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。     

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。     

无线移动信道中Rake接收机的多径分辨系数

本文研究了码分多址移动通信系统中RAKE接收机的特性在无线移动信道中一种新的衡量方式。目前已有的无线移动信道的衡量方式，只侧重于对无线电波传播过程的研究。如大尺寸环境路径损失，小尺寸环境多径衰落等；已有的RAKE接收机特性的衡量方式。即分辨多径个数和，只强调RAKE接收机能处理的多径对其性能的影响。这两种衡量方式已不能很好地衡量信道的特性对目前新型RAKE接收机的影响。本文提出了一种新的联合衡量无线信道及RAKE接收机特性的方式－多径分辨系数，它能很好地衡量无线移动信道对新型RAKE接收机的影响以及新型RAKE接收机算法的先进性。     

卷积码在60 GHz芯片间无线互连系统中的性能分析

针对60 GHz芯片间无线互连系统中信号幅度衰落及多径时延,导致信道产生突发性错误引起误码率增大的问题,从编码增益和译码能耗角度研究了该系统中卷积码的性能.根据60 GHz芯片间无线互连系统特点,分析了适用于此场景的CM7.2信道特性以及编码系统接收信噪比.结合信道编码理论,推导了卷积码的临界距离,得到了编码系统的能效衡量标准.在此理论研究的基础上,通过MATLAB对卷积码进行了蒙特卡洛数值仿真,得到了编码增益,进而分析了最大通信距离.通过QuartusⅡ对卷积码进行了电路能耗仿真,得到了编译码能耗,进而分析了临界距离.综合考虑卷积码的编码增益、译码能耗及有效通信距离,提出了可优先采用的编码方案.为60 GHz芯片间无线互连系统以及其他60 GHz近距离无线通信系统提供了纠错编码方面的技术参考.     

基于分形的多径衰落信道估计

该文研究了多径衰落的分形性质,提出了一种利用分形维数和小波重构来改进最小均方误差方法的新型多径衰落信道估计算法。该算法改进了衰落信道参数估计的准确度,并消除了判决方法的错误传递性。仿真结果表明该算法能较准确地估计出多径衰落信道的参数,显著提高快衰落条件下接收机的误码性能。     

CDMA系统中2-D RAKE接收机的性能研究

CDMA系统中,信号在无线信道中传输,由于多用户同时同频传输和多径衰落的存在,导致多址干扰(MAD和符号间干扰(ISI),使系统接收机的性能下降.空时接收机(2-D RAKE)能够有效地抑制MAI和对抗多径衰落,这里介绍了几种接收机的工作特点,并对各种空时接收机进行了详细的分析和比较.     

空时发射分集CDMA的多径分集接收

本文研究了采用STTD(space time transmit diversity)技术的随机序列扩频CDMA(code division multiple access),在频率选择性慢衰落信道中的单用户RAKE接收机在径数很大情况下的性能,并与没有采用STTD的CDMA系统的RAKE接收机的性能进行了比较.结果表明,STTD技术的采用,增强了多址干扰环境中RAKE接收机的抗衰落性能.本文也给出了由STTD所引入的码间干扰及多址干扰对RAKE接收机性能的影响.     

基于快速解扩滤波器优化的DS-CDMA多用户干扰抑制

该文提出了一种新的DS-CDMA信号检测方法,采用正交锚定的旁瓣抵消器结构和训练序列,基于最小滤波器输出能量准则,实现了解扩滤波器快速非自适应优化,并通过测定码匹配滤波器输出的信号干扰噪声比,有效控制了码匹配滤波器失配对滤波器优化的影响,从而实现了稳健的多用户联合信道干扰抑制。进一步采用RAKE技术,提高了Rayleigh衰落信道中接收机的性能。     

基于可靠性的低复杂度最小均方误差软干扰抵消 MIMO Turbo接收机

计算复杂度高是MIMO 最小均方误差软干扰抵消Turbo接收机面临的主要问题.一种方案提出在迭代检测阶段采用匹配滤波器取代最小均方误差滤波器,以避免矩阵求逆,但会导致性能显著下降.为了克服这一缺点,本文提出一种基于先验信息可靠性的低复杂度最小均方误差软干扰抵消Turbo接收机方案.该方案根据先验信息的可靠性动态选择最小均方误差和匹配滤波检测,从而在显著降低系统复杂度的同时使得引入的性能损失可以忽略不计.同时,通过合理设置选择门限,该方案还可以灵活地在复杂度和性能之间进行折中.     

