ITC/USA 2013 Conference Proceedings / The Forty-Ninth Annual International Telemetering Conference and Technical Exhibition / October 21-24, 2013 / Bally's Hotel & Convention Center, Las Vegas, NV / We investigate pulse position modulation (PPM) and multipulse PPM (MPPM) for free space op- tical channels using bit interleaved coded modulation with iterative decoding. Data bits are first encoded by using a non recursive convolutional code and the coded bits after an interleaver are modulated before transmission. Iterative decoding is performed at the receiver. Optimized mapping is designed for MPPM. A genetic algorithm is used to find the optimized mapping for MPPM. Our simulation results show that a significant improvement in the error performance can be achieved by using optimized mapping and iterative decoding at the receiver.

During the thesis work, a feasibility study of the BPPM error-correction protocol is performed. The beyond pulse position modulation (BPPM) protocol was invented at Ericsson AB and describes a modulation encoding using vertically and horizontally polarized single photons for optical transmission and error-correction. The thesis work is a mixture of both experimental laboratory work and theoretical software simulations which are intended to mimic actual optical fiber transmission. One aspect of the project work involves designing the optical communication system which is used to evaluate the probabilities of transmission errors in the form of false detections and losses of light. During the project work, the BPPM protocol is implemented and used for software simulated error generation and correction. With the available laboratory setup used as the point of reference, error-correction using the BPPM protocol is studied using pulses of light containing more than one photon. The results show that the BPPM protocol can be used to recover some of the information that is lost during optical fiber transmission. Factors such as the size of the codewords, the number of photons per pulse and detection efficiency of the utilized single photon detector (SPD) have a significant impact on the success of the transmission.

Multipulse pulse position modulation (MPPM) has been widely proposed to improve data rate over the traditional pulse position modulation (PPM) in free-space optical communication systems. However, there is no known efficient method of encoding MPPM codewords. Furthermore, MPPM is not the optimal coding scheme (in terms of data rate) given the two main constraints of optical systems (duty cycle and zero runlength). In this work, an improved encoding technique for MPPM is provided as well as an analysis of regions where significant rate gain over MPPM is achievable. A new coding technique based on constrained coding is introduced that allows construction of codes which achieves considerable rate gain over comparable MPPM systems. In addition, our new codes allow for convenient concatenation with an outer-code and are suitable for iterative decoding. Simulation results show that these codes can achieve a $6$ dB coding gain over comparable MPPM systems.

Multipulse pulse position modulation (MPPM) has been widely proposed to improve data rate over the traditional pulse position modulation (PPM) in free-space optical communication systems. However, there is no known efficient method of encoding MPPM codewords. Furthermore, MPPM is not the optimal coding scheme (in terms of data rate) given the two main constraints of optical systems (duty cycle and zero runlength). In this work, an improved encoding technique for MPPM is provided as well as an analysis of regions where significant rate gain over MPPM is achievable. A new coding technique based on constrained coding is introduced that allows construction of codes which achieves considerable rate gain over comparable MPPM systems. In addition, our new codes allow for convenient concatenation with an outer-code and are suitable for iterative decoding. Simulation results show that these codes can achieve a $6$ dB coding gain over comparable MPPM systems.

International Telemetering Conference Proceedings / October 29-November 02, 1990 / Riviera Hotel and Convention Center, Las Vegas, Nevada / This paper describes the technical principle that signals conversion, data-processing and data storage are directly carried out without filling up with the reference pulse for PPM and PPK (pulse position keying). By means of analysis for typical frame structure of PPM/PPK signals, a variety of math models of signal time relationship of the system were found, and based on this, a engineering way and a principle block diagram for signals conversion, data processing and data storage were given out.

