Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-12-17
2003-07-15
Legree, Tracy (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S441000, C370S333000
Reexamination Certificate
active
06594494
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a mobile terminal for use in a mobile communication system. Specifically, the present invention relates to a control of the handing over of the communication channel so as to continue the communication, when a mobile terminal moves from a base station cell of a current base radio station, which is communicating with the mobile terminal, to the base station cell of another base radio station. In a handing over procedure, a supplemental communication channel is provided to the communication channel of the new base radio station.
BACKGROUND ART
In a mobile communication system, when a mobile terminal moves from the base station cell of a communicating base radio station into the cell of a neighboring base radio station, it is necessary to hand over the communication channel to the neighboring base radio station, and to provide a supplemental channel to the neighboring base radio station so as to continue the communication.
Japanese Patent Application JP-A-9-37327 discloses an example of the control of handing over in the prior art mobile communication system.
FIG. 1
is a schematic diagram of the control of handing over disclosed therein. Reference numerals
1
a
,
1
b
,
1
c
denote base radio stations, each of which covers a base station cell
2
a
,
2
b
,
2
c
. Reference numeral
3
denotes a mobile terminal, which is moving in the area of the base station cells
2
a
,
2
b
, and
2
c
. The mobile terminal is communicating with one of the base radio stations.
FIG. 2
is a flow chart showing the control of the handing over. At first, the mobile terminal
3
measures the level and the qualities of communication of the input signal received from the currently communicating base radio station
1
a
(step ST
1
). The qualities of communication include, for example, a bit error rate and a frame error rate. Then the mobile terminal judges whether the received input level and the qualities of the communication are higher than a predetermined value (step St
2
). When they are higher than predetermined values, the procedure returns to the step St
1
. On the other hand, when they are less than the predetermined values, the mobile terminal measures the level and the qualities of communication of the input signals received from the other base radio stations
1
b
,
1
c
. (step St
3
).
When the level of the input signal and the qualities of communication of the input signal received therefrom is higher than a predetermined value, the mobile terminal measures the tendency of changing rate of the level and the qualities of communication of the input signal received from the base radio stations, and judges whether they are increasing or decreasing (step ST
4
).
Then the mobile terminal judges whether there are base stations, the tendency of changing rate of the level or the qualities of communication of the input signal therefrom is increasing (step ST
5
). When there are at least one base radio station, which has such an increasing tendency, the mobile terminal judges whether a plurality of the radio base stations have such an increasing tendency or only one base radio station has such an increasing tendency (step ST
6
).
When only one base station has such an increasing tendency, the communication is handed over to the base radio station (step ST
7
).
FIG. 1
(
a
) shows such a situation. In this case, the communication channel is handed over to the base station cell
2
c
of the base radio station
1
c
. On the other hand, when a plurality of base radio stations have an increasing tendency, the communication channel is handed over to the base radio station, the level of the input signal or the qualities of communication of the input signal received therefrom is the lowest among them (step ST
8
).
FIG. 1
(
b
) shows such a situation. In this case, the communication channel is handed over to the base station cell
2
c
of the base radio station
1
c.
When it is judged that no base radio station has such an increasing tendency in the step ST
5
, the communication channel is handed over to the base station cell of the base radio station, the level of the input signal or the qualities of communication of the input signal received therefrom is the highest (step ST
9
). FIG.
1
(
c
) shows such a situation. In this case, the communication channel is handed over to the base station cell
2
c
of the base radio station
1
c.
Japanese patent application, JP-A-6-292258, discloses another example of the control of handing over in a mobile communication system, in which each of the mobile terminals in the mobile communication system has a function to generate a data for measuring the bit error rate (BER) of the input signal received by the mobile terminal. Each of the base radio stations has a function to receive the data to measure the bit error rate BER, so that the communication channel is handed over to the base station cell of the base radio station, the bit error rate BER of which is the smallest.
In general, it is known that a plurality of communication paths appear between a base radio station and a mobile terminal due to the diffraction and/or the reflection of the electromagnetic wave, and a multi-fading effect due to a plurality of communication paths is observed. In such a circumstance, the level of the input signal received by the mobile terminal shows a Rayleigh's distribution, as shown in FIG.
3
. For avoiding the influence of the fading effect, a temporal mean value of the instantaneous level of the input signals in a certain time interval is often adopted as the level of the input signal. However, because the Rayleigh's distribution is a function of the spatial position, the change of the instantaneous measured level of the input signal depends on the state of the mobile terminal, for example, the velocity and direction of the movement. Therefore, it is difficult to eliminate the influence of the fading effect using such a temporal mean value.
When a moving vehicle, in which a mobile terminal is equipped, moves at a high velocity, it is necessary to shorten the smoothing time of the input signal, and the temporal resolution of the input signal has to be increased, in order to follow the rapid change of the level and/or the qualities of communication of the input signal. On the other hand, when the moving vehicle moves at a low velocity or is nearly stopping, the time for smoothing the input signal has to be long so as to increase the preciseness of the measurement. That is because a simultaneous actuation of a plurality of channels for handing over has to be prevented. Such simultaneous actuation can take place at a marginal area of a base station cell of a base radio station, due to the chattering phenomenon of the input level or qualities of communication of the input signal. However, the mobile terminal of a mobile communication system in the prior art has no means to detect the velocity of the moving object.
When a moving vehicle, in which a mobile terminal is equipped, moves at a high velocity, it is necessary to shorten the smoothing time of the input signal, and the temporal resolution of the input signal has to be increased, in order to follow the rapid change of the level and/or the qualities of communication of the input signal. On the other hand, when the moving vehicle moves at a low velocity or is nearly stopping, the time for smoothing the input signal has to be long so as to increase the preciseness of the measurement. That is because a simultaneous actuation of a plurality of channels for handing over has to be prevented. Such simultaneous actuation can takes place at a marginal area of a base station cell of a base radio station, due to the chattering phenomenon of the input level or qualities of communication of the input signal. However, the mobile terminal of a mobile communication system in the prior art has no means to detect the velocity of the moving object.
It is well known that the frequency of an electromagnetic wave measured in a moving object is shifted compared to the frequency m
Legree Tracy
Rothwell Figg Ernst & Manbeck
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