基于神经网络均衡器的小波包多载波扩频系统

在多径衰落信道下,本文提出了一种基于神经网络均衡器的小波包多载波扩频系统(Neural Network Equalizers Wavelet Packet Spread Spectrum,NNE-WPSS).本文利朋基于最小均方算法(Least Mean Square algorithm,LMS)的复径向基函数神经网络均衡器(Complex Radial Basis Function Network Equalizers,CRBF)来抑制由多径衰落信道引起的码间干扰(Inter-Symbol Interference,ISI)并且利用最大似然算法对解调后的码元进行检测.在多径衰落信道和白高斯噪声情况下,本文分析了基于神经网络均衡器的新型小波包多载波扩频系统的传输性能.仿真结果表明,本文所提出的基于神经网络均衡器的新型小波包多载波扩频系统的性能要优于传统的基于正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)多载波扩频系统;本文提出的复径向基函数神经网络均衡器(CRBF)的性能也优于迫零均衡器(Zero-Forcing Equalizer,ZFE).     

基于复小波包的MC-CDMA系统及上行链路性能分析

文章在分析多载波扩频码分多址的基础上，利用优化生成的复小波包及变换，研究了一种基于复小波包的多载波CDMA系统在多径瑞利衰落环境下的上行链路性能。仿真结果表明该系统要优于通常的MC-CDMA系统和基于实小波包变换的MC-CDMA系统，具有良好的抗衰落能力。并采用多天线分集接收技术进一步完善系统性能，从而增强了系统抗多径干扰和多址干扰的能力，且得到了更低的误码率。     

音频及部分频带干扰下多音调制直接序列扩频的抗干扰性能

多音调制直接序列扩频(multi-tone DSSS)中非正交子载波的频谱重叠会导致窄带干扰,同时对每个子载波产生不同程度影响,而并非若干相同单载波情形的叠加.通过对单用户及异步多用户MT系统在音频及部分频带干扰下相关检测判决统计量及平均误码率的理论计算,完成了干扰机理的定量分析,并通过数值仿真对结果进行验证.结果表明,与单载波直接序列扩频(SC-DSSS)、正交多载波直接序列扩频(正交MC-DSSS)相比,MT系统在同等接收机复杂度及相同频带利用率下具有更高的处理增益,可有效抑制内部子载波串扰,并对外部窄带干扰及多址干扰具有良好的抗干扰性能,是一种低复杂度、高可靠性宽带扩频体制.     

音频及部分频带干扰下多音调制直接序列扩频的顽健性分析

多音调制直接序列扩频（MI, multi-tone DSSS）中非正交子载波的频谱重叠会导致窄带干扰同时对每个子载波产生不同程度影响,而并非若干相同单载波情形的叠加。通过对单用户及异步多用户MT系统在音频及部分频带干扰下相关检测的判决统计量及平均误码率的理论计算,完成了干扰机理的定量分析,并通过数值仿真对结果进行验证。结果表明,与单载波直接序列扩频（SC-DSSS）、正交多载波直接序列扩频(正交MC-DSSS)相比,MT系统在同等接收机复杂度及相同频带利用率下具有更高的处理增益,可有效抑制内部子载波串扰,并对外部窄带干扰及多址干扰具有良好的抗干扰性能,是一种低复杂度、高可靠性的宽带扩频体制。     

基于小波包函数的正交MC-CDMA及其性能

本文将小波包变换理论应用于多载波码分多址(MC-CDMA)系统,提出一种基于小波包函数的正交调制方法.系统中,发端数据串并转换成若干子信道,每个子信道的数据进行直序扩频,不同子信道上的数据以chip调制不同的小波包函数作为基带传输波形.小波包函数的一系列优良性质,使系统能有效地抗多径干扰,抑制子信道串扰、多址干扰等.本文对系统在多径Rayleigh慢衰落信道中的性能,进行了理论分析和计算机仿真.结果表明,本系统比基于DFT的MC-CDMA有较大的性能改善.     

单音及窄带干扰下DSSS系统处理增益精确分析

针对直接序列扩频系统,理论推导出单音干扰和窄带干扰下系统处理增益的精确计算公式,并对所得公式进行了数值仿真。数值仿真结果表明,单音干扰对直接序列扩频系统的干扰能力与其相对于扩频系统的载波位置密切相关;窄带干扰对直接序列扩频系统的干扰能力与其相对于扩频系统的载波位置和干扰带宽密切相关。研究结果可为直接序列扩频系统的设计提供参考。     

多载波直接序列扩频码分多址系统的性能分析

本文将多载波发送信号技术应用于直接序列扩频码分多址系统中。发射机中直接扩频序列与数据序列相乘,然后调制多个载波;接收机对每个载波进行相关,相关器的输出用最大比值合并。这种发送信号具有很好的窄带干扰压缩性能。文中估计了存在部份带宽干扰下系统的性能,并与单载波直扩码分多址系统进行了比较。     

