed for a Rayleigh fading environment. Comparing with the sum-of-sinusoids (SOS) deterministic model and its modifications as a new SOS model, the proposed model reintroduces the randomness to Doppler frequency and initial phase of the sinusoids to have non-deterministic simulators with desired statistical properties. The expressions and simulation results of level crossing rate (LCR) and average fade duration are derived and shown in this paper. Comparison of power spectra reveals that the spectrum spread is much less for our proposed method. Therefore, we would expect reduction in the rapidity of fading which is observed in LCR calculations.     

Capacity of MRC on Correlated Rician Fading Channels

A new exact explicit expression is derived for the ergodic capacity of maximal ratio combining (MRC) schemes over arbitrarily correlated Rician fading channels. This is used to study the effects of channel correlation on the ergodic capacity. Numerical results reveal that both the phase and the magnitude of correlation have an impact on the ergodic capacity of Rician fading channels. This is in contrast to correlated Rayleigh fading, where the phase of the correlation has no effect on the ergodic capacity. It is also observed that negatively correlated branches in Rician fading may lead to an increase in ergodic capacity beyond that obtained by uncorrelated branches.     

Vector Channel Estimation and Multiuser Detection for Multicarrier DS CDMA in Time and Frequency Selective Fading Channels

In a multicarrier direct-sequence code-division multiple access (MC DS CDMA) system, different fading channels for different users and/or different carriers are correlated in general; thus a vector channel model is more appropriate than disjoint scalar channel models. For multiuser MC DS CDMA systems, we propose (1) a generalized vector autoregressive model which accounts for correlation between different user/carrier fading channels, (2) the use of a two-phased algorithm to obtain the proposed model’s parameters, and (3) a receiver structure that consists of a generalized decorrelator followed by maximal-ratio combining (MRC) of uncorrelated carrier channel outputs of each user. The estimated fading coefficients provide the necessary quantities to MRC. The computer simulation results show that the proposed scheme has performance close to the case in which the channel is perfectly known, and outperforms separate scalar channel estimation case.