Se propõe uma estrutura alternativa para equalização adaptativa em rádio digital de microondas, obtida pela introdução de modificações em um cancelador de interferência intersimbólica. A um estágio linear de equalização são acrescentados estágios de cancelamento da interferência intersimbólica que operam com decisões preliminares dos símbolos transmitidos. O número de estágios de decisões preliminares não é restrito a um, no entanto, as decisões preliminares podem assumir níveis intermediários entre os símbolos nominais. Em uma implementação digital da função de equalização, o cancelador de interferência intersimbólica modificado implica em uma menor complexidade do circuito. Isto decorre do número reduzido de bits necessários para codificar as decisões preliminares e da menor sensibilidade do estágio linear do cancelador aos erros de quantização. Para a caracterização da estrutura proposta e do equalizador linear foi realizado um programa para computador pessoal. Particularmente para o cálculo da taxa de erro decorrente da distroção provocada por propagação multipercurso foi desenvolvida um extensão do método da integração numérica da função característica da interferência intersimbólica. O efeito dos erros nas decisões preliminares e dos erros de quantização é levado em conta no método desenvolvido. / An alternative structure is proposed for adaptive equalization in digital microwave radio. It is obtained by the introduction of modifications in an intersymbol interference canceller. Canceller stages, operating with preliminary decisions of the transmitted symbols are added to a conventional linear equalizer stage. The number of canceller stages, though, is not limited to one, and preliminary decisions are allowed to take intermediate levels between the nominal symbols. In a digital implementation of the equalization function, the modified intersymbol canceller implies in lower circuit complexity than does a linear equalizer with equivalent, or even lower, performance. This derives from the small number of bits required to codify the preliminary decisions, and from the lower sensitivity of the canceller\'s linear stage to quantization errors. In order to characterize the performance of the proposed structure and that of the linear equalizer, a personal computer program was built. Particularly, to calculate the error rate due to multipath induced distortion (the receiver\'s signature), an extension to the method of integrating the characteristic function of intersymbol interference was developed. The extension takes into account, within certain validity limits, the effect of errors in the preliminary decisions. The effect of signal and coefficient quantization is also taken into account. The interaction of the modified canceller with the demodulator\'s carrier recovery circuit is compared with that of a linear equalizer, and it is verified that the proposed structure is compatible with already in use methods of accomplishing that function.

Este trabalho apresenta uma nova aplicação de wavelets em sistemas de espalhamento espectral. A aplicação apresentada foi realizada no contexto de detecção multiusuário e pode ser empregada em sistemas de acesso múltiplo por divisão de código. A detecção e a estimação são realizadas através de um algoritmo de inferência bayesiana, empregando o Amostrador de Gibbs e utilizando as wavelets para melhorar a relação sinal ruído na recepção. Na transmissão, um código específico, baseado na wavelet de Haar, modula o sinal contendo a informação preparando-o contra alterações que possam ocorrer devido a características intrínsecas do canal de ruído branco, gaussiano e aditivo. Esta técnica foi aqui denominada de modulação wavelet. Na recepção, uma transformada wavelet de Haar é aplicada ao sinal, gerando coeficientes wavelets. A ortogonalidade da wavelet de Haar torna possível executar um procedimento de cancelamento de ruído, em inglês denoising, que melhora a qualidade da recepção. Para validar a abordagem apresentada neste trabalho, foi executada uma série de simulações. Os resultados mostraram um melhor desempenho sistêmico com o emprego de wavelets. Nas simulações foram observados vários parâmetros de sistema, dentre eles e amplitude do sinal, a taxa de erro de bits (BER, bit error rate) e a variância do sinal. Os resultados foram bastante satisfatórios, indicando uma redução do ruído da ordem de 3dB em relação ao valor sem cancelamento de ruído. Este trabalho abre novas oportunidades de pesquisa para o uso de wavelets em sistemas de espalhamento espectral e telecomunicações em geral. / This work presents a new application of wavelets to spread spectrum systems. The presented application was made in the context of multiuser detection and can be used in code-division multiple access systems. Detection and estimation are performed through a Bayesian inference algorithm and, employing the Gibbs sampler and utilizing wavelets to improve the signal-to-noise ratio at the reception. At the transmission, a specific code based on the Haar wavelet modulates the signal containing the information, preparing it to alterations that may occur due to the intrinsic characteristics of the additive Gaussian noise channel. This technique was here denominated wavelet modulation. At the reception, a Haar wavelet transform is applied to the signal, generating wavelet coefficients. The orthogonality of the Haar wavelet makes it possible to perform a noise cancelling process, called denoising, which enhances the receiving quality. To validate the approach presented in this work, a number of simulations were performed. The results showed a better system performance with the use of wavelets. Several parameters were monitored in the simulations, among them the signal amplitude, de BER (bit error rate), and the signal variance. The results were very satisfactory, indicating a noise reduction of approximately 3dB referred to the value without noise cancelling. This work opens new research opportunities for the use of wavelets in spread spectrum systems and Telecommunications in general.

