Performance evaluation of MIMO-OFDM system based on time-switched transmit diversity

In this paper,a time-switched space-time(TSST) coded orthogonal frequency division multiplexing(OFDM) scheme against the time-varying channels is proposed.In the TSST-OFDM scheme,it is equipped with four transmit antennas,but only double of them are used for coding in every time slot.It is shown that the signal to inter-antenna interference ratio is a function of Doppler frequency in time-varying channels for a given space-time code.The analyses and simulations results validate that the proposed scheme not only gets timeswitched diversity and lower decoding complexity,but also suffers less time-varying impairments.Hence,it exhibits better performance than quasi-orthogonal space-time coded scheme.

Application of transmit diversity for improved robust watermarking

Many common multimedia signal processing, including cropping, filtering, and perceptual coding, make watermark signal fading-like modification. A scheme that applies transmit diversity technique to improve robustness of digital watermarking is presented. First, the scheme decomposes the original image using wavelet pyramid algorithm and chooses the middle-frequency band for transmission channel that the watermark will be embedded into. Then the watermark is pseudo-randomly permuted. The scheme makes use of space-time coding and differential detection technique to embed and extract watermark. The extracting process has access to neither the original image nor channel state information. Experimental results demonstrate that the scheme improves the performance of robust watermarking.

Closed-loop transmit diversity systems with hybrid antenna selection

The paper investigates closed-loop transmit diversity （CLTD） systems with antenna selection technique. The expected received signal-noise-ratio （RxSNR） of the proposed systems is analyzed and compared with CLTD systems. An algorithm is proposed for determining the number of increased transmit antennas in terms of a reduced RF chains without performance degradation. Since a feedback channel is bandwidth-limited, we present a method of quantizing transmit-weight vectors. Simulation results demonstrate advantage of the proposed systems with full and quantized feedback information. Quantized feedback has less effect on the proposed systems than CLTD systems.

Performance of MC-CDMA Systems with Orthogonal Transmit Diversity over Rayleigh Fading Channel

Transmit diversity has been recently proposed to reduce the effects of fading channels in various wireless applications. Orthogonal transmit diersity (OTD) is one of the standardized techniques in 3G systems. In this paper, we apply orthogonal transmit diversity technique to multicarrier CDMA systems. Andlysis and simulation results show that performance benefits can be achieved compared with conventioal MC-CDMA systems in multipath fading channels.

Transmit Diversity Scheme Design for Rectangular Pulse Shaping Based OTFS

This paper investigates the transmission scheme of the orthogonal time frequency space(OTFS)system with multiple antennas.Previous works have studied the multi-antenna transmitter diversity scheme with the ideal pulse shaping in OTFS systems assuming the wireless channels of two consecutive frames duration are invariant.However,the ideal pulse shaping can not be realized in practice and the channel varies rapidly in two consecutive frames in the high-speed mobility scenarios.To this end,we redesign the multi-antenna transmitter diversity scheme to ensure its practicability in the rectangular-pulsebased OTFS systems.At first,the information symbols of each antenna are divided into two half frames along the Doppler domain.Then,the guard symbols are carefully arranged to eliminate the interference between two half frames,and to ensure the equivalent channels of two half frames being identical.By considering the positions of the guard symbols,the transmission codeword is designed and a low complexity linear detection is proposed.Finally,simulation results validate that the bit error rate performance of the proposed scheme has the superiority over the existing works.

Achieving Directionality and Transmit Diversity via Integrating Beam Pattern Scanning (BPS) Antenna Arrays and OFDM

