24 GHz wearable antenna design for wireless body area Networks: An investigation of on-body channel characterisation and Zigbee protocol at 24 GHz

User-centric networks drive the evolution of wireless communication, demanding constant connectivity and services across various domains. MM-wave (24 GHz ISM band) frequencies emerge as a promising solution for WBAN, overcoming challenges posed by the on-body radio channel and achieving reliable communication in diverse environments. This thesis uses multiple antennas to characterise the mm-wave (24 GHz) radio propagation channel for body-centric communication. The aim is to design compact antennas insensitive to human skin and structural deformation, exploring system-level modelling of Zigbee's PHY and MAC layers in the context of mm-wave (24 GHz) Body Area Networks (BWAN).

The first part introduces innovative on-body antenna designs, incorporating split square-ring electromagnetic bandgap (EBG) structures and bow-tie slot antennas, demonstrating high insensitivity to body proximity and bending. The study also proposes Koch fractal antennas backed by EBG structures for improved performance and stable radiation patterns suitable for on-skin mounting. The second part analyses 24 GHz on-body communication system performance and path loss modelling, considering various antenna types. Measurement campaigns confirm the significance of antenna diversity and position in mm-wave propagation on the human body, predicting potential performance for 24 GHz ISM band WBAN systems. The third part evaluates Zigbee protocol performance in body-centric wireless communication within the 24 GHz channel model. Results show good radio link quality for physiological sensor nodes, with lower performance observed in NLOS and PLOS scenarios due to body tissue obstruction. Throughput performance highlights the importance of sensor positioning and MAC layer optimisation.

This thesis advances 24 GHz ISM band WBANs through innovative antennas, introducing 24 GHz path loss modeling, and insights into Zigbee (physical layer and MAC) protocol. It drives future research in advanced designs, propagation modelling, and protocol enhancements, boosting on-body wireless communication capabilities.