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IEEE Conference and Exhibition on Global Telecommunications (GLOBECOM)

作者： Weihua Zhueng Dept. of Electr. & Comput. Eng. Waterloo Univ. Ont. Canada

ISBN: (纸本)0780341988

This paper studies a packetized direct sequence code division multiple access (DS-CDMA) wireless network for providing multimedia services to mobile users. In particular, we focus on channel coding and optimal power control for reverse link transmission using Hadamard-Walsh (H-W) orthogonal sequences for noncoherent demodulation. Because of various multimedia traffic types with different quality of service (QoS) requirements, the concept of perfect power control for voice only DS-CDMA networks cannot be directly applied to the multimedia wireless network. Under the circumstances, we give a new definition to the optimal power control and discuss how to achieve it together with error control techniques in order to maximize the frequency bandwidth efficiency and to guarantee various QoS requirements. Numerical results are presented to evaluate (i) the optimal signal to interference ratio of the received signals at base stations with various transmission accuracy requirements and (ii) the system radio frequency spectrum efficiency versus BER requirement under the assumption of the optimal power control. It is shown that the spectral efficiency (and hence the system capacity) can be significantly increased when using the optimal power control and convolutional coding with ARQ protocol for delay insensitive traffic.

关键词： Channel coding Power control Multiaccess communication Quality of service Wireless networks Error correction RF signals direct-sequence code-division multiple access Error correction codes Demodulation

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An adaptive antenna array with parallel beamformers for indoor radio channel enhancement

An adaptive antenna array with parallel beamformers for indo...

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IEEE Conference on Vehicular Technology (VTC)

作者： Jian-Guo Wang A.S. Mohan School of Electrical Engineering University of Technology Sydney NSW Australia

A method for improving the performance of an uplink direct sequence code division multiple access (DS-CDMA) communication system for an indoor channel is presented. Spatially smoothed MUSIC is used to separate multipath within a chip duration. Angle and time diversity are realized using parallel beamformers with a RAKE receiver for reducing space and frequency selective fading. Three dimensional ray tracing is used for obtaining vector channel impulse response in a multiuser indoor environment incorporating perfect power control. Simulations are carried out inside a corridor of a multistorey building. Numerical results indicate that the proposed smoothed adaptive beamforming method obtains significant improvement in the channel capacity.

关键词： Adaptive arrays Antenna arrays Fading direct-sequence code-division multiple access Multiaccess communication multiple signal classification Multipath channels Frequency diversity Ray tracing Indoor environments

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Asynchronous DS-CDMA detectors robust to timing errors

Asynchronous DS-CDMA detectors robust to timing errors

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IEEE Conference on Vehicular Technology (VTC)

作者： T. Ostman M. Kristensson B. Ottersten Signal Processing Royal Institute of Technology Stockholm Sweden

An asynchronous DS-CDMA system with timing errors is considered. Two different approaches for dealing with the problem are presented. The first method is based on robustifying the MMSE estimator against timing errors. The second approach models the timing errors as an extra noise term and formulates the best linear unbiased estimator of the data symbols. Simulations of the bit error rate indicate that the two approaches have similar performance. However, the difference to non-robustified algorithms is large.

关键词： Multiaccess communication Detectors Timing Delay effects Noise robustness Delay estimation Gaussian noise Additive white noise Signal processing direct-sequence code-division multiple access

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Successive interference cancellation for direct sequence code division multiple access

Successive interference cancellation for direct sequence cod...

