We review the state of the art in worldwide regulation of cognitive radio-based secondary access to radio spectrum. Emerging regulatory trends with regards to incumbent protection and detection, operation parameters of cognitive radio, and secondary licensing models in the United States, United Kingdom, Europe, and elsewhere are reviewed and compared. Particular emphasis is given to cognitive radio operation in unused portions of TV bands, the so-called TV white spaces. Initial views on regulatory feasibility of secondary access to civilian radar and military bands are presented.
We derive analytical bounds for the maximum acceptable message delivery latency and the minimum required retransmission frequency of 802.11-based vehicle-to-vehicle (V2V) communication protocols for rear-end collision avoidance applications. Using a microscopic car-following model of highway traffic combined with a probabilistic two-ray ground propagation model of the V2V wireless channel, we numerically investigate variations in these bounds with mean vehicular velocity, road grip coefficient, V2V packet loss rate and wireless channel fluctuation. Our analysis provides new quantitative guidelines and analytical inputs for the design of adaptive V2V protocols, which are capable of maintaining high reliability and efficiency in the face of large variations in vehicular traffic and V2V network conditions.
Regulation of cognitive radio access to spatially unused portions of TV spectrum (TV White Spaces (TVWS)) via a geolocation database was recently finalized in the US and is under way in the UK. Regulators elsewhere are also evaluating secondary use of TV and other bands. The question of how multiple potentially competing networks should share the TVWS spectrum is yet to be addressed. This is an important challenge as future deployment scenarios are expected to involve a heterogeneous mix of low-power and high-power, narrow-band and wide-band systems. This paper investigates through quantitative modelling aspects of heterogeneous spectrum sharing, taking as example TVWS sharing among low-power, e.g., the IEEE 802.11af standard, and high-power, e.g., the IEEE 802.22, standards.
We used our recently developed mesoscale amphiphilic lattice-Boltzmann method (Nekovee, M.; Coveney, P. V.; Chen, H.; Boghosian, B. M. Phys. Rev. E 2000, 62, 8282-8894) to investigate the dynamics of self-assembly of the bicontinuous cubic phase in a binary water-surfactant system, and the transition from the lamellar structure to a bicontinuous cubic phase. Our study provides insight into how such structures emerge as a result of competing molecular interactions between water and amphiphiles and among amphiphilic molecules themselves, and represents the first application of any lattice-Boltzmann model to amphiphilic systems in three dimensions.
We report the first results of our three-dimensional, mesoscopic, amphiphilic lattice-Boltzmann model, which has been used to simulate the dynamics of self-assembly of ordered cubic and lamellar phases in binary water-surfactant systems. Our results provide insight into the mechanism of ordering of such mesophases in terms of various molecular forces acting between water and surfactant molecules and the mechanism driving the transition from the lamellar to the cubic phase.
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