Modulated Retro-Reflector Transdermal Optical Wireless Communication Systems with Wavelength Diversity over Skin-Induced Attenuation and Pointing Errors

In this work the potential for the enhancement of the outage performance of a common transdermal optical wireless (TOW) communication link is investigated by utilizing both retro-reflective modulation and wavelength diversity techniques. In this respect, an external multi-laser transceiver emits at the same time the interrogating laser signal through different optical wavelengths towards the implanted modulated retro-reflector (MRR), which modulates and reflects the arriving optical beams back to the transceiver unit equipped with the corresponding photo detector apertures, recovering data signals originated from the in-body retro-modulator. Additionally, taking into consideration the stochastic nature of pointing errors effects along with the transdermal path loss, an outage analysis is performed for the proposed TOW architecture. Under these circumstances, by jointly estimating both skin-induced attenuation and misalignment-induced fading, novel, accurate and compact mathematical expressions are derived for the evaluation of outage probability of the total TOW system, using various wavelength diversity retro-reflective configurations. The results demonstrate the feasibility of our suggestions and that the wavelength diversity is as a very efficient method for significantly enhancing the availability of a common retro-reflective TOW link.