Method of judging whether radio receiver is inside or outside service area, circuit for judging the same, and radio selective-calling receiver including the circuit

Abstract

There is provided a method of judging whether a radio receiver is in a first area or a second area, the radio receiver dealing with a plurality of frequency channels, the method including the steps, in sequence, of receiving radio signals, detecting a synchronization signal out of the received radio signals, and transmitting a first signal, judging whether the radio receiver transfers outside a range where transmitted radio signals can be received, based on the first signal, detecting an intensity of electro-magnetic wave for each of the frequency channels, when the radio receiver is judged to transfer outside the range, and judging that the radio receiver is situated in the first area, when all of intensities of electro-magnetic waves are smaller than a threshold value, and judging that the radio receiver is situated in the second area, when at least one of intensities of electro-magnetic waves is greater than the threshold value. In accordance with the method, it is possible to accurately judge whether a radio receiver is situated in a first area such as an area to which radio is interrupted to enter, or in a second area such as an area other than a service area where transmitted radio signal can be received.