International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / Multipath propagation consisting largely of specular reflection components is known to be the major channel impairment in many aeronautical mobile telemetry (AMT) applications. Adaptive equalizers are not effective against flat fading commonly created by strong power delay profile components representing small fractions of the transmitted symbol period. Avoidance and diversity techniques are the only practical means of combating this problem. A new post-detection, no-hit diversity branch selector is described in this paper. Laboratory and limited flight test data comparing non-diversity, selection diversity and intermediate frequency (IF) combining techniques are presented.

ITC/USA 2007 Conference Proceedings / The Forty-Third Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2007 / Riviera Hotel & Convention Center, Las Vegas, Nevada / Multipath propagation continues to be the dominant channel impairment in many aeronautical mobile telemetry (AMT) applications. Avoidance and diversity techniques continue to be the only practical means to combat this problem. In 2004 limited results from the development of a new post-detection, no-hit diversity selector were reported. Late breaking results from flight test were reported orally. A review of the methodology, flight test results and conclusions are presented in this paper. Also presented is an update describing enhancements of the implementation which emphasize operational flexibility as well as support for alternate demodulator products.

In this work, copula models for fitting bivariate response data with Weibull marginal distributions are studied, which are motivated by the need of model fading channels in signal applications. The analytical expressions for the joint probability density function (p.d.f.), and joint cumulative distribution function (c.d.f.) are utilized as the bivariate distribution of the fading channels data with not necessarily identical fading parameters and average powers. The performances of outage probability employing diversity receivers, called as selection combining (SC), equal-gain combining (EGC), and maximal-ratio combining (MRC) of two diversity receivers under bivariate copula models with Weibull marginal distributions are presented. They are also compared with the results in Sagias (2005) where the data assumed to follow the bivariate Weibull distribution. It will be demonstrated that the copula models can approximate the bivariate Weibull distribution used in Sagias (2005) very closely with suitable copula model, and the computations for obtaining the performances of outage probability under SC are much simplified. Keywords and phrases: equal-gain combining, maximal-ratio combining, selection combining

Adaptive modulation and diversity combining represent very important adaptive solutions for future generations of wireless communication systems. Indeed, to improve the performance and the efficiency of these systems, these two techniques recently have been used jointly in new schemes named joint adaptive modulation and diversity combining (JAMDC) schemes. Considering the problem of finding lowcomplexity, bandwidth-efficient, and processing-power efficient transmission schemes for a downlink scenario and capitalizing on some of these recently proposed JAMDC schemes, we propose and analyze three fully joint adaptive modulation, diversity combining, and power control (FJAMDC) schemes. More specifically, the modulation constellation size, the number of combined diversity paths, and the needed power level are determined jointly to achieve the highest spectral efficiency with the lowest possible combining complexity, given the fading channel conditions and the required bit error rate (BER) performance. The performance of these three FJAMDC schemes is analyzed in terms of their spectral efficiency, processing power consumption, and error-rate performance. Selected numerical examples show that these schemes considerably increase the spectral efficiency of the existing JAMDC schemes with a slight increase in the average number of combined paths for the low signal to noise ratio range while maintaining compliance with the BER performance and a low radiated power resulting in a substantial decrease in interference to co-existing systems/users.

