## 4 Materials and Methods
### Methods  
The power consumption of the platforms was evaluated in transmit, receive, and sleep modes. To that end, the different platforms were set to statically operate in these modes. The supply voltage and current consumption were measured in each case in order to obtain the power consumption data. The B2902A SMU has a supply voltage resolution of 10 \(\mu\)V, and it measures the current consumption with a resolution of 100 nA. For our tests, this SMU was configured with a sampling rate of 1 kHz, and 2000 samples (window of 2 s), which were averaged to obtain each final measurement. In the case of MIGOU, its dynamic consumption (as a function of time) was also evaluated. In this case, only raw current measurements were used. On the other hand, the Ruiteng AT35 provides voltage and current values with a resolution of 1 mV and 100 \(\mu\)A, respectively, and it has a measurement refresh rate of 0.5 Hz. Therefore, in this case each result corresponded to a single measurement (window of 2 s). The experiments with which the MarmotE SDR platform was characterized [8; 29] were used as a reference to be able to perform a comparison between the different systems under similar conditions. Specifically, they implemented a PHY layer in the FPGA that is controlled from the MSS. This layer uses a Gaussian minimum-shift keying (GMSK) modulation with a bandwidth-time (BT) product BT = 0.5. It operates in the 2.4 GHz band with a transmission data rate of 250 kbps and an output power of 0 dBm. During the transmit and receive modes, both the FPGA and the MSS were running at 10 MHz. Moreover, they define the MarmotE SDR sleep mode with the MAX2830 transceiver in shutdown mode; the FPGA in reset mode; the required MSS peripherals running at 32 kHz; and the Cortex-M3 halted, waiting for interrupt (WFI). In their design, the TCXO is always enabled, even in this mode. With this configuration they obtained the lowest-power mode from which the system could wake up. On the other hand, as mentioned before, MIGOU supports two modes of operation: BB mode, in which it behaves like a traditional node, and I/Q mode, in which it operates as an SDR system. As shown in Figure 3, depending on the selected mode, different subsystems of the platform were enabled or disabled to ensure an energy-efficient operation. In these active modes, the SmartFusion2 was running at 50 MHz and the AT86 RF215 at 26 MHz. In addition, a sleep mode is defined in which the AT86 RF215 transceiver is set to deep sleep, where the TCXO is disabled; the FPGA is set to Flash*Freeze mode; the Cortex-M3 is halted and put in WFI; and the necessary peripherals of the MSS remain running at 1 MHz, which is the minimum standby clock frequency currently supported by Microsemi. The supply voltage of the transceiver in all the tests was 1.8 V. Table 1 shows a summary of the status of each of the main MIGOU subsystems in the different modes of operation. To evaluate the power consumption of MIGOU in I/Q mode, the same PHY layer and configuration parameters as in the case of MarmotE SDR were used. Alternatively, to evaluate its power consumption in BB mode, an application was developed in YetiOS to continuously send 64-byte packets from a transmitting node to a receiving one. This application waits 5 ms after a packet has been transmitted to send the next one. In this case, the AT86 RF215 was configured to operate in the 2.4 GHz band, but it used a binary frequency-shift keying (BFSK) modulation since the GMSK used in the MarmotE SDR experiments was not supported. In both modulations, the transmitter switches between two alternative frequencies according to the data symbols. The main difference between these two modulations is that in the case of GMSK, this transition between frequencies is carried out in a controlled manner. Furthermore, the AT86 RF215 in this configuration does not allow for a data rate of 250 kbps, so we used 200 kbps, which was the closest allowed value.