In this paper, we introduce a novel merger of antenna arrays with scanning beam patterns, and Orthogonal Frequency Division Multiplexing (OFDM) systems. Controlled time varying phase shifts are applied to the antenna array elements mounted at the base station with beam patterns directed toward the desired user. This creates a small beam pattern movement called Beam Pattern Scanning (BPS). In rich scattering environments BPS creates a time varying environment leading to time diversity exploitable at the receiver enhances its probability-of-error performance. Here, we apply OFDM signals to BPS antenna arrays, and we achieve: (1) directionality, which supports Space Division Multiple Access (SDMA);and (2) a time diversity gain, which leads to high performance. We discuss the structure of the base station antenna array and the OFDM receiver that exploits time diversity. We also introduce the merger of BPS and multi-carrier OFDM (MC-OFDM) systems. In MC-OFDM each bit is transmitted over all sub-carriers after serial to parallel conversion. BPS/ MC-OFDM receiver exploits both time diversity inherent in BPS, and frequency diversity inherent in MC-OFDM transmission technique. Simulation results show high Probability-of-error performance is achie- vable via BPS/OFDM and BPS/MC-OFDM schemes comparing to the traditional OFDM and MC-OFDM, respectively. Simulations also reveal that MC-OFDM system as well as its merger with BPS is capable of mitigating large Peak-to-Average Ratio (PAPR) problem in traditional OFDM system. In addition, performance simulations with coded OFDM (COFDM) and coded MC-OFDM (MC-COFDM) and their merger with BPS are studied.

An efficient training sequences strategy for channel estimation in OFDM systems with transmit diversity

This paper deals with channel estimation for orthogonal frequency-division multiplexing (OFDM) systems with transmit diversity. Space time coded OFDM systems, which can provide transmit diversity, require perfect channel estimation to improve communication quality. In actual OFDM systems, training sequences are usually used for channel estimation. The authors propose a training based channel estimation strategy suitable for space time coded OFDM systems. This novel strategy provides enhanced performance, high spectrum efficiency and relatively low computation complexity.

PERFORMANCE OF CLOSED LOOP TRANSMIT DIVERSITY IN A RAYLEIGH FADING CHANNEL

In this paper, the closed loop transmit diversity technology for the Wideband Code Division Multiple Access(WCDMA) systems is investigated in a multipath Rayleigh fading channel. The RAKE receiver model and the weighing vector algorithm are presented. The performance is theoretically analyzed in terms of the average maximal Signal-to-Noise Ratio(SNR) gain available over the Space-Time block coding based Transmit Diversity(STTD) technology. Theoretic analysis and simulation results show that the closed loop transmit diversity can provide a 3dB performance gain over the open loop scheme in a single path fading channel, while the performance gain decreases dramatically with the increasing inherent multipath diversity of the wireless channel.

Distributed Relay Diversity Systems for OFDM-Based Networks

In this paper, distributed relay diversity systems are analyzed, modeled and evaluated in an Orthogonal Frequency Division Multiplexing (OFDM) based networks. The investigated distributed relay diversity schemes extend the ideas of a single hop transmit antenna schemes such as Cyclic Delay Diversity (CDD), Space Time Transmit Diversity (STTD), transmit Coherent Combining (CC) and Selection Diversity (SD) to distributed diversity systems. In contrast to the classical single hop system, the antennas in the distributed systems belongs to distributed relays instead of being co-located at the transmitter. The distributed relay diversity methods considered in this paper: Relay CDD (RCDD), Relay Alamouti (i.e.STTD), Relay CC (RCC) and Relay SD (RSD) are compared to the traditional 1-hop system. Analytical expressions for the received Signal to Interference Noise Ratio (SINR) are derived and used in a dynamic multi-cell multi-user simulator. Results show considerable SINR gains for both Round Robin and Max-SINR schedulers. The SINR gains translate into substantial cell throughput gains, up to 200%, compared to 1-hop systems. Despite its low complexity, the RCDD scheme has similar performance to that of other more sophisticated 2-hop schemes such as Relay Alamouti and Relay Coherent Combining. Marginally better results are observed for the Relay Selection Diversity scheme.

THE TR-UWB RECEIVER BASED ON SPATIAL DIVERSITY

This paper presents a new Transmitted Reference (TR) Ultra-WideBand (UWB) receiver based on Spatial Diversity (SD), which employs Multi-Antenna Technology (MAT) to improve the performance of TR-UWB receiver. According to the amplitude of correlator output of every antenna branch, this paper analyzed the performances of the proposed TR-UWB receiver employing three different kinds of combination strategies, i.e., Maximum Ratio Combination (MRC), Equal Gain Combination (EGC), and Selective Combination (SC), which are different from conventional ones, and theoretically proved that the performance of EGC is better than MRC. Simulation results verify that when EGC is adopted and BER=10-3, increasing three antennas provides Signal to Noise Ratio (SNR) gain of about 3 dB in CM4 channel and SNR gain of about 2 dB in CM2 channel.