Se propõe uma estrutura alternativa para equalização adaptativa em rádio digital de microondas, obtida pela introdução de modificações em um cancelador de interferência intersimbólica. A um estágio linear de equalização são acrescentados estágios de cancelamento da interferência intersimbólica que operam com decisões preliminares dos símbolos transmitidos. O número de estágios de decisões preliminares não é restrito a um, no entanto, as decisões preliminares podem assumir níveis intermediários entre os símbolos nominais. Em uma implementação digital da função de equalização, o cancelador de interferência intersimbólica modificado implica em uma menor complexidade do circuito. Isto decorre do número reduzido de bits necessários para codificar as decisões preliminares e da menor sensibilidade do estágio linear do cancelador aos erros de quantização. Para a caracterização da estrutura proposta e do equalizador linear foi realizado um programa para computador pessoal. Particularmente para o cálculo da taxa de erro decorrente da distroção provocada por propagação multipercurso foi desenvolvida um extensão do método da integração numérica da função característica da interferência intersimbólica. O efeito dos erros nas decisões preliminares e dos erros de quantização é levado em conta no método desenvolvido. / An alternative structure is proposed for adaptive equalization in digital microwave radio. It is obtained by the introduction of modifications in an intersymbol interference canceller. Canceller stages, operating with preliminary decisions of the transmitted symbols are added to a conventional linear equalizer stage. The number of canceller stages, though, is not limited to one, and preliminary decisions are allowed to take intermediate levels between the nominal symbols. In a digital implementation of the equalization function, the modified intersymbol canceller implies in lower circuit complexity than does a linear equalizer with equivalent, or even lower, performance. This derives from the small number of bits required to codify the preliminary decisions, and from the lower sensitivity of the canceller\'s linear stage to quantization errors. In order to characterize the performance of the proposed structure and that of the linear equalizer, a personal computer program was built. Particularly, to calculate the error rate due to multipath induced distortion (the receiver\'s signature), an extension to the method of integrating the characteristic function of intersymbol interference was developed. The extension takes into account, within certain validity limits, the effect of errors in the preliminary decisions. The effect of signal and coefficient quantization is also taken into account. The interaction of the modified canceller with the demodulator\'s carrier recovery circuit is compared with that of a linear equalizer, and it is verified that the proposed structure is compatible with already in use methods of accomplishing that function.

