Adaptive modulation for space–frequency block coded OFDM systems

The growing popularity of both multiple-input multiple-output (MIMO) and orthogonal frequency division multiplexing (OFDM) systems has created the need for adaptive modulation to integrate temporal, spatial and spectral components together. In this article, an overview of some adaptive modulation schemes for OFDM is presented. Then a new scheme consisting of a combination of adaptive modulation, OFDM, high-order space-frequency block codes (SFBC), and antenna selection is presented. The proposed scheme exploits the benefits of space–frequency block codes, OFDM, adaptive modulation and antenna selection to provide high-quality transmission for broadband wireless communications. The spectral efficiency advantage of the proposed system is examined. It is shown that antenna selection with adaptive modulation can greatly improve the performance of the conventional SFBC–OFDM systems.     

Multilevel space–time trellis coded cooperation with channel state information at transmitter

In this paper, the authors propose a system where a number of cooperating mobile nodes transmit information to a common destination node. Each cooperating node has a set of decoders to detect the information of other nodes and a set of encoders to further encode the decoded information as well as its own information using multilevel space–time trellis coding (MLSTTC) scheme. The coded information is mapped using multi‐resolution modulation partitioning to M‐ary quadrature amplitude modulation constellation. The mapped symbols are weighted based on the available channel state information at transmitting nodes. The weighting of transmitting symbols provides beamforming resulting in receive signal‐to‐noise ratio gain. The weighted symbols are sent to destination node through two transmit antennas. If the information of other nodes has been correctly decoded at the cooperating node, then the destination node receives the information of each node as many times as there are number of transmitting nodes, thus achieving full diversity order. A multistage Viterbi decoder is used at the destination node to extract information of each mobile node. The results indicate that the performance of proposed cooperative MLSTTC system is superior to non‐cooperative MLSTTC system. Copyright © 2016 John Wiley & Sons, Ltd.     

Adaptive modulation with constrained variable power for space–time coded MIMO systems

Practically, the maximum transmission power of transmission systems is limited. This power constraint causes the variable power control derived from no maximum power limitation suffering from performance degradation. In this paper, a constrained variable‐power adaptive M‐ary quadrature amplitude modulation scheme for MIMO systems with space–time coding is developed. Convex optimization is used to derive the switching thresholds of the instantaneous signal‐to‐noise ratio for power control (PC) and adaptive modulation under the constraints of maximum power, average power, and target BER. In the derivation of the relation between modulation and power, the exact BER expression of binary phase shift keying modulation and a tight bound for higher order quadrature amplitude modulation are used to make the PC scheme fulfill the target BER even at low signal‐to‐noise ratio where the previous PC schemes fail to meet the target BER. Numerical results show that the derived control scheme under the power constraints can obtain the spectrum efficiency and BER performance close to the previous control scheme without power limitation. Moreover, it can satisfy the requirements of power limitation and target BER and can effectively avoid the excessive power consumption of previous PC scheme in poor channel condition. Copyright © 2012 John Wiley & Sons, Ltd.     

Multiuser receiver scheme for full‐rate space–time coded CDMA system with imperfect estimation

By introducing a full‐rate space–time coding (STC) scheme, a synchronous CDMA (code division multiple access) system with full‐rate STC is given, and the corresponding uplink performance is investigated in Rayleigh fading channel with imperfect estimation. Considering that existing STC‐CDMA system has high decoding complexity, low‐complexity multiuser receiver schemes are developed for perfect and imperfect estimations, respectively. The schemes can make full use of the complex orthogonality of STC to reduce the high decoding complexity of the existing scheme, and have linear decoding complexity compared with the existing scheme with exponential decoding complexity. Moreover, the proposed schemes can achieve almost the same performance as the existing scheme. Compared with full‐diversity STC‐CDMA, the given full‐rate STC‐CDMA can achieve full data rate, low complexity, and partial diversity, and form efficient spatial interleaving. Thus, the concatenation of channel coding can effectively compensate for the performance loss due to partial diversity. Simulation results show that the full‐rate STC‐CDMA has lower bit error rate (BER) than full‐diversity STC‐CDMA systems under the same system throughput and concatenation of channel code. Moreover, the system BER with imperfect estimation are worse than that with perfect estimation due to the estimation error, which implies that the developed multiuser receiver schemes are valid and reasonable. Copyright © 2010 John Wiley & Sons, Ltd.     

