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.     

Performance analysis of a linear MMSE receiver for bandlimited random-CDMA using quadriphase spreading over multipath channels

This paper analyzes the bit-error-rate (P/sub e/) performance of a linear minimum mean-square error (LMMSE) receiver for bandlimited direct-sequence code-division multiple-access systems which use quadriphase spreading with aperiodic pseudonoise (PN) sequences. The analysis is based on the improved Gaussian approximation (IGA) with focus on chip pulse shaping. It shows that the IGA reduces to the standard Gaussian approximation (SGA) if 1) random quadriphase spreading is employed, 2) the spreading factor takes moderate to large values, and 3) the chip pulse excess bandwidth (BW) is zero. Hence, the SGA, known for its inaccuracy in low regions of P/sub e/, remains an accurate approximation even when the number of active users in the system is small as long as the aforementioned conditions are met. The analysis holds for either matched or different transmit and receive filters. Consequently, closed form conditional P/sub e/ expressions are derived for the coherent selective RAKE and the LMMSE receivers and verified with Monte Carlo simulations. Numerical results are presented to illustrate the performance improvement achieved by the LMMSE receiver which, in contrast to the coherent selective RAKE receiver, not only suppresses interference when the excess BW of chip pulse is nonzero, but also harnesses the energy of all paths of the desired user. Under the examined scenarios tailored toward current narrowband system settings, the LMMSE receiver achieves 60% gain in capacity over the selective RAKE receiver. A third of the gain is due to interference suppression capability of the receiver while the rest is credited to its ability to collect the energy of the desired user diversified to many paths. Future wideband systems will yield an ever larger gain.     

KM序列用作RAKE型CDMA系统扩频码的分析

本文提出将KM 序列用作RAKE型CDMA系统的扩频码.基于一个RAKE接收机模型,分析了CDMA系统性能并提出了适于作RAKE型CDMA系统扩频码的PN序列的特性.接着,分析了KM 序列作RAKE型CDMA系统扩频码的优劣.最后,运用计算机仿真,比较了m序列和KM 序列的互相关特性以及在相干接收机和RAKE接收机下,这两种序列和Gold序列对应的系统平均误码率,从而证实了KM 序列作为扩频码的可行性.     

KM序列用作RAKE型CDMA系统扩频码的分析

本文提出将KM M序列用作RAKE型CDMA系统的扩频码 .基于一个RAKE接收机模型 ,分析了CDMA系统性能并提出了适于作RAKE型CDMA系统扩频码的PN序列的特性 .接着 ,分析了KM M序列作RAKE型CDMA系统扩频码的优劣 .最后 ,运用计算机仿真 ,比较了m序列和KM M序列的互相关特性以及在相干接收机和RAKE接收机下 ,这两种序列和Gold序列对应的系统平均误码率 ,从而证实了KM M序列作为扩频码的可行性     

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.     

Bit error probability analysis for FRAMES WCDMA downlink receivers

The wide-band code-division multiple-access (WCDMA) concept FMA2 developed in the European Future Radio Wide-Band Multiple-Access Systems (FRAMES) project supports variable-data-rate transmission. The data rate can be altered by changing either the spreading factor or by using multiple spreading codes in parallel. In order to facilitate flexible changing of the data rate, variable-length orthogonal Walsh codes are used for channel separation, followed by the scrambling code. Optional short scrambling codes can be used if interference suppression is used. The downlink performance of the FMA2 system using both the conventional RAKE and LMMSE-RAKE receivers is studied. According to the numerical results, the performance of the conventional RAKE receivers is significantly degraded at the highest data rates, whereas the LMMSE-RAKE performs well in those cases also     

A RAKE receiver design for WCDMA FDD uplink with an RLS-based adaptive beamforming scheme

In this paper, we present a RAKE receiver design with adaptive antenna arrays for the wide-band code-division multiple-access (WCDMA) frequency-division duplexing (FDD) uplink. The RLS-based adaptive beamforming scheme is proposed and can be built with the existing one-dimensional RAKE receiver. We adaptively calculate the beamforming weight vector for each multipath of the desired user, and use maximum ratio combining (MRC) to combine each multipath signal in the demodulation process. Two matched filters based on the spreading waveforms are designed in our scheme for WCDMA FDD uplink application. The proposed scheme has the ability of suppressing strong multiuser access interference and the other types of interferers through spatial ing. The tracking capability of the proposed algorithm is demonstrated in the simulation results.     