Este trabalho apresenta uma nova aplicação de wavelets em sistemas de espalhamento espectral. A aplicação apresentada foi realizada no contexto de detecção multiusuário e pode ser empregada em sistemas de acesso múltiplo por divisão de código. A detecção e a estimação são realizadas através de um algoritmo de inferência bayesiana, empregando o Amostrador de Gibbs e utilizando as wavelets para melhorar a relação sinal ruído na recepção. Na transmissão, um código específico, baseado na wavelet de Haar, modula o sinal contendo a informação preparando-o contra alterações que possam ocorrer devido a características intrínsecas do canal de ruído branco, gaussiano e aditivo. Esta técnica foi aqui denominada de modulação wavelet. Na recepção, uma transformada wavelet de Haar é aplicada ao sinal, gerando coeficientes wavelets. A ortogonalidade da wavelet de Haar torna possível executar um procedimento de cancelamento de ruído, em inglês denoising, que melhora a qualidade da recepção. Para validar a abordagem apresentada neste trabalho, foi executada uma série de simulações. Os resultados mostraram um melhor desempenho sistêmico com o emprego de wavelets. Nas simulações foram observados vários parâmetros de sistema, dentre eles e amplitude do sinal, a taxa de erro de bits (BER, bit error rate) e a variância do sinal. Os resultados foram bastante satisfatórios, indicando uma redução do ruído da ordem de 3dB em relação ao valor sem cancelamento de ruído. Este trabalho abre novas oportunidades de pesquisa para o uso de wavelets em sistemas de espalhamento espectral e telecomunicações em geral. / This work presents a new application of wavelets to spread spectrum systems. The presented application was made in the context of multiuser detection and can be used in code-division multiple access systems. Detection and estimation are performed through a Bayesian inference algorithm and, employing the Gibbs sampler and utilizing wavelets to improve the signal-to-noise ratio at the reception. At the transmission, a specific code based on the Haar wavelet modulates the signal containing the information, preparing it to alterations that may occur due to the intrinsic characteristics of the additive Gaussian noise channel. This technique was here denominated wavelet modulation. At the reception, a Haar wavelet transform is applied to the signal, generating wavelet coefficients. The orthogonality of the Haar wavelet makes it possible to perform a noise cancelling process, called denoising, which enhances the receiving quality. To validate the approach presented in this work, a number of simulations were performed. The results showed a better system performance with the use of wavelets. Several parameters were monitored in the simulations, among them the signal amplitude, de BER (bit error rate), and the signal variance. The results were very satisfactory, indicating a noise reduction of approximately 3dB referred to the value without noise cancelling. This work opens new research opportunities for the use of wavelets in spread spectrum systems and Telecommunications in general.

Thesis (Master of Engineering in Electrical Engineering)--Cape Peninsula University of Technology, 2017. / This dissertation presents the development of a quadrature phase shift keying (QPSK) demodulator for nanosatellites that complies with both the limited resources associated with nanosatellites as well as the flexibility and configurability required for a software defined radio (SDR) platform. This research project is a component of a bigger project, which is to develop a high-speed receiver for nanosatellites, and aims to provide a practical solution to the need for communication technologies that support emerging nanosatellite applications, such as Earth observation and communications. The development of the QPSK demodulator follows an all-digital implementation approach. The main reason for selecting this approach is to have a system that is flexible and reconfigurable to comply with the SDR requirements. Another reason for selecting this approach is to comply with the low noise system, low power consumption as well as the small size and weight requirements associated with nanosatellites. The QPSK demodulator is implemented on an IGLOO2 Field Programmable Gate Array (FPGA), due to its robustness to radiation and high-speed capability. Initially, the techniques used to design each subsystem of the QPSK demodulator are selected. Then, algorithms to digitally implement the designed subsystems are produced. Thereafter, the code for the digital QPSK demodulator is written and verified in Matlab first. The simulation of the Matlab-based QPSK demodulator performs satisfactorily. Subsequently, the code to implement the QPSK demodulator on an FPGA (IGLOO2) has been written in Libero, using VHSIC Hardware Description Language (VHDL). The resulting FPGA-based QPSK demodulator has been emulated in Libero (an integration and development environment (IDE) for Microsemi FPGAs) using a test-bench as well as other analysis tools. The test-bench results are visualized using Modelsim. The results show that the demodulator can support data rates up to 13.25 Mbps if 16 samples-per-symbols are used, and up to 26.5 Mbps if 8 samples-per-symbols are used. It also has a very good bit-error-rate performance, which is simulated to be within a factor of 5 of the theoretical limit of QPSK modulation. Finally, the demodulator consumes less than 15 mW at the maximum operating speed. and has been coded to mitigate the effects of space radiation and noise contriution by the demodulator itself.

