Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-06-23
2002-07-23
Trost, William (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S437000, C455S438000, C455S439000, C455S442000, C455S443000, C370S328000, C370S329000, C370S331000, C370S332000
Reexamination Certificate
active
06424833
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mobile communication system and a hand-off method used in the mobile communication system.
2. Description of the Related Art
An electric field level measurement at a mobile terminal and a hand-off method in accordance with the result of the measurement carried out in a mobile communication system will be explained with referring to
FIG. 2
which shows an example of constitution of the mobile communication system. A description will be made for the mobile communication system designed based upon the TIA/EIA-627 (telecommunications industry association/electronic industry association) specifications.
In
FIG. 2
, the mobile communication system designed based on the TIA/EIA-627 specifications corresponds to a cellular type mobile communication system. A communication service area by the cellular type mobile communication system comprises a plurality of cells
20
,
30
,
40
,
50
,
60
,
70
and
80
. Base stations
2
,
3
,
4
,
5
,
6
,
7
and
8
are arranged in each of the cells
20
,
30
,
40
,
50
,
60
,
70
and
80
for providing radio communication with mobile terminals existing in each cell. In this drawing, only
7
cells are shown, however, in an actual case, a large number of cells are constituting communication service area. Control channels having different frequencies from each other are allocated to the adjoining base stations. Each of these base stations
2
,
3
,
4
,
5
,
6
,
7
and
8
is connected to a mobile switching center
1
by way of transmission lines including a control signal line and a communication line. In this mobile communication system, there are plural mobile terminals
9
a
to
9
m
freely moving through the above-explained cell groups.
Now, a mobile terminal
9
a
is located in the cell
20
, and is in a standby state while being tuned to a forward control channel transmitted from the base station
2
, and waiting for a call origination by a user of this mobile terminal or a call termination from the base station. At this time, when this mobile terminal
9
a
executes either a call originating operation or a call receiving operation, an idle communication channel of the base station
2
is allocated for the call by a control operation of the mobile switching center
1
via the transmission line
10
, so that a communication service may be provided.
When the communication service is commenced, the base station
2
edits an electric field level measurement request signal obtained from a forward control channel list of the adjoining base stations provided in this base station
2
. Then, this base station
2
transmits the electric field level measurement request signal to the mobile terminal
9
a
. In other words, the radio signal frequencies of the control channels which are allocated to the respective cells
30
and
40
of the base stations
3
and
4
located adjacent to the base station
2
are contained in the electric field level measurement request signal. The resulting electric field level measurement request signal is notified to the mobile terminals
9
a.
While continuing the communication service, the mobile terminal
9
a
periodically measures electric field levels of the forward control channels of the adjoining base stations
3
and
4
by tuning respective radio signal frequencies notified by the received electric field level measurement request signal. Then, the mobile terminals
9
a
produces an electric level measurement result signal by editing the measured electric field levels of the forward control channels of the adjoining base stations
3
and
4
and an electric field level of the forward communication channel under use for the current communication with the base station
2
. This electric field level measurement result signal is periodically transmitted to the base station
2
from the mobile terminal
9
a.
The base station
2
compares the electric field level of the forward communication channel, which is used in the current communication, included in the electric field level measurement result signal transmitted from the mobile terminal
9
a
with a predetermined threshold value. This threshold value is defined as a minimum electric field level value at which a mobile terminal can continue a communication with a base station in the cell.
When the electric field level measurement value of the forward communication channel used in the current communication becomes smaller than, or equal to the threshold value, namely, is deteriorated, the base station
2
judges that the mobile terminal
9
a
is located at a boundary area of the cell
20
. Then, this base station
2
edits both this electric field level measurement value and the electric field level measurement values of the forward control channels of the adjoining cells
30
and
40
to thereby produce an electric field level deterioration report signal. The base station
2
transmits this electric field level deterioration report signal to the mobile switching center
1
.
In response to the received electric field level deterioration report signal, the mobile switching center
1
refers to a hand-off list provided in the mobile switching center
1
so as to select such an adjoining cell that the electric field level measurement value of the forward control channel being the most optimum value, and executes the hand-off control in such a manner that the current communication by the mobile terminal
9
a
can be switched and continued by a base station in a selected cell.
In such a conventional mobile communication system, when the mobile terminal
9
a
, which had been receiving the communication service in the cell
20
, has moved into the cell
30
while measuring the electric field levels of the forward control channels of the adjoining base stations
3
and
4
in accordance with the electric field level measurement request signal received from the base station
2
, the mobile switching center
1
executes the hand-off control by allocating the idle communication channel available in the hand-off destination base station
3
for continuing the communication service by the mobile terminal
9
a.
On the other hand, while holding the forward control channel information of the adjoining base stations
3
and
4
, which was instructed by the original hand-off base station
2
, the mobile terminal
9
a
continues the periodical electric field level measurement even after the mobile terminal
9
a
has moved in the cell
30
of the hand-off destination base station
3
, and then reports the electric field level measurement result signal to the hand-off destination base station
3
. However, this electric field level measurement result signal is a useless signal with respect to the hand-off destination base station
3
, which will transmit the new electric field level measurement request signal to be used in the cell
30
.
At this time, it could happen that the hand-off destination base station
3
receives this useless electric field level measurement result signal before transmitting the new electric field level measurement request signal to the mobile terminal
9
a
so as to measure the electric field levels of the forward control channels of the adjacent base stations
2
,
4
,
5
and
6
. If the electric field level value of the forward communication channel having been used for the communication in the cell
20
is contained in this useless electric field level measurement result signal, and the value indicates deterioration of the signal level of the forward communication channel, the hand-off destination base station
3
produces the electric field level deterioration report to the mobile switching center
1
.
However, this electric field level deterioration report is produced in accordance with the wrong report from the mobile terminal
9
a
, in which the electric field level measurement request has not yet been renewed.
The mobile switching center
1
executes the hand-off control based on the electric field level deterioration report caused by the wrong report
Aihara Makoto
Iizuka Hiromi
Shiotsuki Hirofumi
Ferguson Keith
NEC Corporation
Trost William
Young & Thompson
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