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     

WCDMA 移动终端用RAKE接收机结构与实现

针对WCDMAFDD下行链路,提出了一种接收机结构。与传统接收机不同,该结构是根据多径来拉动(延时)输入信号,即根据多径把各径的信号延时对齐,而本地码的相位只需一个,来对多径支路解扩,并直接合并输出。该结构可进一步通过串行方法实现,大大减少硬件资源。由于采用全硬件技术,因此,便于ASIC集成。     

Space-Time Receiver for Multi-Rate CDMA Systems: Multi-Code and Variable Spreading Length Access Methods Comparison

This work proposed the linear minimum mean square error (LMMSE) space-timereceivers for synchronous multi-rate direct sequence code devision multipleaccess (DS/CDMA) systems. The performance of the proposed receivers isanalyzed. The high-rate (HR) LMMSE space-time receiver with combiningtechnique can provide essentially the same performance for low-rate (LR) usersas LR LMMSE space-time receiver while eliminate the time delay for the HRusers. The performance of the proposed multi-rate LMMSE space-time receiversare studied in the context of two multi-rate access methods: multi-code (MC)access where high data rate users multiplex their information streams ontomultiple codes, and variable spreading length (VSL) access where signaturesequences of different lengths are assigned to users with different datarates.Through the simulation results, we show that: (a) the proposed multi-rateLMMSE space-time receivers are optimum near-far resistant; (b) the proposedmulti-rate LMMSE space-time receivers have a clear performance improvementcompared to the time only LMMSE dual rate receiver; (c) there is a performancegain of the proposed multi-rate LMMSE space-time receivers compared to themulti-rate decorrelating space-time receiver when near-far ratio (NFR) is low;(d) The performance difference between MMSE combining and MRC in multi-ratesystem is much more pronounced than in single-rate system. Simulations alsoshow that the VSL access method is more robust than MC access methodconsidering changing rate-ratio in multi-rate systems.     

相关MIMO Nakagami衰落信道上MQAM WCDMA系统的性能分析

使用矩生成函数(MGF)方法,推导相关MIMO Nakagami衰落信道上WCDMA系统下行链路中采用组合二维瑞克(2D RAKE)接收机和发送分集的M进制正交幅度调制(MQAM)的平均误符号率精确解析表达式.利用获得的解析表达式,研究天线阵结构(如发射天线和接收天线的数目、天线间的距离)和工作环境(如衰落系数、角度扩展、多径延迟轮廓等)对MQAM WCDMA系统性能的影响.     

A Blind RAKE Receiver With Robust Multiuser Interference Cancelation for DS/CDMA Communications

In this paper, a blind RAKE receiver with robust multiuser access interference cancellation is presented for frequency-selective Rayleigh fading channels. In contrast to a conventional receiver, here, only knowledge of the spreading code and rough timing of the desired user is required. By investigating the code space of the multipath signals and the data vector space, a RAKE filtering vector is developed to extract the desired data from all the paths of the desired user. Our proposed technique not only exploits the characteristics of multipath propagation but also the characteristics of timing offsets that may occur in the receiver, to facilitate the application of a blind linear filter-optimization technique for robust interference suppression. Based on the RAKE filtering vector, interference rejection is implemented by using the auxiliary-vector (AV) technique. Our approach, however, effectively overcomes the sensitivity of the original AV method to multipath propagation and timing offsets. To mitigate the signal cancellation at relatively high signal-to-interference and noise ratios (SINR) resulting from the estimation errors of the RAKE filtering vector, robust strategies are introduced in addition to the linear filter optimization. Simulation results are presented to show the effectiveness of the proposed techniques.     