System Design and Signal Processing for Frequency Diverse Array Radar

Frequency diverse array(FDA)radar has been studied for more than 15 years and has attracted a lot of attention due to its potential advantages over the well-known phased array radar.The representative feature of FDA is range-angle-time-dependent transmit beampattern and its underlying properties are continuously revealed in the research.The formulation and exploitation of the transmit diversity with a frequency increment is the fundamental principle,which brings extra degrees-of-freedom(DOFs)in the transmit dimension.As the FDA radar carries additional information in range,it provides more flexibility in signal processing and also brings in new technical issues.This article overviews the state-of-the-art in FDA radar area and its applications,mainly based on the progress in our group.There are two main catalogs in FDA radar area,namely coherent FDA and FDA-MIMO(multiple-input multiple-output)radars.Potential applications including target parameter estimation,ambiguous clutter suppression,and deceptive jammer suppression are discussed.

2014—2020年血液成分制备技术的应用现状分析

目的 探讨2014—2020年血液成分制备技术的应用现状。方法 选取2014—2020年我国采供血机构执业比对平台血液中心16家,分析其具有旁路系统的血袋耗材、去除白细胞、血液辐照和血浆成分病原体灭活技术的应用情况。结果 16家血液中心中,11家(68.75%)采集全血使用旁路系统分流前端血液。14家(87.50%)开展红细胞成分血储存前去除白细胞,其中去白细胞悬浮红细胞的质控抽检结果显示,200 ml规格白细胞残留量平均值为(0.18~0.42)×106/袋,300 ml规格的平均值为(0.22~0.33)×10~6/袋,400 ml规格的平均值为(0.78~0.86)×106/袋。16家(100.00%)单采血小板均去除白细胞。12家(75.00%)进行红细胞成分血和血小板成分血发放前辐照,辐照技术使用率呈现较大差异。11家(68.75%)血浆成分血进行病原体灭活处理。结论 具有旁路系统的血袋分流前端血液、去除白细胞、辐照和病原体灭活等血液成分制备技术的使用率在不同血液中心呈现较大差异,应用血液成分制备技术预防输血传染病的空间有待进一步提升。

面向6G系统采用智能反射表面辅助的空时空间调制方案

针对现有的近场智能反射表面(IRS)辅助的空间调制(SM)方案频谱效率较低的问题,提出了面向6G系统采用IRS辅助的空时空间调制方案。首先,根据发射天线维度对SSB码字进行堆叠,构建堆叠SSB(SSSB)码字,并通过对SSSB码字基矩阵进行线性组合得到SM矩阵;然后针对SM矩阵设计近场IRS调制技术的信道状态激活方式,将SM矩阵与信道状态激活方式结合生成SSSB-IRS发送端信号矩阵;最后,推导了SSSB-IRS的最大似然译码公式和平均误码率的理论公式。由于采用了灵活的编码和天线激活机制,该方案比现有的典型近场IRS调制方案具有更高的频谱效率,并且可以提供二阶发射分集来对抗信道衰落。仿真结果表明:所提SSSB-IRS方案比现有的近场IRS调制技术方案具有更好的误比特率性能,在频谱效率为6.5b/(s·Hz)、误比特率达到10-5时,所提方案的信噪比增益比坐标交织正交设计的近场IRS方案提升了约4.3dB。