Despite the fact ultra-wideband (UWB) technology has been around for over 30 years, there is a newfound excitement about its potential for communications. With the advantageous qualities of multipath immunity and low power spectral density, researchers are examining fundamental questions about UWB communication systems. In this work, we examine UWB communication systems paying particular attention to transmitter and receiver design. This thesis is specifically focused on a software radio transceiver design for impulse-based UWB with the ability to transmit a raw data rate of 100 Mbps yet encompasses the adaptability of a reconfigurable digital receiver. A 500 ps wide Gaussian pulse is generated at the transmitter utilizing the fast-switching characteristics of a step recovery diode. Pulse modulation is accomplished via several stages of RF switches, filters, and amplifiers on a fully designed printed circuit board specifically manufactured for this project. Critical hardware components at the receiver consist of a bank of ADCs performing parallel sampling and an FPGA employed for data processing. Using a software radio design, various modulation schemes and digital receiver topologies are accommodated along with a vast number of algorithms for acquisition, synchronization, and data demodulation methods. Verification for the design is accomplished through transmitter hardware testing and receiver design simulation. The latter includes bit error rate testing for a variety of modulation schemes and wireless channels using a pilot-based matched filter estimation technique. Ultimately, the transceiver design demonstrates the advantages and challenges of UWB technology while boasting high data rate communication capability and providing the flexibility of a research testbed. / Master of Science

This thesis explores the use of single-photon avalanche diodes (SPADs) for visible light communications (VLC). The high sensitivity of SPADs can potentially enhance the performance of VLC receivers. However, a SPAD-based system has challenges that need to be addressed before it can be considered as a viable option for VLC. The first challenge is the susceptibility of SPAD-based receivers to variations in ambient light. The high sensitivity of SPADs is advantageous for signal detection, but also makes SPADs vulnerable to variations in ambient light. In this thesis, the performance of a SPAD-based receiver is investigated under changing lighting conditions. Analytical expressions to quantify performance are derived, and an experiment is conducted to gain further understanding of system performance. It is shown that a SPAD-based receiver is highly sensitive to illumination changes when on-off keying (OOK) is employed, and that pulse-position modulation (PPM) is a preferred modulation scheme as it is more robust. The second challenge is broadcasting to SPAD-based receivers with different capabilities. A traditional broadcasting scheme is time-sharing, whereby a transmitter sends data to receivers in an alternating manner. Broadcasting to SPAD-based receivers is challenging as receivers may have diverse capabilities. In this thesis, a new multiresolution modulation scheme is proposed, which can potentially improve system performance over the traditional timesharing approach. The performance of the proposed scheme is analyzed, and a proof-of-concept experiment is performed to demonstrate its viability.

Timing offsets result from the use of real clocks that are non-ideal in sampling intervals. These offsets also known as timing jitter were shown to degrade the performance of the two forms of UWB systems impulse radio and orthogonal frequency division multiplexing (OFDM)-based UWB. It was shown that for impulse radio, timing jitter distorts the correlation property of the transmitted signal and the resulting performance loss is proportional to the root-mean-square (RMS) value of the timing jitter. For the OFDM-based UWB, timing jitter introduced inter-channel interference (ICI) and the performance loss was dependent on the product of the bandwidth and the RMS of the timing jitter. A number of techniques were proposed for mitigating the performance degradation in each form of UWB. Specifically, for impulse radio, the methods of pulse shaping and sample averaging were provided, whereas for OFDM-based UWB, oversampling and adaptive modulation were given. Through analysis and simulation, it was shown that substantial gain in signal power-to-noise ratio can be achieved using these jitter-reduction methods.

