频谱有效的差分空时编码CDMA系统

该文针对码分多址(Code-Division Multiple-Access,CDMA)系统提出了频谱有效的差分空时传输方案。考虑包含M个同步共道用户的多用户环境,每一用户配备双发射天线。若接收端配备N2个接收天线,该方案将采用解相关检测器和接收天线分集分离M个用户。基于平坦Rayleigh衰落信道,给出了非相干译码器,它可为每一共道用户提供2(N-1)的最小分集增益。与已有的差分空时编码CDMA系统相比,该方案具有两大优势:第一,仅需增加单个接收天线,该方案可在频谱效率提高1/3的条件下显著地改善系统性能;第二,译码仅具有线性复杂度。     

一种空时块编码OFDM系统中的自适应均衡算法

该文提出了一种适用于Alamouti块编码的多天线发射的OFDM系统的自适应均衡算法。该算法充分利用了Alamouti编码的正交特性和多发射天线的OFDM系统特点,通过灵活的变换对接收信号进行等价的表示;通过对П矩阵求逆的研究使块最小二乘递推算法(BRLS)中的2K2K的矩阵求逆分解为K个22矩阵的求逆,从而降低了运算量和接收机的复杂度。计算机仿真结果证明了该自适应均衡算法的有效性和快速收敛性。     

基于有限字符特性的空时OFDM系统决策反馈信道估计

该文提出了一种适用于空时编码正交频分复用(STC-OFDM)系统盲信道估计算法,利用信号的字符有限特性获取粗信道估计,进而利用映射星座先验知识,采用决策反馈方法得到信道精估计。充分利用了信号的先验知识,以较高的计算复杂度为代价,提高了盲信道估计精度,因此能较好地适用于具有慢时变频率选择性较强的信道,且子载波数不大的系统。与基于子空间盲信道估计算法比较验证了该算法性能。     

Two Schemes of Blind MMSE Multiuser Receiver for Space-Time Coded CDMA Systems

1　IntroductionIthasbeenshownthatthecapacityofwirelesscommunicationsystemscanbeincreaseddramatical lybyemployingmultipletransmittingandreceivingantennas.Space timecodinghasbeenpaidmoreat tentionrecentlybecauseitisaneffectivewaytoex ploitspatialandtemporaldiversity[1～2 ] .Despitealossincodingadvantage,space timeblockcodingcanofferthemaximumdiversitygainbasedononlythelinearprocessingatthereceiver[3～ 4] andhasbeenproposedtobeusedin 3Gsystems.InterferencesuppressionismorechallenginginCDMAsyste…     

A New Modified Gaussian Approximation Detector for Space-Time Bit-Interleaved Coded Modulation Schemes

To reduce the receiver complexity of the space-time bit-interleaved coded modulation (ST-BICM) scheme, this letter describes a turbo-type iterative structure consisting of a modified Gaussian approximation (MGA) detector and an a posteriori probability (APP) decoder. Utilizing the characteristics of the interleaving and the central limited theoretic, the MGA detector first assumes the superposition of the transmitted signals as a Gaussian random variable. Then, P most significant signal combinations are identified to calculate the log-likelihood ratio of each bit. Without any pre-process on the received signals, the proposed method is free of matrix inverse operation and can be applied in systems with more transmit antennas than receive antennas. Furthermore, the performance of the MGA approaches that of the optimal detection     

一种结合频率扩展编码的空时码MIMO OFDM系统性能及实现

该文利用MIMOOFDM系统中宽带信道的频率选择性衰落对不同窄带子载波上传输信号的不同影响,提出了一种结合频率扩展编码(FSC)的空时码设计．仿真结果表明,与其它的MIMOOFDM系统比较,该方法不仅可以有效地利用选择性信道内在的频率分集及保证系统频谱利用率,而且结构简单,容易实现．     

