WCDMA系统中导频符号辅助的空时二维RAKE接收机

针对WCDMA上行链路的时分导频和复扩频方式的特点 ,提出了一种适用于WCDMA系统的线性自适应空时二维RAKE接收机 .利用导频符号进行信道估计 ,并作为空间波束成型器的参考信号 .理论分析和在多用户时变频率选择性衰落信道下的仿真研究表明 ,对导频信号的充分利用可以降低空时二维接收机的实现复杂度 ,所提的接收机能明显提高接收机的输出信干噪比 ,降低误码率     

DS—CDMA通信中的一种2D-Rake接收机

Rake接收机在3G系统中已被广泛使用,实际应用证明它能够有效对抗移动无线信道中的多径衰落。传统Rake接收机有其时域一维处理的局限性,为获得更好的系统性能,本文在分析空时信道模型的基础上提出一种新的空时2D-Rake接收机算法,它将波束形成技术与Rake相结合。这种波束形成算法能够在干扰方向上完全陷零,其权重仅与阵列天线的导向矢量有关,与接收信号无关。最后简要分析了所提出的2D-Rake接收机的性能。仿真结果表明,这种空时2D-Rake接收机与传统Rake接收机相比,具有较好的性能,而且该算法对噪声具有鲁棒性。     

WCDMA中联合迭代信道估计与解码的研究

首先介绍了基于WCDMA系统中RAKE接收机的信道估计方法，然后将Turbo原理引入信道估计，针对WCDMA系统提出两种迭代信道的估计方法。通过使用RAKE接收机或解码之后的软信息来改善整个WCDMA系统的性能，对WCDMA系统中联合运用信道估计与解码技术进行了研究。由于联合信道估计与解码技术可以利用通信系统不同模块之间的“软信息”交换，从而有效地提高了信道估计准确程度和解码器的性能。仿真结果表明，利用解码之后的软信息来修正信道估计的方法较传统的RAKE接收机中的信道估计方法性能有较大改善，在误码率为10^-2左右时，提高大约1dB。     

信道估计误差与估计长度关系的频域分析

本文提出了在已知最大多普勒频移情况下采用平均法估计信道时,信道估计误差与平均区间长度关系的频域分析方法及其完整的解析数学表达式,并给出了据此计算出在不同的移动速度情况下的最佳信道估计长度解析公式,将其应用于Rake接收机中,能大大提高接收机的性能.对于移动速度变化很大的第三代移动通信中连续导频体制的Rake接收机的性能提高有较大的意义及较高的实用性.     

WCDMA系统中空时RAKE接收机的性能

分析了在WCDMA系统的基站中采用含自适应阵列天线的空时RAKE接收机的性能。在建立了WCDMA信道信号模型的基础上,分析了噪声和干扰的统计特性,给出了输出误码率的表达式,并对不同角度扩展情况下的数值仿真结果进行了讨论。     

扩谱系统信道估计优化

本文提出一种易于集成实现的扩谱系统优化接收机信道估计方案，并以WCDMA系统下行链路为例进行了详细的理论推导与分析。给出了其在移动信道环境下的仿真结果。结果表明，改进方案与理想性能仅差约零点几分贝，比一般情形改进至少2dB。     

WCDMA系统STTD发送分集RAKE接收机的性能分析

第三代移动通信系统WCDMA的发送分集方式有两种：开环模式和闭环模式,其中开环模式采用基于空间－时间分组编码的STTD发送分集方式。本文针对WCDMA系统中的STTD发送方式,给出了利用公共导频信道进行信道估计,实现相干RAKE接收的模型算法、性能分析及仿真结果。仿真表明,在总发送比特能量相同的条件下,尤其是在接收机缓慢移动的情况下,采用STTD发送分集的RAKE接收性能优于单天线发送时的RAKE接收机的性能,而在高速移动情况下,STTD发送方式不能提供优于单天线发送时的接收性能。     

WCDMA下行信道RAKE接收机的性能分析

在第三代移动通信WCDMA的最新通信标准^[1]中,下行信道在保留时分复用导频符号的同时,新增了公共导频信道.本文针对WCDMA这一最新改变,给出了利用公共导频信道进行信道估计,实现相干RAKE接收的模型算法、性能分析及仿真结果.仿真表明,利用公共导频信道的RAKE接收机性能明显优于时分插入导频符号辅助的RAKE接收机的性能,尤其在高速及变速运动情况下,而且具有信道估计算法简单、信道跟踪实时性强的特点.     

