Bit Error Rate Analysis for MC-CDMA Systems in Nakagami- Fading Channels
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Bit Error Rate Analysis for MC-CDMA Systems in Nakagami-m Fading Channels Zexian Li Centre for Wireless Communications (CWC), University of Oulu, 90014 Oulu, Finland Email: [email protected]
Matti Latva-aho Centre for Wireless Communications (CWC), University of Oulu, 90014 Oulu, Finland Email: [email protected] Received 24 February 2003; Revised 22 September 2003 Multicarrier code division multiple access (MC-CDMA) is a promising technique that combines orthogonal frequency division multiplexing (OFDM) with CDMA. In this paper, based on an alternative expression for the Q-function, characteristic function and Gaussian approximation, we present a new practical technique for determining the bit error rate (BER) of multiuser MCCDMA systems in frequency-selective Nakagami-m fading channels. The results are applicable to systems employing coherent demodulation with maximal ratio combining (MRC) or equal gain combining (EGC). The analysis assumes that different subcarriers experience independent fading channels, which are not necessarily identically distributed. The final average BER is expressed in the form of a single finite range integral and an integrand composed of tabulated functions which can be easily computed numerically. The accuracy of the proposed approach is demonstrated with computer simulations. Keywords and phrases: multicarrier CDMA, bit error rate, Nakagami fading channel, spread-spectrum communications.
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INTRODUCTION
Multicarrier code division multiple access (MC-CDMA), which efficiently combines CDMA with orthogonal frequency division multiplexing (OFDM), has gained considerable attention as a promising multiple access technique for future mobile communications [1, 2, 3, 4, 5, 6, 7, 8]. MCCDMA is a spread spectrum technique where the signal is spread in the frequency domain. Since the MC-CDMA technique possesses the advantages of both OFDM and CDMA, it has the properties desirable for future systems such as insensitivity to frequency-selective fading channels, frequency diversity, and the capability of supporting multirate service by applying either multicode or variable spreading factor techniques [1]. Many papers have been dedicated to the bit error rate (BER) analysis of MC-CDMA [3, 4, 5, 6, 7]. The performance of MC-CDMA has been studied both for the uplink and the downlink of a mobile communication system [3] in which perfect time synchronization among users was assumed. To get the BER, three approximation methods for the distribution of the sum of independently identically distributed (i.i.d.) Rayleigh random variables (r.v.’s) were employed in the paper: the law of large numbers (LLN) approximation, the small parameter approximation and the central
limit theorem (CLT) approximation. The authors of [5] analyzed the BER performance of MC-CDMA systems with a frequency offset. The CLT approximation was used in the analysis. A performance analysis using the LLN approximation of an MC-CDMA system employing an antenna array at the base station has been presented in [6]. The bit error pro
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