Alamouti-Based Space-Frequency Coding for OFDM

We investigate space-frequency block coding for OFDM systems with multiple transmit antennas, where coding is applied in the frequency domain (OFDM carriers) rather than in the time domain (OFDM symbols). In particular we consider Alamouti's code, which was shown to be the optimum block code for two transmit antennas and time domain coding. We show that the standard decoding algorithm results in significant performance degradation depending on the frequency-selective nature of the transmission channels, such that a low coherence bandwidth results in a huge degradation. The optimum decoding algorithm that alleviates this problem is the maximum-likelihood decoder for joint symbol detection. We present a performance analysis for the investigated space-frequency decoders in terms of the achievable BER results. Furthermore we compare space-time and space-frequency coding and discuss the respective advantages and drawbacks of the different decoding algorithms in terms of their complexity. It should be noted that for the space-time approach we introduce the so-called matched-filter receiver, which shows significantly lower complexity compared to the maximum-likelihood decoder known from literature. The HIPERMAN system serves as an example OFDM system for quantitative comparisons. Andreas A. Hutter received the Dipl.-Ing. (electrical engineering) and the Dr.-Ing. degree from Munich University of Technology (TUM) in 1997 and 2001, respectively. From 1997 to 2000 he was with the research and engineering department (FIZ) of BMW at Munich where he was project leader for the broadband wireless data initiative. In 2000 he was visiting researcher at Stanford University and in 2001 he joined the Swiss Center for Electronics and Microtechnology (CSEM) as senior R&D engineer. His research interests include the characterization of the propagation characteristics of mobile communication channels, signal-processing techniques for multiple antenna systems and the different aspects related to the design of ultra wideband systems. Andreas A. Hutter is co-recipient of the VTC-Fall 1999 best paper award. Selim Mekrazi received his M.Sc. in Digital Communications, Signal Processing and Telecommunications from Université de Rennes 1, Ecole Nationale Supérieure de Télécommunications de Bretagne (ENST Bretagne) and Ecole Supérieure d'Electricité (Sup'Elec), France, in 2003. In October 2003, he joined Eurecom Institue (Sophia-Antipolis, France) where he is currently pursuing his Ph.D in Electrical Engineering. His general interests lie in the areas of information theory, signal processing, digital communications, micro-electronics and public safety systems. Current researches focus on physical layer transmission techniques and implementation aspects for high-throughput, reconfigurable and rapidly deployable systems. Beza Negash Getu was born in Bahir Dar, Ethiopia, on May 27, 1975. From 1992 to 1997, he followed Addis Abeba University and he completed his B.Sc. degree in Electrical Engineering. Following his graduation, he was employed at Bahir Dar University as an assistant lecturer. From June 1998 to August 2000, he studied the Master of Science Program of Delft University of Technology, the Netherlands and obtained his M.Sc. degree in Electrical Engineering. In October 2000, he joined the Antennas and Propagation group of Prof. Dr. Techn. Jorgen Bach Andersen at the Center for Person Kommunikation (CPK) of Aalborg University, Denmark as a Ph.D. student. He worked in the field of Wireless Communications focusing on smart antennas and MIMO systems. The subject are encompasses communication theory, propagation and antenna research with the goal of optimizing link spectral efficiency and bit error rate. During 2002–2003, he spent six months in the Wireless Communications group at CSEM, Neuchatel, Switzerland, working on the same area. Beza N. Getu received the Ph.D. degree from Aalborg University in 2003. Fanny Platbrood received her Dipl.Eng. (M.Sc.EE) Degree in Electrical Engineering from the “Faculté Polytechnique” (Mons-Belgium) in 1996 after having made some research at the University of Rochester (NY-USA) and at the Swiss Federal Institute of Technology (EPFL). She worked as ASIC designer in the VLSI Design Department of Alcatel Bell, Belgium until end 1998. She was more particularly responsible for the ASIC development and testing for ADSL. In fall 1998, she joined the CSEM to work on research and development as an expert in wireless communications. She worked then on the PHY layer development for the WLAN standard HiperLAN Type-2 (H/2). From September 1999 until September 2001, she worked in the ESPRIT SLATS European project where she began first as workpackage leader of the GSM and WCDMA PHY software module development to become later the SLATS project manager for CSEM. In 2001, she was responsible for a UMTS concept study in a receiver structure. Up to end 2003, she worked on the IST SCOUT project on software architectures for re-configurable baseband systems and APIs definition. From 2002 to September 2004, she was responsible for the IST STRIKE project where she worked on Multiple Transmit Multiple Receive (MTMR) coding techniques applied to BFWA systems (HIPERMAN). From 2001 to 2004, she was the technical project manager of the IST PRODEMIS project. From 2003, she is task leader in the IST MAGNET project. She is presently project manager at CSEM and her areas of expertise are in ASIC design, digital and mobile communications. She published conference and magazine papers.     