相关衰落信道上WCDMA系统的安全性能分析

对多输入多输出（MIMO）相关衰落信道上宽带码分多址接入（WCDMA）的安全性能进行评估,一种省时高效的解决方案是理论分析法。推导了相关 Nakagami 衰落信道上采用空时分组码和二维瑞克接收机（2D-Rake）的 WCDMA 系统的非零安全容量概率和安全中断概率的精确解析表达式。利用上述表达式,可以快速地评估收发天线数、天线相关系数、Nakagami衰落系数、平均路径衰减系数等参数对WCDMA系统安全性能造成的影响。数值计算和仿真结果相吻合,证明了以上理论分析的正确性。推导了WCDMA系统渐近安全中断概率的解析表达式。结果表明,WCDMA 系统的安全分集增益为主信道各个可分离路径上的分集增益之和,与窃听信道无关;对于恒定多径强度轮廓的同分布Nakagami衰落信道,WCDMA系统的安全分集增益为主信道的收/发天线数、多径个数以及Nakagami衰落系数四者之积。     

相关时变衰落信道中DSTM非相干接收机的结构与性能

针对空间相关时变衰落信道中的差分空时调制系统,推导得出了一种新的基于信道相关矩阵和时变衰落参数的最优非相干接收机结构,并针对几种特殊信道条件对该接收机进行了简化.实际应用该最优接收机时,基于判决反馈得到的数据,提出了一种次优的非相干接收机结构DF-NCR.理论分析和仿真结果表明,在相关时变衰落信道条件下,采用DF-NCR的差分空时调制系统的误码性能优于传统的差分传输模式.     

A decision-directed spread-spectrum RAKE receiver for fast-fadingmobile channels

The operation of a decision-directed RAKE receiver is described that has the advantage of not requiring any bandwidth overhead for training bits. The performance is illustrated using bit error rate (BER) graphs and burst error length cumulative distribution functions (CDFs) obtained from Monte Carlo simulations. The receiver simulated operates over a fast-fading (100-Hz Doppler) mobile channel at a bit rate of 4.8 kbit/s using a 900-MHz carrier. It is shown that the receiver is not greatly affected by error propagation. However, the incurred lag on the channel impulse response estimate is the major limitation mechanism, and the resulting irreducible BER is quantified for various numbers of taps in our receiver design. The RAKE receiver performance is examined and compared using maximal-ratio, equal-gain, and differential phase combining techniques     

DS-CDMA系统新的空时并联结构 及二维自适应DBF算法

针对直接序列扩频码分多址(DS-CDMA)移动通信接收系统,本文提出了一种新的空时二维信号处理结构,这是一种"智能天线与瑞克(RAKE)接收机的并联连接"(PI-SA&RR)结构.基于PI-SA&RR结构,提出了空时二维自适应数字波束形成(ST2-DADBF)算法.与"二维RAKE接收机"(2-DRR)相比,ST2-DADBF算法不需要对延时-波达方向(DOA)进行估计就能够获得最优空-时域联合输出.与"导频符号辅助相干自适应天线阵列分集接收机"(PSA-CAAADR)相比,ST2-DADBF算法能够使智能天线和RAKE接收机联合参与自适应算法,不需要对RAKE分支信道参数进行估计,是一种真正的二维自适应算法.针对多用户移动通信系统,同时考虑到信道的时延扩展和空间角度弥散的影响,本文给出了一种接收信号的通用模型,基于该模型对ST2-DADBF算法进行了计算仿真.仿真结果表明,ST2-DADBF算法能够在空时二维域中捕获感兴趣用户的各个多径分量,并将这些多径分量同步相干合成,同时抑制其它用户在时域和空域形成的干扰,因而可获得良好的误码率(BER)性能.     

