added 3 research items
We consider an MTC network with limited uplink access resources and massive number of devices. To accommodate the massive traffic, we propose a solution that utilizes device grouping and per-group random access. Following our earlier work in which we studied the scenario where device grouping is based on network densification, we study here the alternative cluster-based solution. Particularly, we propose a two-stage clustering approach where devices are grouped based on their physical locations as well as their traffic pattern distributions, and we propose two alternative methods for the second clustering stage. The first method uses a heuristic kmeans-based approach, while the second is based on submodular-cost function minimization for which we prove a factor-two performance guarantee. We also provide a stochastic geometry analysis for the proposed framework, where we derive expressions of the access and coverage probabilities in the network, which can be used for studying and optimizing the network performance and resource utilization.
With the prevalence of breast cancer among women and the shortcomings of conventional techniques in detecting breast cancer at its early stages, microwave breast imaging has been an active area of research and has gained momentum over the past few years, mainly due to the advantages and improved detection rates it has to offer. To achieve this outcome, specifically designed antennas are needed to satisfy the needs of such systems where an antenna array is typically used. These antennas need to comply with several criteria to make them suitable for such applications, which most importantly include bandwidth, size, design complexity, and cost of manufacturing. Many works in the literature proposed antennas designed to meet these criteria, but no works have classified and evaluated these antennas for the use in microwave breast imaging. This paper presents a comprehensive study of the different array configurations proposed for microwave breast imaging, with a thorough investigation of the antenna elements proposed to be used with these systems, classified per antenna type, and per the improvements that concern the operational bandwidth, the size of the antenna, the radiation characteristics, and the techniques used to achieve the improvement. At the end of the investigation, a qualitative evaluation of the antenna designs is presented, providing a comparison between the investigated antennas, and determining whether a design is suitable or not to be used in antenna arrays for microwave breast imaging, based on the performance of each. An evaluation of the investigated arrays is also presented, where the advantages and limitations of each array configuration are discussed.
Antennas miniaturization is a key challenge in the design of implantable antennas for biomedical applications. Attaining a small antenna size, while effectively communicating at low frequencies, can be a major design hurdle. In this paper, a set of miniaturized and tunable patch antennas is developed. The presented antennas can be tuned to operate at single or multiple frequencies by changing the electrical length. The proposed antennas are of a fixed dimension of 10×16×1.59 mm 3 ; they can be tuned to operate between 363 MHz and 2.74 GHz. The achieved bands comprise the Medical Implant Communication Service (MICS), Wireless Medical Telemetry Service (WMTS), and the Industrial Scientific and Medical (ISM) radio bands. To validate the attained results, an antenna operating at 1.8 and 2.4 GHz is fabricated and tested in vitro. The obtained results are in accordance with the design objectives.
Implanted biomedical devices are witnessing great attention in finding solutions to complex medical conditions. Many challenges face the design of implantable biomedical devices including designing and implanting antennas within hostile environment due to the surrounding tissues of human body. Implanted antennas must be compact in size, efficient, safe, and can effectively work within adequate medical frequency bands. This paper presents an overview of the major aspects related to the design and challenges of in body implanted antennas. The review includes surveying the applications, design methods, challenges, simulation tools, and testing and manufacturing of implantable biomedical antennas.