## 3 Analytical Results
Figure 4 illustrates whether the examined average electrical SNR regime, which ensures an adequate ABER performance, could be implemented or not due to the transdermal pathloss and other power limitations. Specifically, the most power-consumption-demanding biomedical applications with IMDs require a signal PSD from 1 \(\upmu\)W/MHz to 20 \(\upmu\)W/MHz. Within this desirable signal PSD regime, the illustrated results revealed that the attainable average electrical SNR values assumed adequate levels in response to pointing errors with NZB, transdermal pathloss, transmission power requirements and ABER performance requirements. It also became evident that by increasing the transmission power, higher average SNR values were achieved that could lead to more significant mitigations of the joint impact of skin-induced attenuation along with NZB pointing-error effects, as shown in Figures 2 and 3. Alternatively, in an attempt to increase the received signal level so as to address this joint impact, we could use a large photodetector aperture(s). Nevertheless, larger photodiodes lead to limited bandwidth [23], which results in lower data rates. Thus, we tried to keep a balance between power consumption, the photodiode's size aperture and depth of penetration of light through the skin. Figure 3: Average BER evolution over a wide range of electrical average SNR for various link configurations of \(\delta_{m}=8\) mm with spatial diversity and OC along withvarying generalized PE. For a real human body, its specific characteristics, including different skin conditions such as thickness, smoothness, tissue particularities, age, race, sweat, body temperature and anatomy of the intended user, should be taken into consideration. In any case, however, human skin is partially transparent to light at wavelengths ranging from 600 to 1300 nm, while also only 10% to 30% of incident optical power can be transmitted through skin of typical thickness due to skin attenuation [8]. Having fixed the operational wavelength at 1100 nm and having used Equation (4) to evaluate the human skin-induced attenuation coefficient, which presented an accuracy higher than 99.7% for this wavelength region [19], it became evident that even in the worst scenario, the results obtained from a real human body would be slightly different. Moreover, although human body temperature (which usually ranges between 36 and 37 \({}^{\circ}\)C) where the MRR is located is different than the out-of-body typical room temperature (25 \({}^{\circ}\)C), the response of typical MRRs shifts slightly by such temperature and/or wavelength changes. Furthermore, although larger depths in the tissue require larger MRRs size, the dimensions of typical MRRs allow their establishment inside human skin for common medical applications [4]. Additionally, the proposed model seemed to be valid for weak to strong generalized pointing errors. In fact, the investigated pointing-error parameter values covered a wide range of misalignments caused by patients' and/or human organs' realistic movements. In view of the above, we can remark that without loss of generality, the proposed model was in a good agreement with human skin characteristics.