CDMA mobile terminal apparatus

• US 6,556,834 B1
• Filed: 03/23/2000
• Issued: 04/29/2003
• Est. Priority Date: 07/24/1998
• Status: Expired due to Fees

• Current Assignee: Fujitsu Mobile Communications Limited (Fujitsu Limited)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Sawa, Buntaro, Enoki, Masayuki, Kobayashi, Shigeyuki, Hirai, Katsumi
• Primary Examiner(s): Le, Thanh Cong
• Assistant Examiner(s): TRAN, TUAN A
• Application Number:
  US09/533,766
• Time in Patent Office: 1,132 Days
• Field of Search: 455/450, 455/451, 455/452, 455/453, 455/455, 455/464, 370/320, 370/329, 370/335, 370/341, 370/431, 370/437, 370/468, 370/321, 370/328
• US Class Current: 455/464
• CPC Class Codes: H04W 36/30 by measured or perceived connection quality data
• CPC Class Codes: H04W 36/36 by user or terminal equipment

Abstract

In idle handover control, the reception quality of a synchronized pilot channel is classified into quality class “1” with which data can be received without any error, quality class “2” with which data can be received within an allowable error range, or quality class “3” with which data is difficult to receive with high quality, and different thresholds, i.e., 6 dB, 4 dB, and 2 dB, are respectively set for these quality classes. It is checked whether the reception quality of another pilot channel as a synchronization establishment candidate is higher than that of the synchronized pilot channel by a threshold corresponding to a quality class into which the synchronized pilot channel is classified or more. If it is determined that the reception quality of the synchronization establishment candidate is higher by the threshold or more, handover processing is performed. Otherwise, synchronization with the synchronized pilot channel is maintained without handover processing.

Claims

1. A CDMA mobile terminal apparatus having a function of receiving signals respectively transmitted from a plurality of base stations, selecting an optimal one of the signals, and establishing synchronization with the optimal one of the signals, comprising:

a first detector configured to detect a reception quality of a first signal with which synchronization is established;

a second detector configured to detect a reception quality of at least one second signal as a synchronization establishment candidate;

a reference value determination section configured to obtain a determination reference value corresponding to the reception quality of the first signal detected by the first detector, on the basis of information representing a relationship between a reception quality and a determination reference value;

a determination section configured to determine whether or not the reception quality of the second signal detected by the second detector is higher than the reception quality of the first signal detected by the first detector by the determination reference value obtained by the reference value determination section;

a switching controller configured to switch a signal as a synchronization establishment target from the first signal to the second signal, when the determination section determines that the reception quality of the second signal detected by the second detector is higher than the reception quality of the first signal detected by the first detector by the determination reference value obtained by the reference value determination section; and

an inhibiting controller configured to inhibit, when the switching controller switches the signal as the synchronization establishment target from the first signal to the second signal, a processing for determining the reception quality of the second signal and a processing for determining whether or not to switch the signal from the second signal to a third signal, until an intermittent reception mode is set after the synchronization with the second signal is established.

2. A CDMA mobile terminal apparatus having a function of receiving signals respectively transmitted from a plurality of base stations, selecting an optimal one of the signals, and establishing synchronization with the optimal one of the signals, comprising:

a first detector configured to detect a reception quality of a first signal with which synchronization is established;

a second detector configured to detect a reception quality of at least one second signal as a synchronization establishment candidate;

a classification section configured to select one of a plurality of quality classes which are determined in advance, to which the reception quality of the first signal detected by the first detector belongs;

a selection section configured to select one of a plurality of determination reference values respectively corresponding to the plurality of quality classes, as a determination reference value corresponding to the reception quality of the first signal detected by the first detector;

a determination section configured to determine whether or not the reception quality of the second signal detected by the second detector is higher than the reception quality of the first signal detected by the first detector by said selected one of the plurality of determination reference values;

a switching controller configured to switch a signal as a synchronization establishment target from the first signal to the second signal, when the determination section determines that the reception quality of the second signal detected by the second detector is higher than the reception quality of the first signal detected by the first detector by said selected one of the plurality of determination reference values, and

an inhibiting controller configured to inhibit, when the switching controller switches the signal as the synchronization establishment target from the first signal to the second signal, a processing for determining the reception quality of the second signal and a processing for determining whether or not to switch the signal as the synchronization establishment target from the second signal to the third signal, until an intermittent reception mode is set after the synchronization with the second signal is established.