Οι τεχνικές ασύρματης μετάδοσης Ultra Wide Band (UWB) είναι γνωστές εδώ και αρκετές δεκαετίες. Το ϐασικό χαρακτηριστικό των συγκεκριμένων συστη- μάτων είναι η εκπομπή και λήψη σήματος που εκτείνεται σε πολύ μεγάλο εύρος συχνοτήτων. Τα τελευταία χρόνια παρατηρείται διαρκώς αυξανόμενο ερευνητικό ενδιαφέρον γύρω από την περιοχή των τηλεπικοινωνιακών συ- στημάτων που χρησιμοποιούν UWB τεχνικές μετάδοσης, κυρίως λόγω της μεγάλης εφαρμοσιμότητάς της. Στις τηλεπικοινωνιακές εφαρμογές, η χρήση της τεχνικής UWB μπορεί να οδηγήσει σε αύξηση των ταχυτήτων ασύρματης μετάδοσης, λόγω της δυνατότητας εκπομπής μεγάλου αριθμού παλμών σε πολύ μικρό χρονικό διάστημα. Σε εφαρμογές εντοπισμού, το UWB μπορεί να ωθήσει προς την αύξηση της διακριτικής τους ικανότητας. Επίσης, κατάλ- ληλα UWB σήματα μπορούν να χρησιμοποιηθούν όπου υπάρχει ανάγκη για υψηλή διεισδυτικότητα μέσα από εμπόδια. Ο πιο απλός τρόπος μετάδοσης σήματος τέτοιου είδους είναι η εκπομ- πή εξαιρετικά σύντομων παλμών. Ο τρόπος με τον οποίο τα μεταδιδόμενα σύμβολα διαμορφώνουν αυτούς τους παλμούς ποικίλλει. Οι πρώτες UWB εφαρμογές χρησιμοποιούσαν σχεδόν αποκλειστικά την τεχνική Dιαμόρφωσης Θέσης Παλμού (Pulse Position Modulation PPM) γιατί η αντιστροφή πολύ σύντομων παλμών ήταν δύσκολο να υλοποιηθεί. Με αυτή την τεχνική, το κάθε μεταδιδόμενο σύμβολο καθορίζει τη ϑέση του παλμού στο πεδίο του χρόνου. Αργότερα, άρχισαν να χρησιμοποιούνται και τεχνικές Dιαμόρφωσης Πλάτους Παλμού (Pulse Amplitude Modulation PAM). Wστόσο, ένα μεγάλο πλεονέκτημα της μεθόδου PPM είναι οι μειωμένες απαιτήσεις της σε ισχύ, γιατί μεταδίδονται πολύ σύντομοι παλμοί ακολουθούμενοι από σχετικά με- γάλες περιόδους «σιωπής». Η ιδιότητα αυτή, καθιστά τη μέθοδο διαμόρφωσης PPM ιδιαίτερα ελκυστική σε εφαρμογές που απαιτούν χαμηλή κατανάλωση ισχύος. Σε αυτή την εργασία μελετούμε τη δομή ενός συστήματος μετάδοσης δε- δομένων Ultra Wide Band το οποίο χρησιμοποιεί τη μέθοδο διαμόρφωσης PPM. Η συμπεριφορά ενός τέτοιου συστήματος κατά τη μετάδοση μέσα από διάφορα κανάλια παρουσία ϑορύβου εξετάζεται μέσω εξομοίωσης. Είναι γνω- στό ότι τα συστήματα αυτά πλήττονται τόσο από το ϑόρυβο που εισάγεται λό- γω της μετάδοσης, διασυμβολική παρεμβολή, αλλά και παρεμβολή ανάμεσα στους πολλαπλούς χρήστες. Επίσης, οι περιορισμοί που ορίστηκαν στις ΗΠΑ για την μεταδιδόμενη ισχύ ανά συχνότητα των εμπορικών UWB εφαρμογών, οι οποίοι αναμένεται να υιοθετηθούν και στον υπόλοιπο κόσμο, αποτελούν ένα επιπλέον ϑέμα που επηρεάζει την επίτευξη υψηλών ϱυθμών μετάδοσης δεδομένων. Μια λύση είναι η χρήση τεχνικών ισοστάθμισης ή, ισοδύναμα, μεθόδων εκτίμησης του καναλιού που λειτουργούν στο δέκτη. Αν και οι κλασικές τεχνικές ισοστάθμισης ή εκτίμησης καναλιού μπορούν να εφαρμο- στούν με μικρές τροποποιήσεις και σε UWB σήματα διαμορφωμένα με PPM, ένα ϐασικό εμπόδιο είναι τόσο το μεγάλο πλήθος παραμέτρων που πρέπει να εκτιμηθούν (ένα τυπικό κανάλι σε εσωτερικό χώρο μπορεί να έχει ακόμη και πάνω από 150 συντελεστές), όσο και ο πολύ μεγάλος ϱυθμός δειγματοληψίας που απαιτείται. Επίσης, ϕαίνεται ότι μπορούν να αξιοποιηθούν τα ιδιαίτερα χαρακτηριστικά που εμφανίζει η εφαρμογή της διαμόρφωσης PPM σε UWB συστήματα, όπως είναι το ϕαινόμενο πολλαπλών μονοπατιών (multipath) σε συνδυασμό με την υψηλή διακριτικότητα (resolution) του σήματος UWB, ή ακόμη και η δυνατότητα μετάδοσης του ίδιου συμβόλου περισσότερες από μί- α ϕορές. Στα πλαίσια της εργασίας ϑα μελετηθούν και ϑα ενσωματωθούν στο σύστημα υπάρχουσες μέθοδοι εκτίμησης ή ισοστάθμισης καναλιού, οι οποί- ες αποτελούν προϊόν πρόσφατων προσπαθειών προς αυτή την κατεύθυνση. Θα μελετηθεί ο τρόπος με τον οποίο επιδρούν στην απόδοση του συστήμα- τος. Τέλος, ϑα εξεταστεί η δυνατότητα επέκτασης των μεθόδων εκτίμησης καναλιού με σκοπό τη ϐελτίωση της υπολογιστικής τους πολυπλοκότητας, μετατρέποντάς τους σε επαναληπτικούς/προσαρμοστικούς αλγορίθμους. / -

