ITC/USA 2011 Conference Proceedings / The Forty-Seventh Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2011 / Bally's Las Vegas, Las Vegas, Nevada / This paper concentrates on aircraft specific issues and impacts of utilizing a "C" band telemetry system on a new or existing instrumentation system.

Approved for public release, distribution is unlimited / Despite the increase in the demand for high speed Internet services, the last-mile solutions currently available neither are inexpensive enough to attract the majority of the population, nor are they available in low density populated areas. This thesis examines Fixed Broadband Wireless (FBW) as an alternative technology to the current last-mile solutions. The analysis shows that LMDS and MMDS are the most promising emerging FBW technologies and that they are able, by utilizing microwave radio as their fundamental transport medium and using high modulation schemes, to provide digital two-way voice, data, video and Internet services. The thesis shows that both technologies are constrained by free space loss and line-of-sight impairments with rain absorption being the most significant cause of attenuation in the LMDS case, while vegetation and multipath fading play a significant role mostly in the MMDS case. Additionally, it is shown that there is a positive association between the data rate achieved and the level of influence due to Additive White Gaussian Noise (AWGN). Based on the analysis and using the coverage areas, the total capacity, the achieved data rates, the weather and line-of-sight limitations as well as the cost as the most important criteria, it is concluded that LMDS is a preferable solution for enterprise end-users in densely populated urban areas outside the reach of fiber networks, while MMDS targets residential end-users in rural or suburban areas that are not able to receive service through high-speed wireline connections. / Lieutenant Junior Grade, Hellenic Navy

Die extrem große Bandbreite, die UWB-Systeme zur Übertragung von Daten nutzen können, ermöglicht theoretisch eine sehr hohe Datenrate. Eine mögliche Umsetzung der UWB-Technologie ist die sogenannte Multiband-Impuls-Radio-Architektur (MIRA). Dieses UWB-System basiert auf der Übertragung von Daten mittels kurzer Impulse parallel in mehreren Frequenzbändern. Als Empfänger kommen einfache Energiedetektoren zum Einsatz. Diese Komponenten haben entscheidenden Einfluss auf die Leistungsfähigkeit des gesamten Systems. Deshalb liegt der Schwerpunkt dieser Arbeit auf der Untersuchung der Leistungsfähigkeit und im speziellen der Herleitung der Bitfehlerwahrscheinlichkeiten für Energiedetektoren in unterschiedlichen UWB-Kanälen. Aufgrund des sehr einfachen Aufbaus eines Energiedetektors wird dieser auch in vielen anderen Bereichen eingesetzt. So werden Energiedetektoren zur Detektion von freien Bereichen im Übertragungsspektrum bei Cognitive Radio und für weitere unterschiedliche Übertragungssysteme wie z.B. Sensorsysteme mit geringer Datenrate und Übertragungssysteme die zusätzlich Ortung ermöglichen, genutzt.