3. A CDMA mobile terminal apparatus having a function of receiving signals respectively transmitted from a plurality of base stations, selecting an optimal one of the signals, and establishing synchronization with the optimal one of the signals, comprising;

a first detector configured to detect a reception quality of a first signal with which synchronization is established;

a second detector configured to detect a reception quality of at least one second signal as a synchronization establishment candidate;

a reference value determination section configured to obtain a determination reference value corresponding to the reception quality of the first signal detected by the first detector, on the basis of information representing a relationship between the reception quality of the first signal detected by the first detector and a determination reference value;

a first determination section configured to determine whether or not the reception quality of the second signal detected by the second detector is higher than the detected reception quality of the first signal by the obtained determination reference value;

a first switching controller configured to switch a signal as a synchronization establishment target from the first signal to the second signal, when the first determination section determines that the reception quality of the second signal detected by the second detector is higher than the reception quality of the first signal detected by the first detector by the determination reference value obtained by the reference value determination section;

a second determination section configured to determine whether or not the reception quality of the second signal is equal to or higher than a predetermined value, in a time period in which an intermittent reception mode is set after synchronization with the second signal is established, when the first switching controller switches the signal as the synchronization establishment target from the first signal to the second signal;

a third determination section configured to determine whether or not to switch the signal as the synchronization establishment target from the second signal to a third signal, when the second determination section determines that the reception quality of the second signal detected by the second determination section is lower then the predetermined value;

an inhibiting controller configured to inhibit determination by the third determination section, when the second determination section determines that the reception quality of the second signal is equal to or higher than the predetermined value; and

a second switching controller configured to switch the signal as the synchronization establishment target from the second signal to the third signal, after at least a predetermined time period lapses from when the signal as the synchronization establishment target is switched from the first signal to the second signal, when the third determination section determines to switch the signal as the synchronization establishment target from the second signal to the third signal.

4. A CDMA mobile terminal apparatus having a function of receiving signals respectively transmitted from a plurality of base stations, selecting an optimal one of the signals, and establishing synchronization with the optimal one of the signals, comprising:

a first detector configured to detect a reception quality of a first signal with which synchronization is established;

a second detector configured to detect a reception quality of at least one second signal as a synchronization establishment candidate;

a classification section configured to select one of a plurality of quality classes, which are determined in advance, to which the reception quality of the first signal detected by the first detector belongs;

a selection section configured to select one of a plurality of determination reference values respectively corresponding to the plurality of quality classes, as a determination reference value corresponding to the reception quality of the first signal detected by the first detector;

a first determination section configured to determine whether or not the reception quality of the second signal detected by the second detector is higher than the reception quality of the first signal detected by the first detector by said selected one of the plurality of determination reference values;

a first switching controller configured to switch a signal as a synchronization establishment target from the first signal to the second signal, when the first determination section determines that the reception quality of the second signal detected by the second detector is higher than the reception quality of the first signal detected by the first detector by said selected one of the plurality of determination reference values;

a second determination section configured to determine whether or not the reception quality of the second signal is equal to or higher than a predetermined value, in a time period in which an intermittent reception mode is set after synchronization with the second signal is established, when the first switching controller switches the signal as the synchronization establishment target from the first signal to the second signal;

a third determination section configured to determine whether or not to switch the signal as the synchronization establishment target from the second signal to a third signal, when the second determination section determines that the reception quality of the second signal detected by the second determination section is lower then the predetermined value;

an inhibiting controller configured to inhibit determination by the third determination section, when the second determination section determines that the reception quality of the second signal is equal to or higher than the predetermined value; and

a second switching controller configured to switch the signal as the synchronization establishment target from the second signal to the third signal, after at least a predetermined time period lapses from when the signal as the synchronization establishment target is switched from the first signal to the second signal, when the third determination section determines to switch the signal as the synchronization establishment target from the second signal to the third signal.

