PPM调制的超宽带差分接收机

提出一种PPM-DIFF-UWB调制方式及其接收机,该接收机采用三条具有不同延时特性的相关支路实现PPM-UWB信号的差分接收,提供了一种关于PPM调制的超宽带信号的低复杂度的接收方式,可用于实现在密集多径信道下的多径分集接收,且不需要复杂的信道估计以及发送额外的参考信号.理论分析和实验仿真结果表明该接收机的误码性能优于常规的PPM-TR-UWB接收机.     

一种根据扰码特性来提高多径搜索性能的算法

在CDMA系统中，为了对抗多径衰落，使用Rake接收机对接收信号进行处理。在发射端，通过扰码对信号进行加扰处理。Rake接收机对接收的信号进行解扰，相干积分处理，根据功率时堑函数PDP值来计算多径的相位信息。在信噪比比较差的情况下，搜索出来的多径可能是噪声径，这对Rake接收机解调的性能有一定的影响。介绍一种根据扰码自相关特性，来判断搜索出多径是否为噪声径的方法，提高Rake接收机的性能。     

多径信道下辅助矢量接收机性能分析

研究了在直接序列码分多址(DS-CDMA)系统中,多径环境下一种基于RAKE结构的辅助矢量接收机。该接收机在收集多径信号的同时抑制系统中的多址干扰,从收集的多径信号中估计出信道响应矢量,并利用估计出的信道响应矢量对多径信号进行合并,最后进行判决。仿真结果表明,辅助矢量接收机能够有效地去除DS-CDMA系统中的多址干扰,同时具备良好的抗多径衰落性能,误码性能明显优于RAKE接收机。     

基于MMSE信道估计准则的TH—PPM UWB通信系统多径性能分析

基于MMSE估计准则对TH-PPM UWB多径环境下的系统接收性能进行了分析。首先介绍了TH—UWB信道的传播特征,对IEEE UWB信道模型CM1做了仿真,并分析了MMSE多径信道估计特性,在此基础上对幅值最强两条多径信号的多径延时和多径幅值误差的标准方差进行了仿真,结果表明信号越强延时估计误差越小。最后对采用MMSE估计接收和参数已知接收两种方式下系统的性能进行了仿真,结果表明采用MMSE信道估计的Rake接收机性能可以达到信道参数完全已知的Rake接收机性能。     

一种适合WCDMA上行链路的多径搜索算法

RAKE接收机可以有效的对通过多径信道的扩频信号进行分集接收,所以在WCDMA等无线通信系统里得到了广泛的应用。在RAKE接收机进行最大比合并之前,需要对多径进行搜索,多径搜索非常关键,直接关系到接收机的性能。在本文将介绍一种多径搜索的方法,该方法就是根据干扰信号的统计特性,动态的设定一个门限值,以此为参考进行相应的多径选择。通过该方法可以有效地提高RAKE接收机的性能。     

移动通信中的分集接收技术和Rake接收机

由于移动环境的复杂性,无线信号在发送传输和接收过程中有很明显的衰落现象。通过分集接收技术在移动通信特别是第三代移动通信中的应用,介绍了传统Rake接收机和WCDMA中采用的典型Rake接收机的工作原理和结构框图。多径信号的每路信号都可能含有可以利用的信息,所以接收机可以通过接收多路信号来改善信噪比。Rake接收机算法就是通过多个相关接收器接收多径信号中各路信号,并把他们合并在一起,以此为原理基础的。     

抑制DS-UWB多径干扰的RAKE-MLSE接收机

为达到高数据速率，直接序列超宽带（DS-UWB）系统通常使用低扩频增益，在密集多径信道中这可能会增强多径干扰（MPI）从而降低系统的性能。文中将最大序列似然估计（MLSE）引入DS-UWB接收机结构中来抑制MPI。推导了DS-UWB信号的MLSE公式，作为MLSE算法的近似提出采用RAKE-MLSE接收机结构来降低计算复杂度。使用Viterbi算法实现了该接收机，并在IEEE802．15．3a建议的室内信道中对一个DS-UWB系统进行仿真。仿真结果表明该接收机较一般RAKE接收机性能有很大提高。     

