Mobile terminal employing 30kHz/200kHz carrier identification

• US 6,487,399 B1
• Filed: 05/26/1999
• Issued: 11/26/2002
• Est. Priority Date: 05/26/1999
• Status: Expired due to Fees

• Current Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Original Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Inventors: Rajaniemi, Jari, Kananen, Kari
• Primary Examiner(s): Vo, Nguyen T.
• Assistant Examiner(s): Orgad, Edan
• Application Number:
  US09/320,634
• Time in Patent Office: 1,280 Days
• Field of Search: 455/226.1, 455/226.2, 455/226.4, 455/450, 455/464, 455/509, 455/513, 455/553, 455/636, 455/442, 455/443, 455/444, 455/449, 455/437, 455/227, 370/252, 370/335, 370/337, 370/342, 370/465
• US Class Current: 455/226.1
• CPC Class Codes: H04W 48/18 Selecting a network or a communication service
• CPC Class Codes: H04W 88/06 adapted for operation in multiple networks or having at least two operational modes, e.g. multi-mode terminals

Abstract

A method for use by a multi-mode, dual band mobile terminal (10) 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 (16) 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.

Claims

1. A method for use by a mobile terminal 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, and where X>

Y, comprising steps of;

tuning a receiver to a frequency of a candidate one of said first channels and determining a received signal strength indication for a received signal filtered through a filter having a passband of X;

if the received signal strength indication is above a predetermined threshold, 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 tuning the receiver to the frequency of the corresponding one of the second channels;

determining a plurality of received signal strength indications for a received signal filtered through a filter having a passband of Y for the corresponding one of the second channels and also for a plurality of adjacent second channels; and

if the plurality of received signal strength indications are all found to be approximately equal, within some threshold value, verifying the presence of the first carrier.

2. A method as in claim 1, wherein the first carrier is associated with a GSM1900 carrier.

3. A method as in claim 2, wherein the second carrier is associated with a TDMA1900 carrier.

4. A method as in claim 3, wherein the step of verifying operates to verify that the second carrier is not associated with a CDMA1900 carrier.

5. A method as in claim 1, wherein X=200 kHz and Y=30 kHz.

6. A method as in claim 1, and comprising an initial step of camping on a channel of a carrier in a second frequency band, and wherein the steps of tuning are executed without changing a baseband clock frequency from a frequency associated with the channel that the mobile terminal is camped on.

7. A method as in claim 6, wherein the first frequency band is the 1900 MHz band, and wherein the second frequency band is the 800 MHz band.

8. 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.

9. A mobile terminal as in claim 8, wherein the first carrier is associated with a GSM1900 carrier, wherein the second carrier is associated with a TDMA1900 carrier, and wherein X=200 kHz and Y=30 kHz.

10. A mobile terminal as in claim 9, wherein the stored program operates to verify that the second carrier is not associated with a CDMA1900 carrier.

11. A mobile terminal as in claim 8, wherein said mobile terminal is initially camped on a channel of a carrier in a second frequency band, and the receiver is tuned and retuned without changing a baseband clock frequency from a frequency associated with the channel that the mobile terminal is camped on.

12. A mobile terminal as in claim 11, wherein the first frequency band is the 1900 MHz band, and wherein the second frequency band is the 800 MHz band.

13. 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.

14. A method as in claim 13, and further comprising a step of verifying that the assumed GSM1900 carrier is not actually a CDMA1900 carrier.

15. A method as in claim 13, and comprising an initial step of camping on a channel of a carrier in another frequency band, and wherein 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.

16. A method as in claim 15, and wherein the other frequency band is the 800 MHz band.

17. A method as in claim 13, wherein the step of converting the GSM1900 channel number to an equivalent TDMA1900 channel number is accomplished according to the following formula:

${\mathrm{CH}}_{\mathrm{TDMA}}=\mathrm{Round}<br><br>\text{\hspace{1em}<br><br>}<br><br>\text{\hspace{1em}<br><br>}\left(\frac{20<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{CH}}_{\mathrm{GSM}}-10222}{3}\right).$