With code division multiple access (CDMA) systems being the prominent multiple access scheme for the air interface for 3G cellular systems, most standardisation bodies have based their terrestrial cellular systems on DS-CDMA (W-CDMA, UMTS, cdma2000). With 4G systems fast approaching, bringing with them improved services and quality of service standards, there is growing interest in further investigating and developing more efficient multiple access techniques such as multicarrier CDMA (MC-CDMA) systems. MC-CDMA combines multicarrier modulation (MCM), namely OFDM, with CDMA profiting from the benefits of both multiplexing techniques; as such, MC-CDMA is emerging as a possible candidate for the air interface multiple access scheme for 4G cellular systems. Multiple access interference (MAI) is a limiting factor of CDMA systems in terms of system capacity as orthogonally designed spreading sequences lose their orthogonality in the presence of timing misalignments amongst mobile subscribers in a cell; such is the case over the uplink channel. Ensuring orthogonal code properties minimises the MAI over synchronous environments, however, it is when the users are allowed to transmit asynchronously, as is the case over the uplink channel, that MAI inflicts significant performance degradation. In CDMA systems, all subscribers are active on the same frequency band simultaneously and signal separation is facilitated upon reception via the properties of the assigned spreading codes. Under asynchronous conditions the code properties alone do not provide the necessary separation and an additive MAI term remains in the detection process. In addition to the separation abilities of the spreading codes, a further method of deciphering the desired subscriber signal from the interfering subscriber signals is sought. In this thesis we propose a statistical model for both the probability density function (pdf) of the total MAI power and the corresponding bit-error rate (BER) observed during asynchronous CDMA transmission. The modelling offers the full statistic the MAI power and resulting BER, not just the first and second order statistics. In addition to statistically quantifying the MAI power, the thesis also proposes a technique for the successful reduction of MAI caused by asynchronous transmission. This interference reduction technique is derived from an ambiguity domain analysis of the asynchronous CDMA detection problem and its application to both the DS-CDMA and MC-CDMA multiplexing techniques is presented and the results show significant MAI reduction, and thus an improved the BER. A methodology for the approximation of the total MAI power pdf and the resulting BER pdf is proposed for the asynchronous DS-CDMA and MC-CDMA techniques. This methodology is derived for the use of Walsh-Hadamard (WH) and Gold spreading sequences, however, it is applicable to any given set of deterministic spreading sequences. The total MAI power pdfs of both systems are statistically modelled as being Nakagamim distributed and the corresponding BER modelling is derived from the Nakagami-m formulation offering the full statistic of both the incurred MAI power and the achievable BER. The proposed pdf acquisition methodology and statistical models can be used as analysis tools to assess the relative performances of the DS-CDMA and MC-CDMA techniques for a variety of communications environments. Here the asynchronous uplink channel is considered in the absence of fading and the results show a clear distinction between the BER performances of the MC-CDMA and DS-CDMA systems, for which the MC-CDMA system offers a superior performance for the purely asynchronous channel considered. The results suggest a higher resistance to MAI in the MC-CDMA technique in comparison to the DS-CDMA system for the considered transmission scenario. Following ambiguity function analysis of the asynchronous CDMA detection problem, the concept of dual-frequency switching is introduced to the existing DS-CDMA and MC-CDMA techniques giving rise to the proposed dual-frequency DS-CDMA (DF/DSCDMA) and dual-frequency MC-CDMA (DF/MC-CDMA) schemes. Periodically switching the carrier frequency between dual frequency bands at consecutive symbol boundaries facilitates partial CDMA signal separation upon asynchronous reception. Such switching of the carrier frequency induces a separation in frequency between offset interference signals and the reference signal; this is equivalent to shifting the energy concentration of the interference signals away form the ambiguity domain origin (representing the decision variable of the matched filter). Further MAI reduction is demonstrated through careful design of the dual carrier frequencies. The newly proposed DF systems clearly outperform the standard DS-CDMA and MC-CDMA systems when adopting equivalent spreading factors. The DF/DS-CDMA technique in particular achieves the most MAI reduction and in doing so, surpasses all other considered techniques to offer the best BER performance for the purely asynchronous channel considered. In terms of bandwidth usage, the DF/DS-CDMA band width is 1.5 times that of the DF/MC-CDMA system and from the BER results presented, one may argue that DF/MC-CDMA offers the better BER given the bandwidth usage. The multicarrier systems presented, MC-CDMA and DF/MC-CDMA, offer attractive BER performances for the bandwidth used and it is concluded that MC-CDMA is a genuine candidate for the uplink air interface multiple access scheme for future mobile cellular technologies.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-03-08T12:29:03Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) JOAO VICTOR DE CARVALHO EVANGELISTA_DISSERTACAO_VERSAO_FINAL_2016.pdf: 4051425 bytes, checksum: c53a5039b8aa3054c77f2ee82a10849f (MD5) / Made available in DSpace on 2017-03-08T12:29:03Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) JOAO VICTOR DE CARVALHO EVANGELISTA_DISSERTACAO_VERSAO_FINAL_2016.pdf: 4051425 bytes, checksum: c53a5039b8aa3054c77f2ee82a10849f (MD5) Previous issue date: 2016-08-16 / Message authentication, which ensures that a received message comes from its acclaimed sender, is of fundamental importance for secure communication systems. We consider in this work a physical layer authentication system employing tag signals embedded in the message to provide a robust authentication method. This work diverges from previous work in the area when it comes to the tag generation method. While the previous works use methods based on cryptographic hash functions or on the channel side information our system employs unidimensional chaotic maps to generate these tags. Due to the loss of information about the initial condition of chaotic maps, we show that they are strong candidates for the tag generation process. We prove that chaotic tags provide a positive lower bound on the unconditional security of the system. Additionally, we calculate the probability of success for three possible attacks to the authentication system: impersonation, substitution and replay.Finally, we analyze how the system parameters affect these probabilities and some performance metrics (bit error rate, outage probability, probability of false negative) and explore the tradeoff between security and performance in order to provide guidelines to design the system. / A autenticação de mensagem, o que garante que uma mensagem recebida vem de seu aclamado remetente, é de fundamental importância para sistemas de comunicação seguros. Neste contexto, considera-se neste trabalho um sistema de autenticação em camada física empregando tags embutidos nas mensagens proporcionando um robusto método de autenticação. Este trabalho diverge de trabalhos anteriores na área no que se refere ao método de geração de tags. Enquanto os trabalhos anteriores utilizam métodos baseados em funções criptográficas de hash e na informação do estado do canal, nosso sistema emprega mapas caóticos unidimensionais para gerar os tags. Devido ao fato de que a informação sobre a condição inicial se perde ao longo de uma órbita caótica mostraremos que elas são fortes candidatas para o processo de geração de tags. Provamos que tags caóticos garantem um limitante inferior positivo na segurança incondicional do sistema. Adicionalmente, nós calculamos a probabilidade de sucesso de três tipos de ataque: de personificação, de substituição e de repetição. Para finalizar, analisamos como os parâmetros do sistema afetam essas probabilidades e algumas métricas de performance (taxa de erro por bit, probabilidade de interrupção e probabilidade de falso negativo) e os compromissos entre segurança e performance para prover um guia de projeto do sistema.