GPS信号被延时后对定位影响的仿真分析

根据GPS接收通道跟踪环对信号实施跟踪解调的原理,分析了经过人为与自然延时的信号被接收机跟踪解调的必要条件。再根据GPS定位原理和定位求解方程,对被人为与自然延时的信号进入接收机进行定位解算后,信号延时值变化与接收机定位偏差之间的关系进行了仿真分析。     

一种针对转发式欺骗干扰信号的负延时补偿方法

针对卫星导航转发式欺骗干扰中转发信号存在负延时需求而工程上又无法实现的问题,提出了一种负延时补偿方法。该方法根据预设欺骗位置,通过转发式欺骗干扰延时算法,获得各卫星信号通道所需转发延时量;然后基于接收机钟差最小化原则选取最优的延时修正量添加到所有通道的转发信号中。理论分析和仿真结果表明,该方法不影响接收机的定位结果,消除了负延时无法实现的问题对转发式欺骗干扰的限制。     

一种加权的UWB—ATR接收机的性能研究

采用分段加权合并的思想,提出了一种新的加权的UWB-ATR接收机,根据接收信号中的多径分布给予各段不同权重,有效压制了噪声乘积项,权重系数由MMSE估计得出.经过理论分析和IEEE CM3多径信道仿真,结果表明该接收机的误码率性能优于一般ATR接收机.     

A receiver of simple structure for antenna array CDMA systems

In code division multiple access systems, the two-dimensional (2-D) RAKE structure had been proposed using multiple antennas to increase the capacity. It consists of multiple fingers of a beamformer and a correlator. In this paper, we consider a simpler receiver structure. We only use one finger, which consists of one pair of spatial and temporal filters to combine signals. It is shown that the performance of the receiver system is comparable with that of the 2-D RAKE receiver. Furthermore, it is observed that the proposed receiver and the 2-D RAKE receiver have limited near-far resistance by the generation of the space domain due to antenna arrays     

A two-dimensional RAKE receiver architecture with an FFT-based matched filtering

This work proposes a two-dimensional (2-D) RAKE receiver, which is a spatial-temporal matched filter implemented in the frequency domain. To form a beam pattern, we calculate the spatial frequency spectra of received signals on the antenna array using fast Fourier transform (FFT). After FFT beamforming, a bank of FFT-based matched filters is used to perform code matching. Afterward, the code-matched signals are summed up with maximal-ratio combining through a spatial-temporal channel-matched filter implemented in the frequency domain. This 2-D RAKE receiver includes a channel sounder that is used to estimate the spatial and temporal channel impulse response parameters, such as delays, directions of arrivals, and complex gains of multipath components. Monte Carlo simulations have been used to evaluate the receiver bit-error rate performance in both static channel and mobile radio channel environments. Simulation results show that the RAKE receiver performs well in both kinds of channels.     

Conditions and Performance of Ideal RAKE Reception for Ultra-Wideband Signals in Lognormal Fading Channels

In this paper, the conditions and performance of ideal RAKE reception for time hopping Ultra-Wideband (UWB) investigated. Owing to the complex propagation phenomena and specific structure of UWB signals, new problems relevant to the operation of RAKE receivers arise. This motivates us to reconsider the conditions under which a RAKE receiver can work effectively with negligible interference between fingers. Key findings are that the conditions not only relate to the property of time hopping codes, but also modulation methods. An analytical technique is introduced to derive explicit expressions of RAKE performance for various combining methods for a lognormal fading channel. Numerical results show that RAKE reception can largely improve the performance, and equal gain combining has comparable performance to maximum ratio combining.     

采用多径干扰抵消的RAKE接收机

针对多径衰落信道,该文提出了一种基于导频的串行多径干扰抵消技术(SMPIC)和相应的RAKE接收结构,进行了理论分析和计算机仿真,并与常规的RAKE接收进行了比较,结果表明,采用此技术可改善 RAKE接收性能,且结构简单、易于实现。     

CCK demodulation via symbol decision feedback equalizer

A symbol decision feedback equalization (DFE) technique is developed for demodulating complementary code keying (CCK) signals. The efficacy of the proposed receiver is demonstrated on the physical layer (PHY) specified in the IEEE 802.11b wireless local area network (WLAN) standard. Packet error rate (PER) performance is compared with that of the conventional RAKE receiver. The proposed receiver structure and its low complexity variations demonstrate significant performance advantages over the RAKE receiver, especially in severe multipath channels. While a large delay spread can limit the performance of two low-complexity variations discussed here, performance of the optimal symbol DFE receiver is not limited by delay spread as long as the channel signal-to-noise ratio (SNR) is sufficiently high.     