published_or_final_version / abstract / toc / Electrical and Electronic Engineering / Master / Master of Philosophy

In this thesis, novel error rate performance metrics and transmission solutions are investigated for delay limited communication systems and for co-channel interference scenarios. The following four research problems in particular were considered. The first research problem is devoted to analysis of the higher order ergodic moments of error rates for digital communication systems with time- unlimited ergodic transmissions and the statistics of the conditional error rates of digital modulations over fading channels are considered. The probability density function and the higher order moments of the conditional error rates are obtained. Non-monotonic behavior of the moments of the conditional bit error rates versus some channel model parameters is observed for a Ricean distributed channel fading amplitude at the detector input. Properties and possible applications of the second central moments are proposed. The second research problem is the non-ergodic error rate analysis and signaling design for communication systems processing a single finite length received sequence. A framework to analyze the error rate properties of non-ergodic transmissions is established. The Bayesian credible intervals are used to estimate the instantaneous bit error rate. A novel degree of ergodicity measure is introduced using the credible interval estimates to quantify the level of ergodicity of the received sequence with respect to the instantaneous bit error rate and to describe the transition of the data detector from the non-ergodic to ergodic zone of operation. The developed non-ergodic analysis is used to define adaptive forward error correction control and adaptive power control policies that can guarantee, with a given probability, the worst case instantaneous bit error rate performance of the detector in its transition fi'om the non-ergodic to ergodic zone of operation. In the third research problem, novel retransmission schemes are developed for delay-limited retransmissions. The proposed scheme relies on a reliable reverse link for the error-free feedback message delivery. Unlike the conventional automatic repeat request schemes, the proposed scheme does not require the use of cyclic redundancy check bits for error detection. In the proposed scheme, random permutations are exploited to locate the bits for retransmission in the predefined window within the packet. The retransmitted bits are combined using the maximal-ratio combining. The complexity-performance trade-offs of the proposed scheme is investigated by mathematical analysis as well as computer simulations. The bit error rate of the proposed scheme is independent of the packet length while the throughput is dependent on the packet length. Three practical techniques suitable for implementation are proposed. The performance of the proposed retransmission scheme was compared to the block repetition code corresponding to a conventional ARQ retransmission strategy. It was shown that, for the same number of retransmissions, and the same packet length, the proposed scheme always outperforms such repetition coding, and, in some scenarios, the performance improvement is found to be significant. Most of our analysis has been done for the case of AWGN channel, however, the case of a slow Rayleigh block fading channel was also investigated. The proposed scheme appears to provide the throughput and the BER reduction gains only for the medium to large SNR values. Finally, the last research problem investigates the link error rate performance with a single co-channel interference. A novel metric to assess whether the standard Gaussian approximation of a single interferer underestimates or overestimates the link bit error rate is derived. This metric is a function of the interference channel fading statistics. However, it is otherwise independent of the statistics of the desired signal. The key step in derivation of the proposed metric is to construct the standard Gaussian approximation of the interference by a non-linear transformation. A closed form expression of the metric is obtained for a Nakagami distributed interference fading amplitude. Numerical results for the case of Nakagami and lognormal distributed interference fading amplitude confirm the validity of the proposed metric. The higher moments, interval estimators and non-linear transformations were investigated to evaluate the error rate performance for different wireless communication scenarios. The synchronization channel is also used jointly with the communication link to form a transmission diversity and subsequently, to improve the error rate performance.

