Abstract
The Internet of bodies is a network of wearable, ingestible, injectable, and implantable smart objects located in, on, and around the body. Although radio frequency (RF) systems are considered the default choice for implementing on-body communications, which need to be localized in the vicinity of the human body (typically < 5 cm), highly radiative RF propagations unnecessarily extend several meters beyond the human body. This intuitively degrades energy efficiency, leads to interference and co-existence issues, and exposes sensitive personal data to security threats. As an alternative, the capacitive body channel communication (BCC) couples the signal (between 10 kHz-100 MHz) to the human body, which is more conductive than air. Hence, BCC provides a lower propagation loss, better physical layer security, and nJ/bit to pJ/bit energy efficiency. Accordingly, this paper investigates orthogonal and non-orthogonal capacitive body channel access schemes for ultra-low-power IoB nodes. We present the optimal uplink and downlink power allocations in closed-form, which deliver better fairness and network lifetime than benchmark numerical solvers. For a given bandwidth and data rate requirement, we also derive the maximum affordable number of IoB nodes for both directions of orthogonal and non-orthogonal schemes.