Neural network-based techniques for efficient detection of variable-bit-rate signals in MC-CDMA systems working over LEO satellite networks

For a few years, multicarrier modulations have been proposed as valuable alternatives with respect to state-of-the-art single carrier ones due to their resilience against interference and channel distortion effects. In particular, many studies are arising about multicarrier-CDMA (MC-CDMA) techniques that provide improved robustness and flexibility with respect to single-carrier spread-spectrum techniques. Satellite communications considered the employment of MCCDMA for multimedia transmission very recently, especially for what concerns the delivery of variable-bit-rate services over low-earth-orbit (LEO) satellite networks. To this aim, the problems to be faced are mainly related to the development of efficient methodologies for satellite channel estimation, equalization and multi-user detection, in order to exploit in an optimal way the natural diversity inherent to MC-CDMA. In this paper we compare two different neural-network-based approaches for efficient reception of MC-CDMA signals in the case of asynchronous, multi-user, and variable-bit-rate transmission over LEO satellite channels. The first approach introduces neural networks for supporting receiver decision. The second more sophisticated approach exploits neural networks for joint channel estimation and symbol detection. Simulation results will be presented that demonstrate the improved effectiveness of e front matter r 2004 Elsevier B.V. All rights reserved. pro.2004.10.018 as been partially supported by the Italian Ministry of University and Scientific Research within the framework of the t. ng author. Tel.: +39 10 3532792; fax: +39 10 3532134. Abbreviations: EGC, equal gain combining; FEC, forward error fast Fourier transform; GEO, geo-stationary; LEO, low-earth-orbit; LSR, linear shift register; ML, maximumP, multi-layer perceptron; MSE, mean square error; MMSE, minimum mean square error; MUI, multi-user C-CDMA, multicarrier code division multiple access; NN, neural network; OFDM, orthogonal frequency division VSF, orthogonal variable spreading factor; PN, pseudo-noise; VBR, variable bit rate; WLAN, wireless local area sses: [email protected] (C. Sacchi), [email protected] (G. Gera), [email protected] (C.S. Regazzoni).