Two-Stage Blind Detection of Differential Space-Time Block Coded Continuous Phase Modulation

We introduce a space-time (ST) continuous phase modulation (CPM) and its companion noncoherent receiver. Through careful selection of an underlying differential code, the defining characteristics of the CPM transmissions are effectively maintained. Using a set of interference suppressed statistics and taking advantage of the ST differential encoding, the receiver first performs low complexity block detection. Channel estimates are then obtained at a rate notably higher than the CPM symbol rate, enabling a second-stage coherent sequence detector to refine the initial decisions. Simulation results for two CPM formats, with two and four transmit antennas, validate the proposed ST-CPM scheme.     

Decision-Feedback Receiver for Quasi-Orthogonal Space-Time Coded OFDM Using Correlative Coding Over Fast Fading Channels

Orthogonal frequency division multiplexing (OFDM) is robust against frequency selective fading, but it is very vulnerable to time selective fading. In quasi-orthogonal space-time coded OFDM (ST-OFDM) systems, channel variations cause not only inter-carrier interference among different subcarriers in one OFDM block, but also inter-transmit-antenna interference (ITAI). When applied in fast fading channels, common ST-ODFM receivers usually suffer from an irreducible error floor. In this letter, we apply frequency-domain correlative coding combined with a modified decision-feedback detection scheme to effectively suppress the error floor of quasi-orthogonal ST-OFDM over fast fading channels. The effectiveness of the proposed scheme in mitigating the effects of channel time selectivity is demonstrated through comparison with existing schemes such as zero-forcing, two-stage zero-forcing, and sequential decision feedback estimation     

Cross-Layer Multi-Packet Reception Based Medium Access Control and Resource Allocation for Space-Time Coded MIMO/OFDM

In this paper, a cross-layer design framework for multi-input multi-output (MIMO)/orthogonal frequency division multiplexing (OFDM) based wireless local area networks (WLANs) is proposed. In contrast to conventional systems where the medium access control (MAC) and physical (PHY) layers are separately optimized, our proposed methodology jointly designs a multi-packet reception (MPR) based protocol with adaptive resource allocation. Specifically, a realistic collision model is employed by taking into consideration the PHY layer parameters such as channel information, space-time coded beamforming and multiuser detection, as well as sub-carrier, bit, and power allocation. The allocation problem is formulated, so as to maximize the system throughput, subject to the constraints from both the MAC and PHY layers. These constraints depend on the results of access contention, data packets? length, users? spatial correlation and the quality of channel feedback information. An iterative algorithm is then provided to obtain the optimal solution. Simulation results will show that our proposed approach achieves significant improvement in system performance such as average throughput and packet delay, compared with conventional schemes where cross-layer design and optimization is not used.     

一种适用于SF-OFDM系统的波束形成技术

在正交频分复用（OFDM）系统中使用空频传输分集是未来宽带无线通信中的重要技术。由于在各个终端采用多天线进行收发，导致使用空频-OFDM（SF-OFDM）传输分集的系统受到增强的共信道干扰（CCI）。本文提出了一种适用于SF-OFDM系统的波束形成方案，该方案能有效的抑制共信道干扰。在该方案中，基于盲转向的波束形成被应用于SF-OFDM系统中。分析和仿真结果表明，该方案具有良好的共信道干扰抑制能力。此外，该方案能够利用不同波达角（DOA）信号间的相对时延来增强系统性能。     

