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.     

WCDMA中高速下行物理共享信道的RAKE接收机

WCDMA R5版本协议引入了高速下行共享信道用于支持高速业务,为此增加了高速下行物理共享信道（HS—PDSCH）、高速下行控制信道（HS—SCCH）以及高速上行反馈信道（HS—DPCCH）。其中,HS—PDSCH在不同的环境下可以采用16QAM或者QPSK两种调制方式,文中提出了RAKE接收机的接收方案,并在瑞利衰落环境下进行了仿真,同时对仿真结果加以分析。结果表明,此RAKE接收机的性能能够满足接收要求,且易于实现。     

Convolutional Spreading CDMA and Comparison With the DS-CDMA With RAKE Receiver

For synchronous downlink direct-sequence code-division multiple access (DS-CDMA), we introduce a cyclic-prefix (CP)-based convolutional spreading CDMA (CS-CDMA/CP) scheme employing zero correlation zone (ZCZ) codes, which gives a class of multiuser interference (MUI)-free CDMA schemes, including Suehiro's CDMA and block spreading (BS) CDMA as special cases. We show that CS-CDMA/CP employing appropriately selected binary and ternary ZCZ codes have good user capacity, peak-to-average power ratio (PAPR), and transmission power loss, compared with previously proposed BS-CDMA schemes. By simulation, we show the effect of PAPR to its bit-error rate (BER) performance when nonlinear amplifiers are used, and also compare its BER performance with the conventional DS-CDMA scheme employing a RAKE receiver     

Bidirectional iterative ISI canceller for high-rate DSSS/CCK communications

This paper proposes a new RAKE receiver incorporated with a bidirectional iterative intersymbol interference (ISI) canceller in order to reinforce multipath robustness of high-rate direct-sequence spread-spectrum complementary code keying (DSSS/CCK) systems. The proposed RAKE receiver first combines multipath signal components through a channel matched filter (CMF) and removes postcursor-ISI by employing a codeword decision feedback equalizer (DFE). Then, a CCK codeword detector tentatively determines the current CCK codeword symbol and reuses it to subtract precursor-ISI from the previous symbol. Therefore, the ultimate symbol decision is made using the delayed signal with both postcursor-ISI and precursor-ISI cancelled. The detection performance can be more improved through an iterative refinement processing between the postcursor and the precursor components. Simulation results exhibit a significantly improved error rate performance of the proposed receiver compared with that of the legacy RAKE receiver employing only a postcursor DFE. The additional cost for realization of the proposed receiver is one symbol decision delay and reuse complexity of the DFE and the codeword detector.     

一种空时盲自适应RAKE接收机

多址干扰是直扩码分多址系统中的一个主要问题.多用户检测技术和阵列天线已成为解决这一问题的两种主要方法,将这两种方法结合起来的空时处理能大大提高系统的容量和性能.本文提出了一种空时盲自适应RAKE接收机.研究结果表明,该接收机具有较强的抑制多址干扰和克服"远-近"效应的能力,且能快速收敛.     

RAKE Receiver for Channels with a Sparse Impulse Response

We derive the optimal receiver for RAKE diversity combining on channels with a sparse impulse response. The receiver is based on the Bayesian philosophy and thus it requires the knowledge of certain a priori parameters. However, we also derive an empirical Bayesian version of our receiver, which does not require any a priori knowledge, nor the choice of any user parameters. We show that both versions of our detector can outperform a classical training-based maximum-ratio-combining detector.     

A Beamspace-Time Blind RAKE Receiver for Sectored CDMA Systems

A beamspace-time (BT) RAKE receiver is proposed for multiple accessinterference (MAI) suppression and multipath diversity reception insectored wireless CDMA communications. The scheme involves three stages.First, a set of adaptive beamformers encompassing a prescribed angular sectoris constructed on an antenna array, each providing effective suppression ofout-of-sector MAI and reception of in-sector signal. Second, a set of adaptivecorrelators is attached to each beam to combat in-sector MAI. Finally, thebeamspace correlator output data are combined to capture the signal multipathscoherently.The above three-stage operation is performed in a blind mode inthat no training signal is needed. The only information required is the signature,timing and a rough estimate of the angle of arrival (AOA) of the desired signal.     

Troposcatter Test Results for a High-Speed Decision-Feedback Equalizer Modem

A digital data modem which can operate at 1.5, 3.1, 6.3, 9.4, or 12.6 Mbit/s has been developed under the Megabit Digital Troposcatter Subsystem (MDTS) program for operation over Defense Communications System troposcatter links. An adaptive decisionfeedback equalizer (DFE) is used in the demodulator to eliminate intersymbol interference, combine diversity channels, and augument the existing diversity configuration with implicit diversity. This paper presents the results of a field test of the MDTS modem at the Rome Air Development Center troposcatter test facility during the winter of 1976. The field test, which encompassed generally weak signal and strong multipath conditions, yielded excellent performance results at all data rates. The field tests established the capability of the MDTS modem to efficiently communicate digital data over DCS troposcatter links at data rates up to 12.6 Mbit/s.     

