ITC/USA 2010 Conference Proceedings / The Forty-Sixth Annual International Telemetering Conference and Technical Exhibition / October 25-28, 2010 / Town and Country Resort & Convention Center, San Diego, California / RF Communication (COMMS) systems where receivers and transmitters are in motion must be proven rigorously over an array of natural RF link perturbations such as Carrier Doppler shift, Signal Doppler shift, delay, path loss and noise. These perturbations play significant roles in COMMS systems involving satellites, aircraft, UAVs, missiles, targets and ground stations. In these applications, COMMS system devices must also be tested against increasingly sophisticated intentional and unintentional interference, which must result in negligible impact on quality of service. Field testing and use of traditional test and measurement equipment will need to be substantially augmented with physics-compliant channel emulation equipment that broadens the scope, depth and coverage of such tests, while decreasing R&D and test costs and driving in quality. This paper describes dynamic link emulation driven by advanced antenna and motion modeling, detailed propagation models and link budget methods for realistic, nominal and worst-case hardware-in-the-loop test and verification.

ITC/USA 2008 Conference Proceedings / The Forty-Fourth Annual International Telemetering Conference and Technical Exhibition / October 27-30, 2008 / Town and Country Resort & Convention Center, San Diego, California / Although multiple-input multiple-output (MIMO) systems have become increasingly popular, the existence of real time results to compare with those predicted by theory is still surprisingly limited. In this work the hardware description of a MIMO wireless communication system using orthogonal space time block codes (OSTBC) is discussed for two antennas at both the transmitter and receiver. A numerical example for a frequency flat time correlated channel is given to show the impact of channel estimation.

Made available in DSpace on 2016-04-04T18:31:21Z (GMT). No. of bitstreams: 1 Fernando Lino.pdf: 1954006 bytes, checksum: a697088d7a7477d92d2183541ef1e1c6 (MD5) Previous issue date: 2008-02-08 / The literature describes the fast flat fading propagation model in mobile environment as a Rayleigh distribution with different standard deviations which considers only one parameter to describe the channel fading. In the Weibull distribution there are two parameters to be modeled: shape factor and scale factor. The Rayleigh distribution is a particular case of the Weibull distribution where the shape factor has a firm value equals to two. This work has the objective to evaluate, through practical measurements, both parameters in the Weibull distribution at an indoor environment. The results will show the real value of the shape factor parameter and the scale factor as well, indicating that the Weibull distribution is more flexible to describe a fast flat fading channel at an indoor propagation. / A literatura descreve a propaga??o fast flat fading em sistemas m?veis como o modelo de distribui??o Rayleigh com diferentes desvios padr?es, o qual considera apenas um par?metro para descrever o canal de desvanecimento. Na distribui??o de Weibull existem dois par?metros a serem modelados: fator de forma e fator de escala. A distribui??o Rayleigh ? um caso particular da distribui??o de Weibull onde o fator de forma tem um valor igual a dois. Este trabalho tem o objetivo de avaliar, atrav?s de medidas pr?ticas, ambos os par?metros da distribui??o de Weibull em um ambiente indoor. Os resultados ir?o mostrar os reais valores dos par?metros de forma e de escala, indicando que a distribui??o de Weibull ? mais flex?vel para descrever um canal flat fast fading em uma propaga??o indoor.

Dans cette thèse, le compromis entre la consommation d'énergie et le délai dans les réseaux de capteurs sans fil est étudié en exploitant efficacement les liens non fiables. Nous proposons une métrique de l'efficacité énergétique et une métrique de délai moyenne qui sont combinés avec le modèle de lien radio à erreur. En utilisant ces deux métriques et un modèle réaliste de lien radio, nous déduisons la limite inférieure et le front de Pareto du compromis Energie-Délai sont calculés pour trois types de systèmes de communication: la communication multi-saut traditionnelle, la communication opportuniste et la communication coopérative MIMO (CMIMO) dans trois différents canaux: le canal a bruit additif blanc Gaussien, le canal a évanouissements rapides de Rayleigh et le canal a évanouissement de Rayleigh par blocs. Les expressions de ces limites faibles sont obtenues et vérifiées par des simulations bidimensionnelles de réseaux de capteurs distribués aléatoirement. Sur la base de l'expression de la borne inférieure du compromis Energie-Délai, un cadre multi-couche est fourni pour optimiser les paramètres des couches physique, MAC et routage sous contrainte de délai. Les résultats obtenus montrent que pour parvenir à une meilleure performance Energie-Délai, les mécanismes de communication suivants devraient être adoptés selon le type de canal : les communications multi-saut traditionnelles sont les plus performantes pour le canal à bruit additif blanc Gaussien, alors que les communications opportunistes le sont pour les canaux à évanouissements de Rayleigh par blocs et enfin le CMIMO pour les canaux à évanouissements rapides de Rayleigh.