This thesis presents and evaluates how to select the data to be logged in an embedded realtime system so as to be able to give confidence that it is possible to perform an accurate identification of the fault(s) that caused any runtime errors. Several log-selection strategies were evaluated by injecting random faults into a simulated real-time system. An instrument was created to perform accurate detection and identification of these faults by evaluating log data. The instrument’s output was compared to ground truth to determine the accuracy of the instrument. Three strategies for selecting the log entries to keep in limited permanent memory were created. The strategies were evaluated using log data from the simulated real-time system. One of the log-selection strategies performed much better than the other two: it minimized processing time and stored the maximum amount of useful log data in the available storage space. / Denna uppsats illustrerar hur det blev fastställt vad som ska loggas i ett inbäddat realtidssystem för att kunna ge förtroende för att det är möjligt att utföra en korrekt identifiering av fel(en) som orsakat körningsfel. Ett antal strategier utvärderades för loggval genom att injicera slumpmässiga fel i ett simulerat realtidssystem. Ett instrument konstruerades för att utföra en korrekt upptäckt och identifiering av dessa fel genom att utvärdera loggdata. Instrumentets utdata jämfördes med ett kontrollvärde för att bestämma riktigheten av instrumentet. Tre strategier skapades för att avgöra vilka loggposter som skulle behållas i det begränsade permanenta lagringsutrymmet. Strategierna utvärderades med hjälp av loggdata från det simulerade realtidssystemet. En av strategierna för val av loggdata presterade klart bättre än de andra två: den minimerade tiden för bearbetning och lagrade maximal mängd användbar loggdata i det permanenta lagringsutrymmet.

Nowadays, network security plays a major role in the field of wireless communications. Wired networks propagate electrical signals or pulses through cables. Whereas wireless signals propagate through the air. If wireless networks are left open and exposed to the outside world, there are high chances of being misused by others. The intruders take advantage of this, to intercept the wireless signals. This is the reason why an extra level of security is required for wireless networks. The physical layer is one of the important layers of the Open System Interconnection (OSI) model which plays an important role in the network’s physical connections like wireless transmission, cabling, connections etc. The physical layer supports the bit-level transmission between various devices by connecting to the physical medium for synchronized communication.In this thesis, a method is studied for exchanging secret key [1] bits using a pseudo-random sequence generator based on Frequency Division Duplex (FDD) systems. The principle of this method is to generate a secret key in a manner that produces low correlation at the intruder. By uniquely relating the secret key bits to the channel in a private version of the universal codebook, a robust key exchange between the transmitter and the receiver is then performed.

Approved for public release; distribution is unlimited. / Trellis-Coded Modulation (TCM) is employed with quadrature amplitude modulation (QAM) to provide error correction coding with no expense in bandwidth. There are two common implementations of TCM, namely pragmatic TCM and Ungerboeck TCM. Both schemes employ Viterbi algorithms for decoding but have different code construction. This thesis investigates and compares the performance of pragmatic TCM and Ungerboeck TCM by implementing the Viterbi decoding algorithm for both schemes with 16-QAM and 64-QAM. Both pragmatic and Ungerboeck TCM with six memory elements are considered. Simulations were carried out for both pragmatic and Ungerboeck TCM to evaluate their respective performance. The simulations were done using Matlab software, and an additive white Gaussian noise channel was assumed. The objective was to ascertain that pragmatic TCM, with its reduced-complexity decoding, is more suitable to adaptive modulation than Ungerboeck TCM. / Civilian

This thesis deals with the demonstration of bit error rate reduction techniques. In the theory section, different techniques of bit error rate reduction are presented, followed by the introduction of the communication channel and the communication system parameters. Each technique is simulated in Matlab Simulink environment using the additive white Gaussian noise channel model. The simulations are captured in waveform oscillograms of all the signal processing stages. The practical section of this thesis offers a functional laboratory solution demonstrating different ways of transmission: a direct-path signal, a path with a cross-correlation receiver and a path using matched filtering. The individual circuits are described in detail, including waveform oscillograms of the signal processing blocks for illustration. Furthermore, the practical section presents printed circuit boards designs, comprehensive documentation for production, measurement results and a sample laboratory protocol.

This thesis deals with Matlab application developed for simulation of the DVB-T channel coder and decoder. The first part of this thesis includes description of terrestrial digital video broadcasting system and comparison with analogue television. Channel coding and OFDM modulation, used in the DVB-T standard, is described in detail. Application developed in the Matlab environment is described in the second part. The application simulates data transfer of the DVB-T system. Results of the simulated transmission, using developed application are presented in the last part. Namely dependence of the BER on the S/N ratio, using various coder settings, was examined. Maximal possible data rate was determined for these various setting. All obtained values are graphically represented.