Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-12-27
2004-07-06
Gary, Erika (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S442000, C455S067110, C455S226200, C370S338000, C370S349000, C370S394000
Reexamination Certificate
active
06760588
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mobile communication system supplying communication services from a base station to a mobile station such as a cellular phone through a radio channel, and more particularly relates to a mobile communication system in which a mobile station and a plurality of base stations exchange information with each other.
2. Description of the Related Art
A conventional mobile communication system is shown in
FIG. 1. A
mobile communication system
100
shown in
FIG. 1
includes a mobile station
101
, base stations
102
through
108
, radio network controllers
109
and
110
, and a switch station
111
. The switch station
111
, the radio network controllers
109
and
110
, and the base stations
102
through
108
are connected to each other hierarchically. The base stations
102
through
108
form radio zones indicated by broken lines in FIG.
1
. The mobile station
101
capable of moving freely between the radio zones is connected to one of the base stations
102
through
108
in the radio zones, for example, the base station
105
, by a radio channel. The mobile station
101
and the base station
105
connected to each other by the radio channel execute bi-directional communication through the radio channel. Each base station shown in
FIG. 1
communicates with one or more mobile stations through radio channels. Each of the base stations
102
,
104
and
107
is connected to the radio network controller
109
, and communicates with the radio network controller
109
. Similarly, each of the base stations
103
,
105
,
106
and
108
is connected to the radio network controller
110
, and communicates with the radio network controller
110
.
Each of the radio network controllers
109
and
110
is connected to a plurality of base stations, and controls switching a base station communicating with the mobile station
101
when the mobile station
101
moves between the radio zones. The mobile station
101
switches the radio channel when one of the radio network controllers
109
and
110
switches the base station with another base station to be connected with the mobile station
101
, in other words, when one of the radio network controllers
109
and
110
hands over a communication with the mobile station
101
from the base station to another base station. The switch station
111
is connected to the radio network controllers
109
and
110
, and to a plurality of other switch stations or network systems not shown in the figures. The switch station
111
controls a connection between mobile stations located under the switch station
111
, and a connection between a mobile station located under the switch station
111
and a terminal station located under another switch station or another network system.
In a conventional mobile communication system, a radio-channel connection between a base station and a mobile station is executed by following a multiple-accessing method such as an FDMA (Frequency Division Multiple Access) method, a TDMA (Time Division Multiple Access) method, and a CDMA (Code Division Multiple Access) method. Accordingly, the conventional mobile communication system can supply both circuit-switched and packet-switched communication services to mobile stations by having the above-described system structure.
In the above-described mobile communication system
100
, the mobile station
101
selects a base station by which a received-signal strength of the radio channel between the mobile station
101
and the base station becomes the highest among the base stations, for instance, the base station
105
shown in FIG.
1
. The base station
105
selected by the mobile station
101
is referred to as a selected base station. Since directivity of an antenna of the mobile station
101
is low, a signal transmitted from the mobile station
101
reaches a base station, for example, the base station
103
located near the selected base station
105
, while the mobile station
101
is communicating with the selected base station
105
. The signal is also received by the other base stations in addition to the selected base station
105
especially when the mobile station
101
is positioned at a border of the radio zones.
In a mobile communication system using the CDMA method as a transmission method of a radio channel, a plurality of base stations can receive a signal transmitted from a single mobile station simultaneously by using a plurality of radio channels or spreading codes. For instance, as shown in
FIG. 2
, a mobile station
113
is communicating simultaneously with the base stations
106
and
108
by using two spreading codes. Each of the base stations
106
and
108
receives a signal transmitted from the mobile station
101
, and transmits the signal to the radio network controller
110
. The radio network controller
110
combines signals received from the base stations
106
and
108
, and transmits a combined signal to the switch station
111
. The above-described communication method of receiving signals from a plurality of base stations at a radio network controller is generally referred to as soft handover, or site diversity. Two typical methods among various methods of combining signals from the plurality of base stations will be described below.
In the first method, each base station transmits demodulated bit information to a radio network controller. Subsequently, the radio network controller regenerates a signal starting from a block that does not contain any errors such by an error correction word and an error correction word unit. In the second method, each base station transmits a received soft decision signal with received-signal strength Intensity (RSSI) or a “signal to noise and interference” ratio S/(N+I) to the radio network controller. The radio network controller regenerates a signal by combining the above-mentioned information received from each bases station with a maximum ratio. By following the above-described methods, an error rate of the signal transmitted from a mobile station is reduced by combining signals received from a plurality of base stations at the radio network controller.
Since the radio network controller combines signals received from the plurality of base stations in the conventional mobile communication system, the radio network controllers
109
and
110
cannot communicate simultaneously with a mobile station
112
respectively through the base stations
102
and
105
by the multiple base station concurrent reception method, as shown in FIG.
2
. Thus, the conventional mobile communication system cannot continuously supply communication services based on the multiple base station concurrent reception method to a moving mobile station.
Additionally, in the conventional mobile communication system, a processing load at each radio network controller increases with increase in the number of mobile stations by using the multiple base station concurrent reception method in communication except handover. Furthermore, when transmitting signals from a plurality of base stations to a mobile station, in other words, when executing a multiple base station concurrent transmission or a multiple base station in-order transmission, the conventional mobile communication system contains a problem that the system cannot supply constant communication services to the mobile station depending on a position of the mobile station and a problem that a processing load at a communication node uniting the plurality of base stations increases, since the system must control the plurality of base stations all together.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to provide a mobile communication system in which a mobile station and a plurality of base stations communicate with each other. A more specific object of the present invention is to provide a mobile communication system that enables stable communication between communication nodes such as a mobile station and a plurality of base stations, and mini
Okajima Ichiro
Suzuki Yoshifumi
Umeda Narumi
Yamao Yasushi
Davis Temica M.
Gary Erika
NTT DoCoMo Inc.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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