We introduced nested search methods to design (n, k) block codes for arbitrary channels by optimizing an appropriate metric spectrum in each iteration. For a given k, the methods start with a good high rate code, say k/(k + 1), and successively design lower rate codes up to rate k/2^k corresponding to a Hadamard code. Using a full search for small binary codes we found that optimal or near-optimal codes of increasing length can be obtained in a nested manner by utilizing Hadamard matrix columns. The codes can be linear if the Hadamard matrix is linear and non-linear otherwise. The design methodology was extended to the generic complex codes by utilizing columns of newly derived or existing unitary codes. The inherent nested nature of the codes make them ideal for progressive transmission. Extensive comparisons to metric bounds and to previously designed codes show the optimality or near-optimality of the new codes, designed for the fading and the additive white Gaussian noise channel (AWGN). It was also shown that linear codes can be optimal or at least meeting the metric bounds; one example is the systematic pilot-based code of rate k/(k + 1) which was proved to meet the lower bound on the maximum cross-correlation. Further, the method was generalized such that good codes for arbitrary channels can be designed given the corresponding metric or the pairwise error probability. In synchronous multiple-access schemes it is common to use unitary block codes to transmit the multiple users’ information, especially in the downlink. In this work we suggest the use of newly designed non-unitary block codes, resulting in increased throughput efficiency, while the performance is shown not to be substantially sacrificed. The non-unitary codes are again developed through suitable nested searches. In addition, new multiple-access codes are introduced that optimize certain criteria, such as the sum-rate capacity. Finally, the introduction of the asymptotically optimum convolutional codes for a given constraint length, reduces dramatically the search size for good convolutional codes of a certain asymptotic performance, and the consequences to coded code-division multiple access (CDMA) system design are highlighted.

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Recently multiple antenna systems have received significant attention from researchers as a means to improve the energy and spectral efficiency of wireless systems. Among many classes of schemes, Space-Time Block codes (STBC) and Space-Time Trellis codes (STTC) have been the subject of many investigations. Both techniques provide a means for combatting the effects of multipath fading without adding much complexity to the receiver. This is especially useful in the downlink of wireless systems. In this thesis we investigate the impact of channel estimation error on the performance of both STBC and STTC. Channel estimation is especially important to consider in multiple antenna systems since (A) for coherent systems there are more channels to estimate due to multiple antennas and (B) the decoupling of data streams relies on correct channel estimation. The latter effect is due to the intentional cross-talk introduced into STBC. / Master of Science

Opportunistic use of unused spectrum could efficiently be carried out using the paradigm of Cognitive Radio (CR). A spectrum remains idle when the primary user (licensee) is not using it. The secondary nodes detect this spectral hole quickly and make use of it for data transmission during this interval and stop transmitting once the primary starts transmitting. Detection of spectral holes by the secondary is called spectrum sensing in the CR scenario. Spectrum Sensing is formulated as a hypothesis testing problem wherein under H0 the spectrum is free and under H1, occupied. The samples will have different probability distributions, P0 and P1, under H0 and H1 respectively. In the first part of the thesis, a new algorithm - entropy test is presented, which performs better than the available algorithms when P0 is known but not P1. This is extended to a distributed setting as well, in which different secondary nodes collect samples independently and send their decisions to a Fusion Centre (FC) over a noisy MAC which then makes the final decision. The asymptotic optimality of the algorithm is also shown. In the second part, the spectrum sensing problem under impediments such as fading, electromagnetic interference and outliers is tackled. Here the detector does not possess full knowledge of either P0 or P1. This is a more general and practically relevant setting. It is found that a recently developed algorithm (which we call random walk test) under suitable modifications works well. The performance of the algorithm theoretically and via simulations is shown. The same algorithm is extended to the distributed setting as above.

