短波扩频通信的Rake接收技术

短波天波传播存在严重的多径效应。在短波扩频通信中,采用Rake接收技术可利用多径信号的有效能量提高输出信噪比,改善短波通信质量。Rake接收的关键在于多径信号的识别和分离,论文针对短波信道传播特性,对短波扩频通信中的Rake接收技术进行了研究,设计了有效的多径分离和合并方法,仿真结果表明采用Rake接收技术后,误比特性能有了明显的改善。     

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。     

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。     

分集技术及Pake接收机误码率的仿真

Rake接收技术是CDMA蜂窝移动通信系统中的关键技术之一。分集的基本思想是将接收到的多径信号分离成不相关的多路信号,把这些多径信号的能量按一定的规则合并,使接收到的有用信号能量最大化,进而提高接收信号信噪比达到抗衰落的目的。文中以异步DS-CDMA系统为例,论述了分集技术并对Rake接收机的误码率进行了分析与仿真。     

扩频通信系统中Rake接收性能仿真研究

在扩频通信中,Rake接收是抵抗多径衰落的有效方法。本文首先介绍无线移动通信的信道特性,然后对Rake接收的基本原理和接收机结构进行详细描述,并对Rake接收性能进行了仿真比较。仿真结果表明,在多径信道条件下,Rake接收方式能很好的改善接收系统误码性能;采用GOLD序列扩频比m序列扩频方式时,Rake接收方法性能提高的更明显。     

多径超宽带接收机的研究和仿真

对多径IR-UWB信号的Rake接收技术原理和结构进行了详细分析。在此基础上仿真了不同Rake接收机的性能,包括部分Rake和选择性Rake,以及具有不同叉指的Rake接收机的性能。仿真结果表明在具有相同叉指条件下,选择性Rake接收机比部分Rake接收机的性能高出3dB。而在相同接收原理下,叉指越多,接收机的性能越好。而2路选择性Rake接收机和5路部分Rake接收机在较低信噪比的情况下,性能并无很大差别。     

短波低速数据传输关键技术

针对恶劣环境下的军事通信需求,设计了一个直扩-八进制相移键控（DS-8PSK）短波低速数据传输方案。在发送端,用多进制正交扩频来解决频带与信息传榆速率之间的矛盾,设计了一个复合扩频序列提高系统抗干扰性,在接收端,设计了一种改进型Rake接收机来实现分集接收,提高了系统抗多径衰落的能力。最后,用Matlab对数传系统的性能进行仿真验证,仿真结果验证了该方案的有效性。     

短波低速率数据传输研究

以第三代短波通信网络标准中的低速数据传输规程为基础,设计了一种低信噪比且存在多径衰落的信道中数据传输的调制解调方案.方案中利用相关搜索、FFT捕获的方法捕获信号,利用滑动相关完成位同步和信道估计,利用RAKE接收机抗多径衰落,并用DSP实现了数据的低误码率传输.     

W-CDMA系统中基于串并混合相关的多径搜索器的FPGA实现

在DS-CDMA(包括W-CDMA)系统中,Rake接收机可以分离出信号在时间上形成的多径,通过合并同一期望码在各接收路径上的信号,能有效地克服多径衰落对系统性能产生的严重影响.Rake接收机设计上的一个重要问题是,如何准确的搜索到具有足够大SIR的多径分量.本文主要研究W-CDMA系统中NodeB上的利用串并混合相关器进行多径搜索的原理及其FPGA实现.     

一种频率选择性衰落信道下的盲自适应去相关Rake接收机

多用户检测是DS－CDMA系统中的一项关键技术,而Rake接收是解决多径效应的一种有效方法,本文将基于Kalman滤波的多用户检测器与Rake接收相结合,提出了一种频率选择性衰落信道下的盲自适应去相关Rake接收机,研究结果表明,这种接收机具有较强的抑制多址干扰和克服“远－近”效应能力,并且能快速收敛。     

Pilot-Channel-Assisted Log-Likelihood-Ratio Selective Rake Combining for Low-Rate Ultra-Wideband Communications

For ultra-wideband (UWB) communications with signal energy dispersed by a large number of multipath components, the design of a Rake receiver that can provide a desirable output signal-to-noise ratio (SNR) using only a moderate number of fingers becomes an important issue. In this paper, we propose a pilot-channel-assisted log-likelihood-ratio selective combining (PCA-LLR-SC) scheme for UWB Rake receivers to be used in long-range low-rate UWB communications envisioned by the IEEE 802.15.4a PHY specification. The pilot and data channels are constructed using quadrature sinusoidal bursts that have the same Gaussian envelope. The system parameters are optimized through jointly minimizing the channel estimation mean square error and maximizing the receiver output SNR. Extensive simulations confirm that the proposed PCA-LLR-SC scheme is capable of providing robust low-rate UWB communications in fast-fading multipath channels and in the presence of multi-user interference.     