5. A CDMA mobile terminal apparatus having a function of receiving signals respectively transmitted from a plurality of base stations, selecting an optimal one of the signals, and establishing synchronization with the optimal one of the signals, comprising:

a first detector configured to detect a reception quality of a first signal with which synchronization is established;

a second detector configured to detect a reception quality of at least one second signal as a synchronization establishment candidate;

a reference value determination section configured to obtain a determination reference value corresponding to the reception quality of the first signal detected by the first detector, on the basis of information representing a relationship between the reception quality of the first signal detected by the first detector and a determination reference value;

a first determination section configured to determine whether or not the reception quality of the second signal detected by the second detector is higher than the reception quality of the first signal detected by the first detector by the determination reference value obtained by the reference value determination section;

a first switching controller configured to switch a signal as a synchronization establishment target from the first signal to the second signal, when the first determination section determines that the reception quality of the second signal detected by the second detector is higher than the reception quality of the first signal detected by the first detector by the determination reference value obtained by the reference value determination section;

a second determination section configured to determine whether or not to switch the signal as the synchronization establishment target from the second signal to a third signal, in a time period in which an intermittent reception mode is set after synchronization with the second signal is established, when the first switching controller switches the signal as the synchronization establishment target from the first signal to the second signal; and

a second switching controller configured to switch the signal as the synchronization establishment target from the second signal to the third signal, after at least a predetermined time period lapses from when the signal as the synchronization establishment target is switched from the first signal to the second signal, when the second determination section determines to switch the signal as the synchronization establishment target from the second signal to the third signal.

6. A CDMA mobile terminal apparatus having a function of receiving signals respectively transmitted from a plurality of base stations, selecting an optimal one of the signals, and establishing synchronization with the optimal one of the signals, comprising:

a first detector configured to detect a reception quality of a first signal with which synchronization is established;

a second detector configured to detect a reception quality of at least one second signal as a synchronization establishment candidate;

a classification section configured to select one of a plurality of quality classes which are determined in advance, to which the reception quality of the first signal detected by the first detector belongs;

a selection section configured to select one of a plurality of determination reference values respectively corresponding to the plurality of quality classes, as a determination reference value corresponding to the reception quality of the first signal detected by the first detector;

a first determination section configured to determine whether or not the reception quality of the second signal detected by the second detector is equal or higher than the reception quality of the first signal detected by the first detector by said selected one of the plurality of determination reference values;

a first switching controller configured to switch a signal as a synchronization establishment target from the first signal to the second signal, when the first determination section determines that the reception quality of the second signal detected by the second detector is higher than the reception quality of the first signal detected by the first detector by said selected one of the plurality of determination reference values;

a second determination section configured to determine whether or not to switch the signal as the synchronization establishment target from the second signal to a third signal, in a time period in which an intermittent reception mode is set after synchronization with the second signal is established, when the first switching controller switches the signal as the synchronization establishment target from the first signal to the second signal; and

a second switching controller configured to switch the signal as the synchronization establishment target from the second signal to the third signal, after at least a predetermined time period lapses from when the signal as the synchronization establishment target is switched from the first signal to the second signal, when the second determination section determines to switch the signal as the synchronization establishment target from the second signal to the third signal.

7. A hand-over controlling method for a CDMA mobile terminal apparatus having a function of receiving signals respectively transmitted from a plurality of base stations, selecting an optimal one of the signals, and establishing synchronization with the optimal one of the signals, comprising:

detecting a reception quality of a first signal with which synchronization is established;

detecting a reception quality of at least one second signal as a synchronization establishment candidate;

obtaining a determination reference value corresponding to the detected reception quality of the first signal, on the basis of information representing a relationship between a reception quality and a determination reference value;

determining whether or not the detected reception quality of the second signal is higher than the detected reception quality of the first signal by the obtained determination reference value;

switching a signal as a synchronization establishment target from the first signal to the second signal, when it is determined that the reception quality of the second signal is higher than the reception quality of the first signal by the determination reference value; and

inhibiting, when the signal as the synchronization establishment target is switched from the first signal to the second signal, a processing for determining the reception quality of the second signal and a processing for determining whether or not to switch the signal from the second signal to a third signal, until an intermittent reception mode is set after the synchronization with the second signal is established.

