I was just thinking about performing a recursive paging in order to see how much time I have until the battery of a mobile phone run out. Does anyone know if the mobile phone answers at every paging or if it doesn't "listen" all the time? I think it listens periodically. If anyone can give me a clue, that would be appreciated.

- The phone is in "idle" mode (no speech/data traffic) and periodically receives the paging channel (PCH) to find out if its being called. Further the phone measures the signal strength of neighbor cells and every now and then (not that frequent as the above actions) receives the cell information in the broadcast common control channel (BCCH) of the serving cell and of at most six neighbor cells with the strongest signal.

- The time between receiving the PCH is determined by a parameter of the serving cell (BS_PA_MFRMS, range 2 to 9). Its measured in 51-multiframes until the PCH for the phone repeats (if you want to know the details have a look at the GSM specs ;-) . The length of a 51-multiframe is 235.8 ms, this means the time between receiving the PCH is in the range 471.9 ms to 2122.2 ms. In this time the idle phone most of the time sleeps or receives the BCCH of the serving cell or one of the neighbor cells with the strongest signal (at most six).