Signal Quality Assessment for Transdermal Optical Wireless Communications under Pointing Errors

Abstract

In this paper, we assess the signal quality of the out-body to in-body optical communication link, which can be used as a fundamental enabler of novel biomedical appliances, such as medical implants, as well as biological and chemical components monitoring. In particular, we present a mathematical understanding of the transdermal system, which takes into account the optical channel characteristics, the integrated area limitations of the in-body unit, the transceivers’ pointing errors and the particularities of the optical units. Moreover, to accommodate the propagation characteristics, we present a novel simplified, but accurate, transdermal path-gain model. Finally, we extract low-complexity closed-form expressions for the instantaneous and average signal to noise ratio of the transdermal optical link (TOL). Numerical and simulation results are provided for several insightful scenarios and reveal that pointing errors can significantly affect the reliability and effectiveness of the TOL; hence, it should be taken into account in the analysis and design of such systems.

Transdermal Optical Wireless Links with Multiple Receivers in the Presence of Skin-Induced Attenuation and Pointing Errors

“…These signals are forwarded to the transmitter, which emits M data copies of the same part of information towards the internal unit that consists, in turn, of the corresponding receiver(s), DSP unit and the stimulation (STM) unit that eventually stimulates the appropriate nerve. Thus, the internal DSP and STM units are responsible for generating the appropriate stimulations [14,[36][37][38][39]. In this context, the statistical channel model for the examined TOW system is given as [39] y…”

“…where h l,m stands for the deterministic channel coefficient due to the propagation losses of the m-th channel though the skin and h p,m represents the corresponding stochastic process that models the geometric spread due to the presence of pointing errors. The former deterministic term is expressed as [36][37][38][39]…”

“…Nevertheless, this skin-induced attenuation described above remains a major concern in TOW communication since even for the highest tissue transmittance, i.e., for wavelengths between 800 nm and 1300 nm, only 10% to 30% of incident optical power is transmitted through skin of typical thickness, i.e., 2 mm to 6 mm, when the emitter and the detector are aligned [33][34][35]. Considering also the pointing errors due to unavoidable misalignments between transmitter and receiver terminals that is also an effect of primary concern in TOW communication, as well as in the wider FSO communication, the performance and availability of TOW transmissions is further degraded [2,4,7,[36][37][38][39].…”

“…Recently, in [36][37][38], the authors considered the stochastic nature of a TOW link and derived closed-form expressions for the average signal-to-noise-ratio (SNR) and its outage performance, in terms of outage probability metric. In basic terms, they demonstrated that pointing errors can degrade the TOW performance by more than 10%.…”

Opportunities and Challenges for Error Correction Scheme for Wireless Body Area Network—A Survey

“…To support variety of nodes, channels, and QoS requirements in WBAN, are dynamic ECS design and implementation based on the software-defined radio suitable for WBAN as introduced for wireless sensor network in [62][63][64][65] One of the greatest challenges in ECS design on WBAN is to verify the design and expected outcome. Therefore, the creation of simulation settings or tools that resembles the real human bodies is another challenge and would be another research area to explore.…”