Signal scanning systems and methods for multiple-mode cellular radiotelephones

Abstract

Multiple-mode cellular radiotelephones use a wide bandwidth receiving mode while scanning for signals in a narrow bandwidth receiving mode. Thus, when it is desired to scan the received frequency band to search for the presence of narrowband signals, the wider receiver bandwidth is first selected. When significant signal energy is identified in the wider bandwidth, a further scan using the narrowband mode may then be provided in order to locate the narrow bandwidth channel containing the strongest signal. In another embodiment, the signals that are received in the wider bandwidth mode are digitized to obtain complex signal samples. The complex signal samples are then processed to determine energy in each of a plurality of narrower bandwidths corresponding to channels in the narrower bandwidth cellular radiotelephone standards. Accelerated scanning of TDMA cellular channels may be obtained by tuning the cellular radiotelephone to a succession of frequency channels within one TDMA time slot and measuring signal strength for each of the succession of frequency channels. Tuning and measuring is then repeated for remaining ones of the TDMA time slots in the TDMA frame, preferably using the same channels in the same order. For each frequency channel, the signal strength that is the greatest measured signal strength of the frequency channel in all of the TDMA slots is assigned to that frequency channel. The assigned signal strengths may then be used to select a frequency channel for TDMA signal acquisition. Historical information may also be used to accelerate scanning of cellular channels by a cellular radiotelephone.

Dependencies are inferred from the claim text.