Ultra Wideband (UWB) communication systems occupy large bandwidths with very low power spectral densities. This feature makes UWB channels highly rich in multipaths. To exploit the temporal diversity, a UWB receiver usually incorporates Rake reception. Each multipath in the channel carries just a fraction of the signal energy. This phenomenon dictates a Rake receiver with a large number of fingers to achieve good energy capture and output signal to noise ratio (SNR). Eventually, the Rake structure becomes very complex from analysis and design perspectives and incurs higher manufacturing cost. The first contribution of this thesis is to propose channel shortening or time domain equalization as a technique to reduce the complexity of the UWB Rake receiver. It is analyzed that most of the existing channel shortening equalizer (CSE) designs are either system specific or optimize a parameter not critical or even available in UWB systems. The CSE designs which are more generic and use commonly critical cost functions may perform poorly due to particular UWB channel profiles and related statistical properties. Consequently, the main contribution of the thesis is to propose several CSE designs to address the specific needs of UWB systems. These CSE designs not only exploit some general but also some UWB specific features to perform the task more efficiently. The comparative analysis of the proposed CSEs, some existing designs and the conventional Rake structures leads towards the conclusion. It is finally shown that the use of CSE at the receiver front end greatly simplifies the Rake structure and the associated signal processing.

Ultra Wideband (UWB) communication systems occupy large bandwidths with very low power spectral densities. This feature makes UWB channels highly rich in multipaths. To exploit the temporal diversity, a UWB receiver usually incorporates Rake reception. Each multipath in the channel carries just a fraction of the signal energy. This phenomenon dictates a Rake receiver with a large number of fingers to achieve good energy capture and output signal to noise ratio (SNR). Eventually, the Rake structure becomes very complex from analysis and design perspectives and incurs higher manufacturing cost. The first contribution of this thesis is to propose channel shortening or time domain equalization as a technique to reduce the complexity of the UWB Rake receiver. It is analyzed that most of the existing channel shortening equalizer (CSE) designs are either system specific or optimize a parameter not critical or even available in UWB systems. The CSE designs which are more generic and use commonly critical cost functions may perform poorly due to particular UWB channel profiles and related statistical properties. Consequently, the main contribution of the thesis is to propose several CSE designs to address the specific needs of UWB systems. These CSE designs not only exploit some general but also some UWB specific features to perform the task more efficiently. The comparative analysis of the proposed CSEs, some existing designs and the conventional Rake structures leads towards the conclusion. It is finally shown that the use of CSE at the receiver front end greatly simplifies the Rake structure and the associated signal processing.

Proliferation of new wireless technologies has rekindled the interest on the design, analysis and implementation of suboptimal receiver structures that provide good error probability performance with reduced power consumption and complexity particularly when the order of diversity is large. This thesis presents a unified analytical framework to perform a trade-off study for a class of hybrid generalized selection combining technique for ultra-wideband, spread-spectrum and millimeter-wave communication receiver designs. The thesis also develops an exact mathematical framework to analyze the performance of a dual-diversity equal gain combining (EGC) receiver in correlated Nakagami-m channels, which had defied a simple solution in the past. The framework facilitates efficient evaluation of the mean and variance of coherent EGC output signal-to-noise ratio, outage probability and average symbol error probability for a broad range of digital modulation schemes. A comprehensive study of various dual-diversity techniques with non-independent and non-identical fading statistics is also presented. Finally, the thesis develops some closed-form solutions for a few integrals involving the generalized Marcum Q-function. Integrals of these types often arise in the analysis of multichannel diversity reception of differentially coherent and noncoherent digital communications over Nakagami-m channels. Several other applications are also discussed. / Master of Science

In an extensive outdoor propagation study, low antenna heights of 1.7 m are used at both the transmitter and the receiver to measure over 3500 wideband power-delay profiles (PDPs) of the channel for a peer-to-peer communications system. Rural and urban areas are studied in 22 different transmitter-receiver links. The results are used to characterize the narrowband path loss, mean delay, root-mean-square (RMS) delay spread, and timing jitter of the peer-to-peer wideband channel. Small-scale fading characteristics are measured in detail by measuring and analyzing 160 PDPs within each local area. This thesis shows the measurement setup for the calculation of fading rate variance and angular spread and reports the first known attempt to calculate angular spread from track power measurements. New analysis presented in this thesis shows the effect of measurement error in the calculation of angular spread. The expected characteristics of angular spread are derived using two different angle-of-arrival (AOA) models from the literature. Measurement results show initial validation of Durgin's angular spread theory. A new measurement-based algorithm for simulating wideband fading processes is developed and implemented. This simulation technique shows promise in the simulation of high-bit rate peer-to-peer radio communication systems. / Master of Science

