共查询到20条相似文献,搜索用时 15 毫秒
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《现代电子技术》2015,(5)
CDMA移动通信系统中,受到建筑物和地形地貌的影响,通信环境十分复杂,通信系统的通信质量受到严重影响。CDMA系统采用RAKE接收技术,它可以在时间上分辨出细微的多径信号,这样便把多径信号加以利用,克服了多径衰落带来的影响,达到增强接收效果的目的。在对RAKE接收机基础理论进行分析的基础上,采用Matlab仿真软件对不同用户状态下的RAKE接收机性能进行仿真,并对最大比合并、等增益合并、选择式合并这三种合并方式进行比较,给出仿真结果及误码率性能参数。然后,针对CDMA系统中RAKE接收机的性能进行建模仿真,仿真结果表明,CDMA系统中采用RAKE接收机起到了抗多径干扰、提高系统性能的目的。 相似文献
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We develop an analytical framework to quantify the effects of spreading bandwidth on spread-spectrum systems operating in dense multipath environments. Closed-form expressions for the mean and variance of the total RAKE receiver output signal-to-noise ratio are derived. The proposed problem is made analytically tractable by transforming the physical RAKE paths into the virtual path domain 相似文献
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Shin-Yuan Wang Chia-Chi Huang 《Vehicular Technology, IEEE Transactions on》2001,50(1):234-243
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 相似文献
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Ki Jun Kim Soon Yil Kwon Een Kee Hong Keum Chan Whang 《Communications, IEEE Transactions on》2000,48(6):1029-1036
The effect of tap spacing on the performance of a RAKE receiver is analyzed analytically in a frequency-selective fading channel. A continuous time multipath fading channel model is used for the analysis, and the expression of the correlation between the desired signals, interference signals, and noise signals at the output of each branch of the RAKE receiver is derived for various chip waveforms. Since the noise components of each branch signal are correlated to each other, an optimum combining rule based on the maximum-likelihood criterion is derived to gain utmost performance. It is shown that the performance of the system can be improved by setting the tap spacing of the RARE receiver below the chip duration when the bandwidth of the transmitted signal is larger than the inverse of the chip duration. Also, it is shown that the normalized capacity of the system can be increased by using a chip waveform occupying wider bandwidth, which takes advantage of the increased diversity gain merits of a wide-band code-division multiple-access system at the same chip rate. It is noted that the derived combining rule gives diversity gain against the fading process as well as noise whitening processing gain against multiple-access interference at the same time 相似文献
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The combination performance of a truncated decorrelator and a coherent RAKE receiver using pilot symbol-aided channel estimation is evaluated by computer simulation for DS-CDMA in several multipath fading environments. Computer simulation results show that the proposed truncated decorrelator can within a window of several symbols, improve the bit error rate (BER) performances compared to the conventional matched filter receiver in fast Rayleigh fading environments 相似文献
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Quirk K.J. Milstein L.B. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2002,48(3):669-682
As larger diversity and coding gains are introduced into spread-spectrum systems to mitigate the effects of multipath fading and thermal noise, system performance is increasingly being limited by channel estimation error. To properly design these systems, performance measures incorporating the effects of estimation errors are needed. A lower bound on the probability of bit error for a RAKE receiver operating with imperfect phase estimates is presented along with a method to obtain a closed-form expression for its evaluation. Further, this lower bound is compared to an upper bound so that an accurate assessment of system performance can be obtained 相似文献
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为了充分利用瑞克(RAKE)接收机的多径能量利用效果和智能天线(SA)的定向收发作用,研究了RAKE接收机和智能天线的联合使用,提出了基于智能天线的定向二维(2D) RAKE接收机模型,给出了定向2D-RAKE接收机分别在射频、中频和基带的实现框图、工作原理和输出信号表达式,并对它们的性能以及工程实现做了分析讨论。指出基带定向二维RAKE接收机由于可以在基带上通过幅度加权来实现信号的定向收发,其优点是可以利用目前比较成熟的基带信号处理技术,但是由于不能利用相干解调作用来抑制多径干扰(MPI)和多用户干扰(MAI),存在噪声放大问题;射频定向二维RAKE接收机的信噪比增益最大,但工程实现难度较大;中频定向二维RAKE接收机则具有较高的性价比。 相似文献
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In this paper, we integrate the multicarrier signaling technique and the RAKE receiver to design a DS-CDMA system with the capability to increase the data rate, mitigate the effect of correlation among the various subcarriers, and suppress partial-band interference. In the proposed system, a data sequence is serial-to-parallel converted, and multicarrier DS-CDMA is used on each of the parallel data streams. The receiver provides a RAKE for each subcarrier, and the outputs of the RAKEs are combined by a maximal-ratio combiner. We employ a correlated subcarrier and frequency-selective fading channel model to derive the average probability of error of the system and compare the results with those of both a single carrier RAKE system and a multicarrier DS-CDMA system in a frequency selective Rayleigh fading channel with an exponential multipath intensity profile, when multiple access interference and partial-band interference are present 相似文献
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Cheol Mun Myung-Sun Choi Han-Kyu Park 《Vehicular Technology, IEEE Transactions on》2001,50(5):1312-1317
