Performance of Reverse-Link Synchronous DS-CDMA System on a Frequency-Selective Multipath Fading Channel with Imperfect
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Performance of Reverse-Link Synchronous DS-CDMA System on a Frequency-Selective Multipath Fading Channel with Imperfect Power Control Seung-Hoon Hwang Standardization & System Research Group, UMTS System Research Laboratory, LG Electronics, 533 Hogye-dong, Dongan-gu, Anyang-shi, Kyungki-do, Korea Email: [email protected]
Duk Kyung Kim Information & Communication Engineering, Inha University, 253 Yonghyun-dong, Nam-gu, Inchon, Korea Email: [email protected] Received 28 July 2001 and in revised form 12 March 2002 We analyze the performance for reverse-link synchronous DS-CDMA system in a frequency-selective Rayleigh fading channel with an imperfect power control scheme. The performance degradation due to power control error (PCE), which is approximated by a log-normally distributed random variable, is estimated as a function of the standard deviation of the PCE. In addition, we investigate the impacts of the multipath intensity profile (MIP) shape and the number of resolvable paths on the performance. Finally, the coded bit error performance is evaluated in order to estimate the system capacity. Comparing with the conventional CDMA system, we show an achievable gain of from 59% to 23% for reverse-link synchronous transmission technique (RLSTT) in the presence of imperfect power control over asynchronous transmission for BER = 10−6 . As well, the effect of tradeoff between orthogonality and diversity can be seen according to the number of multipaths, and the tendency is kept even in the presence of PCE. We conclude that the capacity can be further improved via the RLSTT, because the DS-CDMA system is very sensitive to power control imperfections. Keywords and phrases: reverse link synchronous transmission technique, frequency-selective multipath fading, imperfect power control.
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INTRODUCTION
Direct-sequence code-division multiple-access (DS-CDMA) has been considered as the most promising multiple-access scheme for the next generation mobile communications, because of its high flexibility in offering various services with variety of rates and its possibility of achieving greater capacity [1, 2]. The capacity of DS-CDMA system is mainly limited by multiple-access interference (MAI), and thus techniques to reduce the MAI, such as multiuser detection or interference cancellation, are currently of great interest [3, 4, 5]. In particular, techniques for reverse links have attracted much attention, as the capacity of a reverse voice cellular network link is smaller than that of the forward link. One reason for this is that the code orthogonality is not maintained, because in the reverse link the arrival times of signals from mobile stations (MSs) at a cell site (CS) are different, given the random geographical distribution of MSs within the cell sector. For terrestrial mobile systems, the reverse link synchronous transmission technique (hereafter, we denote it by
RLSTT) has been proposed to reduce the interchannel interferences over a reverse link [6]. In RLSTT, a closed-form timing control based on a new parameter called the tim
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