## 2 Proposed Scheme and RF Transmission Algorithm
### Signal Decryption
The amplifier operates on the energy supplied by the DC power supply. The feedback path enables real-time adjustments and corrections based on the analysis of the transmitted signal by allowing a portion of the amplified signal to return to the FPGA SoC-Kit. The experimental design considers the collection of real-world biological data. The implemented transmission must be located in the linear region of the power amplifier. The RF-PA under broadband test with high dynamic range for LTE applications has an output power of 1 dB compression of 17.8 dBm, which sends it to saturation levels, so the transmission developed is below this power threshold. Thus, implementing the model and the experimental results are appropriate for the proposed system depicted in Figure 6, which employs a software-defined radio (SDR) transceiver base. The SDR platform includes a system-on-chip (SoC) device and a software and hardware interface for developing the SDR system. For the in-phase (\(I\)) and quadrature (\(Q\)) signals, the RF conversion system uses direct conversion with \(2\times 2\) channels. The testbed configuration includes the following components: a ZFBP-2400-S+ bandpass filter with a bandwidth of 2400 MHz \(\pm\) 100 MHz and an insertion loss of approximately 2 dB; a ZV60-V63+ power amplifier (with a 5 V bias) offering a gain of approximately 20 dB when operated at a frequency of 2.45 GHz; and a ZHDC-16-63-S+ coupler with a high directivity of 32 dB typ. and a return loss of approximately 23 dB. An attenuator with a 20 dB is installed at the input to protect the spectrum analyzer. A 3 dB attenuator is also positioned at the input of the RX channel of the transceiver board to protect the receiving signal below the power threshold. The developed platform contains the following measurement equipment, an FPGA embedded system and an RF transceiver: SIGLENT SSA 3032X Spectrum Analyzer, SIGLENT's headquarters is in Shenzhen, China. The power supply GW INSTEK GPS-3303 is manufactured by Good Will Instrument Co., whose headquarters are in Taipei, Taiwan. Cyclone V FPGA SoC-Kit is manufactured by Intel Corporation (formerly Altera), headquartered in Santa Clara, CA, USA. AD9361 RF Agile Transceiver manufactured by Terasic located in Hsinchu, Taiwan. In relation to the analog devices for signal and power management, the following devices were used: Mini-Circuits ZFBP-2400-S+ Bandpass Filter: Mini-Circuits is based in Brooklyn, New York, USA. Mini-Circuits ZX60-V63+ Power Amplifiers: Mini-Circuits, Brooklyn, New York, NY, USA. Mini-Circuits ZHDC-16-63-S+ Coupler: Mini-Circuits in Brooklyn, New York, NY, USA. Figure 5: Block diagram of the transmission testbed proposed. Part A: Signal transmission and control. Part B: Signal path and measurement. Decryption and Spectral Validation

In a rural sector, RF transmissions provide the advantage of transmitting information without the requirement of Wi-Fi or Ethernet. In this scenario, a line-of-sight transmission of relevant biological information would suit an embedded system like the Cyclone V FPGA development board. The transmission was devised for a carrier frequency of 2.5 GHz to be interpreted by a specialist. The root mean squared error (RMSE) metric, defined in Equation (22), determines the efficacy of the transmitted signal concerning the received ECG signal. \[RMSE=\sqrt{\sum_{n=1}^{N}[x_{tx}(n)-x_{rx}(n)]^{2}}, \tag{22}\]

where \(x_{tx}(n)\) is the ECG transmitted signal and \(x_{rx}(n)\) is the received signal under test. Figure 7 contains a comparison between an \(ECG_{Rx}\) signal and an \(ECG_{TX}\) signal at a heart rate of 1.11 Hz, with a precision of RMSE of 0.0235, using a 128-QAM modulation scheme. Figure 8 illustrates an ECG signal of 1.66 Hz. The demonstration was carried out for a medium-resolution 128-QAM scheme that provides adequate precision for interpreting signals by a medical specialist in the field; the system is adaptable to n-QAM variations. The implementations that have been conducted achieved a precision of RMSE of 0.0180 for ECG signals.