Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-03-11
2001-08-21
Maung, Nay (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S450000, C455S509000, C370S331000, C370S332000, C370S337000
Reexamination Certificate
active
06278878
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mobile communications system such as the digital PHS (Personal Handyphone System), and to a portable terminal for use in such a system.
2. Description of the Prior Art
Conventionally, in the digital PHS system, a base station CS (cordless station) creates one data frame from four transmission slots T
1
to T
4
and four reception slots R
1
to R
4
, as shown in FIG.
6
. On the other hand, a terminal is allowed to use only one reception slot and one transmission slot out of those slots.
For example, a terminal PS
1
, when it receives a signal from a base station CS, uses a reception slot R
1
′ that corresponds to the transmission slot T
1
of the base station CS, and, when it transmits a signal to the base station CS, uses a transmission slot T
1
′ that corresponds to the reception slot R
1
of the base station CS. On the other hand, in another terminal PS
2
, its reception and transmission slots R
2
′ and T
2
′ correspond to the transmission and reception slots T
2
and R
2
, respectively, of the base station CS.
FIG. 7
shows a sequence of steps followed when the communication with a terminal PS
1
is transferred from one base station CS
1
to another base station CS
2
. In step #
1
, the terminal PS
1
is at location (a) shown in FIG.
5
and is “communicating”, i.e. engaged in a communication session, with the base station CS
1
. However, as the terminal PS
1
moves to location (c), the signal strength of the received signal drops significantly, and the communication condition degrades accordingly (step #
2
).
This causes the terminal PS
1
to request the next base station CS
2
to establish a link channel that can be used for a communication session and other purposes (step #
3
). In response, the base station CS
2
allocates a link channel to the terminal PS
1
(step #
4
). Thereafter, the terminal PS
1
establishes synchronism with the base station CS
2
in steps #
6
and #
7
, establishes communication therewith through the allocated channel (steps #
8
to #
20
), and eventually starts a communication session therewith (step #
21
). It takes as long as one second between steps #
3
and #
4
; by contrast, it takes only five milliseconds between two consecutive steps from #
6
to #
20
(e.g. between steps #
5
and #
6
).
In the above sequence of steps, exactly because steps #
3
and #
4
take a comparatively long time, these steps substantially cause termination of the communication session there. This means that it is necessary to start a new communication session again in step #
21
. Inconveniently, this causes the user of the terminal to be charged for a new communication session every time the communication with his or her terminal is transferred from one base station to another. In addition, it is also inconvenient that, in step #
21
, it takes an unduly long time to restart a communication session.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a novel mobile communications system, and a portable terminal for use in it, by use of which communication can be continued without substantially terminating a communication session even when the communication with a particular terminal is transferred from one base station to another as the terminal moves around.
To achieve the above object, according to one aspect of the present invention, in a mobile communications system including a base station for allocating a plurality of pairs of transmission and reception slots to one data frame and a portable terminal for communicating with the base station, at least two pairs of the transmission and reception slots are allocated to one portable terminal so that one pair is used to continue a communication session and the other pair is used to control channels in order to secure a channel for the communication session.
In this system, when the communication condition degrades significantly during a communication session and it is necessary to switch to a channel of the next base station, the switching can be done quickly without terminating the communication session (actually, the communication session is discontinued, but only for a negligibly short time). This is because the next traffic channel is reserved (i.e. established) in advance before the switching takes place. In this way, it is possible to continue a mobile communication session smoothly.
According to another aspect of the present invention, a portable terminal for use in the above mobile communications system is provided with communication condition detecting means for detecting whether or not communication condition is poorer than a first level and whether it is poorer than a second level that is lower than the first level; means for requesting another base station to newly establish a traffic channel when the communication condition drops below the first level; and means for switching from a currently used traffic channel to the newly established traffic channel when the communication condition drops below the second level.
REFERENCES:
patent: 5157661 (1992-10-01), Kanai et al.
patent: 5276906 (1994-01-01), Felix
patent: 5327577 (1994-07-01), Uddenfeldt
patent: 5329635 (1994-07-01), Wadin et al.
patent: 5416778 (1995-05-01), Chan et al.
patent: 5483668 (1996-01-01), Malkamaki et al.
patent: 5627880 (1997-05-01), Rozanski et al.
patent: 5663954 (1997-09-01), Hakkanen et al.
patent: 5898925 (1999-04-01), Honkasalo et al.
Arent Fox Kintner Plotkiun & Kahn, PLLC
Maung Nay
Rohm & Co., Ltd.
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