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This thesis describes the implementation of the physical layer for an experimental low-power wireless communication device. The system utilizes differential coherent correlation and threshold-based detection to produce a robust random-access packet-based communications protocol. Prior to implementing the system in hardware, the detection algorithm was rigorously simulated with a software model in C. The simulations revealed the tradeoffs between the packet miss performance and different system parameters such as input bit precision and threshold value. Having determined a suitable configuration, the detection algorithm was implemented on an FPGA platform. The focus of the FPGA design was on throughput and resource utilization. The final system utilizes approximately 6% of the slices available on a Xilinx Virtex II XC2V8000 FPGA and has a throughput of about 5 MChips/Second.

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ITC/USA 2009 Conference Proceedings / The Forty-Fifth Annual International Telemetering Conference and Technical Exhibition / October 26-29, 2009 / Riviera Hotel & Convention Center, Las Vegas, Nevada / Data-aided symbol synchronization for bursty communications utilizes a predetermined modulation sequence, i.e., a preamble, preceding the payload. For effective symbol synchronization, this preamble must be designed in accordance with the modulation format. In this paper, we analyze preambles for shaped offset quadrature phase-shift keying (SOQPSK) waveforms. We compare the performance of several preambles by deriving the Cram´er-Rao bound (CRB), and identify a desirable one for the Telemetry Group variant of SOQPSK. We also demonstrate, via simulation, that the maximum likelihood estimator with this preamble approaches the CRB at moderate signal-to-noise ratio.

In the last few years Wireless Sensor Networks (WSNs) have become an interesting field of research mainly due to the challenges and constraints of their design and the broad range of potential applications they can provide. One of the most important constraints is the limited energy resources of the sensor nodes that directly influences the design of the Medium Access Control (MAC) layer, as it is the responsible of controlling the transceiver that is the most consuming component of a sensor node. In this thesis the limitations of preamble sampling, one of the most well-known MAC protocols for WSNs, have been studied. Moreover, a new approach, called Low power listening with Wake up after Transmissions MAC (LWT-MAC), has been designed with the goal to overcome preamble sampling limitations while maintaining its reduced energy consumption and simplicity. The performance results obtained have shown that the LWT-MAC protocol is able to significantly improve the performance of WSNs. / Les xarxes de sensors sense fils han esdevingut una interessant àrea de recerca degut als reptes que presenta el seu disseny i a la gran quantitat d’aplicacions potencials que poden proporcionar. Un dels principals problemes d’aquestes xarxes és la limitació en els recursos energètics dels nodes sensors, cosa que afecta directament al disseny del nivell Medium Access Control (MAC), degut a què és el responsable de controlar la ràdio, el component de major consum energètic d’un node sensor. En aquesta tesi s’estudien les limitacions d'un dels protocols MAC per xarxes de sensors més conegut: preamble sampling. A més, s’ha dissenyat un nou protocol, anomenat Low power listening with Wake up after Transmissions MAC (LWT-MAC), amb l’objectiu de reduir les limitacions de preamble sampling però mantenint el seu baix consum energètic i la seva simplicitat. Els resultats obtinguts mostren que el protocol LWT-MAC és capaç de millorar de forma significativa el rendiment de la xarxa.

International Telemetering Conference Proceedings / October 21, 2002 / Town & Country Hotel and Conference Center, San Diego, California / For faster acquisition in bursted environments for SMS (Short Messaging Service) and other lower-bit rate applications, non-coherent detection techniques are proposed. Non-Coherent detection demodulators are proposed because faster acquisition capability in bursted environments can result in a reduced amount of preamble bits in the messaging frame, i.e. less overhead, resulting in an effective increase in spectral efficiency. Reducing the preamble can also provide performance enhancement opportunities for Feher Quadrature Phase Shift Keying (FQPSK) [1] and for other systems. The preamble can also be varied to provide for better Bit Error Rate (BER) performance. The lower bit rate environment also gives the opportunity to employ simpler architectures in lieu of preamble modification. Several non-coherent detection alternatives are described.