Low Complexity Rake Receivers in Ultra-Wideband Channels

One of the major issues for the design of ultra-wideband (UWB) receivers is the need to recover the signal energy dispersed over many multipath components, while keeping the receiver complexity low. To this aim we consider two schemes for reduced-complexity UWB Rake receivers, both of which combine a subset of the available resolved multipath components. The first method, called partial Rake (PRake), combines theirs/ arriving multipath components. The second is known as selective Rake (SRake) and combines the instantaneously strongest multipath components. We evaluate and compare the link performance of these Rake receivers in different UWB channels, whose models are based on extensive propagation measurements. We quantify the effect of the channel characteristics on the receiver performance, analyzing in particular the influence of small-scale fading statistics. We find that for dense channels the performance of the simpler PRake receiver is almost as good as that of the SRake receiver, even for a small number of fingers. In sparse channels, however, the SRake outperforms the PRake significantly. We also show that for a fixed transmitted energy there is an optimum transmission bandwidth     

一种改进的基于二维扩频的WCDMA非Rake接收机

针对WCDMA发射的扩频信号,不同于传统的Rake接收算法,本文采用变换域处理技术,提出了一种充分利用多径能量的二维扩频接收技术。分析了这种充分利用多径能量的二维扩频接收机的算法复杂度。通过计算机仿真,比较了传统的Rake接收算法、充分利用多径能量的二维扩频接收算法的误码率性能。结果表明,在Rake接收机难以精确分辨信道中的每条多径的情况下,使用充分利用多径能量的二维扩频接收机具有更好的误码率性能。     

Performance of Multicarrier CDMA Rake System over Rayleigh Fading Channel

Based on the theory of multicarrier (MC) technique and the Rake receiver, a multicarrier DS-CDMA Rake system is proposed, where a data sequence multiplied by a spreading sequence modulates multiple carriers. The receiver provides a Rake for each subcarrier, and the outputs of the Rakes are combined by a maximal-ratio combiner. The average probability of error of the system is derived from an uncorrelated subcarrier and frequency-selective fading channel model. The system performances are evaluated over Rayleigh fading channel with an exponential multipath intensity profile(MIP) and with a rectangular MIP, respectively, when multipath interference is present. It is found that this kind of model has larger superiority in an exponential MIP than in a rectangular MIP.     

P-order metric UWB receiver structures with superior performance

The generalized Gaussian probability density function is shown to better approximate the probability density function of the multiple access interference in ultra-wide bandwidth systems than the Gaussian approximation and the Laplacian density approximation. Two ultra-wide bandwidth receiver structures based on this new approximation using a p-order metric receiver decision statistic are investigated for the detection of time-hopping ultra-wide bandwidth wireless signals in multiple access interference channels. The first receiver outperforms both the conventional matched filter ultra-wide bandwidth receiver and the soft-limiting ultra-wide bandwidth receiver when only multiple access interference is present in UWB channels. The second new receiver with adaptive limiting threshold outperforms the conventional matched filter ultra-wide bandwidth receiver, the soft-limiting ultra-wide bandwidth receiver, and the adaptive threshold soft limiting ultra-wide bandwidth receiver in all multiple access interference-plus-noise environments. In multipath channels, a new Rake receiver based on the p-order metric receiver is proposed for signal detection. Mathematical analysis and numerical results show that this new Rake receiver can achieve larger signal-to-interference-plus-noise ratio than the standard matched filter Rake receiver when multipath components are resolvable in UWB channels.     

60 GHz芯片间无线互连系统中的Rake接收性能

在60 GHz芯片间无线互连信道中存在着多径干扰问题,采用Rake接收是提高系统性能的重要手段。针对脉冲超宽带( IR-UWB)的芯片间无线互连系统,分析了多径信道下Rake接收机的误码性能。在IEEE 802.15.3 c信道模型基础上,对不同分支数以及不同合并方案下的选择Rake ( S-Rake)和部分Rake(P-Rake)接收机误码性能进行了研究。仿真结果表明采用支路数为2的P-Rake在数据速率为10 Gb/s时仍具有良好的抗多径性能,这为芯片间无线互连系统的Rake接收方案提供了技术参考。     

超宽带Rake接收机的性能分析

超宽带信号经多径信道传播会产生严重的时间弥散，采用Rake接收是提高超宽带接收机性能的重要手段。文中首先介绍了加性高斯白噪声信道模型和IEEE802．15．3a标准信道模型。通过比较分析几种典型调制的超宽带冲激无线电信号的最佳接收机，推广到Rake接收机的性能分析。重点分析并仿真了不同信道、不同调制方式、不同判决方式、不同合并方式、不同速率的情况下Rake接收机的性能。     

Smart UWB System Based on STC and TR Techniques for BER Performance Enhancement and Interference Rejection

In this research, a novel smart UWB system is introduced. The proposed system is based on using an adaptive maximum ratio combining (MRC) Rake receiver. The proposed adaptive Rake receiver uses Genetic algorithm (GA) to adaptively select the delays of the fingers of the Rake receiver depending on the channel impulse response. It adaptively selects the delays that will allow the Rake receiver to capture most of the energy in the multipath components with minimum complexity. This adaptive Rake receiver is referred to as a GA Rake. The adaptive GA Rake is applied to a single-input single-output and space time coding (STC) multi-input single-output UWB systems. The performance of those systems using a GA Rake is compared to their performance when using a conventional MRC-Rake receiver and showed a great enhancement in performance with less receiver complexity. Also, in this paper, the smart UWB system using STC is modified by using the time reversal (TR) pre-coding technique. The modified system is referred to as a TR smart UWB system. This modification leads to more enhancements in performance and more reduction in receiver complexity over the smart UWB system. Moreover, this paper also shows the ability a TR smart UWB system in combating interference from other UWB systems.