The number of digital projects aimed at documenting and preserving communities' intangible cultural heritage (ICH) has grown considerably in recent years. These projects take advantage of the advancement of digital technologies to enable local communities to manage their ICH, in tune with the deprofessionalisation of heritage practices. However, additional work is needed to overcome some of the barriers that are emerging in these endeavours, especially related to long-term sustainability and the technical knowledge required. The thesis follows the progress of two case studies that used wikis to enable participation in the documentation of cultural heritage. Using action research, the researcher introduced or tried to improve the use of wikis in these case studies. The first case study involved a Scottish heritage wiki at a national level, but the project ran into many problems. Although the software was appropriate for facilitating public engagement, the research showed that the emphasis should be put on local heritage rather than national, and that face-to-face interactions providing engagement and training activities should have been more widely used as well. The second case study was the analysis of a wiki dedicated to collating and documenting the ICH of the Isle of Jura, Scotland. The problems encountered in this case study point to the presence of pre-existing conflicts and the contentious nature of heritage on the island as barriers to the project. The main argument of the thesis is that involvement in digital cultural heritage can enhance community empowerment, but that this depends upon social dimensions of community cohesion and engagement as well as technical knowledge of the software and technologies involved.

ME|EMO provides a method to help users to express, visualize and share emotions through digital nonverbal communication. This application will enable the users to map their emotions to colors and encourage users to paint their feelings. A canvas with uncolored images and a color palette with color coded emotions creates an environment for expressing and visualizing the feelings. The result is an image file in the form of a simple piece of modern art with the possibility of sharing it through social networks, or to record the emotions and save precious moments of life. Technology development, new ways of communication, digital tools, apps, social media, have helped people to have a better life by giving people the opportunity to communicate easier with loved ones and friends. ME|EMO tries to enhance the way of modern communication (digital text-based) such as social networks or modern healthcare systems, by supporting the emotional side of communications.

En la actualidad, el Perú ocupa el puesto número 65 de un total de 140 países a nivel mundial, con respecto al tiempo que le dedica la población al voluntariado (CAF, 2018). Además, en Europa, se ha presentado un estancamiento durante los últimos cinco años: África un incremento de 2% y, finalmente, Asia, Oceanía y América un decrecimiento de 2%, 1% y 2%, respectivamente (CAF, 2018). Según este panorama, el voluntariado a nivel mundial presenta un decrecimiento alarmante debido a la carencia de personal voluntario que apoye a las organizaciones e instituciones sin fines de lucro. Con la presente investigación se busca encontrar la relación entre las variables comunicación digital e influencers con la captación online de voluntarios, con la finalidad de que las organizaciones sin fines de lucro puedan considerarlas durante su proceso de captación de manera eficiente. Para lograr lo mencionado se utilizaron técnicas de recolección de datos de tipo cualitativos y cuantitativos. El presente estudio se centrará en voluntarios jóvenes, con un rango de edad entre los 15 y 29 años, y que participan de manera activa en una organización sin fines de lucro. Cabe mencionar que los resultados de esta investigación podrán ser generalizados a toda organización, institución o empresa que cuente con voluntarios. / Currently, Peru occupies the 65th position of a total of 140 countries worldwide, with respect to the time the population dedicates to volunteering (CAF, 2018). In addition, in Europe, there has been a stagnation during the last five years: Africa an increase of 2% and, finally, Asia, Oceania and America a decrease of 2%, 1% and 2%, respectively (CAF, 2018). According to this scenario, worldwide volunteering shows an alarming decrease due to the lack of volunteer staff that support nonprofit organizations and institutions. This research seeks to find the relationship between the variables digital communication and influencers with the online recruitment of volunteers, so that non-profit organizations can consider them during their recruitment process efficiently. To achieve the aforementioned qualitative and quantitative data collection techniques were used. The present study will focus on young volunteers, with an age range between 15 and 29 years, and who actively participate in a non-profit organization. It should be mentioned that the results of this research may be generalized to any organization, institution or company that has volunteers. / Trabajo de investigación