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Joint Turbo Equalization and Multiuser Detection of MC-CDMA Signals with Low Envelope Fluctuations

Silva, P. ; Dinis, R.

IEEE Transactions on Vehicular Technology Vol. 58, Nº 5, pp. 2288 - 2298, June, 2009.

ISSN (print): 0018-9545
ISSN (online): 0018-9545

Scimago Journal Ranking: 0,87 (in 2009)

Digital Object Identifier: 10.1109/TVT.2008.2010051

In this paper we consider the uplink transmission in MC-CDMA (MultiCarrier - Coded Division Multiple Access) systems. As other multicarrier signals, MC-CDMA signals have high envelope fluctuations and a high PMEPR (Peak-to-Mean Envelope Power Ratio) which leads to amplification difficulties. This is particularly important for the uplink transmission, since an efficient, low-cost power amplification is desirable at the MTs (Mobile Terminals). Moreover, the transmission over time-dispersive channels destroys the orthogonality between spreading codes, which might lead to significant MAI (Multiple Access Interference) levels.
To reduce the envelope fluctuations of the transmitted signals, while maintaining the spectral efficiency, the MC-CDMA signal associated to each MT (Mobile Terminal) is submitted to a clipping device, followed by a frequency-domain filtering operation. However, the nonlinear distortion effects can be high when an MC-CDMA transmitter with reduced envelope fluctuations is intended (e.g., a small clipping level and/or when successive clipping and filtering operations are employed).
In this paper, we define an iterative receiver that jointly performs a turbo-MUD (MultiUser Detection) and the estimation and cancelation of the nonlinear distortion effects.
Our performance results show that the proposed receiver structure allows good performances, very close to the linear receiver ones, even for high system load and/or when a PMEPR as low as 1.7 dB is intended for each MT.