基于导频符号辅助的天线选择分集方案

在大多数散射环境下,天线分集是减小多径效应的一种实际、有效的技术,在分析Alamouti两发一收发射分集方案的基础上,介绍了一种基于导频符号辅助的发射天线选择分集方案.该方案通过引入反馈和导频符号辅助技术,在发射端对两个发射天线进行天线选择,给出的仿真结果表明,运用分集技术可大大改善无线通信系统的性能,该方案性能优于Alamouti两发一收发射分集方案,并且发送功率要低于Alamouti两发一收方案.     

A Novel Wavelet Packet Division Multiplexing Based on Maximum Likelihood Algorithm and Optimum Pilot Symbol Assisted Modulation for Rayleigh Fading Channels

Wavelet packet division multiplexing (WPDM) is a high-capacity, flexible, and robust multiple-signal transmission technique. In this paper, a novel WPDM system based on optimum pilot symbol assisted modulation (OPSAM) and a maximum likelihood (ML) algorithm is studied for Rayleigh fading channels. The ML detecting algorithm and the new discrete wavelet packet transform structure, which is based on pilot symbol assisted modulation (PSAM) using a least mean squares algorithm, are two novel aspects of the presented system. An expression for the bit error rate of the WPDM scheme on quadrature phase-shift keying (QPSK) is derived in the presence of flat fading and Gaussian noise. It is demonstrated by simulation results that the OPSAM WPDM scheme can provide greater immunity to flat fading channels and Gaussian noise than the OPSAM orthogonal frequency division multiplexing scheme, the differential QPSK WPDM scheme, and the normal PSAM WPDM scheme.     

Adaptive Minimum Symbol Error Rate Beamforming Assisted Detection for Quadrature Amplitude Modulation

We consider beamforming assisted detection for multiple antenna aided multiuser systems that employ the bandwidth efficient quadrature amplitude modulation scheme. A minimum symbol error rate (MSER) design is proposed for the beamforming assisted receiver, and it is shown that this MSER design provides significant performance enhancement, in terms of achievable symbol error rate, over the standard minimum mean square error (MMSE) design. A sample-by-sample adaptive algorithm, referred to as the least symbol error rate, is derived for adaptive implementation of the MSER beamforming solution. The proposed adaptive MSER scheme is evaluated in simulation using Rayleigh fading channels, in comparison with the adaptive MMSE benchmarker.     

Pilot Symbol Assisted Hybrid Detection for OFDM‐Based Spatial Multiplexing Systems

In this paper, we provide a new detection scheme for a pilot symbol assisted interference nulling and cancellation operation to reduce unexpected effects owing to parallel transmission in orthogonal frequency division multiplexing (OFDM)‐based spatial multiplexing systems. We have shown that the investigated OFDM vertical Bell laboratories layered space time (VBLAST) detection based on hybrid processing performs better than ordinary OFDM‐VBLAST detections based on serial processing and parallel processing, respectively.     

多径衰落信道中导引符号辅助的二维扩频相干解调的性能分析

在多径衰落信道中,本文分析了导引辅助的二维扩频相干解调的误码率性能.提出了信道的时频二维相关区域的概念,给出了信道时频二维信道相关特性的计算方法.结果表明,分析与仿真的误码率相近;当二维扩频的扩频增益对应的时频二维区域大于信道的时频二维相关区域时,再增大扩频增益会导致误码率性能变差.     

多径衰落信道中导引辅助二维扩频的导引功率优化

在多径衰落信道中,针对BPSK调制的广义二维扩频系统,该文分析了导引符号与数据符号的功率比对导引辅助相干解调的误码率性能的影响,在系统总的发射功率一定的条件下,优化了导引符号与数据符号的功率比。结果表明,分析结果与仿真结果相吻合,导引符号与数据符号功率比的最优值是由多径信道的信噪比、多普勒频移、多径时延、低通滤波器的特性等因素决定的。     