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MILCOM, Military Communications Conference

作者： J.M. Holtzman WINLAB Rutgers University Piscataway NJ USA

Conventional DS/CDMA detectors operate by enhancing a desired user while suppressing other users, considered as interference (multiple access interference, MAI) or noise. A different viewpoint is to consider other users not as noise but to jointly detect all users' signals (multiuser detection). This has significant potential of increasing capacity and near/far resistance. Optimal multiuser detection is, however, too complex to implement, thus motivating the search for suboptimal algorithms. Our objective is to underline the need for simplicity and to discuss what is a relatively simple form of multiuser detection, successive interference cancellation. The cancellation scheme uses only components already present in a conventional detector.< >

关键词： Interference cancellation direct-sequence code-division multiple access Multiuser detection Detectors Signal detection Base stations Interference suppression multiple access interference Noise cancellation Energy capture

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A hybrid spreading/despreading function with good SNR performance for band-limited DS-CDMA

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IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS 1996年第8期14卷 1576-1582页

作者： Yu, L Salt, JE TELECOMMUN RES LABS SASKATOONSK S7N 0W0CANADA

The efficiency of a direct-sequence spread-spectrum code-division multiple-access (DS-CDMA) system depends heavily on the shape of the spectrum of the spread signal. Maximum efficiency is obtained with an ideal brick-wall bandpass spectrum. There are two approaches toward achieving such a spectrum. One is to use a simple spreader that produces a broad spectrum and then follow it with a precise, high order filter to band limit the spectrum. A second approach, which is the approach taken in this paper, is to use a spreader that produces a spectrum close to the ideal spectrum and then employ a simple fitter to control the out-of-band power. The proposed spreader/despreader is based on a simple hybrid function and can be easily implemented. An analysis provides a compact expression for the signal-to-noise ratio (SNR) of a RAKE receiver. The expression includes the effects of baseband, intermediate frequency (IF) and RF filtering as well as the effects of the spectral densities of the spreading/despreading functions. The analysis shows that the proposed spreader/despreader yields superior performance over a conventional pseudo noise (PN) spreading/despreading mechanism.

关键词： Spectra direct-sequence code-division multiple access direct sequence spread spectrum spectrum coding Intermediate frequencies telecommunication services Spreaders RAKE receivers code division multiple access Spectral density

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Performance evaluation of DS-CDMA system with M-ary orthogonal signaling

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IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY 1996年第1期45卷 57-63页

作者： Hong, EK Kim, KJ Whang, KC Yonsei University Seodaemun-gu Seoul KR Dept. of Electr. Eng. Yonsei Univ. Seoul South Korea

In this paper, the effects of signature sequence on the performance of direct-sequence code-division multiple-access (DS-CDMA) systems employing Walsh M-ary orthogonal signaling are considered. The mean-squared value of multiple access interference (MAI) is derived by treating the signature sequence as deterministic. The numerical results show that Walsh orthogonal signaling changes the original properties of signature sequences, and a different choice of signature sequence results in significant performance difference. These results can be used as guides in selecting signature sequences for systems that employ Walsh M-ary orthogonal signaling.

关键词： Walsh functions code division multiple access pseudonoise codes radiofrequency interference spread spectrum communication telecommunication signalling DS-CDMA system Walsh M-ary orthogonal signaling deterministic sequence direct sequence code division mu Common Channel Signaling Spread spectrum communication direct-sequence code-division multiple access code division multiple access Walsh functions pseudonoise codes Performance Evaluation Radiofrequency interference CDMA mobile communications

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Spectral efficiency of a power-controlled CDMA mobile personal communication system

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IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS 1996年第3期14卷 559-569页

作者： Gass, JH Noneaker, DL Pursley, MB Clemson University Clemson SC USA

The spectral efficiency is determined for a direct-sequence code-division multiple-access (CDMA) communications system that employs rapid closed-loop power control on a channel with doubly selective fading. The sensitivity of the spectral efficiency to the chip rate of the direct-sequence waveform and the number of taps in the rake receiver is considered. The effectiveness of the power-control method is also examined for different power-control delays, delay spectra, and Doppler spreads. The implications of the results for the design of personal communication systems are discussed.

