## 4 Experimental Results and Discussion
In the insets are reported: (A) multiple acquisitions of \(U_{T}(t)\) for the evaluation of the amplitude and phase jitters resulting lower than 150 mV and 100 ps, respectively; (B) the \(U_{R}(t)\) and the related \(S_{R}(t)\) signals; (C) the \(S_{R}(t)\) eye diagram showing amplitude and phase jitters lower than 100 mV and 150 ps, respectively. All the measurements have been performed by using WAVEMASTER 8600A digital oscilloscope (LeCroy). Figure 6 demonstrates that the received and decoded data stream \(S_{R}(t)\) correctly matches with the transmitted one (\(S_{T}(t)\)) showing a time delay of about 18 ns mainly due to clock recovery and data decoding processes. Moreover, referring to the inset B) of Figure 6, it has been experimentally evaluated also the overall impulse response of the transmission channel by means of the time-domain analysis of the received pulsed signal \(U_{R}(t)\). Furthermore, it is important to highlight that the proposed system is not based on IR-UWB modulation and does not employs RF electrical pulses and/or antennas to transmit the modulated/pulsed signals. On the other hand, the duration of the generated optical pulses is lower than 1 ns. Thus, in principle, the proposed architecture implementing the optical pulsed coding technique complies with the standards UWB specifications on the generation of pulsed signals. In this regards, Figure 7 reports the overall power spectrum of the transmitted pulsed signal \(U_{T}(t)\) generated by the coding system showing high spikes that, in principle, could affect the overall power efficiency of the system. Nevertheless, an effective trade-off between transmission data rate, power efficiency and BER has been achieved. In particular, the experimental data demonstrate that the pulse characteristics and specifications comply and satisfy the standard mask defined by the Federal Communications Commission (FCC) on the power spectrum of modulated/pulsed signals (i.e., the power emission limits of the signals for communications) [24]. Moreover, Figure 7 shows a primary lobe with a bandwidth of about 1.25 GHz corresponding to the inverse of the laser pulse duration (i.e., \(1/800\) ps) so validating and confirming the theoretical expectations. Figure 5: Experimental set-up: picture of the overall implemented system and the related block scheme showing its main components. Figure 6: Main signals related to the transmitter and the receiver blocks. From top to bottom: \(\mathrm{CLK}_{T}\) (green), \(S_{T}(t)\) (yellow), \(U_{T}(t)\) (purple), \(S_{R}(t)\) (blue). In the insets: (**A**) multiple acquisitions of \(U_{T}(t)\) for the evaluation of the amplitude and phase jitters; (**B**) \(U_{R}(t)\) and the related \(S_{R}(t)\); (**C**) the eye diagram of \(S_{R}(t)\). Finally, in order to perform a comparative analysis with the state-of-the-art on transcutaneous biotelemetry, Table 1 summarises the main performances of different solutions reported in literature and those ones presented in this Paper. More in detail, in RF-based solutions, high data rates are achieved at low power consumptions and good power efficiencies with high BER values [9; 10; 12]. A very low BER with a satisfactory data rate are obtained in [11; 13] even if at the expenses of a strong increase of the RF system power consumption and power efficiency. Considering now the solutions based on optical wireless links, 100 Mbps is the highest achieved data rate with reduced power consumptions and good power efficiencies and BER values [4; 14; 15]. This represents the best trade-off among the main parameters of interest. On the other hand, the solution proposed in this paper shows the highest data rate and the best BER value among the optical link solutions. The mean value of the transmitter power consumption is 4.6 mW corresponding to a 35.9 pJ/bit power efficiency of the overall implantable unit.