经符号成形的数字信号调制制式识别

提出了一种对经过符号成形的调制信号进行识别的新算法,利用特征参数提取与决策树分类器相结合对8种常用数字信号进行调制识别。首先详细介绍了符号成形对调制信号及信号瞬时参数提取的影响,然后选取特征参数通过决策树分类器进行识别分类,最后进行了计算机仿真,仿真表明该算法能够有效识别经符号成形的数字信号,且与无符号成形的数字信号调制识别方法相比。有着更好的识别性能。     

Data-Aided Symbol Timing Estimation for Linear Modulation

Timing phase estimation (TPE) plays the key role in feedforward (FF) symbol timing.For reasons of performance often data-aided (DA) methods are preferred. But frequently, they turn out to be critical with respect to theimplementation and the spectrum efficiency (due to the required overhead).This paper presents three DA TPE methods for quadrature pulse amplitude modulation (PAM). In spite of their very low complexity, these methods closelyapproach the theoretical limit for timing estimation with respect to the estimation variance, even at low SNR. This enables power efficient transmission.Further, they employ a CAZAC (constant amplitude, zero auto-correlation)sequence as training-sequence (TS), or a sequence with similar correlationproperties. Since such sequences are suited for almost all DA receiver tasks, a high spectrum efficiency can be obtained by the use of a single TS. A generalization of the proposed methods for DA TPE withrespect to the choice of the TS is also shown. The presented methods can be applied to noncoherent receivers. They are suited for high data-rate applications, since they can work with an oversampling factor of 2.     

基于脉宽调制技术的位同步

提出了一种用于数字通信的位同步方法,它是基于脉宽调制技术的间接插入导频法.推导了脉宽调制处理后信号的功率谱密度.试验结果表明,脉宽调制处理后的信号的功率谱密度中含有码元同步信号,基于脉宽调制技术的位同步方法不仅适合于双极性信号传输,还适合于单极性信号传输.该技术具有简洁、可靠的特点.     

MIMO-OFDM系统信道估计中的最优导频设计

推导了MIMO-OFDM系统最优频域导频序列设计准则,推广传统两天线正交导频设计法到了任意天线时的设计,提出了一种导频信号峰均比为1,能达到正交导频时信道估计均方误差MSE下界的频域导频序列设计方法。并用仿真评估分析所提方法与传统设计方法在不同序列长度和天线数目情况下的性能差异,仿真结果表明采用这里所采用的正交导频序列设计方法可以减少序列的长度,提高系统的性能。     

一种结合空时编码的导频辅助信道估计方法

多输入多输出-正交频分复用(MIMO-OFDM)作为一种高速率无线通信的有效方式,其信道估计技术具有非常重要的位置。将OFDM技术与基于发射分集的空时格码相结合,构造了一个基于空时格码的OFDM模型。基于MIMO-OFDM系统的导频设计准则及特性,提出了一种空时编码OFDM系统中基于导频的辅助信道估计方法。仿真实验结果表明信道估计的性能接近理想信道情况下的性能。     

一种利用导频实现OFDM符号同步的算法

对于多载波系统,载波频率的偏移会导致子信道之间产生干扰。而对于要求子载波保持严格正交的OFDM系统,载波频率的偏移所带来的影响会更加严重。因此,同步在OFDM系统中是一个十分重要的问题。主要从理论和仿真2个角度分析OFDM系统中的符号同步问题,并给出一种利用导频实现符号同步的算法。     

Optimum Pulse Shaping in Digital Angle Modulation

This paper presents a technique for optimizing the baseband pulse shapes in digital angle modulated signals to minimize the fraction of out-of-band power for a given channel bandwidth. As examples of practical interest, the optimization is carried out for channel bandwidths up to three times the bit rate and for the range of modulation indices usually encountered in digital transmission. Results for MSK-type signals appear as a special case.     

