The effect of mobile speed on the forward link of the DS-CDMA cellular system (original) (raw)
Related papers
Effect of Time Diversity on the Forward Link of the DS-CDMA Cellular System
Wireless Personal Communications - WIREL PERS COMMUN, 1998
A direct-sequences code division multiple access system has been accepted as a digital cellular standard (IS–95) in North America [1]. This digital cellular standard employs a powerful rate 1/2, constraint length 9, convolutional code in its forward link. It is well-known that in a Rayleigh fading channel the performance of a channel code depends very heavily on the interleaving depth and the relative variations of the channel characteristics. In slow fading channels, since the input symbols to the channel decoder are highly correlated, the bit-error-rate at the output of the channel decoder may be unacceptably high. Interleavers of large dimensions can reduce the correlation of the input signal to the channel decoder at the expense of an intolerable delay. In this paper we examine the performance of the IS–95 system, at the mobile receiver, for different channel fade rates. Also, we present a simple time diversity technique which employs multiple receive antennas. The multiple rece...
1999 IEEE 49th Vehicular Technology Conference (Cat. No.99CH36363), 1999
A b s h c t -The performance of a DSCDMA system over a multipath fading channel is evaluated. Rake receiver is employed to combat channel distortion introduced by multipath and temporal variation due to fading. Error-correction coding commonly employed in modern digital mobile systems, results in a substantial improvement for a system in fading channels. A combination of coding and interleaving effectively provides additional diversity, and minimf%ea the adverse effect of error bursts. In thh paper, we study the impact of interlever size on the error rate of a DSCDMA ryatem under different fading conditions. Closed-loop power control is employed with interleaving/coding to deal with slowly fading channek. This combination help the system performance not to be too sensitive to fade rate. The Mettiveness of using low rate convolutional code is also studied. Simulation results show that reducing the code rate does not always result in improved pertbrmance. In fact, constraint length must be increaned while reducing the code rate so that the resultant code can provide an improved peflormance.
Improving channel decoder performance on the CDMA forward link
IEEE Transactions on Wireless Communications, 2005
This work improves channel decoder performance on the code-division multiple-access (CDMA) forward link through more accurate calculation of the channel code trellis path metrics used to decode convolutional and turbo codes. This is achieved by performing the metric calculations with better channel state estimates. Channel state estimation involves determining desired signal amplitude and interference plus noise variance at the channel decoder input. Two options are presented for performing this estimation. Standard estimation is a simple scheme that results from assuming all CDMA forward link interference and noise can be lumped into a single additive white Gaussian noise process. Improved estimation is a new and more accurate technique that separately accounts for the intracell interference and intercell interference plus thermal noise processes. Simulations show that the decoding of convolutional and turbo codes is significantly improved by the more accurate channel state information provided by improved estimation.
Coding and Interleaving in CDMA
1997
The purpose of this paper is to give an overview of the channel coding and interleaving techniques which can be used with CDMA systems. The basic methods for block and convolutional channel coding are presented. A short presentation of interleaving is also given. One interleaving scheme called block interleaving is taken as an example. Finally, the implementation of channel coding and interleaving in one CDMA system, IS-95, is presented. Also a short look at the proposed wideband CDMA systems is given.
Performance Evaluation for Cellular CDMA
IEEE Journal on Selected Areas in Communications, 1992
In this paper, we consider the performance of a cellular radio direct-sequence code-division multiple access system. The base-to-mobile link is modeled as a flat Rayleigh fading channel, with all signals transmitted from a given base station fading in unison. For the mobile-to-base link, we use a similar model, except that the waveforms from all users are assumed to experience independent fading. Finally, we show the effects of imperfect power control.
Forward-link performance of CDMA cellular system
IEEE Transactions on Vehicular Technology, 2000
The impact of the propagation path-loss exponent ( ) on the forward performance of a direct-sequence code-division multiple-access (DS-CDMA) cellular system is investigated. For this purpose, a simple analytical model based on the inverse power-of-distance law is developed. The problem of finding proper power-control factors is considered. According to , the proper power-control factors are estimated for optimum performance. With these factors, results show that the capacity is reduced by a half by changing from 4.5 to 2.5. For this range in , power control can approximately double the capacity compared to the case of no power control. Index Terms-Code-division multiple-access (CDMA) cellular, system performance. Mostafa S. Ismail (S'94) received the B.Sc. and M.Sc. degrees in electrical engineering from the University of Mosul, Baghdad, Iraq, in 1987 and 1991, respectively. He is working toward the Ph.D. degree in electrical engineering at the University of Technology Malaysia, Kuala Lumpur, Malaysia. His current research interests are in the modeling and analysis of mobile communication systems. Tharek A. Rahman (M'90) received the B.
Design and performance analysis of a convolutionally codedoverlapping multicarrier DS/CDMA system
IEEE Transactions on Vehicular Technology, 2000
In this paper, we consider convolutionally coded multicarrier direct-sequence code-division multiple access (DS/CDMA) systems using overlapping subchannels in time-limited and band-limited channels. A tight bound on the bit error probability of the decoder output is obtained in Rayleigh fading channels when the channel state information is ideally available. It is shown that the proposed system, the convolutionally coded overlapping multicarrier DS/CDMA system with a symbol mapping method utilizing the diversity, outperforms the conventional single carrier and nonoverlapping multicarrier systems using the same convolutional code. It is also shown that the proposed system can provide a larger system capacity and more effectively combat the partial band interference than the conventional ones.
Data Throughput Analysis for the Uplink of CDMA Cellular Networks (1569776355)
This article analyses the data throughput of the uplink of a DS-CDMA cellular network, using random and Walsh spreading sequences, the matched filter and multiuser detector decorrelator (MUD-D). The mathematical modelling of the system described above takes into consideration an additive white gaussian noise channel with exponential path loss, perfect power control and internal and external co-channel interference. Within this context different modulations such as QPSK and M-QAM (16, 64 and 256-QAM) are used.
Efficient performance analysis of asynchronous cellular CDMA over Rayleigh-fading channels
IEEE Communications Letters, 2000
The bit error rate (BER) analysis of a directsequence code-division multiple-access (DS-CDMA) cellular system over a Rayleigh-fading channel often results in complicated expressions even though the Gaussian approximation is applied. A combined probability density function (pdf) approach for the forward link and a mean-method technique for the reverse link are proposed to significantly reduce the computational complexity. The simplified BER expressions are derived and yield accurate results.