NB-IOT in a nomadic use case

We’re doing an experiment where our wearable NB-IoT device is ‘walked’ around the village by a test person. We want to sent (Tx) a measurement every minute. Obviously, the device will see different cells when walking around. To save battery, we do not want to reregister to the network every Tx. Instead we would like to stay connected to one cell as long as possible, but detect if the current cell is out of range and then connect to the nearest cell. Question: how to detect when a signal is lost? CGATT or COPS do not seem to provide reliable information for this. Any suggestions ?