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Analytical evaluation of nonlinear effects in MC-CDMA signals
Publication . Dinis, Rui; Silva, Paulo
The MC-CDMA signals (multicarrier coded division multiple access) have strong envelope fluctuations which make them very prone to nonlinear effects. These effects can be both intentional (such as the ones inherent to a nonlinear signal processing for reducing the envelope fluctuations) or not (such as the ones inherent to a nonlinear power amplification). In this paper we present an analytical tool for the performance evaluation of nonlinear effects in MC-CDMA signals which takes advantage of the Gaussian-like behavior of MC-CDMA signals with a large number of subcarriers and employs results on memoryless nonlinear devices with Gaussian inputs so as to characterize statistically the signals at the output of the nonlinear device. This characterization is then used for an analytical computation of the SIR levels (signal-to-interference ratio) and the BER performance (bit error rate). A set of numerical results is presented and discussed, showing the accuracy of the analytical BER performance analysis in the presence of nonlinear effects.
Analytical evaluation of nonlinear effects in MC-CDMA signals
Publication . Dinis, Rui; Silva, Paulo
In this paper we present an analytical tool for the per formance evaluation of nonlinear effects in MC-CDMA signals. This tool takes advantage of the Gaussian-like behavior of MC-CDMA signals with a large number of subcarriers and employs results on memoryless nonlinear devices with Gaussian inputs so as to characterize statis tically the signals at the output of the nonlinear device. This characterization is then used for an analytical com putation of the SIR levels (Signal-to-Interference Ratio) and the BER performance (Bit Error Rate). A set of numerical results is presented and discussed, showing the accuracy of the proposed analytical BER per formance analysis.
A turbo SDMA receiver for strongly nonlinearly distorted MC-CDMA signals
Publication . Silva, Paulo; Dinis, Rui
In this paper we consider the use of SDMA (Space Division Multiple Access) techniques for the uplink of MC-CDMA systems (MultiCarrier -Coded Division Multiple Access) where the transmitted signals face strong nonlinear distortion effects. We define an iterative receiver that jointly performs a turbo-MUD (Multiuser Detection) as well as estimation and cancellation of the nonlinear distortion effects.
An iterative detection technique for DS-CDMA signals with strong nonlinear distortion effects
Publication . Dinis, Rui; Silva, Paulo
Whenever a DS-CDMA signal (direct sequence code division multiple access) is the sum of several components associated to different spreading codes (e.g., the DS-CDMA signal to be transmitted by the BS (Base Station) in the downlink, or any multicode DS- CDMA signal), it has high envelope fluctuations, and a high PMEPR (Peak-to-Mean Envelope Power Ratio) setting strong linearity requirements for the power amplifiers. For this reason, it is desirable to reduce the envelope fluctuations of the transmitted signals. A promising class of nonlinear signal processing schemes, combining a nonlinear operation in the time- domain with a linear, frequency-domain filtering operation, was recently proposed for reducing the envelope fluctuations (and, inherently, the PMEPR) of DS-CDMA signals, while maintaining the spectral occupation of the corresponding conventional DS-CDMA signals. However, the performance degradation due to the nonlinear distortion effects on the transmitted signals can be relatively high, especially when a low PMEPR is intended. This can be especially serious if different powers are assigned to different spreading codes. To avoid significant performance degradation in these situations, we consider improved receiver where there is an iterative estimation and cancelation of nonlinear distortion effects. Our performance results show that the proposed receiver allows significant performance improvements after just a few iterations, even when we have strong nonlinear distortion effects.
A turbo SDMA receiver for strongly nonlinearly distorted MC-CDMA signals
Publication . Silva, Paulo; Dinis, Rui
This paper considers the use of space division multiple access (SDMA) techniques for the uplink of multi-carrier code division multiple access (MCCDMA) systems, where the transmitted signals face strong nonlinear distortion effects. The signal transmitted by each mobile terminal (MT) is submitted to a nonlinear operation consisting of a clipping device followed by a frequency-domain filtering operation, so as to reduce the envelope fluctuations and peak-to-mean envelope power ratio (PMEPR) while maintaining the spectral occupation of conventional MC-CDMA signals. At the base station, an iterative receiver employing multiple antennas jointly performs turbo multi-user detection and the estimation and cancellation of nonlinear distortion effects. Performance results show that the proposed receiver structures can achieve good performances that are very close to those obtained with linear transmitters, even for high system load and/or when a very low-PMEPR MC-CDMA transmission is intended for each MT.
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Funding agency
Fundação para a Ciência e a Tecnologia
Funding programme
Orçamento de Funcionamento/POSC
Funding Award Number
POSI/CPS/46701/2002