8. A hand-over controlling method for a CDMA mobile terminal apparatus having a function of receiving signals respectively transmitted from a plurality of base stations, selecting an optimal one of the signals, and establishing synchronization with the optimal one of the signals, comprising:

detecting a reception quality of a first signal with which synchronization is established;

detecting a reception quality of at least one second signal as a synchronization establishment candidate;

selecting on of a plurality of quality classes which are determined in advance, to which the detected reception quality of the first signal belongs;

selecting one of a plurality of determination reference values respectively corresponding to the plurality of quality classes, as a determination reference value corresponding to the detected reception quality of the first signal;

determining whether or not the detected reception quality of the second signal is higher than the detected reception quality of the first signal by said selected one of the plurality of determination reference values;

switching a signal as a synchronization establishment target from the first signal to the second signal, when it is determined that the detected reception quality of the second signal is higher than the detected reception quality of the first signal by said selected one of the plurality of determination reference values; and

inhibiting, when the signal as the synchronization establishment target is switched from the first signal to the second signal, a processing for determining the reception quality of the second signal and a processing for determining whether or not to switch the signal as the synchronization establishment target from the second signal to a third signal, until an intermittent reception mode is set after the synchronization with the second signal is established.

9. A hand-over controlling method for a CDMA mobile terminal apparatus having a function of receiving signals respectively transmitted from a plurality of base stations, selecting an optimal one of the signals, and establishing synchronization with the optimal one of the signals, comprising:

detecting a reception quality of a first signal with which synchronization is established;

detecting a reception quality of at least one second signal as a synchronization establishment candidate;

obtaining a determination reference value corresponding to the detected reception quality of the first signal, on the basis of information representing a relationship between the detected reception quality of the first signal and a determination reference value;

determining whether or not the detected reception quality of the second signal is higher than the detected reception quality of the first signal by the obtained determination reference value;

switching a signal as a synchronization establishment target from the first signal to the second signal, when it is determined that the detected reception quality of the second signal is higher than the detected reception quality of the first signal by the obtained determination reference value;

determining whether or not the detected reception quality of the second signal is equal to or higher than a predetermined value, in a time period in which an intermittent reception mode is set after synchronization with the second signal is established, when the signal as the synchronization establishment target is switched from the first signal to the second signal,

determining whether or not to switch the signal as the synchronization establishment target from the second signal to a third signal, when it is determined that the detected reception quality of the second signal is lower than the predetermined valve;

inhibiting determination by the third determination section, when it is determined that the reception quality of the second signal is equal to or higher than the predetermined value; and

switching the signal as the synchronization establishment target from the second signal to the third signal, after at least a predetermined time period lapses from when the signal as the synchronization establishment target is switched from the first signal to the second signal, when it is determined to switch the signal as the synchronization establishment target from the second signal to the third signal.

10. A hand-over controlling method for a CDMA mobile terminal apparatus having a function of receiving signals respectively transmitted from a plurality of base stations, selecting an optimal one of the signals, and establishing synchronization with the optimal one of the signals, comprising

detecting a reception quality of a first signal with which synchronization is established,

detecting a reception quality of at least one second signal as a synchronization establishment candidate,

selecting one of a plurality of quality classes which are determined in advance, to which the detected reception quality of the first signal belongs;

selecting one of a plurality of determination reference values respectively corresponding to the plurality of quality classes, as a determination reference value corresponding to the detected reception quality of the first signal;

determining whether or not the detected reception quality of the second signal is higher then the detected reception quality of the first signal by said selected one of the plurality of determination reference values;

switching a signal as a synchronization establishment target from the first signal to the second signal, when it is determined that the detected reception quality of the second signal is higher than the detected reception quality of the first signal by said selected one of the plurality of determination reference values;

determining whether or not the reception quality of the second signal is equal to or higher than a predetermined value, in a time period in which an intermittent reception mode is set after synchronization with the second signal is established, when the signal as the synchronization establishment target is switched from the first signal to the second signal;

determining whether or not to switch the signal as the synchronization establishment target from the second signal to a third signal, when it is determined that the detected reception quality of the second signal is lower than the predetermined value;

inhibiting determination by the third determination section, when it is determined that the reception quality of the second signal is equal to or higher than the predetermined value; and

switching the signal as the synchronization establishment target from the second signal to the third signal, after at least a predetermined time period lapses from when the signal as the synchronization establishment target is switched from the first signal to the second signal, when it is determined to switch the signal as the synchronization establishment target from the second signal to the third signal.

