Σχεδιασμός πομποδεκτών για ασύρματα ψηφιακά τηλεπικοινωνιακά συστήματα

Abstract

Through the worldwide research on wireless communications, it becomes increasingly clear that the dominant consideration in the design of systems employing such technologies will be their ability to perform adequately over channels perturbed by a host of impairments. Based on this target, this dissertation aims at designing low-complexity digital transceivers operating over wireless fading channels. Special emphasis is placed upon designing transceivers with no channel estimation capabil- ities, since the latter is one of the most di±cult tasks performed at the receiver. The key to achieving this goal, was the thorough study of fading channels, as well as the connection of the fading statistics with the error performance of communications systems. Towards this concept, a long-term performance criterion is presented, which is proved to be more reliable compared to classic ones, regarding the error performance estimation. Utilizing the proposed long-term criterion, a novel method is developed, which is applied to equal gain diversity systems, enabling them to operate over fading channels with strong power decay pro?les. Under the same concept, an optimum receiver is proposed, which does not ne- cessitate any channel amplitude estimation and operates optimally over any fading conditions, achieving the minimum error performance. The performance of low-complexity transceivers is improved by employing a novel adaptive- modulation system, in the absence of channel estimation, while the requirements of adaptive- transmission systems are revisited. Furthermore, under the framework for reducing the com- plexity of diversity systems, a novel adaptive generalized selection combining receiver is intro- duced, which limits the number of activated diversity branches, leading to lower energy and power resources consumption.