关键词： Spectra spectral efficiency direct-sequence code-division multiple access RAKE receivers Power control selective fading Doppler effect COMMUNICATION SYSTEMS closed-loop power control

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Analysis of DS-CDMA parallel interference cancellation with phase and timing errors

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IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS 1996年第8期14卷 1522-1535页

作者： Buehrer, RM Kaul, A Striglis, S Woerner, BD MOTOROLA INC ARLINGTON HTSIL 60004 ERICSSON GE LYNCHBURGVA 24502

We consider the use of multistage parallel interference cancellation at the base station of a code-division multiple-access (CDMA) wireless system. Previous work in this area has demonstrated the potential for significant improvements in capacity and near-far resistance. However, most previous work has assumed perfect synchronization with the signals of interest. Practical systems will experience phase jitter and timing errors. We undertake an analysis of the effects of phase and timing errors, obtaining a closed form result for bit-error rate (BER) performance after an arbitrary number of stages of cancellation in an additive white Gaussian noise (AWGN) channel. This result is shown to agree well with simulations. Simulation results are also presented for the important case of frequency selective Rayleigh fading. The results from both analysis and simulations demonstrate that interference cancellation is fairly robust to phase and timing errors.

关键词： direct-sequence code-division multiple access parallel interference cancellation Phase jitter TIMING ERROR Interference cancellation code division multiple access Phase AWGN CANCELLATIONS

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DS-CDMA synchronization in time-varying fading channels

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IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS 1996年第8期14卷 1636-1642页

作者： Strom, EG Parkvall, S Miller, SL Ottersten, BE UNIV FLORIDA DEPT ELECT ENGN GAINESVILLE FL 32611 USA EDUC GRP INDIVIDUAL DEV STOCKHOLM SWEDEN

Herein, the problem of estimating propagation delays of the transmitted signals in a direct-sequence code-division multiple access (DS-CDMA) system operating over fading channels is considered. Even though this study is limited to the case when the propagation delays are fixed during the observation interval, the channel gain and phase are allowed to vary in time. Special attention is given to the near-far problem which is catastrophic for the standard acquisition algorithm. An estimator based on subspace identification techniques is proposed, and the Cramer-Rao bound, which serves as an optimality criterion, is derived. The Cramer-Rao bound is shown to be independent of the near-far problem, which implies that there is no fundamental reason for propagation delay estimators to be near-far limited. Furthermore, the proposed algorithm is experimentally shown to be robust against the near-far problem.

关键词： direct-sequence code-division multiple access time varying Fading channels Cramer-Rao bounds Propagation delay time-varying channels

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Concatenated orthogonal PN spreading sequences and their application to cellular DS-CDMA systems with integrated traffic

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IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS 1996年第3期14卷 547-558页

作者： Fong, MH Bhargava, VK Wang, Q Department of Electrical and Computer Engineering University of Victoria Victoria BC Canada

In this paper, we investigate the application of the concatenated orthogonal/PN spreading scheme for a cellular direct sequence code-division multiple access (DS-CDMA) system with integrated traffic. The performance of the system is evaluated in terms of user capacity. In order to incorporate traffic with a wide range of source rates, line rates (adjusted data rates before spreading) have to be selected for transmission. For traffic with source rates higher than the line rate of concern, we propose the use of concatenated orthogonal/PN spreading sequences to subdivide a high rate stream into parallel line rate streams. Therefore, in this paper, we first analyze the properties of the concatenated orthogonal/PN spreading sequences. The results are used to evaluate their performance for homogenous voice traffic in various cellular mobile environments with multipath fading, lognormal shadowing, and path loss. Our results show that the proposed spreading scheme offers a significant improvement in the forward link capacity as compared to using the conventional nonconcatenated long PN sequence, especially if the multipath fading is Rician (e.g., microcellular and indoor picocellular systems). Incorporating the notion of line rate, we then evaluate the performance of a system with integrated voice and video traffic. Special emphasis is placed on the effect of line rate selection on the overall capacity which leads to the optimal selection of line rates.

关键词： Data transfer rates Traffic video traffic direct-sequence code-division multiple access optimal selection line rate Multipath fading path loss link capacity spreading sequence CDMA mobile communications

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