11. A hand-over controlling method for a CDMA mobile terminal apparatus having a function of receiving signals respectively transmitted from a plurality of base stations, selecting an optimal one of the signals, and establishing synchronization with the optimal one of the signals, comprising

detecting a reception quality of a first signal with which synchronization is established;

detecting a reception quality of at least one second signal as a synchronization establishment candidate,

obtaining a determination reference value corresponding to the detected reception quality of the first signal, on the basis of information representing a relationship between the detected reception quality of the first signal and a determination reference value,

determining whether or not the detected reception quality of the second signal is higher then the detected reception quality of the first signal by the obtained determination reference value,

switching a signal as a synchronization establishment target from the first signal to the second signal, when it is determined that the detected reception quality of the second signal is higher then the detected reception quality of the first signal by the determination reference value;

determining whether or not to switch the signal as the synchronization establishment target from the second signal to a third signal, in a time period in which an intermittent reception mode is set after synchronization with the second signal is established, when the signal as the synchronization establishment target is switched from the first signal to the second signal; and

switching the signal as the synchronization establishment target from the second signal to the third signal, after at least a predetermined time period lapses from time at when the signal as the synchronization establishment target is switched from the first signal to the second signal, when it is determined to switch the signal as the synchronization establishment target from the second signal to the third signal.

12. A hand-over controlling method for a CDMA mobile terminal apparatus having a function of receiving signals respectively transmitted from a plurality of base stations, selecting an optimal one of the signals, and establishing synchronization with the optimal one of the signals, comprising

detecting a reception quality of a first signal with which synchronization is established;

detecting a reception quality of at least one second signal as a synchronization establishment candidate;

selecting one of a plurality of quality classes which are determined in advance, to which the detected reception quality of the first signal belongs;

selecting one of a plurality of determination reference values respectively corresponding to the plurality of quality classes, as a determination reference value corresponding to the detected reception quality of the first signal;

determining whether or not the detected reception quality of the second signal is equal or higher than the detected reception quality of the first signal by said selected one of the plurality of determination reference values;

switching a signal as a synchronization establishment target from the first signal to the second signal, when it is determined that the detected reception quality of the second signal is higher then the detected reception quality of the first signal by said selected one of the plurality of determination reference values,

determining whether or not to switch the signal as the synchronization establishment target from the second signal to a third signal, in a time period in which an intermittent reception mode is set after synchronization with the second signal is established, when the signal as the synchronization establishment target is switched from the first signal to the second signal; and

switching the signal as the synchronization establishment target from the second signal to the third signal, after at least a predetermined time period lapses from when the signal as the synchronization establishment target is switched from the first signal to the second signal, when it is determined to switch the signal as the synchronization establishment target from the second signal to the third signal.

13. A computer program for use in a CDMA mobile terminal apparatus having a function of receiving signals respectively transmitted from a plurality of base stations, selecting an optimal one of the signals, and establishing synchronization with the optimal one of the signals, said computer program capable of performing a method comprising:

detecting a reception quality of a first signal with which synchronization is established;

detecting a reception quality of at least one second signal as a synchronization establishment candidate;

obtaining a determination reference value corresponding to the detected reception quality of the first signal, on the basis of information representing a relationship between a reception quality and a determination reference value;

determining whether or not the detected reception quality of the second signal is higher than the detected reception quality of the first signal by the obtained determination reference value;

switching a signal as a synchronization establishment target from the first signal to the second signal, when it is determined that the reception quality of the second signal is higher then the reception quality of the first signal by the determination reference value, and

inhibiting, when the signal as the synchronization establishment target is switched from the first signal to the second signal, a processing for determining the reception quality of the second signal and a processing for determining whether or not to switch the signal from the second signal to a third signal, until an intermittent reception mode is set after the synchronization with the second signal is established.