Evolution from symbol‐level space–time coded MIMO to chip‐level space–time coded MIMO: a review

Space–time coded multiple‐input multiple‐output (MIMO) technology is an important technique that improves the performance of wireless communication systems significantly without consuming bandwidth resource. This paper first discusses the characteristics and limitations of traditional symbol‐level space–time coding schemes, which work largely on the basis of an assumption that signals are sent to a block‐fading channel. Therefore, the symbol‐level space–time coding schemes rely on symbol‐level signal processing. Taking advantage of orthogonal complementary codes, we propose a novel MIMO scheme, in this paper, based on chip‐level space–time coding that is different from the traditional symbol‐level space–time coding. With the help of space–time–frequency complementary coding and multicarrier modem, the proposed scheme is able to achieve multipath interference‐free and multiuser interference‐free communications with simple a correlator detector. The proposed chip‐level space–time coded MIMO works well even in a fast fading channel in addition to its flexibility to achieve diversity and multiplexing gains simultaneously in varying channel environments. Copyright © 2012 John Wiley & Sons, Ltd.     

适用于非常模信号的常数模新算法

常数模算法在对非常模信号进行均衡时,稳态均方误差无法收敛至零.对常数模算法中的代价函数进行修正,该代价函数能将非常模信号的多个幅度模值变换成单一幅度模值,从而使新算法的稳态均方误差为零.理论分析和仿真结果证明了新算法的优良性能.     

Progressive image transmission over differentially space‐time coded OFDM systems

In this paper, we consider progressive image transmission over differentially space‐time coded orthogonal frequency‐division multiplexing (OFDM) systems and treat the problem as one of optimal joint source‐channel coding (JSCC) in the form of unequal error protection (UEP), as necessitated by embedded source coding (e.g., SPIHT and JPEG 2000). We adopt a product channel code structure that is proven to provide powerful error protection and employ low‐complexity decision‐feedback decoding for differentially space‐time coded OFDM without assuming channel state information. For a given SNR, the BER performance of the differentially space‐time coded OFDM system is treated as the channel condition in the JSCC/UEP design via a fast product code optimization algorithm so that the end‐to‐end quality of reconstructed images is optimized in the average minimum MSE sense. Extensive image transmission experiments show that SNR/BER improvements can be translated into quality gains in reconstructed images. Moreover, compared to another non‐coherent detection algorithm, i.e., the iterative receiver based on expectation‐maximization algorithm for the space‐time coded OFDM systems, differentially space‐time coded OFDM systems suffer some quality loss in reconstructed images. With the efficiency and simplicity of decision‐feedback differential decoding, differentially space‐time coded OFDM is thus a feasible modulation scheme for applications such as wireless image over mobile devices (e.g., cell phones). Copyright © 2006 John Wiley & Sons, Ltd.     

Differential space–time modulation for DS‐CDMA systems

Differential space–time modulation (DSTM) schemes were recently proposed to fully exploit the transmit and receive antenna diversities without the need for channel state information. DSTM is attractive in fast flat fading channels since accurate channel estimation is difficult to achieve. In this paper, we propose a new modulation scheme to improve the performance of DS‐CDMA systems in fast time‐dispersive fading channels. This scheme is referred to as the differential space–time modulation for DS‐CDMA (DST‐CDMA) systems. The new modulation and demodulation schemes are especially studied for the fast fading down‐link transmission in DS‐CDMA systems employing multiple transmit antennas and one receive antenna. We present three demodulation schemes, referred to as the differential space–time Rake (DSTR) receiver, differential space–time deterministic (DSTD) receiver, and differential space–time deterministic de‐prefix (DSTDD) receiver, respectively. The DSTD receiver exploits the known information of the spreading sequences and their delayed paths deterministically besides the Rake‐type combination; consequently, it can outperform the DSTR receiver, which employs the Rake‐type combination only, especially for moderate‐to‐high SNR. The DSTDD receiver avoids the effect of intersymbol interference and hence can offer better performance than the DSTD receiver. Copyright © 2001 John Wiley & Sons, Ltd.     

