Communication terminal, and over-interference prevention method

Details Communication terminal, and over-interference prevention method Communication terminal, and over-interference prevention method

2001-01-31

2004-04-06

Maung, Nay (Department: 2684)

Telecommunications

Transmitter and receiver at separate stations

Plural transmitters or receivers

C455S453000

Reexamination Certificate

active

06718181

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a communication terminal such as a mobile station in the CDMA (Code Division Multiple Access) radio communication system, which performs multiple access, using the spread spectrum for digital radio communication; and a method for transmission power control for the same.
BACKGROUND ART
The CDMA method is one of techniques for multiple access when a plurality of stations simultaneously communicate each other in the same frequency band for mobile communication like car and cellular telephones. Though the FDMA (Frequency Division Multiple Access) method, the TDMA (Time Division Multiple Access) method and so on have been well-known as other techniques, the CDMA method may realize more efficient use of frequencies, and accommodate more users, comparing with those of the above techniques.
In the CDMA method, a signal of a certain user is an interference one for other users, and, similarly, signals of other users become interference signals for the above user, as a plurality of users share the same frequency band. Therefore, the signal-to-interference ratio (SIR) is required to be constant, independent of the location of a mobile station to obtain uniform communication quality in a service area. Each mobile station is required to control the transmission power, especially, in the case of an uplink from a mobile station to a base station, so that the power of signals sent from each mobile station, when the signals are received at a base station, may be constant in order to reduce interference with signals of an adjacent stations using the same frequency, and so on.
In the case of bidirectional communication using the CDMA method, the FDD (Frequency Division Duplex) method with different transmission carrier frequencies, respectively, for an uplink and a downlink has been generally used. For the CDMA/FDD, transmission power control (TPC) has been generally performed in a closed-loop manner, where received power is measured at a base station, and, based on the received power, instructions to increase or reduce the transmission power are given to a mobile station.
Moreover, when there is caused a rapid increase in the received power, which can not be followed in the closed-loop manner, at the mobile station, TPC has been performed in an open-loop manner, as disclosed in Japanese published unexamined application Hei 8-32514, where the mobile station performs self control of the transmission power so that the sum of the transmission and the received powers may be constant in order not to increase interference with signals of other mobile stations. In the above case, when the transmission power is reduced, there is a possibility to cut out the own link, though there is no increase in the interference with signals of other mobile stations.
The case where the link is cut out as described above will be described, referring to FIG.
1
. In
FIG. 1
, it is assumed that, though the mobile station MS
1
is in a service area of a base station BS
2
, and in a shorter distance from the station BS
2
, a mobile station MS
1
performs communication (path c) with a base station BS
1
, as the station BS
2
can not be seen from the station MS
1
because of a building
1
between them. In the above configuration, the station MS
1
transmits large transmission power for communication with the station BS
1
.
Moreover, the base station BS
2
communicates with mobile stations MS
2
, MS
3
in the service area (cell) through paths b, a, respectively.
When the mobile station MS
1
moves in the direction of the arrow, the station BS
2
comes into the sight of the station MS
1
. At this point, the station MS
1
performs self reduction in the transmission power so as to prevent interference with signals of other mobile stations MS
2
, MS
3
at the station BS
2
. When the station MS
1
reduces the transmission power, the link for the station MS
1
is cut out, as there is not enough power necessary for communication between the stations MS
1
, BS
1
.
When the link is cut out as illustrated above, users may not place full confidence in the communication services, as they themselves are required to perform reconnection procedures, and much complex operations for the above procedures.
DISCLOSURE OF INVENTION
The object of the present invention is to offer a communication terminal, which performs radio communication without cutting-out of a link and with no increased interference with other stations even in a service area under unfavorable visibility, and a method for transmission power control for the above terminal.
The subject matter of the present invention is to reduce interference effects on other terminals: only control data necessary for a handover operation and signals required for link maintenance are transmitted at the same transmission rate as that one before a rapid increase in a received power at a terminal side, and transmission of information other than the above data and signals is performed at a rapidly reduced rate, when there is the above rapid increase; and, reducing the above transmission rate causes reduction in the power required for transmission, and, accordingly, the above effects may be reduced. Thereafter, procedures for a handover operation are performed with the control data, if required. When there is no need to perform the handover operation, the transmission signal power is reduced without reduction in the transmission rate.


REFERENCES:
patent: 5590177 (1996-12-01), Vilmur et al.
patent: 0682419 (1995-11-01), None
patent: 0697799 (1996-02-01), None
patent: 0918402 (1999-05-01), None
patent: 02274131 (1990-11-01), None
patent: 8-32514 (1996-02-01), None
patent: 8-65265 (1996-03-01), None
patent: 10056420 (1998-02-01), None
patent: 1998 077725 (1998-11-01), None
patent: 2001 0019655 (2001-03-01), None
Korean Office Action dated Feb. 21, 2003 with English translation.
Korean Office Action dated Apr. 18, 2003 with English translation.

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