不同频率位置的窄带干扰对DSSS通信性能的影响分析

衡量窄带干扰抑制算法性能高低的一个主要标准是评估干扰处于最恶劣频率位置时的干扰输出平均功率的大小。在扩频序列周期很长且严格平衡的理想条件下,最恶劣干扰的频率位置为DSSS信号载波频率。基于典型的m序列DSSS系统,分析了处在不同频率位置的窄带干扰对DSSS系统的影响,所得结果与理想条件有所不同,这对于扩频系统的设计与应用具有指导意义。     

直扩系统对抗窄带干扰能力的影响因素分析

通过将得到的窄带干扰信号经过直接序列扩频接收系统的解扩解调模块后的形式,推导出了窄带干扰下直接序列扩频通信系统处理增益的表达式,从理论上分析系统对抗窄带干扰的特性,对影响其抗干扰能力的因素进行了多方面的分析。利用Matlab仿真得出其抗干扰能力不仅与扩频倍数有关,与窄带干扰的形式以及干扰相对载波的位置等因素相关的结论,为进一步研究和提高直接序列扩频系统对抗窄带干扰的能力打下基础。     

基于自适应小波包变换的直接序列扩频通信窄带干扰抑制技术

本文提出一种基于小波包变换的直接序列扩频通信窄带（单、多音）干扰抑制技术。该技术通过小波包分解将信号和干扰分离,然后再对滤波处理后的分解结果进行小波包合成,以此达到窄带干扰去除的目的。文中对这种方案的性能进行了分析并给出了仿真结果。结果表明,与传统的方法相比,它具有较好的误比特率性能,较快的干扰定位速度和简单的计算复杂度。是宽带系统中行之有效的窄带干扰抑制方法,尤其适合于窄带干扰以近似于比特率的速度快速变化的场合。     

A SCHEME OF M-ARY MULTI-CARRIER SPREAD SPECTRUM BASED ON WAVELET PACKET

A novel scheme of M-ary multi-carrier spread spectrum based on wavelet packet is proposed. Its performance is investigated for a multipath, slow Rayleigh fading channel. The performance advantages of the system over that based on DFT are demonstrated by both analytical and simulation methods.     

A scheme of m -ary multi-carrier spread spectrum based on wavelet packet

A novel scheme of M-ary multi-carrier spread spectrum based on wavelet packet is proposed. Its performance is investigated for a multipath, slow Rayleigh fading channel. The performance advantages of the system over that based on DFT are demonstrated by both analytical and simulation methods. Supported by the National Natural Science Foundation of China (No.60172029)     

LTE后续演进中基于频谱聚合的协同通信

大带宽无线传输有两个实现途径,一是设计频带更宽的单一系统,一是进行不同系统间的协同设计。前者是在同一种空口内采用基于多载波的频谱聚合,后者是在不同空口之间采用基于多载波并行传输的频谱聚合。通过多载波并行传输实现系统内和系统间频谱聚合,可以充分利用现有射频技术和器件,降低设备的研制和运营成本。而系统间的频谱聚合,特别是异构系统间的频谱聚合,除了可以扩展传输带宽的基本功能之外,还可以解决频分复用系统对非对称业务的支持以及时分双工保护带的利用问题,对运营商更具有商业上的现实意义。     

MC-CDMA调制在散射通信信道下的性能分析

为提高对流层散射通信系统容量和抗干扰能力,对散射信道下的多载波扩频方案进行研究.基于所建立的Rayleigh 分布对流层散射信道模型,分析了频域扩频多载波技术MC-CDMA的系统性能,对典型散射信道下的系统误码率进行了分析与仿真.结果表明:MC-CDMA可有效提升散射通信系统容量,单用户时系统误码率性能较好,随着用户数和散射信道多普勒频移的增大,系统误码率随之增大,需采用多址干扰控制和子载波干扰消除技术来改善系统误码率性能.     

