## 2 Related Work  
Nowadays, there are many SDR platforms that are widely used both in academia and industry. Among them, the most broadly used are Ettus Research USRPs [18], BladeRF [19], HackRF [20], WARP [21], ADALM-PLUTO [22], and LimeSDR [23]. However, as mentioned in the previous section, all of them are based on high-performance chips, so their power consumption is in the order of watts,something unsuitable in most cases for a battery-powered end-device. Moreover, all these platforms are only radio frontends, so an additional processor-based system is required to manage them.  
Multiple works [24; 25; 26] use the RTL-SDR USB dongle [27], which is a low-cost commercial digital video broadcasting terrestrial (DVB-T) TV receiver, along with a Raspberry Pi as an SDR platform. The power consumption of this solution is still above one watt, but it is a very economical option, and thanks to the use of the Raspberry Pi, allows for the use of helpful SDR libraries, such as GNU Radio [28]. Apart from consumption, another drawback of this solution is that it only embeds a receiver, which considerably limits the development options.  
MarmotE SDR [29] and \(\upmu\)SDR [30] are two low-cost and sub-watt SDR platforms, which were specifically designed to be battery-powered. In terms of hardware architecture, both are practically equivalent. Their processing backend is based on the Microsemi SmartFusion SoC. This device integrates a flash-based FPGA fabric and an ARM Cortex-M3 processor. Thus, it gives more flexibility than traditional fixed-function microcontroller units (MCUs) without the excessive cost of soft processor cores on traditional FPGAs. Moreover, compared to SRAM-based FPGAs, flash-based FPGAs have a much lower static consumption, which is crucial for low-power operation. As a radio frontend, both platforms use a 2.4 GHz I/Q transceiver of the MAX283X family from Maxim Integrated. This device allows for direct access to the I/Q components of the baseband signals and it integrates almost all the circuitry required to implement the radio frontend functions.  
These two works have proved the feasibility of this kind of platform in terms of cost, size, power consumption, and the utilization of FPGA logic resources to approach the CR research from the end-device perspective. However, it is still possible to go further. When analyzing the consumption data of MarmotE SDR [8; 29], it can be seen that the radio transceiver is responsible for more than half of the power consumption in those modes in which it is active, reaching 60% of the total consumption in the receive mode and 86% in the transmit mode. Therefore, this component constitutes one of the most critical parts of the design, with a high impact in the overall energy utilization. In addition, it only operates in the 2.4 GHz band, limiting the possibilities of experimentation. On the other hand, in sleep mode, MarmotE SDR has a total power leakage of 70.8 mW, of which 50 mW (71%) are drawn by the SmartFusion and 20 mW (28%) by the temperature compensated crystal oscillator (TCXO), which is used to drive the radio transceiver and is always enabled by design, even in this low-power mode. Moreover, the SmartFusion does not support any ultra-low-power mode, while its new version, SmartFusion2, does.  
As shown in the results of this work, the consumption of these low-power SDR platforms is still much larger than that of traditional end-devices. In addition, the implementation and evaluation of the PHY/MAC layers for SDR systems implies a major commitment of time and money because of its complexity. This is a price that must be paid when working with SDRs, even when these layers do not include any cognitive feature. The lack of a platform that allows for benefitting from both the flexibility and processing capacity of SDRs, and the energy efficiency and agility of development of traditional nodes, has inspired this work.