Kalibrate, or kal, can scan for GSM base stations in a given frequency band and can use those GSM base stations to calculate the local oscillator frequency offset. See http://thre.at/kalibrate Copyright (c) 2010, Joshua Lackey (jl@thre.at)
PodgroupConnectivity/kalibrate-uhd
Kalibrate GSM frequency scanner and clock offset calculator
C++BSD-2-Clause