Performance Analysis of Multiband Complex Wavelet Based MC-CDMA System with Space Diversity Combining in Rayleigh Fading Channel

In this paper, the multiband complex wavelet used as multi-carrier basis function is optimized. On the basis of analyzing the principle of multi-carrier code division multiple access (MC-CDMA), a new multiband complex wavelet based MC-CDMA (MBCW-MC-CDMA) system model is proposed, and space diversity combining (SDC) technique is employed to improve the system performance further. The uplink performance of proposed MBCW-MC-CDMA system with SDC technique is investigated in Rayleigh fading channel, and corresponding bit error rate (BER) analysis is given in detail. Without any cyclic prefix (CP), the system can avoid the decrease of spectrum efficiency and data rate of conventional MC-CDMA with CP. By comparison, our scheme outperforms real wavelet packet based MC-CDMA and slightly outperforms conventional MC-CDMA with CP via utilizing superior properties of the optimized multiband complex wavelet. Theoretical analysis and simulation result show that the application of SDC technique can improve the proposed system ability to combat spatial fading and various interferences effectively. Moreover, the proposed system based on SDC technique has superior BER performance over conventional DFT and SDC based MC-CDMA system and real wavelet packet and SDC based MC-CDMA system. Xiangbin Yu received the M.S degrees in Communication and Information Systems from Hohai University, Nanjing, China, in 2001; and his Ph.D. in Communication and Information Systems in 2004 from National Mobile Communications Research Laboratory at Southeast University, China. Now he is working as a Postdoctoral Researcher in Information and Communication Engineering Postdoctoral Research Station at Nanjing University of Aeronautics and Astronautics, Nanjing, China. His research interests include multi-carrier digital communication, space-time coding and digital signal processing in modern communications. Xiaodong Zhang received the M.S degrees from Nanjing University of Posts and Telecommunications, Nanjing, China, in 1998. In 2002, he received the Ph.D. degree from Southeast University, Nanjing, China. His research interests include contemporary signal processing and digital communications. DaZhuan Xu received the M.S degrees and Ph.D. in Communication and Information Systems from Nanjing University of Aeronautics and Astronautics in 1986 and 2001, respectively. He is now a full professor in Nanjing University of Aeronautics and Astronautics, Nanjing, China. Prof.Xu is a Senior Member of China Institute of Electronics (CIE). His research interests include digital communications, soft radio, coding theory, medical signal processing. Guangguo BI was graduated from Nanjing Institute of Technology, Nanjing, China, in 1960. He is now a professor in the Department of Radio Engineering of Southeast University, Nanjing, China. Prof.Bi is a fellow and a member of the board of Director of the China Institute of Communications, and a senior member of IEEE. His research interests include digital communications, personal communications network, spread spectrum communications, and intelligent information processing. He has published more than 200 papers in above areas.     

Cooperative Communication Based on Spectrum Aggregation in LTE Further Evolution

The implementation of wide band radio transmission may occur in two parallel ways:designing a new system with larger bandwidth,or constructing a cooperative system based on existing systems.The former is a spectrum aggregation scheme based on multi-carrier transmission within one system,while the latter fulfills spectrum aggregation based on multi-carrier transmission among systems.On the one hand,the advantage of the multi-carrier transmission scheme within a system and among systems is that the existing R...     

SAR图像小波包子带编码

针对合成孔径雷达(SAR)数据具有高动态范围、固有斑点噪声和纹理边缘处具有重要高频率成分等特性,将小波包子带编码方法应用于高分辨率SAR图像数据的压缩,根据各子带重要性不同采用不同量化方法,在小波包分解后引入跨频带的矢量量化方法。研究结果表明,此方案在图像分解、量化编码上均较传统方法有显著提高。     

A novel random wireless packet multiple access method using CDMA

Random packet CDMA, a novel packet-based multiple access scheme for connectionless, uncoordinated random channel access is proposed. Random packet CDMA, or RP-CDMA, utilizes a novel packet format which consists of a short header and a data portion. Each header is spread with a unique spreading code which is identical for all users and packets, while the data portion of each packet is spread by a randomly chosen spreading sequence. The receiver operates in two stages: header detection and data detection. For header detection a conventional spread spectrum receiver is sufficient. Headers are spread with a large enough processing gain to allow detection even in severe interference. The data portion is decoded with a sophisticated receiver, such as a multiuser detector, which allows for successful decoding of overlapping active packets. It is shown that the RP-CDMA system is detector capability limited and that it can significantly outperform spread ALOHA systems whose performance is limited by the channel collision mechanism. RP-CDMA also experiences a much smaller packet retransmission rate than conventional or spread ALOHA, and provides better spectral efficiencies.     

Eye-movement-controlled transform image coders

An image-coding scheme which combines transform coding with a human visual system (HVS) model is described. The system includes an eye tracker to pick up the point of regard of a single viewer. One can then utilize that the acuity of the HVS is less in the peripheral vision than in the central part of the visual field. A model of the decreasing acuity of the HVS, which can be applied to a wide class of transform coders is described. Such a coding system has large potential for data compression.In this paper, we have incorporated the model into four different transform coders, one from each of the main classes of transform coders. Two of the coders are block-based decomposition schemes, the discrete cosine transform-based JPEG coder and a lapped transform scheme. The two others are subband-based decomposition schemes, a wavelet based and a wavelet packet-based scheme.