差错控制编码差分酉空时调制系统迭代检测法

针对采用差错控制编码的差分酉空时调制系统,在平坦及频率选择性衰落瑞利信道下提出了一种迭代检测法。差分酉空时调制可视为递归卷积码,使用差错控制编码后的差分酉空时调制可视为一种串行级联码。提出了一种差分酉空时调制的软输出后验概率译码器以及迭代检测法,以获得附加的编码增益。仿真结果表明,在平坦及频率选择性衰落瑞利信道下,所提方案均可得到优异的系统性能。     

Space-Time Coded Beamforming for DS CDMA Downlink

1　Introduction　 In 3G mobile system, Code Division Multiple Access(CDMA) is a promising multiple access techniques. It iswell know that BeamFormin ( BF), Space Time Coding(STC) and Multiuser Detection(MUD) techniques in CDMAsystem can effectively resist Multi Path Interference (MPI),MAI and near far effects. So the system capacity will be im proved greatly by employing these techniques[1,2,8]. In Ref.[3] introduces Water Filling(WF) theory into STC to assignth…     

On Trellis Coded Noncoherent Space-Time Modulation

Unitary space-time modulation (USTM) is well-tailored for noncoherent space-time modulation. Trellis coded USTM (TC-USTM) can obtain significant coding gains over uncoded USTM for the noncoherent block fading channel. Conventional TC-USTM schemes expand the signal set of uncoded USTM by a factor of two. In this letter, we propose a new TC-USTM scheme in which the size of USTM set is not limited to be just double for uncoded USTM. However, in TC-USTM schemes, because signals of the same trellis branch are transmitted over the same fading coefficients, one trellis branch can only obtain one temporal diversity. In this letter, we also propose a new trellis coded noncoherent space-time modulation scheme by interleaving space-time signals. The proposed scheme can enlarge temporal diversity at the price of increased complexity and delay. Simulation results demonstrate the excellent error performances of codes found by computer searches for both schemes.     

FEC编码的空间调制方案综述

空间调制系统作为多输入多输出技术(Multi-input Multi-output,MIMO)的一种,优点是在减少多天线方案的复杂度和成本的同时,始终能够保证较高的数据传输速率。在每个信道使用间隙下,仅使用一根选定的天线(称为活动天线)发送数据信号,并且活动天线空间位置作为数据传输的附加维度。然而,空间调制技术的分析和设计依然面临许多挑战,编码空间调制方案就是其中一种。针对编码空间调制方案,重点论述了Trellis码、BMST码、LDPC码以及多元LDPC码等信道编码空间调制方案,并且分析了这几种方案的特点以及它们在MIMO中的应用。     

Space-Time Coded Systems using Continuous Phase Modulation

We develop space-time trellis coded (STC) schemes using continuous-phase modulation (CPM). We employ the Rimoldi model of CPM to create a decomposed model of STC-CPM. The decomposition separates the coding from the modulation. The space-time encoding and the inherent CPM encoding is combined into a single trellis encoder on the ring of integers modulo-. This is followed by a bank of memoryless modulators. The model allows the search for good space-time codes to take into account the inherent encoding of the modulation.     

CPM编码调制发展前景

连续相位调制（CPM）技术是一类恒包络的数字调制技术,CPM信号的恒包络这一特性使它们对于非线性信道和衰落信道具有很强的抵抗性．特别适用于卫星通信和移动无线通信信道。与PSK调制方式相比,CPM调制系统不仅能够提供较高的频谱效率,而且具有一定的编码增益,这是因为接收器可以利用相位成型滤波器引入的记忆特性。CPM调制系统可以分解为一个连续相位编码器（CPE）和一个无记忆调制器（MM）的级联,因此出现了多种卷积码与CPM结合的调制方案,例如串行级联连续相位调制、基于环的串行级联连续相位调制、实用的连续相位调制、卷积编码器与扩展信道编码器的串行级联,等等。其中,基于环的串行级联连续相位调制具有很好的性能,在交织增益、自由距离、误码平层和收敛门限可能成为未来连续相位编码调制系统的发展方向。     

