Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-10-25
2004-08-17
Gary, Erika (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S432100, C455S439000, C455S442000, C455S443000, C455S403000, C455S406000
Reexamination Certificate
active
06778830
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a mobile telecommunication system and a channel handoff system between the mobile telecommunication systems. The present invention relates more specifically to a mobile telecommunication system and a channel handoff system between the mobile telecommunication systems intended to check deterioration of a service quality at the time of a handoff between mobile telecommunication systems provided by different vendors or operators.
In a conventional CDMA (Code Divisional Multiple Access) mobile telecommunication system under TIA (TELECOMMUNICATIONS INDUSTRY ASSOCIATION)/ET (Interim Standard)-95, a handoff to a CDMA or FDMA (Frequency Divisional Multiple Access) telecommunication system. has been performed as shown in FIG. 
1
.
FIG. 1
 shows a schematic diagram illustrative of a conventional mobile telecommunication system.
CDMA mobile telecommunication system 
100
 comprises mobile telephone terminal 
1
 of subscriber's own, radio base station (hereinafter referred to as BS) 
10
 and radio base station control unit (hereinafter, referred to as BSC) 
12
. BS 
10
 establishes a radio communication with mobile telephone terminal 
1
 within its own service area. BSC 
12
 controls the communication processing of radio BS 
10
 and mobile telephone terminal 
1
. It is assumed that mobile telephone terminal 
1
 has already completed an establishment of a communication with the concerned BS 
10
, to connect the terminal 
1
 with a subscriber of a PSTN (public switched telephone network), or another subscriber within the service area of the concerned base station 
1
. In addition to the above-described communication control, BSC 
12
 carries out a call channel handoff control.
It is further assumed that mobile telecommunication system 
200
 is a CDMA or an FDMA mobile telecommunication system which provides a telecommunication service under management of a vendor or an operator differing from that of system 
100
. Mobile telecommunication system 
200
 as well comprises mobile telephone terminal 
1
, BS 
20
 and BSC 
22
.
While mobile telecommunication systems 
100
 and 
200
 each have a plurality of radio base stations and radio base station control units connected to provide telecommunication services in cooperation, only one radio base station and only one radio base station control unit are represented for each of the mobile telecommunication systems in 
FIG. 1
 for simplicity of the explanation. It is also assumed that BS 
10
 in mobile telecommunication system 
100
 and BS 
20
 in mobile telecommunication system 
200
 have overlapping service areas 
34
, and that each of the systems 
100
 and 
200
 has a capacity to provide a sufficiently high-quality service in the individual overlapping service area.
However, a problem comes up in the overlapping service area when neighboring mobile telecommunication systems that manage telecommunication services are provided by different vendors/operators.
It is ordinary that a radio communication interface for a frequency, for example, used in the communication between a mobile telephone terminal and a radio base station differs depending on a vendor/operator of the telecommunication system.
For this reason, mobile telephone terminal 
1
 in overlapping service area 
34
 cannot afford to establish calls at the same time between the terminal 
1
 itself and both of radio base stations 
10
 and 
20
 provided by different vendors/operators.
As a result, when mobile terminal 
1
, which has had an established communication with BS 
10
, is required to establish a new communication with BS 
20
 of a different vendor or a different operator, it is necessary both to perform a handoff in the overlapping service area and to synchronize the communication in a wireless region between mobile terminal 
1
 and BS 
20
.
Now, referring to 
FIG. 1
, suppose there is a case where mobile terminal 
1
 moves in the direction from {circle around (
1
)} toward {circle around (
6
)}. While moving within the service area 
14
 of mobile telecommunication system 
100
, mobile terminal 
1
 maintains the established communication with base station 
10
 and BSC 
12
 through radio transmission path 
10
r. 
As mobile terminal 
1
 advances further toward {circle around (
6
)} through point {circle around (
2
)} to {circle around (
3
)}, it starts to enter overlapping service area 
34
. Mobile radio terminal 
1
, upon reaching a hard handoff boundary point{circle around (
4
)}, notices BSC 
12
 by means of BS 
10
 that the electric-field intensity of the radio signal transmitted from BC 
10
 of mobile telecommunication system 
100
 has reduced to less than a channel-drop threshold predetermined to judge whether or not the concerned call is to be dropped from mobile telecommunication system 
100
, as well as notices the field intensities of the radio signals transmitted from the peripheral base stations (cf. C
1
 and C
2
 in FIG. 
2
).
FIG. 2
 is a time sequence diagram illustrative of procedures to perform a handoff of a call between the two radio telecommunication systems.
BSC 
12
, when receiving a notice C
2
, judges whether mobile telecommunication system 
200
 can provide a better quality of service in its coverage service area 
24
 to mobile telephone terminal (MT) 
1
 of interest than mobile telecommunication system 
100
 can in its own coverage service area 
14
, based on the information about the field intensities included in the received notice C
2
.
In case that BSC 
12
 judges the system 
200
 to be preferred to offer a better quality of service, then BSC 
12
 of mobile telecommunication system 
100
 sends, to BSC 
22
 of mobile telecommunication system 
200
, a request for reserving a call channel of BS 
20
 in order to reserve a new call channel of mobile telecommunication system 
200
 to be used after the hard handoff (cf. 
FIG. 2
, C
3
 and C
4
). BSC 
12
 also sends, to mobile terminal 
1
 through BS 
10
, a hard-handoff signal to handoff the call to mobile telecommunication system 
200
 (cf. 
FIG. 2
, C
5
 and C
6
).
Mobile terminal 
1
 performs a hard handoff upon receiving the hard-handoff signal and transmits a hard-handoff completion signal to BSC 
22
 through BS 
20
 (cf. 
FIG. 2
, C
7
 and C
8
).
BSC 
22
, when receiving the-handoff completion signal, sends a request for releasing the concerned call channel of BS 
10
 to BSC 
12
 of mobile telecommunication system 
100
 so that the call channel employed before the handoff will be freed.
Mobile telephone terminal 
1
 thereafter is normally in an established communication with BS 
20
 and BSC 
22
 through radio transmission path 
20
r 
in coverage service area 
24
 of mobile telecommunication system 
200
.
In the case mobile telephone terminal 
1
 moves in the direction from {circle around (
6
)} toward {circle around (
1
)}, the terminal 
1
 maintains an established communication with BS 
20
 and BSC 
22
 through radio transmission path 
20
r 
while the terminal 
1
 stays in coverage service area 
24
 of mobile telecommunication system 
200
.
As mobile terminal 
1
 advances further toward {circle around (
1
)}, it comes to enter overlapping service area 
34
. Mobile radio terminal 
1
, upon reaching near a hard handoff boundary point {circle around (
3
)}, notices BSC 
22
 by means of BS 
20
 that the electric-field intensity of the radio signal transmitted from BC 
20
 of mobile telecommunication system 
200
 has reduced to less than a call-channel drop threshold predetermined to judge whether or not the concerned call is to be dropped from mobile telecommunication system 
200
, as well as notices the field intensities of the radio signals transmitted from the peripheral base stations (cf. C
11
 and C
12
 in FIG. 
3
).
BSC 
22
, when receiving a notice C
12
, judges whether mobile telecommunication system 
100
 can provide a better quality of service in its coverage service area 
14
 to mobile terminal 
1
 of interest than mobile telecommunication system 
200
 can in its own coverage service area 
24
, based on the information about the
Oizumi Yasuhiro
Shiotsuki Hirofumi
Foley & Lardner LLP
Gary Erika
NEC Corporation
Nguyen David Q
LandOfFree
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