## 5 Results and Discussion
This reduction is mainly due to the new radio front-end used, which went from consuming 733.7 mW in transmission mode to 95.4 mW, and from 172.4 mW in reception mode to 55.9 mW. This change has many implications in terms of performance. First, the maximum I/Q sample rate went from 22 MSpns in MarmotE SDR to 4 MSpns in MIGOU, which limits the communication bandwidth and the instantaneous sensing. On the other hand, while the MAX2830 transceiver only operates in the 2.4 GHz band, the AT86 RF215 also supports the operation of multiple sub-1 GHz bands, covering the ranges from 389.5 to 510 MHz and from 779 to 1020 MHz. Finally, the baseband cores included in the AT86 RF215 transceiver represent a highly differentiating feature between both solutions. They allow for a highly efficient implementation of multiple PHY layers, which gives MIGOU the hybrid radio capability, i.e., being able to operate as a traditional node when the flexibility of the SDR is not necessary. In this way, the development time, the computational load of the node, and the power consumption were reduced, as seen in Figure 5.  
Specifically, in transmit mode, the power consumption is reduced by 45.5%, from 299.6 mW in I/Q mode to 163.4 mW in BB mode. More precisely, the consumption of the AT86 RF215 drops from 95.4 mW to 49.3 mW, and that of the SmartFusion2 from 200.9 mW to 110.8 mW, as a result of putting the FPGA in Flash*Freeze mode. In receive mode, consumption is reduced by 23.3%, down from 55.9 mW to 43.0 mW in the transceiver and from 142.2 mW to 108.1 mW in the SoC. It should be noted that in both transmit and receive modes, the power consumption of MIGOU's SmartFusion2 is higher than that of the SmartFusion on MarmotE SDR. This is because the first one was running at 50 MHz, while the second one was running at 10 MHz. Figure 5: Power consumption of the evaluated platforms in the following modes of operation: (a) transmit mode, (b) receive mode, and (c) sleep mode. In sleep mode, MIGOU consumes 22.8 mW, 32.2% of the MarmotE SDR's consumption in the same mode. This is mainly due to two factors. First, because in MarmotE SDR, the TCXO remains active during this mode, which is solvable with minimal changes. The other factor is the Flash*Freeze mode offered by the SmartFusion2. While the SmartFusion consumes 50 mW, the SmartFusion2 only consumes 22.8 mW. There is still a large difference in the power consumption in the sleep mode between MIGOU and the YetiMote-type platforms. This is due to the different performance of the low-power modes of the MCUs and of this type of SoC. However, it is still possible to reduce the power consumption of MIGOU by using an SmartFusion2 with a smaller amount of logical elements, which would limit its processing capacity, or to use an MCU and an independent Microsemi Igloo2 FPGA [13]. In this way, it would be possible to cut the power of the FPGA externally during the sleep mode. However, this approach compromises response times, and the throughput and communication flexibility between the two devices. For these reasons, and since the objective of this work is not only to develop a low-power experimental platform, but also one with a high flexibility and high performance, the benefits of the SoC-based approach were finally considered more appropriate. As mentioned in Section 4.2, each MIGOU power consumption value presented so far corresponds to the average of 2000 samples taken in a 2-s window. These data, as well as the maximum and minimum values in that window, are shown in Table 4. In addition, Figure 6 shows the raw power consumption measurements of our platform as a function of time. Observing both the table and the figure, two aspects stand out: power consumption in BB mode has a larger range of oscillation, and it changes in a faster and more repetitive way.