There has been phenomenal interest in applying space-time coding techniques in wireless communications in the last two decades. In general, the benefit of applying space-time codes in multiple-input, multiple-output (MIMO) wireless channels is an increase in transmission reliability or system throughput (capacity). However, such a benefit cannot be obtained in some wireless systems where size or other constraints preclude the use of multiple antennas. As such, wireless relay communications has recently been proposed as a means to provide spatial diversity in the face of this limitation. In this approach, some users or relay nodes assist the transmission of other users information. This dissertation contributes to the advancement of wireless relay communications by investigating the performance of various relaying signal processing methods under different practical fading environments. In particular, it examines two main relaying methods, namely decode-and-forward (DF) and amplify-and-forward (AF).<p> For DF, the focus is on the diversity analysis of relaying systems under various practical protocols when detection error at relays is taken into account. In order to effectively mitigate the phenomenon of error propagation, the smart relaying technique proposed by Wang et al. in [R1] is adopted. First, diversity analysis of a single-relay system under the scenario that only the relay is allowed to transmit in the second time slot (called Protocol II) is carried out. For Nakagami and Hoyt generalized fading channels, analytical and numerical results are provided to demonstrate that the system always obtains the maximal diversity when binary phase shift keying (BPSK) modulation is used. Second, a novel and low-complexity relaying system is proposed when smart relaying and equal gain combing (EGC) techniques are combined. In the proposed system, the destination requires only the phases of the channel state information in order to detect the transmitted signals. For the single-relay system with M-ary PSK modulation, it is shown that the system can achieve the maximal diversity under Nakagami and Hoyt fading channels. For the K-relay system, simulation results suggest that the maximal diversity can also be achieved. Finally, the diversity analysis for a smart relaying system under the scenario when both the source and relay are permitted to transmit in the second time slot (referred to as Protocol I) is presented. It is shown that Protocol I can achieve the same diversity order as Protocol II for the case of 1 relay. In addition, the diversity is very robust to the quality of the feedback channel as well as the accuracy of the quantization of the power scaling implemented at the relay.<p> For AF, the dissertation considers a fixed-gain multiple-relay system with maximal ratio combining (MRC) detection at the destination under Nakagami fading channels. Different from the smart relaying for DF, all the channel state information is assumed to be available at the destination in order to perform MRC for any number of antennas. Upperbound and lowerbound on the system performance are then derived. Based on the bounds, it is shown that the system can achieve the maximal diversity. Furthermore, the tightness of the upperbound is demonstrated via simulation results. With only the statistics of all the channels available at the destination, a novel power allocation (PA) is then proposed. The proposed PA shows significant performance gain over the conventional equal PA.

In this thesis, we propose a novel architecture for hybrid radio frequency (RF)/free–space optics (FSO) wireless systems. Hybrid RF/FSO systems are attractive since the RF and FSO sub–systems are affected differently by weather and fading phenomena. We give a thorough introduction to the RF and FSO technology, respectively. The state of the art of hybrid RF/FSO systems is reviewed. We show that a hybrid system robust to different weather conditions is obtained by joint bit–interleaved coded modulation (BICM) of the bit streams transmitted over the RF and FSO sub–channels. An asymptotic performance analysis reveals that a properly designed convolutional code can exploit the diversity offered by the independent sub–channels. Furthermore, we develop code design and power assignment criteria and provide an efficient code search procedure. The cut–off rate of the proposed hybrid system is also derived and compared to that of hybrid systems with perfect channel state information at the transmitter. Simulation results show that hybrid RF/FSO systems with BICM outperform previously proposed hybrid systems employing a simple repetition code and selection diversity.