导频符号辅助干扰删除多用户检测器的研究

根据宽带码分多址（ ＷＣＤＭＡ） 系统的特点,提出并分析了一种导频符号辅助干扰删除多用户检测器（ＰＳＡＩＣ）,分析结果表明,该方法充分利用了ＷＣＤＭＡ系统中的帧结构,在不增加物理信道的情况下,实现接收信号的相干解调,并与多址干扰删除器相连,可以大大提高系统的性能,增加系统的容量,当干扰删除器的级数为２ 时,其性能有较大的改善,复杂度也不高     

基于软件无线电的GMSK调制解调位同步算法

研究改进了一种基于软件无线电的GMSK调制解调全数字位同步算法.改进的位同步算法只需要简单的平方和累加运算,算法结构简单,能降低对硬件的要求,适合实现可重复软加载全数字解调.实验结果表明,此算法比数字锁相环方法实现起来更简单、更方便,同步效果也较好.     

一种无线光通信中脉冲位置调制的符号同步方法

脉冲位置调制(pulse position modulation,PPM)是无线光通信的经典调制方式之一.符号同步是实现PPM正确解调的关键技术.在分析帧同步码型和长度要求的基础上,设计了一种PPM帧结构,提出了利用帧同步来实现PPM符号同步的方法.论述了其工作原理,并分析了其同步性能.结果表明该方法建立时间短,同步概率高,并具有自动调整功能,可实现性强.     

Optimum Joint Slot and Symbol Synchronization for the Optical PPM Channel

A maximum-likelihood statistic for pulse-position-modulation (PPM) symbol synchronization in the absence of slot synchronization is derived for the direct-direction optical channel from noisy observations of randomly modulated data, observed through a windowMsymbols wide. Two approximations to the optimal rule that are easier to implement are also derived and their performance analyzed by computer simulations. It is seen that the performance of one approximation, which is quite easy to implement, is almost identical to the more complex approximation.     

Optimum Pulse Shapes for Pulse-Amplitude Modulation Data Transmission Using Vestigial Sideband Modulation

When designing pulse-amplitude modulation (PAM) systems for use over bandpass channels having restricted bandwidth, one may be led to use single-sideband (SSB) or vestigial sideband (VSB) transmission in order to maximize transmission rate. Carefully shaped pulses must be used to minimize degradation due to intersymbol interference (isi). In this paper VSB pulses are derived that have no inherent isi, and in addition have maximum immunity in a mean-squared-error (MSE) sense to timing and carrier phase errors. The results here generalize on those of Franks who treated the SSB case. The optimum VSB pulses are shown to be identical to those of Franks at the band edges, and to have vestigial roll-off characteristics of a similar discontinuous nature. It is also shown that one may allocate available bandwidth to the vestigial roll-off band band and Nyquist roll-off band in any way desired. The final performance for the optimum pulse depends only on the total bandwidth used. These results are shown to apply as well to a system employing a matched filter. The case of random timing and phase errors is also considered, and optimum pulses are again found. Several mathematical properties of the optimal pulses are given physical justification and geometric insight through error ellipses, and optimal signal shapes are plotted for various cases of special interest.     

一种数字音频广播系统的正交频分复用调制符号生成器的FPGA设计

介绍了基于数字音频广播系统的正交频分复用调制符号的生成原理和参数要求,采用改进的基二蝶形单元结构和改进的地址生成单元,在FPGA上利用较少的硬件资源完成了一种对768个子载波模式的调制符号生成系统的硬件设计.该设计具有可配置性、相对较少硬件资源、较高精度的特点,最终采用Altera公司的StratixⅡ系列FPGA来综合实现,经验证功能正确,精度较高,最高工作频率为88.79MHz,占用逻辑单元数仅6553个.     

酉空时调制系统中基于多符号差分检测的软检测器

该文设计了一种适用于差分酉空时调制体制的低复杂度软检测算法。该算法基于多符号差分检测,为软判决译码模块提供编码比特的对数似然比信息。仿真表明,在通常容许的误码范围内,采用所提出的软检测算法构建的差分酉空时调制系统比原硬判决系统节省2～4dB的信号功率,并解除了基于单符号差分检测的软检测算法在快衰落信道下的错误平层。