RAKE接收机中功率测量滤波器的设计

本文分析了多径衰落信道的相关特性，计算了利用RAKE接收机实时测量信号功卓的误差。结果表明，采用RAKE接收机进行测量可以显著提高测量的准确性．同时，研究了各种因素对测量滤波器性能的影响。     

Performance of Super-Orthogonal Convolutional Coding for Ultra-Wideband Systems in Multipath and Multiuser Channels

This paper investigates the application of super-orthogonal convolutional codes (SOCC) to a direct-sequence based ultra- wideband (DS-UWB) system under a realistic environment including inter-symbol interference (ISI) and multiuser interference (MUI). The effect of MUI and ISI on the performance of SOCC is analyzed by using both maximum ratio combining (MRC) RAKE receiver and minimum mean-squared error (MMSE) RAKE receiver followed by matched filter receiver. The analysis shows that in the case of employing simple MRC-RAKE receiver, the performance of SOCC is ffected by MUI and ISI because of the short length of the spreading sequence. In order to combat MUI and ISI, a code-hopping scheme is proposed in conjunction with SOCC. The results show that SOCC scheme outperforms the higher-rate conventional convolutional coded scheme for multipath and multiple access channels. Furthermore, the use of MMSE-RAKE receiver to suppress interference is analyzed and the subsequent increase of the system capacity is observed.     

Downlink Specific Linear Equalization for Frequency Selective CDMA Cellular Systems

We derive and compare several linear equalizers for the CDMA downlink under frequency selective multipath conditions: minimum mean-square error (MMSE), zero-forcing (ZF), and RAKE. MMSE and ZF equalizers are designed based on perfect knowledge of the channel. The downlink specific structure involves first inverting the multipath channel to restore the synchronous multi-user signal transmitted from the base-station at the chip-rate, and then correlating with the product of the desired user's channel code times the base-station specific scrambling code once per symbol to decode the symbols. ZF equalization restores orthogonality of the Walsh-Hadamard channel codes on the downlink but often suffers from noise gain because certain channel conditions (no common zeros) are not met; MMSE restores orthogonality only approximately but avoids excessive noise gain. We compare MMSE and ZF to the traditional matched filter (also known as the RAKE receiver). Our formulation generalizes for the multi-channel case as might be derived from multiple antennas and/or over-sampling with respect to the chip-rate. The optimal symbol-level MMSE equalizer is derived and slightly out-performs the chip-level but at greater computational cost. An MMSE soft hand-off receiver is derived and simulated. Average BER for a class of multi-path channels is presented under varying operating conditions of single-cell and edge-of-cell, coded and un-coded BPSK data symbols, and uncoded 16-QAM. These simulations indicate large performance gains compared to the RAKE receiver, especially when the cell is fully loaded with users. Bit error rate (BER) performance for the chip-level equalizers is well predicted by approximate SINR expressions and a Gaussian interference assumption.     