FDA-MIMO雷达噪声卷积式干扰抑制方法

基于数字射频存储器(digital radio frequency memory,DRFM)产生的噪声卷积灵巧干扰兼具压制式和欺骗式干扰的效果,严重降低了雷达系统的探测性能。为解决此问题,本文提出了一种采用频率分集阵(frequency diversity array,FDA)-多输入多输出(multiple-input-multiple-output,MIMO)雷达的噪声卷积灵巧干扰对抗方法。经由雷达发射信号和噪声信号卷积调制所得的干扰信号在距离-多普勒维与目标回波呈现不同的分布特性。据此,首先利用干扰信号在多普勒域的白噪声特性获取多普勒清晰区的干扰样本,然后在此基础上逐距离门挑选样本以获得干扰协方差矩阵,最后通过距离-角度二维匹配滤波器抑制距离不匹配的主瓣干扰信号。仿真试验验证了本文所提抗干扰方法的有效性。

基于区间算法的频控阵阵元位置误差分析

频控阵通过在各阵元的发射基频上引入一个微小的频率偏移,可以产生距离和角度相关的波束,这使得频控阵在信息和信号处理中更加灵活。但是,大多数文献在分析频控阵时,都假设阵元位置是理想而无误差的。而在实际情况中,阵元位置往往会存在制造误差,这必定会让实际发射波束的各项性能指标偏离理论设计的性能指标。而目前,几乎没有关于频控阵阵列位置误差分析的文献,因此迫切需要寻找一种对频控阵阵元位置误差进行分析的方法。提出一种基于区间分析算法的频控阵阵列位置误差分析方法,以分析各阵元位置误差对波束性能的影响。该方法首先假设各阵元位置误差在某个已知的区间,然后通过一系列数值计算得到误差对波束性能影响的上界和下界,最后通过仿真实验验证此方法的有效性。

MIMO技术在机载超短波通信中的应用

多输入多输出(Multiple Input Multiple Output,MIMO)技术的核心是在通信系统的收发2端通过多天线进行射频信号的接收和发送,通过多径信道的叠加增加通信系统容量,降低接收信噪比,提高传输速率和通信质量。结合机载超短波通信的特点,提出了一种双收双发技术,介绍了该技术的需求、信号处理设计、设备设计、系统设计以及实验验证。该技术不仅可以提高接收灵敏度,还可以利用双天线较好的覆盖性在一定程度上改善超短波通信的连续性和可靠性,对提高超短波通信质量具有重要意义。

一种频控阵抗主瓣欺骗干扰的方法

针对雷达发射信号时采用频控阵模式、接收信号时采用相控阵模式的抗主瓣欺骗干扰方法,研究了一种干扰置零方法,在频控阵发射方向图的主瓣对准需鉴别目标的位置时,使其他目标位于方向图的零陷处,解决了在使用频控阵进行目标鉴别时其他位置处目标若位于频控阵方向图较高旁瓣上时仍能对雷达形成干扰的问题。计算机仿真结果证明了所使用的干扰置零方法具有可行性和有效性。

Diversity order of decode-and-forward MIMO relaying with transmit antenna selection

This article analyzes the diversity order of several proposed schemes, where the transmit antenna selection （TAS） strategies are combined with low-complexity decode-and-forward （DF） protocols in the multiple-input multiple-output （MIMO） relaying scenario. Although antenna selection is a suboptimal form of beamforming, it enjoys the advantages of tractable optimization and low feedback overhead. Specifically, this article proposes schemes that combine TAS strategies with fixed decode-and-forward （FDF） and selection decode-and-forward （SDF） protocols. Following that, the asymptotic expressions of outage probabilities are derived and the diversity order of the proposed schemes analyzed. These kinds of combination of transmit antenna selection strategies and low-complexity decode-and-forward protocols can achieve partial diversity order in the MIMO relaying scenario. The numerical simulations verify the analysis.

CMA Performance in CDMA Transmit Diversity System

Plenty of work have been done on Space-Time processing in which multiple transmit / receive antennas are used in conjunction with coding to exploit both spatial diversity and time diversity. Constant Mode Algorithm （CMA） is an efficient blind adaptive Multi-User Detection （MUD） algorithm for CDMA systems. In this paper, we put forward a novel receiver, which combines CMA blind adaptive Multi-user Detection with STBC technique, and compare the performances of the system using different CM algorithms including SDCMA （ Steepest-Descent CMA）, Standard Linearity Confine CMA（SLCCMA） and Least Squares CMA（LSCMA）. Simulations have been done with multi-path Rayleigh channel.