His thesis focused on the theme of Orthogonal Frequency Division Multiplexing (OFDM), one of the most used techniques in wireless systems (such as WiFi, 4G LTE, UWB and WiMAX). The aim with this work was to develop post-compensation techniques to overcome the impairments from wireless and nonlinear channels.

Specifically, this work focuses on the transmission of OFDM signals in an uplink radio-over-fiber system. In these systems, wireless signals are transported through an optical fiber based network and therefore it is not necessary to use expensive/complex electrical elements near the antennas.

The high capacity of the fiber and its very low attenuation makes radio-over-fiber an attractive solution for wireless signal distribution. These systems can be used to distribute wireless signals for in-building networks (such as homes, theatres, airports and shopping malls), as well as in outdoor scenarios.

However, in order to obtain reliable transmissions it is necessary to perform several signal processing operations such as channel estimation and signal equalisation, which are still not well exploited in the literature.

The main contributions of this research work are the development of optimum receiver structures for signal equalisation, iterative algorithms capable of reducing their complexity and the development of a channel estimator structure optimised for uplink systems. As a case study the researcher has considered the transmission of WiFi and UWB standards using an optical fiber based network.

It was found that the proposed structures were suitable for radio-over-fiber systems without resorting to pre-distortion techniques. This is important since it reduces the complexity of wireless devices and base stations, leaving all complex operations to the central station.

UTM/INESC TEC, May 2012