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.     

Consistent estimation of Rayleigh fading channel second-orderstatistics in the context of the wideband CDMA mode of the UMTS

We address the problem of estimating the second-order statistics of a frequency-selective Rayleigh channel in the context of the wideband CDMA mode of the UMTS. The data to be transmitted are sent over slots on which the channel is assumed to remain constant. Each slot contains a pilot symbol sequence from which it is possible to estimate the current value of the channel. The covariance matrix of the channel is usually estimated by a denoised version of the empirical covariance matrix of the trained channel estimate. However, in the UMTS, this estimate is not consistent in the sense that if the number of slots used to estimate it tends to infinity, it does not converge to the true covariance matrix of the channel. We propose a new consistent estimate of the covariance matrix and evaluate the performances of two Wiener-like channel estimation schemes based on the proposed estimate. The performances of the new approach are evaluated by means of the bit error rate provided by a RAKE receiver based on the proposed channel estimates. It is shown that our estimate of the covariance matrix allows significant improvement in the performance of the RAKE receiver     

60 GHz芯片间无线互连系统的MMSE-RAKE接收机误码性能分析

针对60 GHz芯片间无线互连信道中存在的多径衰落问题,将匹配滤波器和最小均方误差算法应用到60 GHz脉冲通信系统,重点分析多径信道下采用最小均方误差合并算法的RAKE接收机的误码性能。在IEEE 802.15.3c信道模型的基础上,对采用不同合并方式、不同干扰用户数目下的RAKE接收机误码性能进行了研究。仿真结果表明,随着干扰芯片数量的增加,引入匹配滤波器和最小均方误差算法的RAKE接收机不仅降低了接收机的采样率,而且有效提高了系统抗多用户干扰的能力,为芯片间无线互连系统的RAKE接收机设计提供了技术参考。     

Multipath combining scheme in single-carrier transmission systems

In this letter, we introduce and investigate the RAKE combining receiver which is widely used in the code-division multiple access (CDMA) systems to the non-spectrum-spreading single-carrier transmission system. The initial estimate of the transmitted data is obtained by linear single-carrier equalizers, and then all the multipath signals are constructed from this initial solution and channel impulse response. By interference cancellation (IC) technique, we can acquire every multipath component in the received signal after cancelling the sum of all the other multipath signals constructed. Finally, all the components are combined together using selection combining (SC), equal gain combining (EGC) or maximal ratio combining (MRC), so that temporal diversity gain from the combined output can be obtained. Simulation results show that bit error rate (BER) performance of the new combining receiver based on zero forcing (ZF) and minimum mean square error (MMSE) equalizers can achieve the SNR gain dramatically in the SUI-5 wireless communication link.     

2-D rake receiver based on space-time channel parameter estimation

2-D RAKE receiver is an efficient way to realize the space-time processing for CDMA systems with aperiodic spreading codes. The Direction Of Arrival (DOA) and the relative time delay of every user's multipath must be known to realize the 2-D RAKE receiver. In the third generation CDMA mobile communication system, auxiliary pilot channel is used in the uplink channels. The different user's Vector Channel Impulse Response (VCIR) can be estimated from the pilot channel easily. The VCIR contains spatial and temporal information. In this paper, by utilizing the known pulse shape function, a parameter matrix method used to estimate the Spatial Signature Vector (SSV) and the relative time delay is proposed in frequency domain. The DOA can be estimated from the SSV. By reconstructing the SSV and utilizing approximate Capon space filter, the performance of the 2-D RAKE receiver with uniform circular array can be improved with a little additional computation work.     

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.