Τεχνικές και αλγόριθμοι επεξεργασίας σήματος για τη μείωση της πολυπλοκότητας του υλικού σε ασύρματα συστήματα επικοινωνιών πολλαπλών εισόδων - πολλαπλών εξόδων
Θεοφιλάκος, Παναγιώτης - Θεόφιλος Ν.
This doctoral dissertation deals with the development and evaluation of signal processing techniques for reducing the hardware complexity of MIMO systems. Despite their potential of dramatic improvements in terms of link reliability and spectral efficiency, the practical application of MIMO systems has been limited, mainly due to the increased manufacture cost and energy consumption of the RF chains. The research results of the dissertation are presented in two parts: In the first part, the performance analysis of HS/MRC receivers operating over independent and identically distributed (i.i.d.) K fading channels is evaluated through a moments generating function based approach. The K distribution is known to accurately approximate the Rayleighlognormal distribution, which is commonly used to model fading over terrestrial mobile or land mobile satellite environments. In the second part, antenna subarray formation, a novel RF preprocessing technique for reducing the hardware complexity of MIMO systems, is developed and explored. With this method, each RF chain is allocated to a combined and complexweighted response of a subset of antenna elements. Therefore, the performance is dramatically improved with respect to conventional antenna selection and can even approach the performance of the fullcomplexity system. Novel, analytical, antenna subarray formation algorithms based on either instantaneous channel state information or longterm channel statistics, are introduced. The capacity performance of the proposed algorithms, as well as the system parameters effecting it, are thoroughly examined. Furthermore, the impact of hardware and signal processing nonidealities on the performance is examined. Finally, tight theoretical upperbounds on the ergodic capacity of the proposed technique in rich scattering environments are derived.