Adaptive Spread Spectrum Multicarrier Multiple Access over Wirelines
Résumé
In this paper, we investigate the dynamic resource allocation adapted to spread spectrum multicarrier multiple access (SS-MC-MA) systems in a multiuser power line communication (PLC) context. The developed adaptive system is valid for uplink, downlink, as well as for indoor and outdoor communications. The studied SS-MC-MA system is based on classical multicarrier modulation like DMT, combined with a spread-spectrum (SS) component used to multiplex several information symbols of a given user over the same subcarriers. The multiple access task is carried out using a frequency division multiple access (FDMA) approach so that each user is assigned one or more subcarrier sets. The number of subcarriers in each set is given by the spreading code length as in classical SS-MC-MA systems usually studied in the wireless context. We derive herein a new loading algorithm that dynamically handles the system conguration in order to maximize the data throughput. The algorithm consists in an adaptive subcarrier, code, bit and energy assignment algorithm. Power spectral density constraint due to spectral mask specications is considered as well as nite order modulations. In that case, it is shown that SS-MC-MA combined with the proposed loading algorithm achieves higher throughput than DMT in a multiuser PLC context. Because of the nite granularity of the modulations, some residual energy is indeed wasted on each subcarrier of the DMT spectrum. The combining of a spreading component with digital multitone (DMT) allows to merge these amounts of energy so that one or more additional bits can be transmitted in each subcarrier subset leading to signicant throughput gain. Simulations have been run over measured PLC channel responses and highlight that the proposed system is all the more interesting than the SNR is low.
Domaines
Autre
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