A base station determines a window of time for arrival of uplink signals, wherein the window of time includes a start based on a first expected time of arrival for a first uplink signal from a first UE and an end based on a second expected time of arrival for a second uplink signal from a second UE. The base station detection detects a false base station, such as a L1 man-in-the-middle false base station, based on an uplink signal being received outside of the determined window of time for the arrival of uplink signals.