MOBILE TERMINAL EMPLOYING 30KHZ/200KHZ CARRIER IDENTIFICATION

摘要

A method for use by a multi-mode, dual band mobile terminal(10) for identifying a presence of a GSM1900 carrier thatis channelized into first channels having a bandwidth of200kHz, and for distinguishing the GSM1900 carrier from atleast a TDMA1900 carrier that is channelized into secondchannels having a bandwidth of 30kHz. The method includessteps of (a) tuning a receiver (16) to a frequency of acandidate GSM1900 channel; (b) determining a value of areceived signal strength indicator (RSSI) using a 200kHzreceiver passband filter; (c) if the RSSI value is above apredetermined threshold, converting the frequency of thecandidate GSM1900 channel into a frequency of a TDMA1900channel using a predetermined relationship; (d) retuningthe receiver to the frequency of the TDMA1900 channel; (e)determining a RSSI value using a 30kHz receiver passbandfilter for the TDMA1900 channel, and also for at least twoadjacent TDMA1900 channels, assuming that two adjacentTDMA1900 channels are not used together in a same cell;and, if the at least three RSSI values are all found to beapproximately equal within some threshold value, (f) makingat least an initial assumption of the presence of theGSM1900 carrier. A further step can be executed ofverifying that the assumed GSM1900 carrier is not actuallya CDMA1900 carrier. The method has an initial step ofcamping on a channel of a carrier in another frequency band(e.g., a TDMA800 channel), and the steps of tuning andretuning are executed without changing a baseband clockfrequency from a frequency associated with the channel thatthe mobile terminal is camped on.