Differential space–time network coding in MIMO two‐way relay channel network

This paper focuses on noncoherent detection scheme for multiple‐input multiple‐output two‐way relay channel network with two two‐antennas source nodes and one single‐antenna relay node. An orthogonal differential space–time network coding (ODSTNC) scheme based on relay detection and forward protocol is proposed. The proposed scheme combines space–time coding with network coding, and the differential modulation and detection are used in both multiple access stage and broadcast stage. The multiple‐symbol differential detection is employed at the relay. The maximum likelihood decision and its low‐complexity sphere decoding decision are given. The upper and lower bounds on the average symbol error probability for this system under differential binary phase shift keying (DBPSK) are derived, and a diversity order of 2 is confirmed to be achieved. The simulation results show that the ODSTNC scheme has good performance, and it is available for the applications of far distance signal transmission between two terminals where channel state information is unknown. Copyright © 2014 John Wiley & Sons, Ltd.     

Concatenation of space‐time block codes and turbo trellis coded modulation (ST‐TTCM) over Rician fading channels with imperfect phase

In this paper, the performance of space time‐turbo trellis coded modulation (ST‐TTCM) is evaluated over Rician and Rayleigh fading channels with imperfect phase. We modify Baum–Welch (BW) algorithm to estimate the fading and phase jitter parameters for multi‐antenna configurations. Thus, we assume that the channel parameters change slower than carrier frequency. We know that, at high data rate transmissions over wireless fading channels, space–time block codes (STBC) provide the maximal possible diversity advantage. Here, the combined effects of the amplitude and the phase of the received signal are considered, each one modelled by Rician and Tikhonov distributions, respectively. We investigate space time‐turbo trellis coded modulation (ST‐TTCM) for 8‐PSK for several Rician factor K and phase distortion factor η. Thus, our results reflect the degradations both due to the effects of the fading on the amplitude and phase noise of the received signal while the channel parameters are estimated by BW algorithm. Copyright © 2004 John Wiley & Sons, Ltd.     

Layered space–time block code for hybrid satellite–terrestrial broadcasting systems

Multiple‐input multiple‐output (MIMO) is a topic of high interest for the next generation of broadcasting systems. Even if they have begun to be proposed for the second generation of terrestrial digital TV, there are still gaps in the deployment of MIMO schemes in single‐frequency networks. This deployment becomes more critical when a hybrid satellite–terrestrial transmission is adopted because of the different aspects of the respective transmission links. In this paper, we propose to apply a layered space–time block code (LSTBC) for MIMO schemes in this hybrid transmission for next‐generation handheld (NGH) systems. The contribution of this paper is multi‐fold. First, we detail the land mobile satellite channel specifications describing the satellite link. Then, we propose to apply a MIMO scheme between the antennas of the satellite site and the terrestrial site. Then, we introduce the LSTBC scheme for NGH broadcasting systems. The proposed code is based on a layered construction designed to be efficient in shadowing regions. This efficiency is verified in a line‐of‐sight situation but also in low, moderate and deep shadow situations. The LSTBC scheme is then a very promising candidate for NGH systems with MIMO transmission. Copyright © 2012 John Wiley & Sons, Ltd.     

A robust adaptive weighted constant modulus algorithm for blind equalization of wireless communications systems under impulsive noise environment

A robust adaptive weighted constant modulus algorithm is proposed for blind equalization of wireless communication systems under impulsive noise environment. The influence of the impulsive noise is analyzed based on numerical analysis method. Then an adaptive weighted constant modulus algorithm is constructed to adaptively suppress impulsive noise. Theoretical analysis is provided to illustrate that the proposed algorithm has a robust equalization performance since the impulsive noise is adaptively suppressed. Moreover, the proposed algorithm has stable and quick convergence due to avoidance of large misadjuntment and adoption of large step size. Simulation results are presented to show the robust equalization performance and the fast convergence speed of the proposed algorithm under both impulsive noise and Gaussian noise environments.     

Baud-spaced constant modulus blind equalization via hybrid genetic algorithm and generalized pattern search optimization

The present paper deals with the formulation of the baud-spaced constant modulus blind equalization in the presence of Gaussian noise as an unconstrained optimization problem via the use of genetic algorithm and generalized pattern search (GPS) algorithm. Simulation results show that the proposed approach is more robust to the adopted initialization strategy and much more likely to outperform the classical constant modulus algorithm in terms of minimum-squared error, intersymbol interference and error vector magnitude quantities.     