Bit error probability of a matched filter in a Rayleigh fadingmultipath channel in the presence of interpath and intersymbolinterference

The exact bit error probability of a matched filter receiver in a known discrete Rayleigh fading multipath channel is determined for a binary antipodal system. The matched filter receiver or the RAKE is one form of a diversity receiver. Traditionally, both the interpath interference (IPI) and the intersymbol interference (ISI) caused by the non-ideal autocorrelation function of the bit waveform are neglected in the analysis of the RAKE. Previously, the exact matched filter bounds; which include IPI, were derived. This bound gives the performance of the matched filter if only one symbol is transmitted. In our analysis, a symbol sequence is transmitted instead of only one symbol. Thus, our analysis includes both IPI and ISI as well as the correlation between the paths, The analysis permits direct comparisons between different kinds of bit waveforms     

Comparison of MC-CDMA with DS-CDMA using frequency domain and time domain RAKE receivers

In this paper a multicarrier CDMA (MC-CDMA) system with a soft decision differential phase shift keying (DPSK) frequency domain RAKE receiver is described. We compare a MC-CDMA system with a direct sequence CDMA system using RAKE receivers. In contrast with previous MC-CDMA systems, guard intervals are not used and the carriers are spaced at the reciprocal of the bit rate, optimising the usage of the bandwidth. In this way a comparison can be made between the multicarrier CDMA system described and a direct sequence (DS-CDMA) system with the same bandwidth. The results presented are received bit error rates from Monte Carlo simulations. The simulations are conducted in a multipath channel with Rayleigh fading and 300 Hz Doppler spectrum with additive white Gaussian noise. It is shown that the multicarrier CDMA matched filter receiver performs favourably compared to the direct sequence CDMA matched filter receiver for 1 -path fading. For a single user at a receive bit error rate of 1×10^–3 in the 4-path fading channel the multicarrier RAKE receiver requires no knowledge of the channel delay spread and performs 3 dB worse than the DS-CDMA RAKE receiver simulated. The performance of the MC-CDMA RAKE receiver for a single user increases with increasing channel dispersion. The performance of the DS-CDMA RAKE receiver for multiple user is superior to that of the MC-CDMA RAKE receiver.     

Multiuser detection for DS-CDMA UWB in the home environment

We demonstrate the effectiveness of multiuser detection for an ultra-wideband (UWB) pulse based direct sequence spread spectrum system using code division multiple access. Extensive simulations were run using channel soundings of the 2-8 GHz band collected in a residential setting and characterized by a high level of multipath fragmentation. We show that the adaptive minimum mean square error (MMSE) multiuser detection (MUD) receivers are able to gather multipath energy and reject intersymbol and interchip interference for these channels to a much greater extent than RAKE receivers with 4 and 8 arms. We also demonstrate the adaptive MMSE is able to reject a narrowband IEEE 802.11a OFDM interferer, even for signal-to-interference ratio as severe as -30 dB. We show the adaptive MMSE exhibits only a 6 dB penalty relative to the single user case for the heavy multi-access interference (number of asynchronous users equal to spreading code length). The practical RAKE receivers were incapable of effectively rejecting either the strong narrowband interference or the heavily loaded wideband interference. Even more moderate levels of interference caused significant degradation in the performance of the practical RAKE receivers.     

MMSE interference suppression for direct-sequence spread-spectrumCDMA

We consider interference suppression for direct-sequence spread-spectrum code-division multiple-access (CDMA) systems using the minimum mean squared error (MMSE) performance criterion. The conventional matched filter receiver suffers from the near-far problem, and requires strict power control (typically involving feedback from receiver to transmitter) for acceptable performance. Multiuser detection schemes previously proposed mitigate the near-far problem, but are complex and require explicit knowledge or estimates of the interference parameters. In this paper, we present and analyze several new MMSE interference suppression schemes, which have the advantage of being near-far resistant (to varying degrees, depending on their complexity), and can be implemented adaptively when interference parameters are unknown and/or time-varying, Numerical results are provided that show that these schemes offer significant performance gains relative to the matched filter receiver. We conclude that MMSE detectors can alleviate the need for stringent power control. In CDMA systems, and may be a practical alternative to the matched filter receiver     

On the architecture and performance of an FFT-based spread-spectrumdownlink RAKE receiver

