Error Performance Estimation of Modulated Retroreflective Transdermal Optical Wireless Links with Diversity under Generalized Pointing Errors

Abstract

Recent developments in both optical wireless communication (OWC) systems and implanted medical devices (IMDs) have introduced transdermal optical wireless (TOW) technology as a viable candidate for extremely high-speed in-body to out-of-body wireless data transmissions, which are growing in demand for many vital biomedical applications, including telemetry with medical implants, health monitoring, neural recording and prostheses. Nevertheless, this emerging communication modality is primarily hindered by skin-induced attenuation of the propagating signal bit carrier along with its stochastic misalignment-induced fading. Thus, by considering a typical modulated retroreflective (MRR) TOW system with spatial diversity and optimal combining (OC) for signal reception in this work, we focus, for the first time in the MRR TOW literature, on the stochastic nature of generalized pointing errors with non-zero boresight (NZB). Specifically, under these circumstances, novel analytical mathematical expressions were derived for the total average bit error rate (BER) of various system configurations. Their results revealed significant outage performance enhancements when spatial diversity was utilized. Moreover, taking into consideration the total transdermal pathloss along with the effects of stochastic NZB pointing errors, the critical average signal-to-noise ratio (SNR) metric was evaluated for typical power spectral-density values.

Energy-Efficient Emerging Optical Wireless Links

“…The authors in [5] utilized a continuous wave laser operating at 854.52 nm with a low transmit power of 2.9 mW along with an electro absorption modulator at the retroreflector side and a 4 cm 2 skin sample of a 10 months old laboratory rat to prove the feasibility of established real retro-reflective TOW links. The authors of [144,145], for a power spectral density of 1 µW/MHz, presented encouraging ABER results of 10 −5 to 10 −4 for a reasonable use of wavelength and spatial diversity configurations. Bearing in mind that the most demanding medical applications with IMDs require a signal power density spectrum from 1 µW/MHz to 20 µW/MHz, the authors in [145] showed that over this power density spectrum region, they achieved the proper average SNR values, which were required to drastically address the major effects that degrade TOW performance.…”

“…The authors of [144,145], for a power spectral density of 1 µW/MHz, presented encouraging ABER results of 10 −5 to 10 −4 for a reasonable use of wavelength and spatial diversity configurations. Bearing in mind that the most demanding medical applications with IMDs require a signal power density spectrum from 1 µW/MHz to 20 µW/MHz, the authors in [145] showed that over this power density spectrum region, they achieved the proper average SNR values, which were required to drastically address the major effects that degrade TOW performance. Additional experimental work is needed for retro-reflective TOW systems in order to play a key role in energy-efficient wireless telemetry with medical implants.…”

Average Capacity Evaluation Performance for Transdermal Optical Wireless Communications under the Effect of Pointing Error

“…Accurate pointing error process is modeled by nonzero stochastic model which is composed of two components known as the boresight and jitter. The boresight component represents a fixed displacement between the beam and the detector center, while the jitter is the beam center random offset at the detector plane [5], [15], [17][18][19][20][21].…”

“…In TOWs, the direct model and modulator retroreflective (MRR) are usually used to configure the transdermal optical link [19][20][21]. In the direct configuration, the external unit acts as the transmitter in order to convey the external modulated stimulated signal through the skin to the implanted unit to produce the proper stimulation.…”

“…Their results reveal that pointing errors drastically affect the reliability and effectiveness of the link and should be taken into consideration when designing a transdermal OWC link. Finally, average BER results for MRR TOW system with spatial diversity were provided by [21], under the effect of pointing error. The authors provided novel analytical mathematical expression for the BER, which takes into account the effect of NZB pointing error, channel induced skin attenuation and average SNR.…”