Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1996-09-26
2001-03-27
Le, Thanh Cong (Department: 2749)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S456500, C455S440000, C455S428000
Reexamination Certificate
active
06208861
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a cellular communication system, and in particular to a method for monitoring radio channels for channel switching in a mobile communication terminal such as a cellular telephone.
2. Description of the Related Art
In cellular communications, it is necessary to transfer a connection from one cell to another without interruption. For this end, a mobile terminal monitors radio channels of adjacent cells at all times so that, when the condition of a radio channel being used becomes worse and that of an adjacent radio channel becomes better, the mobile terminal changes the communication channel to the adjacent radio channel having a better radio condition.
One method of monitoring radio channels when the mobile terminal is moving has been disclosed in Japanese Patent Unexamined Publication No. 3-104330. In this method, the duration of measuring the strength level of a received signal is varied according to a velocity of the moving mobile terminal. As shown in
FIG. 1
, a mobile terminal has a transmission and reception system including an antenna
10
, a radio transmitter-receiver
11
, and a modulator-demodulator
12
. The mobile terminal is further provided with a fading frequency detector
13
, a received level detector
14
, and a controller
15
.
The fading frequency detector
13
detector facing frequency which is used to estimate a velocity of the mobile terminal by the controller
15
. More specifically, the fading frequency detector
13
, receiving an intermediate frequency signal from the radio transmitter-receiver
11
, detects the envelope of a received signal strength. By comparing it with a predetermined household level, the fading frequency detector
13
counts the number of times the envelope has decreased below the predetermined threshold level for a predetermined time period to produce the fading frequency. When the fading frequency is low, it is estimated that the mobile terminal is moving at a relatively low velocity. Conversely, when the fading frequency is high, it is estimated that the mobile terminal is moving at a relatively high velocity.
Based on the estimated velocity, the duration of measuring the strength level of a received signal is changed. At a low velocity, the measuring duration is long enough to produce a significant averaged level of the strength level of the received signal. On the other hand, at a high velocity, the measuring duration is short so as to rapidly determine whether to transfer from one cell to another.
However, the velocity estimation method mentioned above cannot assure continued accuracy because the received signal strength varies due to not only the movement velocity of the mobile terminal but also multipath fading which is a characterization of radio propagation. More specifically, variations in received signal strength due to the multipath fading cause the fading frequency to change, resulting in reduced accuracy of the velocity estimation based on the fading frequency. This causes undesirable channel switching in a radio zone or a delay in transferring from a radio zone to another. In this manner, according to the conventional control method, it is difficult to transfer a connection with reliability. Further, since the measuring duration is relatively long at a low velocity, the power consumption is increased.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a communication control method which can optimize channel monitoring so that switching to another radio channel with reliability regardless of the velocity of a mobile terminal can be achieved.
Another object of the present invention is to provide a mobile terminal which can switch channels reliably and save the battery power at any velocity of the mobile terminal.
Still another object of the present invention is to provide a cellular telephone with improved communication quality regardless of the movement velocity of the cellular telephone.
According to the present invention, a mobile communication terminal is provided with a GPS (Global Positioning System) receiver wherein a movement velocity of the mobile communication terminal is obtained based on GPS data received by the GPS receiver. An intermittent period of time during which the channel condition of a radio channel is monitored, is changed according to the movement velocity. Since the GPS data provides an accurate position of the mobile communication terminal, an accurate movement velocity of the mobile communication terminal is obtained regardless of cellular radio propagation characterization. The radio channel is periodically monitored wherein the frequency of monitoring is determined according to the accurate movement velocity of the mobile communication terminal. More specifically, the lower the movement velocity of the mobile communication terminal, then the less often the radio channel is monitored. That is, the lower the movement velocity, then the longer the intermittent period.
According to an aspect of the present invention, in a mobile terminal which is located in a communication area divided into a plurality of smaller radio zones, the GPS data are received from at least three GPS satellites and a movement velocity of the mobile terminal is detected based on the GPS data. An intermittent period is changed according to the movement velocity of the mobile terminal and the channel condition is monitored during the intermittent period with a constant monitoring time for each intermittent period. By comparing the channel condition of a first radio channel being used to that of a second radio channel, channel switching is performed from the first radio channel to the second radio channel when the channel condition of the second radio channel is better than that of the first radio channel.
Preferably, the intermittent period becomes longer as the movement velocity of the mobile terminal is reduced. Conversely, the intermittent period becomes shorter as the movement velocity of the mobile terminal is increased.
According to another aspect of the present invention, a mobile communication terminal periodically monitors channel conditions of a first radio channel of a first radio zone being used and a second radio channel of a second radio zone adjacent to the first radio zone. After detecting a movement velocity of the mobile communication terminal based on the GPS data as described above, the mobile communication terminal changes an intermittent period according to the movement velocity thereof and monitors the channel condition of the second radio channel during the intermittent period with a constant monitoring time for each intermittent period.
It is preferable that the channel condition of the second radio channel is not monitored when the movement velocity of the mobile communication terminal is zero.
Further, in addition to the intermittent period, it is preferable that a whole monitoring time period may be changed according to the movement velocity of the mobile communication terminal. The channel condition of the second radio channel is monitored during the intermittent period for the whole time period which has been changed according to the movement velocity of the mobile communication terminal.
REFERENCES:
patent: 4903212 (1990-02-01), Yokouchi et al.
patent: 5396647 (1995-03-01), Thompson et al.
patent: 5491834 (1996-02-01), Chia
patent: 0453726 (1991-10-01), None
patent: 0512789 (1992-11-01), None
patent: 3104330 (1991-05-01), None
WPI Abstract Accession No. 91-173933, corresponding to JPA 3-104330 (Sep. 9, 1989).
Armstrong Darnell R.
Cong Le Thanh
NEC Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
LandOfFree
Mobile terminal with GPS function does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Mobile terminal with GPS function, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Mobile terminal with GPS function will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2517114