Abstract: This paper considers a cognitive radio (CR) network, in which the unlicensed (secondary) users (SUs) are allowed to concurrently access the spectrum allocated to the licensed (primary) users, provided that the interference of SUs with the primary users (PUs) satisfies certain constraints. It is more general and owns a stronger challenge to ensure the quality of service (QoS) of PUs, as well as to maximize the sum-rate of SUs. On the other hand, the multiple-antenna mobile user case has not been well investigated for the target problem in the open literature. We refer to this setting as multiple input multiple output multiple access channels (MIMO-MAC) in the CR network. Subject to the interference constraints of SUs and the peak power constraints of SUs, the sum-rate maximization problem is solved. To efficiently maximize the achievable sum-rate of SUs, a tight pair of upper and lower bounds, as an interval, of the optimal Lagrange multiplier is proposed. It can avoid ineffectiveness or inefficiency when the dual decomposition is used. Furthermore, a novel water-filling-like algorithm is proposed for the inner loop computation of the proposed problem. It is shown that this algorithm used in the inner loop computation can obtain the exact solution with a few finite computations, to avoid one more loop, which would be embedded in the inner loop. In addition, the proposed approach overcomes the limitation of Hermitian matrices, as optimization variables. This limitation to the optimization problem in several complex variables has not been well investigated so far. As a result, our analysis and results are solidly extended to the field of complex numbers, which are more compatible with practical communication systems.
Abstract: The key for enabling the next generation of advanced driver assistance systems (ADAS), the cooperative systems, is the availability of vehicular communication technologies, whose mandatory installation in cars is foreseen in the next few years. The definition of the communications is in the final step of development, with great efforts on standardization and some field operational tests of network devices and applications. However, some inter-vehicular communications issues are not sufficiently developed and are the target of research. One of these challenges is the construction of stable networks based on the position of the nodes of the vehicular network, as well as the broadcast of information destined to nodes concentrated in a specific geographic area without collapsing the network. In this paper, a novel algorithm for geo-broadcast communications is presented, based on the evolution of previous results in vehicular mesh networks using wireless sensor networks with IEEE 802.15.4 technology. This algorithm has been designed and compared with the IEEE 802.11p algorithms, implemented and validated in controlled conditions and tested on real vehicles. The results suggest that the characteristics of the designed broadcast algorithm can improve any vehicular communications architecture to complement a geo-networking functionality that supports a variety of ADAS.
Abstract: Wearable and ultraportable electronics coupled with pervasive computing are poised to revolutionize healthcare services delivery. The potential cost savings in both treatment, as well as preventive care are the focus of several research efforts across the globe. In this review, we describe the motivations behind wearable solutions to real-time cardiovascular monitoring from a perspective of current healthcare services, as well as from a systems design perspective. We identify areas where emerging research is underway, namely: nanotechnology in textile-based wearable monitors and healthcare solutions targeted towards smart devices, like smartphones and tablets.
Abstract: In this paper, a switchable textile communication system working at 2.45 GHz ISM band is presented and studied for different locations within a realistic on-body environment. A 3D laser scanner is used to generate a numerical phantom of the measured subject to improve the accuracy of the simulations which are carried out for different body postures. For the off-body communications, the system is acting as an aperture coupled microstrip patch antenna with a boresight gain of 1.48 dBi. On-body communication is achieved by using a textile stripline, which gives approximately 5 dB transmission loss over 600 mm distance. The system is switched between on and off-body modes by PIN diodes. Common issues, such as shape distortion and body detuning effects which the textile antenna may experience in realistic use are fully discussed. Robust antenna performance is noted in the on-body tests, and an additional 3 dB transmission coefficient deduction was noticed in the most severe shape distortion case.
Abstract: In this paper, we describe some promising solutions to the modern need for wearable, energy-aware, miniaturized, wireless systems, whose typical envisaged application is a body area network (BAN). To reach this goal, novel materials are adopted, such as fabrics, in place of standard substrates and metallizations, which require a systematic procedure for their electromagnetic characterization. Indeed, the design of such sub-systems represents a big issue, since approximate approaches could result in strong deviations from the actual system performance. To face this problem, we demonstrate our design procedure, which is based on the concurrent use of electromagnetic software tools and nonlinear circuit-level techniques, able to simultaneously predict the actual system behavior of an antenna system, consisting of the radiating and of the nonlinear blocks, at the component level. This approach is demonstrated for the design of a fully-wearable tri-band rectifying antenna (rectenna) and of a button-shaped, electrically-small antenna deploying a novel magneto-dielectric substrate. Simulations are supported by measurements, both in terms of antenna port parameters and far-field results.
Abstract: This paper presents a study into radiation pattern measurements of an electrically small dielectric resonator antenna (DRA) operating between 2.4 and 2.5 GHz in the industrial, scientific and medical (ISM) radio band for body-centric wireless communication applications. To eliminate the distortion of the radiation pattern associated with the unwanted radiation from a metallic coaxial cable feeding the antenna we have replaced it with a fibre optic feed and an electro-optical (EO) transducer. The optical signal is then converted back to RF using an Opto-Electric Field Sensor (OEFS) system. To ensure traceable measurements of the radiation pattern performance of the wearable antenna a generic head and torso solid anthropomorphic phantom model has been employed. Furthermore, to illustrate the benefits of the method, numerical simulations of the co-polar and cross-polar H-plane radiation patterns at 2.4, 2.45, and 2.5 GHz are compared with the measured results obtained using: (i) an optical fibre; and (ii) a metallic coaxial cable.