Spread-spectrum modulation techniques have been adopted for many current and future military comm... more Spread-spectrum modulation techniques have been adopted for many current and future military communication systems to accommodate high data rates with high link integrity, even in the presence of significant multipath effects and interfering signals. A more recent synergistic combination is a direct-sequence spread-spectrum (DSSS) signaling with the use of integrally coordinated frequency hopping (FH) and/or time-hopping (TH) modulation, generically dubbed hybrid spread-spectrum (HSS). A highly useful form of this transmission scheme for many types of command, control, and sensing applications is the specific code-related combination of standard DSSS modulation with "fast" frequency hopping (FFH), wherein multiple frequency hops occur within a single data-bit time. In this paper, detailed error-probability analyses are performed for a hybrid DS/FFH system over standard Gaussian and fading-type channels, progressively including the effects from wide-band, partial-band, and follow-on jamming, multi-user interference and/or varying degrees of Rayleigh and Rician fading. In addition, a simulation-based study of the DS/FFH performance is performed and compared to several forms of existing standard DSSS and FHSS wireless networks. The parameter space of HSS is also explored to further demonstrate the adaptability of the waveform for varied harsh RF signal environments.
In this paper, we describe an approach to quantify state-level renewable energy policies for a de... more In this paper, we describe an approach to quantify state-level renewable energy policies for a decision maker/investor. We describe the construction of a computational module - a rule-based system - to evaluate state incentives and their impacts on renewable energy investment. We aim to quantify the policy bias of states towards renewable technologies and identify profitable markets for investment, both long- and short-term. We also present how the ability to estimate the expected return from tax credits and incentives for a proposed project can be included while strategizing investment in large renewable energy generation projects.
Due to nodes mobility and environmental changes in mobile ad hoc networks, the ad hoc channel is ... more Due to nodes mobility and environmental changes in mobile ad hoc networks, the ad hoc channel is time varying and subject to fading. As a consequence of these variations, the statistical characteristics of the received signal vary continuously, giving rise to a Doppler power spectral density (DPSD) which varies from one observation instant to the next. Therefore, the traditional models can no longer capture and track complex time variations in the propagation environment. These time variations compel us to introduce more advanced dynamical models in order to capture higher order dynamics of the ad hoc channel. Stochastic ad hoc channel models, in which the evolution of the dynamical channels is described by a stochastic state space representation, are derived. The parameters of the stochastic state space models are determined by approximating the band limited DPSD. Two approximating methods are considered. The first one is simple and the second one is the complex cepstrum method. Inphase and quadrature components of the proposed stochastic ad hoc channel models are derived. Numerical results show that link performance for ad hoc case is worse than cellular case, but the performance gap shrinks with increased mobility
This paper is concerned with stochastic modeling of wireless fading channels, parameter estimatio... more This paper is concerned with stochastic modeling of wireless fading channels, parameter estimation, and system identification from measurement data. Wireless channels are represented by stochastic state-space form, whose parameters and state variables are estimated using the expectation maximization algorithm and Kalman filtering, respectively. The latter are carried out solely from received signal measurements. These algorithms estimate the channel inphase and quadrature components and identify the channel parameters recursively. The proposed algorithm is tested using measurement data, and the results are presented.
Spread-spectrum modulation techniques have been adopted for many current and future military comm... more Spread-spectrum modulation techniques have been adopted for many current and future military communication systems to accommodate high data rates with high link integrity, even in the presence of significant multipath effects and interfering signals. A more recent synergistic combination is a direct-sequence spread-spectrum (DSSS) signaling with the use of integrally coordinated frequency hopping (FH) and/or time-hopping (TH) modulation, generically dubbed hybrid spread-spectrum (HSS). A highly useful form of this transmission scheme for many types of command, control, and sensing applications is the specific code-related combination of standard DSSS modulation with "fast" frequency hopping (FFH), wherein multiple frequency hops occur within a single data-bit time. In this paper, detailed error-probability analyses are performed for a hybrid DS/FFH system over standard Gaussian and fading-type channels, progressively including the effects from wide-band, partial-band, and follow-on jamming, multi-user interference and/or varying degrees of Rayleigh and Rician fading. In addition, a simulation-based study of the DS/FFH performance is performed and compared to several forms of existing standard DSSS and FHSS wireless networks. The parameter space of HSS is also explored to further demonstrate the adaptability of the waveform for varied harsh RF signal environments.
In this paper, we describe an approach to quantify state-level renewable energy policies for a de... more In this paper, we describe an approach to quantify state-level renewable energy policies for a decision maker/investor. We describe the construction of a computational module - a rule-based system - to evaluate state incentives and their impacts on renewable energy investment. We aim to quantify the policy bias of states towards renewable technologies and identify profitable markets for investment, both long- and short-term. We also present how the ability to estimate the expected return from tax credits and incentives for a proposed project can be included while strategizing investment in large renewable energy generation projects.
Due to nodes mobility and environmental changes in mobile ad hoc networks, the ad hoc channel is ... more Due to nodes mobility and environmental changes in mobile ad hoc networks, the ad hoc channel is time varying and subject to fading. As a consequence of these variations, the statistical characteristics of the received signal vary continuously, giving rise to a Doppler power spectral density (DPSD) which varies from one observation instant to the next. Therefore, the traditional models can no longer capture and track complex time variations in the propagation environment. These time variations compel us to introduce more advanced dynamical models in order to capture higher order dynamics of the ad hoc channel. Stochastic ad hoc channel models, in which the evolution of the dynamical channels is described by a stochastic state space representation, are derived. The parameters of the stochastic state space models are determined by approximating the band limited DPSD. Two approximating methods are considered. The first one is simple and the second one is the complex cepstrum method. Inphase and quadrature components of the proposed stochastic ad hoc channel models are derived. Numerical results show that link performance for ad hoc case is worse than cellular case, but the performance gap shrinks with increased mobility
This paper is concerned with stochastic modeling of wireless fading channels, parameter estimatio... more This paper is concerned with stochastic modeling of wireless fading channels, parameter estimation, and system identification from measurement data. Wireless channels are represented by stochastic state-space form, whose parameters and state variables are estimated using the expectation maximization algorithm and Kalman filtering, respectively. The latter are carried out solely from received signal measurements. These algorithms estimate the channel inphase and quadrature components and identify the channel parameters recursively. The proposed algorithm is tested using measurement data, and the results are presented.
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Papers by Mohammed Olama