14. A computer program for use in a CDMA mobile terminal apparatus having a function of receiving signals respectively transmitted from a plurality of base stations, selecting an optimal one of the signals, and establishing synchronization with the optimal one of the signals, said computer program capable of performing a method comprising:

detecting a reception quality of a first signal with which synchronization is established;

detecting a reception quality of at least one second signal as a synchronization establishment candidate;

selecting one of a plurality of quality classes which are determined in advance, to which the detected reception quality of the first signal belongs,

selecting one of a plurality of determination reference values respectively corresponding to the plurality of quality classes as a determination reference value corresponding to the detected reception quality of the first signal,

determining whether or not the detected reception quality of the second signal is higher than the detected reception quality of the first signal by said selected one of the plurality of determination reference values;

switching a signal as a synchronization establishment target from the first signal to the second signal, when it is determined that the detected reception quality of the second signal is higher than the detected reception quality of the first signal by said selected one of the plurality of determination reference values; and

inhibiting, when the signal as the synchronization establishment target is switched from the first signal to the second signal, a processing for determining the reception quality of the second signal and a processing for determining whether or not to switch the signal as the synchronization establishment target from the second signal to a third signal, until an intermittent reception mode is set after the synchronization with the second signal is established.

15. A computer program for use in a CDMA mobile terminal apparatus having a function of receiving signals respectively transmitted from a plurality of base stations, selecting an optimal one of the signals, and establishing synchronization with the optimal one of the signals, said computer program capable of performing a method comprising;

detecting a reception quality of a first signal with which synchronization is established;

detecting a reception quality of at least one second signal as a synchronization establishment candidate;

obtaining a determination reference value corresponding to the detected reception quality of the first signal, on the basis or information representing a relationship between the detected reception quality of the first signal and a determination reference value;

determining whether or not the detected reception quality of the second signal is higher than the detected reception quality of the first signal by the obtained determination reference value;

switching a signal as a synchronization establishment target from the first signal to the second signal, when it is determined that the detected reception quality of the second signal is higher than the detected reception quality of the first signal by the obtained determination reference value;

determining whether or not the detected reception quality of the second signal is equal to or higher than a predetermined value, in a time period in which an intermittent reception mode is set after synchronization with the second signal is established, when the signal as the synchronization establishment target is switched from the first signal to the second signal;

determining whether or not to switch the signal as the synchronization establishment target from the second signal to a third signal, when it is determined that the detected reception quality of the second signal is lower than the predetermined value,

inhibiting determination by the third determination section, when it is determined that the reception quality of the second signal is equal to or higher than the predetermined value; and

switching the signal as the synchronization establishment target from the second signal to the third signal, after at least a predetermined time period lapses from when the signal as the synchronization establishment target is switched from the first signal to the second signal, when it is determined to switch the signal as the synchronization establishment target from the second signal to the third signal.

16. A computer program for use in a CDMA mobile terminal apparatus having a function of receiving signals respectively transmitted from a plurality of base stations, selecting an optimal one of the signals, and establishing synchronization with the optimal one of the signals, said computer program capable of performing a method comprising

detecting a reception quality of a first signal with which synchronization is established;

detecting a reception quality of at least one second signal as a synchronization establishment candidate;

selecting one of a plurality of quality classes which are determined in advance, to which the detected reception quality of the first signal belongs;

selecting one of a plurality of determination reference values respectively corresponding to the plurality of quality classes, as a determination reference value corresponding to the detected reception quality of the first signal;

determining whether or not the detected reception quality of the second signal is higher than the detected reception quality of the first signal by said selected one of the plurality of determination reference values;

switching a signal as a synchronization establishment target from the first signal to the second signal, when it is determined that the detected reception quality of the second signal is higher than the detected reception quality of the first signal by said selected one of the plurality of determination reference values;

determining whether or not the reception quality of the second signal is equal to or higher then a predetermined value, in a time period in which an intermittent reception mode is set after synchronization with the second signal is established, when the signal as the synchronization establishment target is switched from the first signal to the second signal;

determining whether or not to switch the signal as the synchronization establishment target from the second signal to a third signal, when it is determined that the detected reception quality of the second signal is lower then the predetermined value;

inhibiting determination by the third determination section, when it is determined that the reception quality of the second signal is equal to or higher than the predetermined value; and

switching the signal as the synchronization establishment target from the second signal to the third signal, after at least a predetermined time period lapses from when the signal as the synchronization establishment target is switched from the first signal to the second signal, when it is determined to switch the signal as the synchronization establishment target from the second signal to this third signal.

