Telecommunications – Radiotelephone system – Including private cordless extension system
Reexamination Certificate
2000-03-23
2003-04-29
Le, Thanh Cong (Department: 2684)
Telecommunications
Radiotelephone system
Including private cordless extension system
C455S450000, C455S455000, C370S431000, C370S437000
Reexamination Certificate
active
06556834
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a mobile terminal apparatus used in, for example, a cellular radio communication system and, more particularly, to a mobile terminal apparatus using CDMA (Code Division Multiple Access) as a radio access scheme.
Recently, a mobile communication system using CDMA has attracted attention.
A CDMA mobile communication system uses spread spectrum communication and communicates, for example, as follows. A communication apparatus on the transmitting side modulates digital speech data or image data by digital modulation such as PSK modulation. The apparatus then converts the modulated data into a wideband baseband signal by using a spreading code. The apparatus converts the spread transmission signal into a signal having a radio frequency, and transmits it. A communication apparatus on the receiving side despreads the received radio frequency signal by using a code identical to the spreading code used by the communication apparatus on the transmitting side. This apparatus digitally demodulates the reception signal after this despreading by digital demodulation such as PSK demodulation, thereby reconstructing reception data.
CDMA has, for example, the following advantages which neither FDMA (Frequency Division Multiple Access) nor TDMA (Time Division Multiple Access) has:
(1) The use of a spread spectrum technique makes it possible to maintain high communication quality with respect to changes in communication environment such as fading.
(2) The use of a RAKE reception scheme makes it possible to perform soft handover and realize stable handover without causing any short break.
(3) Since many users share one radio frequency signal, a high frequency utilization efficiency can be attained.
In a CDMA mobile terminal apparatus, however, power consumption is generally high, and the battery life is short as compared with a mobile terminal apparatus using FDMA or TDMA.
In a cellular radio communication system, so-called handover is performed to switch one radio channel to another radio channel with which synchronization is to be established upon movement of a mobile terminal apparatus. In the handover, the mobile terminal apparatus detects the reception quality of a signal arriving from a base station, and determines on the basis of the detection result whether to perform switching. When the above reception quality is to be detected, a mobile terminal apparatus using FDMA or TDMA detects the reception electric field strength of a radio signal arriving from a base station. In contrast to this, a mobile terminal apparatus using CDMA must demodulate a radio signal arriving from a base station into a baseband signal first, and then perform digital processing for the signal. This is because, many mobile terminal apparatuses share one radio frequency (carrier) in CDMA, and digital signal processing including despreading processing for a spreading code must be performed to separate the respective channels.
For this reason, in the CDMA mobile terminal apparatus, many circuits in the reception system as well as the radio receiver operate in handover. As a consequence, a large current is consumed by the reception system.
In addition, in the CDMA mobile terminal apparatus, in the handover, the reception quality of a synchronized channel is compared with the reception qualities of other channels as synchronization establishment candidates to determine whether there is any channel whose reception quality is higher than that of the synchronized channel by a predetermined threshold or more. If a channel as a synchronization establishment candidate that meets this condition is found, the synchronized channel is switched to the channel of the synchronization establishment candidate.
In a conventional CDMA mobile terminal apparatus, however, the threshold for determining the reception quality is fixed to a predetermined value regardless of the reception quality of a synchronized channel. Even if, therefore, the reception quality of a synchronized channel is relatively good, and handover is not essentially required, handover is unconditionally performed whenever a channel as a synchronization establishment candidate higher in reception quality than this synchronized channel is found. As a consequence, handover occurs frequently, and much power is consumed by the terminal apparatus every time handover is performed.
In addition, in the CDMA mobile terminal apparatus, every time handover is performed, the reception qualities of all neighboring channels associated with the new channel with which synchronization is established are measured. For this reason, great power is consumed for every handover. As a result, the continuous standby time is greatly shortened.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a CDMA mobile terminal apparatus which reduces power consumption by reducing unnecessary handover, thereby prolonging the battery life.
In order to achieve the above object, according to the first aspect of the present invention, there is provided a CDMA mobile terminal apparatus having a function of receiving signals respectively transmitted from a plurality of base stations, selecting an optimal signal from the signals, and establishing synchronization with the selected signal, characterized by comprising:
First detection means for detecting a reception quality of a first signal with which synchronization has been established, second detection means for detecting a reception quality of at least one second signal as a synchronization establishment candidate, means, having information representing a correspondence between the reception quality of the first signal and a plurality of threshold values which is set in advance to change in accordance with the reception quality, for obtaining, on the basis of the information, a threshold value corresponding to the reception quality of the first signal which is detected by the first detection means, determination means for determining whether the reception quality of the second signal, detected by the second detection means, is higher than the reception quality of the first signal, detected by the first detection means, by not less than the obtained threshold value, and switching control means for performing processing for switching a synchronization establishment target signal from the first signal to the second signal only when the determination means determines that the reception quality of the second signal is higher than the reception quality of the first signal by not less than the obtained threshold value.
The second aspect of the present invention is characterized by comprising first detection means for detecting a reception quality of a first signal with which synchronization has been established, second detection means for detecting a reception quality of at least one second signal as a synchronization establishment candidate, quality classification means for classifying the reception quality of the first signal, detected by the first detection means, according to a plurality of different predetermined quality classes, a memory for storing predetermined threshold values in correspondence with the respective quality classes, selection means for selecting a threshold value corresponding to the reception quality of the first signal, detected by the first detection means, from the memory, determination means for determining whether the reception quality of the second signal, detected by the second detection means, is higher than the reception quality of the first signal, detected by the first detection means, by not less than the threshold value selected by the selection means, and switching control means for performing processing for switching a synchronization establishment target from the first signal to the second signal only when the determination means determines that the reception quality of the second signal is higher than the reception quality of the first signal by not less than the selected threshold value.
According to the first and second aspects of the
Enoki Masayuki
Hirai Katsumi
Kobayashi Shigeyuki
Sawa Buntaro
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
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