As resources are limited, radio spectrum becomes congested due to the growth of wireless applications. However, measurements address the fact that most of the licensed spectrums experience low utilization even in intensively teeming areas. In the exertion to improve the utilization of the limited spectrum resources, cognitive radio networks have emerged as a powerful technique to resolve this problem. There are two types of user in cognitive radio networks (CRNs) named as primary user (PU) and secondary user (SU). Therein, the CRN enables the SU to utilize the unused licensed frequency of the PU if it possibly finds the vacant spectrum or white space (known as opportunistic spectrum access). Alternatively, SU can transmit simultaneously with the PU provided that transmission power of SU does not cause any harmful interference to the PU (known as spectrum sharing systems). In this thesis work, we study fundamental knowledge of the CRNs and focus on the performance analysis of the single input multiple output (SIMO) system for spectrum sharing approach. We assume that a secondary transmitter (SU-Tx) has full channel state information (CSI). The SU-Tx can adjust its transmit power not to cause harmful interference to the PU and obtain an optimal transmit rate. In particular, we derive the closed-form expressions for the cumulative distribution function (CDF), outage probability and an analytical expression for symbol error probability (SEP). / As resources are limited, radio spectrum becomes congested due to the growth of wireless applications. However, measurements address the fact that most of the licensed spectrums experience low utilization even in intensively teeming areas. In the exertion to improve the utilization of the limited spectrum resources, cognitive radio networks have emerged as a powerful technique to resolve this problem. There are two types of user in cognitive radio networks (CRNs) named as primary user (PU) and secondary user (SU). Therein, the CRN enables the SU to utilize the unused licensed frequency of the PU if it possibly finds the vacant spectrum or white space (known as opportunistic spectrum access). Alternatively, SU can transmit simultaneously with the PU provided that transmission power of SU does not cause any harmful interference to the PU (known as spectrum sharing systems). In this thesis work, we study fundamental knowledge of the CRNs and focus on the performance analysis of the single input multiple output (SIMO) system for spectrum sharing approach. We assume that a secondary transmitter (SU-Tx) has full channel state information (CSI). The SU-Tx can adjust its transmit power not to cause harmful interference to the PU and obtain an optimal transmit rate. In particular, we derive the closed-form expressions for the cumulative distribution function (CDF), outage probability and an analytical expression for symbol error probability (SEP). / Iqbal Hasan Haider, cell: +46704571807 MD. Fazla Rabby, cell: +46734965477

Fluid antenna systems (FAS) are an emerging technology that promises a signif icant diversity gain even in the smallest spaces. Motivated by the groundbreaking potentials of liquid antennas, researchers in the wireless communication community are investigating a novel antenna system where a single antenna can freely switch positions along a small linear space to pick the strongest received signal. However, the FAS positions do not necessarily follow the ever-existing rule separating them by at least half the radiation wavelength. Previous work in the literature param eterized the channels of the FAS ports simply enough to provide a single-integral expression of the probability of outage and various insights on the achievable perfor mance. Nevertheless, this channel model may not accurately capture the correlation between the ports, given by Jake’s model. This work builds on the state-of-the-art and accurately approximates the FAS channel while maintaining analytical tractabil ity. The approximation is performed in two stages. The first stage approximation considerably reduces the number of multi-fold integrals in the probability of outage expression, while the second stage approximation provides a single integral represen tation of the FAS probability of outage. Further, the performance of such innovative technology is investigated under a less-idealized correlation model. Numerical results validate our approximations of the FAS channel model and demonstrate a limited performance gain under realistic assumptions. Further, our work opens the door for future research to investigate scenarios in which the FAS provides a performance gain compared to the current multiple antennas solutions.

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In recent years, research on the design and performance evaluation of suboptimal receiver implementations has received considerable attention owing to complexity in the realization of the optimal receiver algorithms over wireless channels. This thesis addresses the effects of using reduced complexity receivers for the Satellite Digital Audio Radio (SDAR), Code Division Multiple Access (CDMA) and UltraWideband (UWB) communications technologies. A graphical-user-interface simulation tool has been developed to predict the link reliability performance of the SDAR services in the continental United States. Feasibility study of receiving both satellite and terrestrial repeater signals using a selection diversity (single antenna) receiver has also been performed. The thesis also develops a general mathematical framework for studying the efficacy of a sub-optimal generalized selection combining (GSC) diversity receiver over generalized fading channel models. The GSC receiver adaptively combines a subset of M diversity paths with the highest instantaneous signal-to-noise ratios (SNR) out of the total L available diversity paths. The analytical framework is applicable for rake receiver designs in CDMA and UWB communications. / Master of Science