含软方向判决的修正CMA盲均衡新算法

提出了一种新颖的盲均衡算法MCMA SDD,它一方面在代价函数中同时包含了幅度和相位的信息,另一方面,增加了并行的软方向判决(SDD)盲均衡算法,使得MCMA SDD算法无需载波跟踪环就能够纠正相位的失真;在低信噪比条件下具有较快的收敛速度和较低的稳态均方误差。     

An insight into space–time block codes using Hurwitz–Radon families of matrices

It is shown that for four-transmitter systems, a family of four-by-four unit-rate complex quasi-orthogonal space–time block codes, where each entry equals a symbol variable up to a change of sign and/or complex conjugation, can be generated from any two independent codes via elementary operations. The two independent groups of codes in the family generally have different properties of diversity, but the codes in each group have the same diversity provided that the differential symbol constellation is symmetric. It is also shown that for four-transmitter systems, an eight-by-four unit-rate complex linear dispersion space–time block code can be constructed by using Hurwitz–Radon families of matrices of size eight such that diversity three is guaranteed even when all symbols are independently selected from any given constellation. This code is so far the only known unit-rate linear dispersion code that has diversity no less than three for four transmitters under any given constellation.     

On the performance of two‐way relay channels using space–time codes

In this paper, we explore the advantages of network coding and space–time coding in improving the performance of two‐way‐relayed communications where two terminals absent of direct links exchange information through a single relay in between. Network coding allows embracing the interference from other terminals thereby turning it into a capacity boost. The application of space–time codes yields higher capacity by exploiting the spatial diversity. The joint performance of both techniques is studied in this paper. Specifically, we consider the class of decode‐and‐forward (DF) relaying strategy, evaluated in terms of symbol error rate using BPSK and QPSK modulations by both theoretical analysis and simulation. Based on our results, DF outperforms the amplify‐and‐decode and partial‐decode‐and‐forward protocols. Copyright © 2011 John Wiley & Sons, Ltd.     

On the performance of recursive space–frequency codes and iterative decoding in wideband OFDM‐MIMO systems: simulated and measured results

In this paper, we study the performance of a bandwidth efficient space–frequency turbo encoding scheme over wideband channels. Results are presented for simulated wideband MIMO channels consisting of two transmit antennas and up to two receive antennas. In addition, wideband channel measurements undertaken with practical multi‐element antenna structures at both the access point (AP) and mobile terminal (MT) are presented. Analysis is in terms of channel capacity, 10% channel outage capacity and space–frequency iterative decoding for an lEEE802.11a physical layer complaint modem. It is shown when operating with a spectral efficiency of 1.2 bits/s/Hz, the iterative decoded space–time codes comes within approximately 4.7 dB of 10% outage capacity over Rayleigh fading wideband channels with two transmit and two receive antennas. Over measured channels the iterative decoding scheme performs within 7.7 dB 10% of outage capacity. Losses due to channel state information estimation are also investigated. Copyright © 2004 John Wiley & Sons, Ltd.     

Interlevel‐correlated orthogonal space–time block codes based on the expanded signal constellation

Orthogonal space–time block codes provide full diversity with a very simple decoding scheme. However, they do not provide much coding gain. For a given space–time block code, we combine several component codes in conjunction with set partitioning of the expanded signal constellation according to the coding gain distance (CGD) criterion. By providing proper interlevel coding between adjacent blocks, we can design an orthogonal space–time block code with high rate, large coding gain, and low decoding complexity. The error performance of an example code is compared with some codes in computer simulation. These codes are compared based on the situation of the same transmission rate, space diversity order, and state complexity of decoding trellis. Copyright © 2010 John Wiley & Sons, Ltd.     

基于MIMO系统的MDCMA盲均衡算法

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.     

一种适用于强脉冲噪声下的对数型恒模盲均衡算法

针对脉冲噪声下恒模算法(Constant Modulus Algorithm,CMA)失败的问题,通过分析脉冲噪声的影响,提出了一种基于最小均方（Least Mean Square,LMS）准则的对数型恒模算法（Logarithmic-type CMA,LT-CMA）。LT-CMA利用对数函数的非线性变换特性自适应地抑制强脉冲噪声对误差函数的影响,并且利用l2-范数进行信号归一化处理以增强算法的稳健性。仿真结果表明,所提出的LT-CMA可以适应于高斯噪声环境和脉冲噪声环境;与经典自适应均衡算法相比,在收敛速度和稳健性两方面上,所提出的LT-CMA都有显著的提升。