The bit error rate (BER) performance and the characteristics of a two-dimensional (2-D) RAKE receiver operating in a correlated frequency-selective Nakagami-fading environment are analyzed. Correlated fading between array elements whose fading statistics are identical across the same RAKE branch, as well as an arbitrary number of RAKE-branches with arbitrary finding statistics, are assumed. We derived an approximated signal-to-noise ratio (SNR) statistics for one RAKE branch with correlated multiple antennas, which is extended to that for multiple RAKE branches with arbitrary fading statistics, i.e., a 2-D RAKE receiver. The receiver's performance and characteristics are analyzed using the cumulative distribution function of the SNR at the 2-D RAKE receiver output and the BER under various conditions, Numerical results show that the improvement In performance of the 2-D RAKE receiver is brought about by the average SNR and diversity gains, which are identified by two parameters specifying the gamma distribution of SNR 相似文献
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Kawahara K. Kitajima K. Takine T. Oie Y. 《Selected Areas in Communications, IEEE Journal on》1997,15(5):903-913
In transport-layer protocols such as TCP over ATM networks, a packet is discarded when one or more cells of that packet are lost, and the destination node then requires its source to retransmit the corrupted packet. Therefore, once one of the cells constituting a packet is lost, its subsequent cells of the corrupted packet waste network resources. Thus, discarding those cells will enable us to efficiently utilize network resources, and will improve the packet loss probability. We focus on tail dropping (TD) and early packet discard (EPD) as selective cell discard schemes which enforce the switches to discard some of the arriving cells instead of relaying them. We exactly analyze the packet loss probability in a system applying these schemes. Their advantages and limits are then discussed based on numerical results derived through the analysis 相似文献
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The focus of this paper is to characterize the performance of a RAKE receiver tracking the L strongest multipath components and to quantify the effects of the chip rate on spread spectrum systems operating in dense multipath frequency-selective fading environments. Analytical expressions for the symbol error probability are derived in terms of the chip rate, multipath spread of the channel and an arbitrary number of combined paths 相似文献
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This paper presents field test measurement results from a postdetection RAKE receiver system using a time-window control loop (TWCL). TWCL is a code synchronization scheme, and its performance with delay paths is better than the performance, in terms of acquisition and tracking, without delay paths because of the path-diversity effect. This receiver is suitable for systems that use short spreading codes such as wireless local area networks because it employs a matched filter for despreading. The RAKE method is a simple integral demodulation method used to combine correlation peaks including delay paths in a time window, and two-branch-antenna combining diversity is available. A field test is implemented while walking in an urban area, including the no-line-of-sight situation, taking into consideration microcellular systems. The results show that when the bit error rate is 10-3 and the spreading-chip rate is 4.096 Mchip/s, path-diversity gain from the theoretical differential quadrature phase-shift keying value is more than 12 dB without antenna diversity. This path-diversity gain value corresponds to a path-diversity reception gain of between two and three. Using two-branch-antenna diversity, the total of path- and antenna-diversity gain is up to 18 dB in the no-line-of-sight situation. From the above results, it is clear that this RAKE receiver is effective even in the no-line-of-sight situation and that TWCL provides good performance under the given field conditions 相似文献
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Jia-Chin Lin 《Electronics letters》1998,34(16):1550-1551
A RAKE receiver achieving joint blind multipath diversity combining and code tracking is proposed. An improved known modulus adaptive algorithm is exploited to perform multipath diversity combining and to support the modified code tracking in the blind mode. Computer simulation results have indicated very attractive behaviour of the proposed technique 相似文献
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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 相似文献
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Relationship between ADC performance and requirements of digital-IF receiver for WCDMA base-station 总被引:2,自引:0,他引:2
Hae-Moon Seo Chang-Gene Woo Pyung Choi 《Vehicular Technology, IEEE Transactions on》2003,52(5):1398-1408
The recent rapid development of digital wireless systems has led to the need for multistandard, multichannel radiofrequency (RF) transceivers. The paper presents the relationship between the performance of a bandpass-sampling analog-to-digital converter (ADC) and the requirements of a digital intermediate-frequency receiver for a wideband code-division multiple-access (WCDMA) base-station. As such, the ADC signal-to-noise ratio (SNR), the derivation of the receiver sensitivity using the SNR/spurious free dynamic range (SFDR) of the ADC, the effect of the ADC clock jitter and receiver linearity, plus the relationship between the receiver IF and the ADC sampling frequency are all analyzed. As a result, when a WCDMA base-station receiver has a data rate of 12.2 kbps, bit error rate (BER) of 0.001, and channel index, k, of 5 (sampling frequency of 122.88 MHz and IF of 92.16 MHz), the performance of a bandpass-sampling ADC was analytically determined to require a resolution of 14 bits or more, SNR of 66.6 dB or more, SFDR of 86.5 dBc or more, and total jitter of 0.2 ps or less, including internal ADC jitters and clock jitters. 相似文献