Erasure Insertion in RS-Coded SFH MFSK Subjected to Tone Jamming and Rayleigh Fading

The achievable performance of Reed Solomon (RS) coded slow frequency hopping (SFH) assisted M-ary frequency shift keying (MFSK) using various erasure insertion (EI) schemes is investigated, when communicating over uncorrelated Rayleigh fading channels in the presence of multitone jamming. Three different EI schemes are considered, which are based on the output threshold test (OTT), on the ratio threshold test (RTT) and on the joint maximum output-ratio threshold test (MORTT). The relevant statistics of these EI schemes are investigated mathematically and based on these statistics, their performance is evaluated in the context of error-and-erasure RS decoding. It is demonstrated that the system performance can be significantly improved by using error-and-erasure decoding invoking the EI schemes considered. Index Terms—Tone jamming, OTT, RTT, MO-RTT, SFH, error-and-erasure decoding (EED)

On the Sum of Order Statistics and Applications to Wireless Communication Systems Performances

We consider the problem of evaluating the cumulative distribution function (CDF) of the sum of order statistics, which serves to compute outage probability (OP) values at the output of generalized selection combining receivers. Generally, closed-form expressions of the CDF of the sum of order statistics are unavailable for many practical distributions. Moreover, the naive Monte Carlo (MC) method requires a substantial computational effort when the probability of interest is sufficiently small. In the region of small OP values, we propose instead two effective variance reduction techniques that yield a reliable estimate of the CDF with small computing cost. The first estimator, which can be viewed as an importance sampling estimator, has bounded relative error under a certain assumption that is shown to hold for most of the challenging distributions. An improvement of this estimator is then proposed for the Pareto and the Weibull cases. The second is a conditional MC estimator that achieves the bounded relative error property for the Generalized Gamma case and the logarithmic efficiency in the Log-normal case. Finally, the efficiency of these estimators is compared via various numerical experiments

Aproximações estatísticas para somas de variáveis aleatórias correlacionadas dos tipos Rayleigh e exponencial com aplicação a esquemas de combinação de diversidade

Orientador: José Cândido Silveira Santos FilhoDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: Somas de variáveis aleatórias são amplamente aplicadas em sistemas de comunicação sem fio. Exemplos incluem equalização linear, detecção de sinais, fenômenos de interferência e esquemas de combinação de diversidade. No entanto, a formulação exata para as funções estatísticas dessas somas, como a função densidade de probabilidade e a função distribuição acumulada, requer em geral um tratamento matemático complicado, o que tem motivado a busca por soluções aproximadas mais simples. Apesar de haver várias propostas de aproximação disponíveis na literatura, muitas das quais obtidas usando-se a tradicional técnica de casamento de momentos, elas não oferecem um bom ajuste em regime de alta relação sinal-ruído. Sabe-se, porém, que essa é uma região primordial para a análise de desempenho de sistemas de comunicação em termos de métricas importantes como taxa de erro de bit e probabilidade de interrupção. Mais recentemente, com o intuito de contornar essa limitação, foi proposta uma nova técnica promissora conhecida como casamento de assíntotas, capaz de fornecer aproximações para estatísticas de somas de variáveis aleatórias positivas com um ótimo ajuste em regime de alta relação sinal-ruído. Ainda assim, essa técnica foi inicialmente implementada apenas para o caso de somas de variáveis independentes, não sendo até então aplicável para somas de variáveis correlacionadas. Neste trabalho, uma nova análise assintótica é proposta, a partir da qual é possível generalizar o uso do casamento de assíntotas para o caso correlacionado. A análise proposta é ilustrada para somas de variáveis Rayleigh e somas de variáveis exponenciais com correlação e parâmetros de desvanecimento arbitrários. Além disso, deduzem-se expressões assintóticas em forma fechada com o intuito de obter novas aproximações simples e precisas em regime de alta relação sinal-ruído. Como exemplos de aplicação, esquemas práticos de combinação de diversidade são abordados, quais sejam, combinação por ganho igual e combinação por razão máxima. Por fim, resultados numéricos mostram o excelente desempenho das aproximações propostas em comparação com as aproximações obtidas via casamento de momentosAbstract: Sums of random variables are widely applied to wireless communications systems. Examples include linear equalization, signal detection, interference phenomena, and diversity-combining schemes. However, the exact formulation for the statistical functions of these sums, such as the probability density function and the cumulative distribution function, requires in general a complicated mathematical treatment, which has motivated the search for simple approximate solutions. Although there are several approximate proposals available in the literature, many of which obtained through the traditional moment-matching technique, they do not offer a good fit under the regime of high signal-to-noise ratio. It is well-known that this regime is a paramount region for the performance analysis of communications systems in terms of important metrics such as bit error rate and outage probability. More recently, in order to circumvent this limitation, a new promising technique known as asymptotic matching was proposed, capable of providing approximations for statistics of the sum of random variables with an excellent fit under the regime of high signal-to-noise ratio. Even so, this technique was initially proposed for the sum of mutually independent variables only, and thus it has not been applicable to sums of correlated variables. In this work, a novel asymptotic analysis is proposed, from which it is possible to generalize the application of asymptotic matching to the correlated case. The proposed analysis is illustrated for sums of Rayleigh and sums of exponential variables with arbitrary correlation and arbitrary fading parameters. Furthermore, closed-form asymptotic expressions are derived in order to obtain new simple and precise approximations under the regime of high signal-to-noise ratio. As application examples, practical diversity-combining schemes are addressed, namely, equal-gain combining and maximal-ratio combining. Finally, numerical results show the excellent performance of the proposed approximations in comparison to the approximations obtained via moment matchingMestradoTelecomunicações e TelemáticaMestre em Engenharia ElétricaCAPE