CoordenaÃÃo de AperfeiÃoamento de NÃvel Superior / Neste trabalho, foram investigadas as caracterÃsticas de operaÃÃo de um Acoplador Direcional NÃo-Linear(NLDC) Duplo SimÃtrico, trabalhando com pulsos de , em duas diferentes aplicaÃÃes: ObtenÃÃo de portas lÃgicas E e OU, sob ModulaÃÃo Por PosiÃÃo de Pulsos (PPM); obtenÃÃo de portas lÃgicas E e OU, sob ModulaÃÃo Por Amplitude de Pulsos (PAM). A investigaÃÃo à realizada, atravÃs de simulaÃÃes numÃricas, utilizando-se do mÃtodo de Runge Kutta de quarta ordem. Na primeira aplicaÃÃo, à analisada a possibilidade da realizaÃÃo de operaÃÃes lÃgicas pelo Acoplador Direcional NÃo-Linear (NLDC) Duplo SimÃtrico sem perda. Considerando a operaÃÃo das portas lÃgicas, foram utilizadas as quatro possÃveis combinaÃÃes para dois pulsos, nas fibras 1 e 2, modulados pela posiÃÃo temporal (PPM) nos nÃveis lÃgicos 0 ou 1. Foram investigados os efeitos de uma variaÃÃo no parÃmetro de ajuste da modulaÃÃo PPM, ou seja, no deslocamento inicial do pulso em relaÃÃo ao pulso referencial, ou informaÃÃo nÃo modulada, e na diferenÃa de fase entre os pulsos sÃlitons fundamentais de entrada devidamente modulados. Na segunda aplicaÃÃo, o NLDC duplo simÃtrico à submetido à modulaÃÃo PAM, utilizando-se tambÃm, das quatro combinaÃÃes possÃveis para os dois pulsos, nas fibras de entrada. Foram investigados os efeitos da variaÃÃo no parÃmetro de ajuste da modulaÃÃo PAM na amplitude inicial do pulso em relaÃÃo à amplitude de referÃncia, ou sinal sem modulaÃÃo, e tambÃm observada a amplitude de saÃda modulada versus uma diferenÃa de fase entre os pulsos sÃlitons fundamentais de entrada devidamente modulados. Nas duas aplicaÃÃes foram obtidas portas lÃgicas E e OU. / In this work, the performance study of a Symmetric Dual-Core Non-Linear Directional Coupler (NLDC), working with pulses of , in two different applications have been investigated: accomplishment of logical gates AND and OR, under Pulse Position Modulation (PPM); accomplishment of logical gates AND and OR, under Pulse Amplitude Modulation (PAM). The investigation is based in a numerical simulation study, using the fourth order Runge Kutta numerical method. In the first application, the possibility of the accomplishment of logical operations by Symmetric Dual-Core Non-Linear Directional Coupler (NLDC) without loss is analyzed. Considering the operation of the logical gates, the four possible combinations for two pulses, on the input fibers, modulated by the temporal PPM in the logical levels 0 or 1, were used. The effects of a variation in the coding parameter offset of the PPM modulation, that is, in the displacement of the input pulse relative to the reference time level, was investigated. In the second application, the symmetric dual-core NLDC is submitted to PAM modulation, using the four possible combinations for two pulses on the input fibers, were used, as well. The effects of a variation in the coding parameter offset of the PAM modulation relative to the reference amplitude, was investigated. The modulated output amplitude versus a phase difference between the input pulses , was also studied. On the two applications, logical gates AND and OR was observed.