Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1999-04-13
2003-03-11
Trost, William (Department: 2683)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C455S436000, C455S437000, C455S438000, C455S439000, C455S443000, C370S331000
Reexamination Certificate
active
06532221
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a handoff method of mobile communications systems such as CDMA Code Division Multiple Access communications system, mobile communication system, PCS Personal Communications Service, and satellite communications system, and more particularly to, a handoff method of mobile communications system in which whether a handoff is to be performed or not is decided after detecting pilot signal strengths of a mobile station and a base station which has been already connected, so that it is possible to control a handoff generation number, preventing unnecessary load.
2. Description of the Conventional Art
In general, as shown in
FIG. 1
, a mobile communication system for communicating while movement is composed of mobile station
10
in which communication service of a mobile communication subscriber is requested and communication service of a mobile communication system is provided, base station
20
for exchanging signals with the mobile station
10
at a wireless area, control station
30
for control the base station
20
to perform signal process between the base station
20
and a switching station
40
, and the switching station
40
which is connected to the control station
30
and performs switching connection between mobile communication nets, thereby connecting a mobile communication net with another communication net.
The operation of the general mobile communication system, which is constructed as above, is as follows.
When a mobile communication subscriber having a mobile station is in a service area of the base station
20
and requests a mobile communication service, the switching station
40
detects a position of the mobile station
10
under the control of the control base
30
and performs mobile communication service according to the request of the mobile station
10
.
FIG. 2
shows boundary areas of base stations of a general mobile communications system.
An area in which communication service from one base station is possible is called a cell. The cell is defined by pilot signal strength, which is output through a pilot channel from the base station. Therefore, in case that a mobile station is positioned at a cell boundary, it is possible to realize a base station of which service area a mobile station belongs to by detecting an input pilot signal strength of the mobile station which is transmitted to the base station.
When the mobile station
10
is located in a service area of a first base station
21
and removes in a service area of a second base station
22
, the communicating mobile
10
has to perform handoff to keep on the communication. Wherein the handoff means an operation to automatically convert communication line to keep the mobile station's communication when the mobile station removes from one cell to another cell.
FIG. 3
is a flow chart for explaining a handoff method of a conventional mobile communications system.
As shown in
FIG. 3
, the handoff method includes the steps of comparing a pilot signal strength, which is input from the mobile station to a neighboring base station, with a pilot detection threshold value (steps ST
1
-ST
2
), and transmitting handoff request message if the pilot signal strength of the neighboring base station is over than the pilot detection threshold value (step ST
3
-ST
4
).
Now the handoff method of the conventional mobile communications system will be described in more detail with reference to FIG.
1
and FIG.
2
.
First, when the mobile station
10
is in the service area of the first base station
21
and served by the first base station
21
, the pilot signal strength of the first base station
21
is detected and a signal detection message is transmitted from the mobile station
10
to the first base station
21
.
The mobile station
10
approaches to a handoff area and, in step ST
1
, when the pilot signal strength of the second base station
22
among various pilot signal strengths is larger than the pilot detection threshold value, a signal detection message is transmitted to the first base station
21
for handoff to the second base station
22
. The signal detection message includes information as to pilot off-set and the pilot signal strength for distinguishing the base stations
21
and
22
.
In step ST
2
, the received signal detection message is transmitted to a base station controller by the first base station
21
and the pilot signal strength of the second base station
22
is compared with the pilot detection threshold value by the base station controller. In steps ST
3
and ST
4
, a handoff to the second base station
22
is requested when the pilot signal strength of the second base station
22
is larger than the pilot detection threshold value, as a result of the comparison.
According to the handoff to be performed as above, it becomes possible to continuously communicate even when the mobile station
10
removes from the service area of the first base station
21
to that of the second base station
22
.
However, the conventional communications system has disadvantages that the pilot signal strength of a base station which is serving the mobile station
10
is not considered so that unnecessary handoff may be caused, increasing handoff frequency, even in case that the pilot signal strength of the base station currently serving the mobile station
10
is larger than the mobile station requires for communication.
Further, as the handoff generation frequency increases, unnecessary overload is applied to the mobile communications system.
SUMMARY OF THE INVENTION
Therefore, the present invention is derived to resolve the disadvantages of the conventional techniques and it is an object of the present invention to provide a handoff method of a mobile communications system wherein, in case that a cell is defined by a sector, it is decided whether a handoff is to be performed or not after detecting pilot signal strengths of a mobile station and a base station which is already connected to the mobile station and then detecting pilot signal strengths of neighboring base stations, so that handoff generation frequency is efficiently controlled, preventing unnecessary overload of the system.
It is another object of the present invention to provide a handoff method of a mobile communications system wherein, in case that a cell is defined by a plurality of sectors, it is decided whether a handoff is to be performed or not after detecting a pilot signal strength of a sector which is in service and then detecting pilot signal strengths of neighboring sectors, so that handoff generation frequency is efficiently controlled, preventing unnecessary overload of the system.
In order to achieve the above objects of the present invention, according to an aspect of the present invention, a handoff method of a mobile communications system, in which a cell is defined by a sector, characterized in that a handoff request is made to a base station having a predetermined level of pilot signal strength by using a pilot signal strength of a base station which is in service, a predetermined threshold value and pilot signal strength of neighboring base stations.
In order to achieve the above objects of the present invention, according to another aspect of the present invention, a handoff method of a mobile communications system, in which a cell is defined by a sector, includes a first step of receiving a signal detection message from a mobile station and comparing a pilot signal strength of a base station which is in service with a threshold value for pilot checking of neighboring base stations, a second step of determining that the neighboring base stations are required to be checked their pilot signal strengths if the pilot signal strength of the base station which is in service is smaller than the threshold value for checking pilot of neighboring base stations, and comparing the pilot signal strength of the base station which is in service with pilot signal strengths of the neighboring base stations, and a third step of distinguishi
Chung Chae-Hun
Kim Hong
Cave LLP Bryan
Ferguson Keith
Hyundai Electronics Co. Ltd.
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