Iterative Decoding of Orthogonal Space-Time Coded CPM Systems

We present an iterative decoding/demodulation technique for an orthogonal space-time coded continuous-phase modulation (OST-CPM) system. A low-complexity soft input and soft output (SISO) demodulator is developed based on the bidirectional soft output Viterbi algorithm (BSOVA) for the multiple antennas CPM systems. By taking advantage of the orthogonal structure, the complexity of extrinsic information extraction can be significantly reduced at each iteration.Shengli Fu received the B.S. and M.S. degree in telecommunication engineering from Beijing University of Posts and Telecommunications, Beijing, China, in 1994 and 1997, respectively. In 2000, he enrolled at the Wright State University, Dayton, OH, where he received the M.S. degree in Computer Engineering. He currently pursues his Ph.D. degree in the Department of Electrical and Computer Engineering at the University of Delaware.His research interests include information and coding theory, MIMO wireless communication systems, and acoustic and visual signal processing.Genyuan Wang received B.Sc and MS. degrees in Mathematics from the Shanxi Normal University, Xian, China, in 1985 and 1988, respectively, and his Ph.D. degree in Electrical Engineering from Xidian University, Xian China, in 1998.From July, 1988 to September 1994, he worked at Shanxi Normal University as an Assistant Professor and then an Associate Professor. From September 1994 to May 1998, he worked at Xidian University as a research assistant. Currently, he is Post-Doctoral Fellow at Department of Electrical and Computer Engineering, University of Delaware. His research interests are radar imaging and radar signal processing, adaptive filter, OFDM system, channel equalization and space-time coding.Xiang-Gen Xia (M97,S00) received his B.S. degree in mathematics from Nanjing Normal University, Nanjing, China, and his M.S. degree in mathematics from Nankai University, Tianjin, China, and his Ph.D. degree in Electrical Engineering from the University of Southern California, Los Angeles, in 1983, 1986, and 1992, respectively.He was a Senior/Research Staff Member at Hughes Research Laboratories, Malibu, California, during 1995--1996. In September 1996, he joined the Department of Electrical and Computer Engineering, University of Delaware, Newark, Delaware, where he is a Professor. He was a Visiting Professor at the Chinese University of Hong Kong during 2002–2003. Before 1995, he held visiting positions in a few institutions. His current research interests include space-time coding, MIMO and OFDM systems, and SAR and ISAR imaging. Dr. Xia has over 100 refereed journal articles published, and 6 U.S. patents awarded. He is the author of the book Modulated Coding for Intersymbol Interference Channels (New York, Marcel Dekker, 2000).Dr. Xia received the National Science Foundation (NSF) Faculty Early Career Development (CAREER) Program Award in 1997, the Office of Naval Research (ONR) Young Investigator Award in 1998, and the Outstanding Overseas Young Investigator Award from the National Nature Science Foundation of China in 2001. He also received the Outstanding Junior Faculty Award of the Engineering School of the University of Delaware in 2001. He is currently an Associate Editor of the IEEE Transactions on Mobile Computing, the IEEE Signal Processing Letters, the IEEE Transactions on Signal Processing, the International Journal of Signal Processing, and the EURASIP Journal of Applied Signal Processing. He was a guest editor of Space-Time Coding and Its Applications in the EURASIP Journal of Applied Signal Processing in 2002. He is also a Member of the Signal Processing for Communications Technical Committee and the Sensor Array and Multichannel (SAM) Technical Committee in the IEEE Signal Processing Society.     

Serially Concatenated Space-Time Coded Continuous Phase Modulated Signals

We investigate the detection of space time codes (STC) modulated using continuous phase modulation (CPM), in quasi-static fading channels. A symbol-by-symbol iterative detector with an optimum front-end is derived, and its reduced-complexity implementation is considered. Also, we have introduced several full-rank STC-CPM systems, constructed by combining full-diversity STCs with simple, widely-used CPM schemes, and introducing a small frequency offset. According to the simulation results, the bit error rate (BER) performance of the detector for quasi-static fading is around 1 dB from the case without fading. Furthermore, a comparison of the performance of the proposed detector with results from previous work on STC-CPM showed an improvement in the range of 2-3 dB. Moreover, the detector is robust to the errors in estimating the channel state information (CSI), which is a desirable feature for practical implementation.