Range estimation in FMCW SDR radars with unsynchronized receivers

Frequency-modulated continuous wave (FMCW) radars are widely used in applications such as automotive sensing and remote monitoring. Implementing these systems on software-defined radio (SDR) platforms offers flexibility but also introduces challenges, such as synchronization and isolation between the transmitter and receiver, processing large volumes of data, and digital signal processing. This paper proposes two methods for range detection in FMCW radars using unsynchronized SDR platforms for the transmitter and receiver. In both approaches, a direct signal between the transmitting and receiving antennas, positioned a few centimeters apart, serves as a reference. The first method employs FFT on the squared magnitude of the received signal to estimate the range, while the second method adapts the classical matched filter technique. The proposed methods also enable the receiver to operate with a lower sampling rate than the transmitter. Tests were conducted using LimeSDR platforms with a frequency deviation of 58 MHz (corresponding to the sweep bandwidth), an output power of 10 dBm, and a central frequency of 2.4 GHz, targeting distances between 5.27 m and 28.45 m. The first method achieved an average error of 3.5% with matching sampling rates, while the second method reduced the error to 2.15%. When halving the receiver's sampling rate, the average errors increased to 4.28% and 2.33%, respectively. These results demonstrate the potential of the proposed methods for flexible and efficient radar implementations on SDR platforms.