Η υλοποίηση πρακτικών ασύρματων συστημάτων επικοινωνίας δεδομένων στην τεχνολογία UWB παρουσιάζει ιδιαίτερες προκλήσεις, κυρίως λόγω της χαμηλής ισχύος εκπομπής και της πολύ σύντομης διάρκειας των παλμών που χρησιμοποιούνται, οι οποίοι θα πρέπει να στέλνονται με πολύ μεγάλες ταχύτητες για την επίτευξη των επιθυμητών ρυθμών μετάδοσης. Το κανάλι μετάδοσης είναι ιδιαίτερα επιλεκτικό ως προς την συχνότητα και εξαιρετικά πυκνό και πλούσιο σε πολυοδικές συνιστώσες με αρκετά μεγάλες καθυστερήσεις. Αυτές οι συνιστώσες μπορούν να ανιχνευθούν και να συλλεχθούν χρησιμοποιώντας κατάλληλες δομές δεκτών RAKE, οι οποίοι τις συνθέτουν ώστε να μεγιστοποιηθεί η ενέργεια του ωφέλιμου σήματος, αυξάνοντας την απόδοση του συστήματος. Οι δομές αυτές παρουσιάζουν την καλύτερη απόδοση σε τέτοια συστήματα, αλλά έχουν μεγάλη υπολογιστική πολυπλοκότητα, καθώς για την ικανοποιητική απόδοση του συστήματος πρέπει να συνδυάσουν πολλές συνιστώσες, δεδομένης και της χαμηλής ισχύος εκπομπής της τεχνολογίας. Συνεπώς, για την υλοποίηση ενός πρακτικού και αποδοτικού συστήματος, σημαντικό ζήτημα αποτελεί ο τρόπος επιλογής και συνδυασμού των συνιστωσών μέσω ενός αλγορίθμου που θα χρησιμοποιεί τον μικρότερο δυνατό αριθμό δακτύλων. Στόχοι της διατριβής ήταν η μελέτη της τεχνολογίας UWB, η διερεύνηση των παραμέτρων των παλμικών UWB συστημάτων, η μελέτη και εξομοίωση μοντέλων του καναλιού, η κατανόηση των οποίων είναι απαραίτητη για την αποτελεσματική ανίχνευση του σήματος και τον σχεδιασμό των αλγορίθμων ψηφιακής επεξεργασίας του σήματος, η διερεύνηση δεκτών RAKE καθώς και εναλλακτικών δομών, οι εξομοιώσεις πομποδέκτη παλμικού UWB σε επίπεδο συστήματος με έμφαση στον RAKE και τον εκτιμητή καναλιού, η διερεύνηση παραμέτρων και τεχνικών για την υλοποίηση σε υλικό και τέλος η ανάπτυξη, ο σχεδιασμός και υλοποίηση μιας πρακτικής δομής δέκτη με RAKE αποδιαμορφωτή και εκτιμητή καναλιού που συνδυάζει χαμηλή πολυπλοκότητα και ικανοποιητική απόδοση. Παρουσιάζονται και συγκρίνονται τρεις νέες διαφορετικές προσεγγίσεις σχεδίασης, οι οποίες βασίζονται σε προτεινόμενο υβριδικό αλγόριθμο (HPS) για την μείωση της πολυπλοκότητας του RAKE και δίνονται αποτελέσματα που αφορούν στην αξιοποίηση του υλικού και στις επιδόσεις του συστήματος. Tα αποτελέσματα παρουσιάζουν το trade-off ανάμεσα στην συλλογή ενέργειας, την απόδοση του δέκτη και την πολυπλοκότητά του. Η αποτελεσματικότητα των προτεινόμενων αρχιτεκτονικών επαληθεύεται μέσω ειδικής πλατφόρμας αναδιατασσόμενου υλικού στην οποία υλοποιήθηκε η σχεδίαση. / Τhe implementation of practical wireless data communications systems for the UWB technology is very challenging due to the use of low-power ns-duration pulses which have to be sent in a high-frequency in order to achieve the desirable data rates. The UWB channel is highly frequency selective and it is characterized by dense and rich multipath propagation and large multipath delay spreads in some cases. A RAKE receiver can be employed in order to exploit multipath diversity and effectively capture the desired signal energy which is dispersed over the various multipath components, helping to mitigate fading. However, the particular nature of UWB results in very low-energy paths which, in conjunction with high multipath diversity, leads to a RAKE receiver that must exploit a large number of MPCs in order to optimize the received SNR. Thus, for the implementation of a low-complexity system it is important to define a novel method for the selection and combining of MPCs and develop an algorithm that is able to utilize a minimum number of fingers in the RAKE structure. Our work was focused in the study of UWB technology, the investigation of the parameters of IR-UWB systems, the study and understanding of the channel models which is necessary for the design of practical and efficient DSP algorithms, the investigation of RAKE type receivers as well as other alternative structures, the system-level simulations of the IR-UWB transceiver with emphasis given to the algorithms for the RAKE demodulator and channel estimator, the investigation of the parameters and techniques for the implementation of the system in hardware and finally, the development, design, and implementation of a practical receiver structure that includes a RAKE demodulator and a channel estimator and combines low complexity and satisfactory performance. The ultimate goal of this work is the presentation and investigation of the proposed channel estimator and (MRC)-RAKE receiver architecture which is based on a proposed novel hybrid algorithm called HPS. Three different design approaches aiming to a practical system implementation in an FPGA are proposed and compared and system/algorithm performance, hardware utilization results are provided. The obtained results demonstrate the trade-off between energy capture, performance and receiver complexity. The effectiveness of the proposed architectures is verified on a special FPGA platform which was used for the implementation of the receiver structure.