17. A computer program for use in a CDMA mobile terminal apparatus having a function of receiving signals respectively transmitted from a plurality of base stations, selecting an optimal one of the signals, and establishing synchronization with the optimal one of the signals, said computer program capable of performing a method comprising:

detecting a reception quality of a first signal with which synchronization is established,

detecting a reception quality of at least one second signal as a synchronization establishment candidate;

obtaining a determination reference value corresponding to the detected reception quality of the first signal, on the basis of information representing a relationship between the detected reception quality of the first signal and a determination reference value;

determining whether or not the detected reception quality of the second signal is higher than the detected reception quality of the first signal by the obtained determination reference value;

switching a signal as a synchronization establishment target from the first signal to the second signal, when it is determined that the detected reception quality of the second signal is higher than the detected reception quality of the first signal by the determination reference value;

determining whether or not to switch the signal as the synchronization establishment target from the second signal to a third signal, in a time period in which an intermittent reception mode is set after synchronization with the second signal is established, when the signal as the synchronization establishment target is switched from the first signal to the second signal; and

switching the signal as the synchronization establishment target from the second signal to the third signal, after at least a predetermined time period lapses from when the signal as the synchronization establishment target is switched from the first signal to the second signal, when it is determined to switch the signal as the synchronization establishment target from the second signal to the third signal.

18. A computer program for use in a CDMA mobile terminal apparatus having a function of receiving signals respectively transmitted from a plurality of base stations, selecting an optimal one of the signals, and establishing synchronization with the optimal one of the signals, said computer program capable of performing a method comprising:

detecting a reception quality of a first signal with which synchronization is established;

detecting a reception quality of at least one second signal as a synchronization establishment candidate;

selecting one of a plurality of quality classes which are determined in advance, to which the detected reception quality of the first signal belongs;

selecting one of a plurality of determination reference values respectively corresponding to the plurality of quality classes, as a determination reference value corresponding to the detected reception quality of the first signal;

determining whether or not the detected reception quality of the second signal is equal or higher than the detected reception quality of the first signal by said selected one of the plurality of determination reference values;

switching a signal as a synchronization establishment target from the first signal to the second signal, when it is determined the detected reception quality of the second signal is higher than the detected reception quality of the first signal by said selected one of the plurality of determination reference values;

determining whether or not to switch the signal as the synchronization establishment target from the second signal to a third signal, in a time period in which an intermittent reception mode is set after synchronization with the second signal is established, when the signal as the synchronization establishment target is switched from the first signal to the second signal; and

switching the signal as the synchronization establishment target from the second signal to the third signal, after at least a predetermined time period lapses from when the signal as the synchronization establishment target is switched from the first signal to the second signal, when it is determined to switch the signal as the synchronization establishment target from the second signal to the third signal.

19. A mobile communication apparatus for use in a CDMA system, which includes a plurality of base stations each of which broadcasts control signals, the mobile communication apparatus receiving the control signals, selecting a first signal of the signals and synchronizing with the selected first one of the signals, the mobile communication apparatus comprising:

a first detector configured to detect a quality of the synchronized first signal;

a second detector configured to detect a quality of a second signal to be synchronized with the apparatus;

a storage section configured to store qualities and threshold values, each value corresponding to a respective one of the signal qualities;

a first determination section configured to determine one of the threshold values which corresponds to the detected quality of the received first signal, based on the stored threshold values and the stored values of the signal qualities;

a second determination section configured to determine whether the detected quality of the second signal is higher than the detected quality of the received first signal by the determined threshold value;

a changing section configured to change a signal to be synchronized, from the first signal to the second signal, if the detected quality of the second signal is higher than the detected quality of the received first signal by the determined threshold value; and

a disabling section configured to disable determining the quality of the second signal and disable determining whether to change the signal to be synchronized from the second signal to a third signal, until after the mobile communication apparatus synchronizes with the second signal and terminates the synchronization with the first signal.