This paper describes a spread-spectrum downlink RAKE receiver that computes data detection in the frequency domain. We assume a pilot signal is transmitted with data signals for channel sounding. The pilot signal does not degrade the receiver bit error rate (BER) performance because the receiver estimates the pilot signal and subtracts the estimated pilot signal from the received signal before data detection. A spreading code matched filter, a channel matched filter, and a sounding receiver are implemented by fast Fourier transform (FFT)-based matched filtering and integrated in a unified architecture. Monte Carlo simulation is used to evaluate the receiver BER performance in both a static channel and a mobile radio channel. Simulation results show that the RAKE receiver performs well in both kinds of channels     

Multistage MMSE PIC Space–Time Receiver With Non-Mutually Exclusive Grouping

The arrival of new data services for wireless mobile communications requires an efficient use of the available bandwidth. Interference-limited cellular systems based on code-division multiple access (CDMA) can benefit from multiuser detection (MUD) and beamforming with antenna array to reduce multiple-access interference. Group-based techniques have been proposed to reduce the complexity of space-time MUD and have been shown to provide a performance-complexity tradeoff between matched filtering and full MUD. In this paper, the intergroup interference, which is a limiting factor in group-based systems, is reduced using multistage parallel interference cancellation after group-based minimum mean square error (MMSE) linear filtering. In addition, the extra resources that are available at the receiver are exploited by sharing users among groups. The proposed receiver is shown to converge, as the number of stages increases, to the full space-time MMSE linear MUD filter. The results show that the new approach provides bit error rate (BER) performance close to the full MUD receiver at a fraction of the complexity.     

Near Optimum and Highly Efficient Decision-Feedback Receivers for Direct Sequence Ultra-Wideband Radio

This paper investigates three decision- feedback receivers for Direct-Sequence Ultra-Wideband Radio (DS-UWB) based on two-channel BPSK modulation with ternary spreading code. A compact and insightful vector-matrix signal model is built up for receiver design under UWB channel dispersion over many consecutive symbols. First, we consider the design of a RAKE with Decision Feedback (RAKE-DF) receiver. Using the Gaussian approximation technique, we derive its analytic performance under no error propagation. It is shown that the RAKE-DF receiver suffers from a significant error floor due to the uncancelled pre-cursor ISI (or pre-ISI abbreviated). Next, we design the MMSE-DF receiver to achieve a better performance by suppressing the pre-ISI, too. However, the MMSE receiver requires costly matrix inversion. Then a new receiver is investigated as the third one, which is called the RAKE with Bi-Directional Decision Feedback (RAKE-BDDF) receiver, for efficiently canceling both the post-(cursor) ISI and pre-ISI at symbol rate. It cannot only attain the matched filter bound approximately, but also maintain a similar complexity as that of the RAKE-DF receiver. Simulation and semi-analytic BER curves are included for performance comparison of the three receivers in the presence of the CM2 and CM4 UWB channels.     

Experiments on pilot symbol-assisted coherent multistageinterference canceller for DS-CDMA mobile radio

A three-stage coherent multistage interference canceller (COMSIC) employing pilot symbol-assisted (PSA) channel estimation for replica generation of multiple access interference (MAI) is implemented and its performance in the presence of frequency selective multipath fading is experimentally evaluated by a multipath fading simulator. A fast transmission power control (TPC) method suitable for COMSIC is also proposed, in which the signal-to-interference plus background noise power ratio (SIR) at the matched filter (MF) based RAKE receiver is measured to achieve a short TPC delay and the target signal-to-interference ratio value is compensated by an outer loop so that the measured block error rate (BLER) is equal to the prescribed target value. The experimental results show that as expected the COMSIC satisfactorily reduces the MAI even when the number of active users is equal to the spreading factor in a multipath fading environment, and thus, improves the bit error rate (BER) performance in a multiuser environment. The results also show that the proposed fast TPC method with a two-slot delay associated with COMSIC works satisfactorily and the combination of COMSIC and fast TPC significantly decreases the transmission power of a mobile station (required transmission power of a mobile station with COMSIC at the average BER of 10^-3 is decreased by approximately 2.0 (3.0) dB compared with the MF-based RAKE receiver with (without) antenna diversity reception). This extends the cell coverage, battery life, and increases the system capacity in the reverse link