Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2001-09-19
2004-11-02
Ramakrishnaiah, Melur (Department: 2643)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S437000, C455S436000, C370S331000
Reexamination Certificate
active
06813495
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of hand-over processing in which a base station to be connected to a mobile terminal is switched when the mobile terminal moves from one service area covered by one base station to another service area covered by another base station.
The present application claims priority of Japanese Patent Application No.2000-285528 filed on Sep. 20, 2000, which is hereby incorporated by reference.
2. Description of the Related Art
In mobile communication systems such as a PHS (Personal Handy-phone System), hand-over processing is performed when a mobile terminal moves from a service area covered by one base station to another service area covered by another base station.
Conventional hand-over processing will be described by referring to FIG.
8
. In
FIG. 8
, for example, when a mobile terminal
1
is located in a service area
4
covered by a base station
2
, the mobile terminal
1
is carrying out communications with the base station
2
over a wireless communication line. If the mobile terminal
1
moves and enters a service area
5
covered by a base station
3
, the mobile terminal
1
performs hand-over processing in which the base station
2
being presently connected to the mobile terminal
1
is switched to the base station
3
to which the mobile terminal
1
is to be connected next.
In the conventional hand-over processing method, communications with the mobile terminal
1
being presently operated for a telephone call are terminated on a temporary basis, in order to perform the hand-over processing to hunt another base station with which the mobile terminal
1
is newly communicated. This hand-over processing takes about 2 seconds to complete its processing, which arises a problem that communication is interrupted for about 2 seconds in the middle of the call.
To solve such the problem, hand-over processing is proposed in which high-speed hand-over processing is made possible by providing one mobile terminal with two radio wave receiving sections. In the proposed high-speed hand-over processing, when a base station is switched, while the telephone voice communication is being continued by using one of the two radio wave receiving sections, a base station to which connection of the mobile terminal is handed over is hunted by using another radio wave receiving section. When the base station to which the mobile terminal is to be connected is found, switching to the base station is done, thus obtaining an effect of shortening the time of voice interruption.
FIG. 9
is a schematic block diagram showing configurations of such the mobile terminal
1
that has two radio wave receiving sections. The mobile terminal
1
includes one radio wave receiving section made up of a wireless section
10
, a synthesizer
11
, and a decoder
12
and he other radio wave receiving section made up of a wireless section
20
, a synthesizer
21
, and a decoder
22
. The mobile terminal
1
further includes a switching unit
40
used to switch data fed from the decoder
12
or decoder
22
and a switching control section
30
used to control the switching unit
40
.
The switching control section
30
detects a receiving level of a radio wave that the wireless sections
10
and
20
are receiving and performs hand-over processing, as shown in a flowchart of
FIG. 10
, based on the receiving level.
Next, the conventional hand-over processing will be described by referring to FIG.
10
.
The mobile terminal
1
is measuring, at fixed intervals, a receiving level of the radio wave transmitted from the base station being presently operated for the telephone voice communication with the mobile terminal
1
. If a receiving level of a radio wave transmitted from a base station is sufficiently high, the mobile terminal
1
carries out communications with the communication line connected to the base station and performs processing of the telephone voice communication (Step
901
). Here, the description will be made by assuming that the radio wave from the base station is received by the wireless section
10
and the synthesizer
11
.
When the radio wave receiving level becomes lower than a fixed level (hereinafter, the fixed level being referred to as a “hand-over processing level”), the hand-over processing is started (Step
902
). When the hand-over processing is started, base station hunting processing to hunt a base station to which connection of the mobile terminal
1
is to be handed over is performed the wireless section
20
and synthesizer
21
(Step
903
). In the base station hunting processing, by selecting only base stations which can provide the receiving level being level than a fixed level “D” (hereinafter referred to as a “hand-over selection level”), candidates for a base station to which the connection of the mobile terminal
1
is to be handed over are determined. Then, when the base station to which the connection of the mobile terminal
1
is handed over is determined, the hand-over processing is performed by controlling the wireless section
20
so as to receive radio waves from the determined base station and by instructing the switching control section
30
to control the switching unit
40
so as to select data fed from the decoder
22
(Step
904
).
In such the conventional hand-over processing method, though the time required for the hand-over processing can be shortened, it is necessary to set the hand-over processing level at a higher value, compared with cases of ordinary hand-over processing methods, in order to maintain excellent speech quality.
When the mobile terminal
1
moves to a region in which base stations exist sparsely, in some cases, the radio wave receiving level that the base station being presently operated for the telephone voice communication provides is below the hand-over processing level all the time. In such the case, in the conventional hand-over processing method, since the hand-over level and hand-over selection level are set as fixed values, the mobile terminal
1
always performs the base station hunting, thus causing an increase in power consumption and a shortened life of a battery.
Moreover, when a case of high speed movement of the mobile terminal
1
by a car or a like is compared with a case of low speed movement of the mobile terminal
1
on foot or a like, since a level of speech quality at which the user feels comfortable varies due to an effect of fading, the hand-over processing level which is set at the fixed values is different from the hand-over processing level that can provide an optimum speech quality.
Furthermore, when the hand-over selection level is set at the fixed value, since the hand-over selection level has to be set at a somewhat high level in order to ensure good communication quality, even if a base station is one to which the connection of the mobile terminal
1
is to be handed over, when the receiving level that the base station can provide does not reach the hand-over selection level, the base station cannot be selected as the base station to which the connection of the mobile terminal
1
is to be handed over.
As described above, the conventional hand-over processing method, since the hand-over selection level and hand-over processing level are set at the fixed value, cannot properly handle various conditions of radio waves in which the mobile terminal
1
is put, which causes degradation in speech quality and needless and wasteful hunting of the base station, and increases power consumption.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to provide a method for hand-over processing in which excellent speech quality is maintained and needless and wasteful hunting of a base station is not performed by coping properly with various conditions of radio waves in which a mobile terminal is put, which can reduce power consumption.
According to a first aspect of the present invention, there is provided a hand-over processing method for performing hand-over processing in a mobile terminal capable
Asaga Satoshi
Sasaki Teruo
Dickstein Shapiro Morin & Oshinsky LLP.
NEC Corporation
Ramakrishnaiah Melur
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