Diseño de estrategias de sincronización y estimación de canal para la mejora de comunicaciones multiportadora en redes inteligentes de energía

Abstract

In the last decades, there has been a growing interest in Power-Line Communications (PLC) systems due to their key role in the smart grids development. The power distribution network is present in residential, commercial and industrial areas, so it becomes a transmission medium that presents a low-cost deployment of digital communications system, in order to meet the needs of automation and control. However, PLC channels present high frequency selectivity due to the multipath effect and various noise sources, which make the development of reliable communications systems challenging. Orthogonal Frequency Division Multiplexing (OFDM) has been proposed as an efficient solution for PLC systems due to its robustness against frequency selective fading channels. However, OFDM systems require adequate synchronization and channel estimation and equalization for proper performance. This thesis contributes to the development of efficient synchronization and channel estimation strategies for OFDM-PLC systems, which represent a decrease in the associated complexity with respect to existing strategies in the literature, while maintaining competitive performance. Firstly, we design a novel pilot symbol generated from complementary pair of sequences, pursuing adequate correlation properties, reduced complexity signal processing, and the necessary flexibility to apply coarse synchronization techniques based on auto-correlation (AC) and cross-correlation (CC), and to perform fine synchronization and channel estimation based on CC. With respect to coarse synchronization, a comprehensive comparison is made between AC and CC based techniques under the particular conditions of the PLC channel. Then, a fine synchronization algorithm is developed from the efficient CC of the proposed pilot symbol, where the computations performed can be reused to obtain an estimate of the channel impulse response, reducing the complexity of the ensemble with respect to an individual approach for each stage. A statistical analysis of the metrics proposed in the coarse synchronization stage as well as those of the fine synchronization stage is performed, and appropriate detection thresholds are derived for the synchronization algorithms in each case. Finally, the proposed joint synchronization and channel estimation is evaluated under a transmission scenario in which the number of active subcarriers is limited by means of an electromagnetic compatibility spectral mask. The degradation of the correlation properties of the proposed pilot symbol is evaluated, and therefore the detection thresholds used in the coarse and fine synchronization stages are redefined. A modification of the CC in the receiver is proposed, filling the inactive subcarriers in order to counteract the harmful effect of the spectral mask in the channel estimation strategy. Throughout the work, an analysis of the complexity associated with the computation of the proposed algorithms in the different scenarios is carried out, and it is verified that the proposal represents an option of reduced complexity thanks to the design of the proposed pilot symbol and its efficient correlation architecture.