DS-CDMA中基于MMSE相关器的RAKE接收机

该文研究了DS-CDMA中用于频率选择性多径信道RAKE接收机的限阶MMSE相关器的性能,这种基于CSA(Correlations Subtractive Architecture)结构的MMSE相关器很适用于频率选择性多径信道。通过用MMSE柑关器取代普通多用户RAKE接收机的传统相关器,可以达到与扩展到多个码元的MMSE接收机相近的BER性能。CSA产生MMSE相关器不需要矩阵的逆变换,降低了运算复杂度,有利于直接取代普通RAKE接收机的相关器。     

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。     

The Soft-Feedback ISI Canceller-Based Turbo Equalizer for Multilevel Modulations

In this paper, we investigate the soft-feedback equalizer (SFE) proposed by Lopes et al. for multilevel modulations. The SFE is based on intersymbol interference canceller structure and is compared to both soft-decision feedback turbo equalizer (SDFE) and the exact solution of MMSE linear equalizer (Exact-MMSE-LE) by means of EXIT chart analysis and BER simulations. Interesting results reveal that, for multilevel modulations, the SFE not only exhibits the same low complexity, low SNR threshold and fast convergence as SDFE but also reaches matched filter bound after a large number of iterations.     

卫星移动通信RAKE接收机误码率性能分析

分析了基于CDMA低轨道卫星移动通信RAKE接收机的误码率性能。在给出郊区环境和城市环境两个 卫星移动通信信道模型的基础上,本文针对郊区环境模型,推导出二进制正交FSK调制方式下,最大比合并RAKE 接收机的系统平均误码率公式,并在不同阴影遮蔽参数条件下,对提出的公式进行了数值分析。     

DS-CDMA系统中一种盲2D RAKE接收机的研究

研究了一种盲2-D RAKE接收机,该接收机结合扩频序列的时间结构特征与天线阵的空间选择性实现空域RAKE滤波,再对期望信号多径进行频域RAKE合并.分析结果表明该接收机能大大减小多址干扰,具有较强的抗近-远效应能力,且所需先验知识少,结构简单,计算量小.     

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     

OFDM技术抗ISI和ICI的性能分析

应用 OFDM技术的一个最主要的优点是他可以有效地对抗多径时延扩展。本文详细介绍了 OFDM技术的基本原理、实现方法、循环前缀和保护间隔。此外还讨论了 OFDM技术的抗符号间干扰和信道间干扰的性能     

二维RAKE接收机中一种新的信道矢量估计算法

在二维RAKE接收机中，通常仅用导频信道来估计信道矢量，当导频功率较低时，估计误差较大。本文提出一种新的信道矢量估计算法，该算法采用导频信道与业务信道联合估计技术，通过分集组合两个信道的估计结果，使信道矢量的估计精度得到了提高，仿真结果表明，该算法能有效地降低系统的误码率。     

Passband Timing Recovery in an All-Digital Modem Receiver

The performance of conventional modem receivers, where adaptive equalization is achieved by a digital transversal filter with tap gains spaced at the symbol interval, depends critically on the choice of the sampling phase. In this paper, a digital timing recovery loop is described and analyzed in the case of passband quadrature amplitude modulated data signals. Under conditions likely to be encountered on actual voiceband communication channels, the clock phase derived is shown to prevent spectral nulls and to accurately approximate the optimum timing phase for an infinite equalizer. Computer simulations show that the proposed system is capable of fast timing acquisition.     

一种基于DSP的低复杂度DTMB数字电视接收机的频域均衡器

基于DSP的数字电视接收机,具有低成本和低复杂度的优点,是未来数字电视接收机的发展方向。然而,基于DSP的数字电视频域均衡,需要大量的复数除法,给接收机的实现带来了巨大的困难。本文提出了一种基于DSP的低复杂度的、兼容单、多载波的DTMB接收机频域均衡器。本文的频域均衡器先将复数除法转换为实数除法,再对除数进行PCM A-Law和-Law压缩编码,然后以压缩编码后的码字作为索引进行查表,得到除数的倒数,最后通过乘法实现频域均衡器。仿真结果表明,本文的基于DSP的频域均衡方法,存储空间较少,消耗的指令周期数较少,运算速度快,同时性能较高。     

A Low-Complexity Adaptive Multi-Beam Space-Time Receiver for CCI/ISI Cancellation over Frequency Selective Multipath Channels

A space-time (ST) receiver is proposed for combating the cochannelinterference (CCI) and intersymbol interference (ISI) in a frequency-selectivemultipath environment. The scheme involves two stages. First, a set ofadaptive beamformers pointed at a prescribed angular sector in space isconstructed on an oversampled antenna array, each providing effectivesuppression of CCI and reception of desired signals. Second, afractionally-spaced decision feedback equalizer (DFE) follows to eliminate theISI left in beamformer outputs. In particular, both the beamformers and DFEcan be realized in the form of a generalized sidelobe canceller (GSC) with theaid of channel estimation, and partial adaptivity is incorporated for reducedcomplexity processing and improved convergence. The proposed ST receiver canbe employed as a multi-beam smart antenna system which is suitable forcellular communications. Computer simulations demonstrate that it can achievenearly the same performance as the optimal ST minimum mean square error (MMSE)DFE with a much lower implementation complexity.