Within the field of religious studies, the definition of religion is constantly debated. While subjective definitions of this concept may be useful in day to day conversation, what happens when “religion” and other religious language is mentioned in constitutionally entrenched documents and policies? Drawing on critical theory, this thesis examines the biases associated with the the protection of freedom of religion and the preamble to Canada’s constitution which states that, “Canada is founded upon principles that recognize the supremacy of God and rule of law”.

Les préambules constitutionnels sont répandus à travers le monde, depuis le constitutionnalisme de la fin du XVIIIème. A ce jour, plus de deux constitutions sur trois dans le monde en sont précédées. Pourtant, leur nature suscite un faible intérêt pour la doctrine, voire même un rejet. Pourtant, l'intérêt que leur porte constituants contemporains et l'utilisation qui en est faite par les juges constitutionnels invalide cette position de principe. Il convient de s'attacher à la variété des préambules constitutionnels à travers le monde, en dégager des fonctions et comprendre leurs utilisations contentieuses (ce qui n'exclut nullement la possibilité que certaines juridictions constitutionnelles ne s'y réfèrent pas). A ces fins, une approche marco-comparative puis micro-comparative semblent nécessaires pour embrasser cet objet juridique rarement étudié de manière systématique. / Constitutional Preambles are worldwide spread from the late 18st Century constitutionalism. And today, more than two to three constitutions are opened with such a Preamble. Yet, regarding to their particuliar nature, law studies dealing with them are quite rare, if not deny them. However, the certain onstituents'interest to them and their use by constitutional judges just disprove it. A broad and methodic study dealing with the wide range of Preambles shall be established in ordre to understand their functions and their judicial uses - though a jurisdiction can not use them. To that end, a broad - macro-comparativ - and then a micro-comparativ study must be done, since a systematic study on Preambles has not been done.

A Wireless Sensor Network (WSN) is a collection of tiny devices called sensor nodes which are deployed in an area to be monitored. Each node has one or more sensors with which they can measure the characteristics of their surroundings. In a typical WSN, the data gathered by each node is sent wirelessly through the network from one node to the next towards a central base station. Each node typically has a very limited energy supply. Therefore, in order for WSNs to have acceptable lifetimes, energy efficiency is a design goal that is of utmost importance and must be kept in mind at all levels of a WSN system. The main consumer of energy on a node is the wireless transceiver and therefore, the communications that occur between nodes should be carefully controlled so as not to waste energy. The Medium Access Control (MAC) protocol is directly in charge of managing the transceiver of a node. It determines when the transceiver is on/off and synchronizes the data exchanges among neighbouring nodes so as to prevent collisions etc., enabling useful communications to occur. The MAC protocol thus has a big impact on the overall energy efficiency of a node. Many WSN MAC protocols have been proposed in the literature but it was found that most were not optimized for the group of WSNs displaying very low volumes of traffic in the network. In low traffic WSNs, a major problem faced in the communications process is clock drift, which causes nodes to become unsynchronized. The MAC protocol must overcome this and other problems while expending as little energy as possible. Many useful WSN applications show low traffic characteristics and thus a new MAC protocol was developed which is aimed at this category of WSNs. The new protocol, Dynamic Preamble Sampling MAC (DPS-MAC) builds on the family of preamble sampling protocols which were found to be most suitable for low traffic WSNs. In contrast to the most energy efficient existing preamble sampling protocols, DPS-MAC does not cater for the worst case clock drift that can occur between two nodes. Rather, it dynamically learns the actual clock drift experienced between any two nodes and then adjusts its operation accordingly. By simulation it was shown that DPS-MAC requires less protocol overhead during the communication process and thus performs more energy efficiently than its predecessors under various network operating conditions. Furthermore, DPS-MAC is less prone to become overloaded or unstable in conditions of high traffic load and high contention levels respectively. These improvements cause the use of DPS-MAC to lead to longer node and network lifetimes, thus making low traffic WSNs more feasible. / Dissertation (MEng)--University of Pretoria, 2008. / Electrical, Electronic and Computer Engineering / MEng / Unrestricted

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