Generalized decorrelating discrete-time rake receiver

In this paper, we introduce the generalized decorrelating discrete-time RAKE receiver (GD-DTR) for single antenna systems and extend it to multi-antenna (e.g. MIMO) systems. The GD-DTR benefits from the correlated nature of multiple access interference while being robust against channel estimation errors. It is a combination of two other advanced RAKE reception methods namely, the discrete-time version of the generalized RAKE (G-RAKE) receiver and the decorrelating discrete-time RAKE receiver (D-DTR). The G-RAKE was proposed for correlated interference mitigation. The D-DTR improves performance in the presence of channel estimation errors in diffuse channels. Our results show that the performance of the discrete-time G-RAKE (G-DTR) could be worse than a conventional discrete-time RAKE receiver (C-DTR) when there are channel estimation errors in the system. Unlike G-DTR, our proposed GD-DTR provides gains up to 0.7 dB at a raw bit error rate of 10^-2 in the presence of channel estimation errors compared to C-DTR. For the MIMO case, the gain of the MIMO GD-DTR compared to MIMO C-DTR are 1 dB and 1.1 dB at a raw bit error rate of 10^-2 in 2 transmit 2 receive antenna (2times2) and 3times3 systems respectively, if there is no correlation between the antennas. For a highly correlated receive antenna case, the gain increases to 4 dB.     

适用于HSDPA的码片均衡干扰加权抵消联合接收机

随着因特网与多媒体业务的需求,WCDMA引入了高速下行链路分组接入(HSDPA)技术将其下行链路数据传输速率提高到10Mbps。为了提高HSDPA传输的性能,该文提出了一种新的码片均衡干扰加权抵消联合接收机(LMMSE-IWC)。理论分析与计算机模拟结果表明LMMSE-IWC性能优于传统的Rake接收机和LMMSE码片均衡器。     

LMMSE detection for DS-CDMA systems in fading channels

The linear minimum mean-squared-error (LMMSE) criterion can be used to obtain near-far resistant receivers in direct-sequence code-division multiple-access systems. The standard version of the LMMSE receiver (postcombining LMMSE) minimizes the mean-squared error between the filter output and the true transmitted data sequence. Since the detector depends on the channel coefficients of all users, it cannot be implemented adaptively in fading channels due to severe tracking problems. A modified criterion for deriving LMMSE receivers (precombining LMMSE) in fading channels is presented. The precombining LMMSE receiver is independent of the users' complex channel coefficients, and it effectively converts the time-varying Rayleigh fading channel to an equivalent fixed additive white Gaussian noise channel from the point of view of updating the detector. The performance of the LMMSE receivers in fading channels is studied via computer simulations and numerical analysis. The results show that the postcombining LMMSE receiver has potentially larger capacity, but it cannot be used in fast fading channels. The precombining LMMSE receiver has slightly worse capacity than the postcombining LMMSE receiver, but remarkably larger capacity than the conventional RAKE receiver at the signal-to-noise ratios of practical interest     

An optimum combining and concatenated-RAKE for dual-antenna mobileterminals in UMTS

The downlink of UMTS employs variable spreading factor and multicode to support variable data rate transmissions. In multicode and low spreading factor scenarios, interpath interference (IPI) among code channels is a principle factor that needs to be taken into consideration in system design. For example, the RAKE receiver with conventional maximum-ratio-combining suffers greatly from the presence of IPI. We present a new receiver structure that effectively incorporates an optimum combining scheme and dual-antenna diversity to enhance system performance     

A Design of WCDMA RF Transceiver with Its Performance Measuring

A 2-GHz radio frequency transceiver is presented and implemented for third generation mobile communications using wide-band code division multiple access （WCDMA） scheme. Performance measuring systems are introduced for transmitter channel and receiver sensitivity, respectively. The transceiver achieves maximum output power of 22 dBm, dynamic range of 85 dB, adjacent channel power rejection ratio （ACPR） of -41dB@5MHz, and receiver sensitivity of-119.6 dBm for 128-kb/s data at 3.84-Mcps spreading rate. The measured results indicate the conformity to the required commercial 2.0-GHz WCDMA specification and 3GPP requirements.     

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     

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.