一种基于带通RAKE接收机的多载波解调方法

ＣＤＭＡ２０００采用多载波和直接序列扩频两种方式来达到提供宽带数据业务的目的。针对ＣＤＭＡ２０００前向信道的三载波调制方式,提出了一种基于带通ＲＡＫＥ接收机的多载波解调方法。这种方法避开了设计多比特的基带数字滤波器,从而大大降低了实现的复杂度。文章首先分析了三载波的调制结构。根据ＲＡＫＥ接收机的原理,推导出相应的带通ＲＡＫＥ接收机模型并给出解调结构,最后,用ＳＰＷ软件对此模型进行仿真并给出了传真结     

二维定向瑞克接收机实现方案比较研究

为了充分利用瑞克(RAKE)接收机的多径能量利用效果和智能天线(SA)的定向收发作用,研究了RAKE接收机和智能天线的联合使用,提出了基于智能天线的定向二维(2D)RAKE接收机模型,给出了定向2D-RAKE接收机分别在射频、中频和基带的实现框图、工作原理和输出信号表达式,并对它们的性能以及工程实现做了分析讨论。指出基带定向二维RAKE接收机由于可以在基带上通过幅度加权来实现信号的定向收发,其优点是可以利用目前比较成熟的基带信号处理技术,但是由于不能利用相干解调作用来抑制多径干扰(MPI)和多用户干扰(MAI),存在噪声放大问题;射频定向二维RAKE接收机的信噪比增益最大,但工程实现难度较大;中频定向二维RAKE接收机则具有较高的性价比。     

Performance of a Multicarrier CDMA System with Rayleigh Fading Multipath Channels

This paper examines the performance of a multicarrier CDMA system in a Rayleigh fading channel without a RAKE receiver. Since the multicarrier technique is a diversity reception technique used in the frequency domain, the signal is transmitted at different frequency bands and undergoes different fading. The superimposed signal of the multipath components after going through the mobile channel will be processed by an Fourier Transform to enter the frequency domain, where the time delays in various paths are converted to the phase shifts in the compound signal. In this paper, we use sounding bits to extract the characteristics of the mobile channel and to partly remove the multipath effect. From the simulation, it is found that the multicarrier technique is simpler than the technique used in the single carrier system with a RAKE receiver while producing a better performance than that of the RAKE receiver.     

An adaptive multiuser receiver for CDMA systems

A new real-time, digital adaptive multiuser receiver structure is proposed for the uplink in a mobile communications system employing code division multiple access (CDMA). The receiver efficiently implements the decorrelating detector of Lupas and Verdu (1989) and can be adapted to incorporate decision feedback to further improve the detector performance. While the basic receiver design is presented for synchronous CDMA over AWGN channels, experimental evaluation of the receiver for the asynchronous case verifies its robustness for cases when the relative user delays are small compared to the symbol duration as in microcellular scenarios. An efficient decorrelating RAKE combiner for frequency-selective multipath channels is also proposed and analyzed. Performance evaluation of the detector via computer simulation scenarios is conducted in support of analytical results to substantiate its potential for real-time operation     

A multipath interference cancellation technique for WCDMA downlink receivers

In this paper, we present a simple interference cancellation technique for the downlink of wideband code‐division multiple‐access (WCDMA) systems in multipath environment. With the same knowledge required by a RAKE receiver, the present method acts as an equalizer and cancels the interfering multipath signals from the received signal to retrieve the orthogonality property of the received signal. The present receiver has a simple structure and it has significant performance gain against the RAKE receiver. In addition, the noise enhancement is negligible when there is a line of sight path or the channel power delay profile has an exponential decaying form. Copyright © 2006 John Wiley & Sons, Ltd.