LTESS-track: A Precise and Fast Frequency Offset Estimation for low-cost SDR Platforms

The availability of very cheap RTL-SDR "dongle" devices has unleashed the popularity of Software-Defined Radio (SDR) projects in the last years, both among academics and hobbyists. The main success factors are the very affordable price ($25 USD), ease of use and wide availability of open-source SDR software. One important performance aspect of SDR receivers is related to the accuracy and stability of the Local Oscillator (LO). We present LTESS-track, an LO frequency offset evaluation method that relies on the Synchronization Signals (SS) transmitted by LTE base stations as reference. We compare LTESS-track with other publicly available tools for frequency offset estimation and show that our method can perform reliable measurements in less than 1 second, orders of magnitude faster than software publicly available. We leverage LTESS-track to assess the actual LO performances of two popular RTL-SDR models with and without Temperature Controlled Local Oscillator (TCXO). The experimental results show that the latest generation of RTL-SDR (with TCXO), despite being very low cost, has surprising excellent LO stability, well within the maximum tolerance of 1 ppm declared in the specifications.