Mobile terminal employing 30khz/200khz carrier identification

Abstract

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. The method includes steps of (a) tuning a receiver ( ) to a frequency of a candidate GSM1900 channel; (b) determining a value of a received signal strength indicator (RSSI) using a 200 kHz receiver passband filter; (c) if the RSSI value is above a predetermined threshold, converting the frequency of the candidate GSM1900 channel into a frequency of a TDMA1900 channel using a predetermined relationship; (d) retuning the receiver to the frequency of the TDMA1900 channel; (e) determining a RSSI value using a 30 kHz receiver passband filter for the 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, (f) making at least an initial assumption of the presence of the GSM1900 carrier. A further step can be executed of verifying that the assumed GSM1900 carrier is not actually a CDMA1900 carrier. The method has an initial step of camping on a channel of a carrier in another frequency band (e.g., a TDMA800 channel), and the steps of tuning and retuning are executed without changing a baseband clock frequency from a frequency associated with the channel that the mobile terminal is camped on.