Optimization of high-bit rate communications over powerlines : exploitation of OFDM/CDMA hybrid schemes
The study presented throughout this document focuses on the optimization of a digital transmission system for high throughput communications over powerlines, using OFDM/CDMA schemes. This study takes part of a project aiming at giving a solution to the home Internet access task using the power lines of the electrical local area loop as a transmission medium. In the first part of the document, the specifications of the communication system are studied. A detailed state of the art of CPL technilogy is firts proposed, including a description of the network structure and of the propagation caracteristics. Several transmission techniques are then investigated to give an efficient solution to multiuser point-to-multipoint and multicell communication needs. The particular combination of OFDM and CDMA commonly referred to as SS-MC-MA, is eventually chosen, and a frame structure is proposed. The second part of the manuscript is dedicated to the study of synchronization and channel estimation schemes. The effects of synchronization inaccuracies are first detailed in order to specify the system timing synchronization constraints. A synchronization procedure is then proposed, and new algorithms are derived, following to different approaches, denoted 'temporal' and 'frequential'. Both approaches carry out a joint estimation of synchronization errors and of the channel state. A comparative study is then led through simulations. The last part of the document focuses on resource allocation in the case of SS-MC-MA systems assuming perfect channel state information at the transmitter. The principles of adaptive modulations in DMT is first recalled and discussed in the context of the study. Under the constraint of a power spectral density (PSD) limitation, novel allocation algorithms are developped in the case of the SS-MC-MA waveform. It is then demonstrated that the spreading component of SS-MC-MA allows a better energy exploitation than DMT. As a consequence, it is shown that SS-MC-MA outperforms DMT in terms of throughput or robustness maximization, under PSD limitations. Many simulation results exhibit this main conclusion in different communication environments.