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

Abstract

The last few years, the scientific field of optical wireless communications (OWC) has witnessed tremendous progress, as reflected in the continuous emergence of new successful high data rate services and variable sophisticated applications. One such development of vital research importance and interest is the employment of high speed, robust, and energy-effective transdermal optical wireless (TOW) links for telemetry with implantable medical devices (IMDs) that also have made considerable progress lately for a variety of medical applications, mainly including neural recording and prostheses. However, the outage performance of such TOW links is significantly degraded due to the strong attenuation that affects the propagating information-bearing optical signal through the skin, along with random misalignments between transmitter and receiver terminals, commonly known as pointing error effect. In order to anticipate this, in this work we introduce a SIMO TOW reception diversity system that employs either OOK or more power-effective L-PPM schemes. Taking into account the joint impact of skin-induced attenuation and non-zero boresight pointing errors, modeled through the suitable Beckmann distribution, novel closed-form mathematical expressions for the average BER of the total TOW system are derived. Thus, the possibility of enhancing the TOW availability by using reception diversity configurations along with the appropriate modulation format is investigated. Finally, the corresponding numerical results are presented using the new derived theoretical outcomes.

OAM light propagation through tissue

“…Scattering of photons in the tissue leads to loss of signal power which lead to high bit-error-rate (BER). Advances in the field of OWC and new technologies have led to studies of better communication through tissue and have reduced the BER [29][30][31][32] . Increasing beam permeability can contribute to further reducing the BER, and increase of communication reliability.…”

Signal Intensity Estimation in Transdermal Optical Wireless Links with Stochastic Pointing Errors Effect

“…At the transmitter's side, the out-of-body unit is assumed to consist of a data capturing unit which converts external stimulations into electrical signals followed by a digital signal processing (DSP) unit which digitizes and compresses data into OOK-modulated signals through an optical laser source. After traversing the skin channel, these data modulated with OOK light signals are collected through a PIN photodiode at the implanted receiver's side which comprises, in turn, a DSP and a stimulation unit (STM) which generate the appropriate nerve stimulations [16][17][18][19][20][21]. Considering thus a direct-detection receiver along with shot noise-limited conditions, the optimum receiver architecture for detection of modulated signals is based on photon counting process to render a proper decision concerning the transmitted data symbols [26].…”

“…where K a is the deterministic channel coefficient due to skin-induced attenuation and K p denotes the stochastic process that models the geometric spread due to pointing errors [16][17][18][19][20][21].…”

“…What these papers have in common is the operation with appropriate wavelengths within the optical tissue window, i.e., between 600 and 1300 nm, as an attempt to minimize photon absorption inside skin [6,15], as well as the use of On-Off Keying (OOK) modulation formats, while pointing errors have been considered either as a deterministic effect or as a negligible one. Lately, authors in [16][17][18][19] and more recently authors in [20][21][22] evaluated the stochastic nature of pointing errors which arise from the realistic relative motion between the transmitter and the receiver terminals along with the transdermal path loss. Their results demonstrate that pointing errors can significantly aggravate the already important TOW performance degradation due to skin-induced attenuation, even within the optical tissue window [13,14].…”

“…Their results demonstrate that pointing errors can significantly aggravate the already important TOW performance degradation due to skin-induced attenuation, even within the optical tissue window [13,14]. Moreover, while OOK with intensity modulation/direct detection (IM/DD) is the most feasible modulation scheme mainly due to its simplicity, it requires the detector threshold estimation and adjustment according to each of the respective varying fading channel states [21,[23][24][25].…”