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Cooperation diversity and orthogonal frequency division multiplexing (OFDM) are two key technologies for the modern wireless communication systems. The cooperative communication systems considered through this work use the OFDM technology and they are composed of: one transmitter with a nonlinear power amplifier (PA), one or more amplify-and-forward (AF) relays, also having a nonlinear PAs, and one destination node. In this dissertaion, it is initially proposed an optimal receiver, in the signal to noise ratio (SNR) sense, for a nonlinear cooperative AF system. The proposed receiver uses the maximum ratio combining (MRC) diversity technique to combine the received signas, assuming that both the source-destination and source-relay-destination links are available. In the sequel, closed-form expressions for the instantaneous SNR and outage probability of the considered system are developed. The outage analysis is then extended to the case of a multi-hop system, that is, with multiple serial relays. Finally, an outage analysis is also proposed for a nonlinear AF OFDM system using a Selection Combining receiver, considering two cases: one relay and multiple parallel relays. Numerical simulation results are presented through the work, evaluating the performance of the proposed receiver and theoretical expressions. / A diversidade cooperativa e a multiplexaÃÃo por divisÃo de frequÃncias ortogonais (Orthogonal Frequency Division Multiplexing - OFDM) sÃo duas das principais tecnologias para os sistemas de comunicaÃÃo sem fio modernos. Os sistemas de comunicaÃÃo cooperativos considerados neste trabalho de dissertaÃÃo utilizam a tecnologia OFDM e possuem: uma fonte com amplificador de potÃncia nÃo linear, um ou mais repetidores (relays) do tipo amplifica-e-encaminha (Amplify-and-Forward - AF), tambÃm com amplificadores de potÃncia (Power Amplifier - PA) nÃo lineares, e um nà destino. PropÃe-se inicialmente um receptor Ãtimo, no sentido da razÃo sinal ruÃdo (Signal-to-Noise Ratio - SNR) para um sistema OFDM cooperativo nÃo linear. Usando a tÃcnica de diversidade por combinaÃÃo de razÃo mÃxima (Maximal Ratio Combining - MRC) para tratar os sinais recebidos, o receptor proposto considera tanto as informaÃÃes oriundas do caminho direto (fonte-destino) como as provenientes do repetidor. Posteriormente, sÃo apresentadas expressÃes para o cÃlculo da SNR instantÃnea e da probabilidade de outage do sistema proposto. Fez-se ainda, uma proposta de expressÃo para o cÃlculo da probabilidade de outage do sistema considerando mÃltiplos relays em sÃrie. Por fim, propÃe-se expressÃes para o cÃlculo da probabilidade de outage do sistema utilizando receptor Selection Combining para um e para mÃltiplos relays dispostos paralelamente. Resultados de simulaÃÃo sÃo apresentados durante todo o trabalho, evidenciando o desempenho do receptor e das expressÃes propostas.

Different diversity techniques such as Maximal-Ratio Combining (MRC), Equal-Gain Combining (EGC) and Selection Combining (SC) are described and analyzed. Two branches (N=2) diversity systems that are used for pre-detection combining have been investigated and computed. The statistics of carrier to noise ratio (CNR) and carrier to interference ratio (CIR) without diversity assuming Rayleigh fading model have been examined and then measured for diversity systems. The probability of error (p_e) vs CNR and (p_e) versus CIR have also been obtained. The fading dynamic range of the instantaneous CNR and CIR is reduced remarkably when diversity systems are used [1]. For a certain average probability of error, a higher valued average CNR and CIR is in need for non-diversity systems [1]. But a smaller valued of CNR and CIR are compared to diversity systems. The overall conclusion is that maximal-ratio combining (MRC) achieves the best performance improvement compared to other combining methods. Diversity techniques are very useful to improve the performance of high speed wireless channel to transmit data and information. The problems which considered in this thesis are not new but I have tried to organize, prove and analyze in new ways.