Level Crossing Rate of Macrodiversity System in the Presence of Multipath Fading and Shadowing

Macrodiversity system including macrodiversity SC receiver and two microdiversity SC receivers is considered in this paper. Received signal experiences, simultaneously, both, long term fading and short term fading. Microdiversity SC receivers reduces Rayleigh fading effects on system performance and macrodiversity SC receiver mitigate Gamma shadowing effects on system performance. Closed form expressions for level crossing rate of microdiversity SC receivers output signals envelopes are calculated. This expression is used for evaluation of level crossing rate of macrodiversity SC receiver output signal envelope. Numerical expressions are illustrated to show the influence of Gamma shadowing severity on level crossing rate

Wireless multiuser communication systems: diversity receiver performance analysis, GSMuD design, and fading channel simulator

Multipath fading phenomenon is central to the design and analysis of wireless communication systems including multiuser systems. If untreated, the fading will corrupt the transmitted signal and often cause performance degradations such as increased communication error and decreased data rate, as compared to wireline channels with little or no multipath fading. On the other hand, this multipath fading phenomenon, if fully utilized, can actually lead to system designs that provide additional gains in system performance as compared to systems that experience non-fading channels.;The central question this thesis tries to answer is how to design and analyze a wireless multiuser system that takes advantage of the benefits the diversity multipath fading channel provides. Two particular techniques are discussed and analyzed in the first part of the thesis: quadrature amplitude modulation (QAM) and diversity receivers, including maximal ratio combining (MRC) and generalized selection combining (GSC). We consider the practical case of imperfect channel estimation (ICE) and develop a new decision variable (DV) of MRC receiver output for M-QAM. By deriving its moment generating function (MGF), we obtain the exact bit error rate (BER) performance under arbitrary correlated Rayleigh and Rician channels, with ICE. GSC provides a tradeoff between receiver complexity and performance. We study the effect of ICE on the GSC output effective SNR under generalized fading channels and obtain the exact BER results for M-QAM systems. The significance of this part lies in that these results provide system designers means to evaluate how different practical channel estimators and their parameters can affect the system\u27s performance and help them distribute system resources that can most effectively improve performance.;In the second part of the thesis, we look at a new diversity technique unique to multiuser systems under multipath fading channels: the multiuser diversity. We devise a generalized selection multiuser diversity (GSMuD) scheme for the practical CDMA downlink systems, where users are selected for transmission based on their respective channel qualities. We include the effect of ICE in the design and analysis of GSMuD. Based on the marginal distribution of the ranked user signal-noise ratios (SNRs), we develop a practical adaptive modulation and coding (AMC) scheme and equal power allocation scheme and statistical optimal 1-D and 2-D power allocation schemes, to fully exploit the available multiuser diversity. We use the convex optimization procedures to obtain the 1-D and 2-D power allocation algorithms, which distribute the total system power in the waterfilling fashion alone the user (1-D) or both user and time (2-D) for the power-limited and energy-limited system respectively. We also propose a normalized SNR based GSMuD scheme where user access fairness issues are explicitly addressed. We address various fairness-related performance metrics such as the user\u27s average access probability (AAP), average access time (AAT), and average wait time (AWT) in the absolute- and normalized-SNR based GSMuD. These metrics are useful for system designers to determine parameters such as optimal packet size and delay constraints.;We observe that Nakakagami-m fading channel model is widely applied to model the real world multipath fading channels of different severity. In the last part of the thesis, we propose a Nakagami-m channel simulator that can generate accurate channel coefficients that follow the Nakagami-m model, with independent quadrature parts, accurate phase distribution and arbitrary auto-correlation property. We demonstrate that the proposed simulator can be extremely useful in simulations involving Nakagami-m fading channel models, evident from the numerous simulation results obtained in earlier parts of the thesis where the fading channel coefficients are generated using this proposed simulator