Mobile terminal employing 30kHz/200kHz carrier identification

A mobile terminal comprising a receiver having a first filter with a bandwidth of X and a second filter with a bandwidth of Y, where X>Y, said receiver having an output providing a received signal strength indication (RSSI), and further comprising a controller coupled to said receiver and a stored program executed by said controller for identifying a presence of a first carrier that is channelized into first channels having a bandwidth X, and for distinguishing the first carrier from a second carrier that is channelized into second channels having a bandwidth Y, where the first carrier and the second carrier each occupy at least a portion of a same first frequency band, comprising circuitry for tuning said receiver to a frequency of a candidate one of said first channels and for determining a RSSI value for a received signal filtered through said first filter, said stored program being responsive to a condition that the RSSI value is above a predetermined threshold for converting the frequency of the candidate one of the first channels into a frequency of a corresponding one of said second channels in accordance with a predetermined relationship, and for retuning the receiver to the frequency of the corresponding one of the second channels and then determining a plurality of received signal strength indications, for a received signal filtered through said second filter, for the corresponding one of the second channels and also for a plurality of adjacent second channels;

• and said stored program being responsive to a condition wherein the plurality of received signal strength indications are all found to be approximately equal, within some threshold value, for verifying the presence of the first carrier.

A method for use by a multi-mode, dual band mobile terminal for identifying a presence of a GSM1900 carrier that is channelized into first channels having a bandwidth of 200 kHz, and for distinguishing the GSM1900 carrier from at least a TDMA1900 carrier that is channelized into second channels having a bandwidth of 30 kHz, comprising steps of:

• tuning a receiver to a frequency of a candidate GSM1900 channel number;
• determining a value of a received signal strength indicator (RSSI) using a 200 kHz receiver passband filter;
• if the RSSI value is above a predetermined threshold, converting the candidate GSM1900 channel number into a frequency of an equivalent TDMA1900 channel number using a predetermined relationship;
• retuning the receiver to the frequency of the equivalent TDMA1900 channel number;
• determining a RSSI value using a 30 kHz receiver passband filter for the equivalent TDMA1900 channel, and also for at least two adjacent TDMA1900 channels, assuming that two adjacent TDMA1900 channels are not used together in a same cell;
• and
• if the at least three RSSI values are all found to be approximately equal, within some threshold value, making at least an initial assumption of the presence of the GSM1900 carrier.