Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
2002-02-25
2004-05-18
Tran, Congvan (Department: 2683)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S017000, C455S522000, C370S318000, C375S317000
Reexamination Certificate
active
06738646
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a base station apparatus and communication method to be used in a cellular communication system.
BACKGROUND ART
In a cellular communication system, one base station performs radio communication with a plurality of communication terminals simultaneously. In such a cellular communication system, there is a demand for transmission efficiency to be increased.
As a method of increasing the transmission efficiency over the down link from a base station to a communication terminal, a method is proposed of performing scheduling that for allocating communication resources to communication terminals by means of time division, and of further setting a transmission rate for each communication terminal according to communication quality to transmit data. Hereinafter, this method is referred to as “adaptive modulation communication”.
Adaptive modulation communication will be described below using FIG.
1
. In
FIG. 1
, it is assumed that a base station
11
is currently performing communication with communication terminals
12
through
14
, which are within the cell area
15
covered by this base station
11
. Communication terminals
20
through
22
are within the range of the cell area
15
, but perform communication with a base station (not shown) other than this base station
11
.
First, the base station
11
transmits a pilot signal to communication terminals
12
through
14
. Each of communication terminals
12
through
14
estimates communication quality according to a CIR (Carrier to Interference Ratio) etc., using the pilot signal transmitted from the base station
11
, and calculates a transmission rate at which communication is possible. Also, based on the transmission rate at which communication is possible, each of communication terminals
12
through
14
selects a communication mode indicating a combination of packet length, error correction, and modulation method, and transmits a signal indicating the communication mode to the base station
11
.
Based on the communication mode selected by each of communication terminals
12
through
14
, the base station
11
performs scheduling, sets a transmission rate for each communication terminal, and notifies a signal indicating communication resource allocation to each of communication terminals
12
through
14
via a control channel.
The base station
11
transmits data only to the relevant communication terminal in its assigned time via a data channel. For example, when time t
1
is assigned to communication terminal
12
, in time t
1
the base station
11
transmits data only to communication terminal
12
, and does not transmit to communication terminals
13
and
14
. Also, transmission power when the base station
11
transmits data to communication terminals
12
through
14
is always constant.
Parallel to adaptive modulation communication, ordinary CDMA (Code Division Multiple Access) communication is performed in parallel between the base station
11
and communication terminals
12
through
14
in a different band from that for adaptive modulation communication.
However, in above-described conventional adaptive modulation communications, the following problem arises. Referring again to
FIG. 1
, the base station
11
transmits data to each of communication terminals
12
through
14
always using fixed power, regardless of the distances to communication terminals
12
through
14
. This power is high enough to ensure that reception quality is sufficiently good at all communication terminals in the cell area
15
.
Consequently, there is a possibility that, among communication terminals performing adaptive modulation communication with a base station other than base station
11
(hereinafter referred to as “another base station”), communication terminals within the cell area
15
covered by base station
11
(in
FIG. 1
, communication terminals
20
through
22
) may receive interference due to a signal transmitted to any one of communication terminals
12
through
14
from base station
11
. As a result, the communication quality of a communication terminal receiving interference in this way will deteriorate.
For example, if the time when base station
11
transmits data to communication terminal
12
via a data channel is coincident with the time when another base station transmits data to communication terminal
20
via a data channel, communication terminal
20
receives interference due to the signal transmitted from base station
11
to communication terminal
12
.
Also, if base station
11
transmits adaptively modulated signals to a plurality of communication terminals (for example, communication terminals
12
through
14
) at the same time, the communication quality of that plurality of communication terminals will deteriorate because delayed waves of the signals transmitted to that plurality of communication terminals will cause mutual interference.
As explained above, in above-described conventional adaptive modulation communications there is a problem in that an adaptively modulated signal transmitted from a base station causes interference with a communication terminal performing adaptive modulation communication with another base station, or with a communication terminal performing communication with the same base station at the same time.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide a base station apparatus and communication method that suppress interference to a communication terminal performing communication with another base station apparatus or a communication terminal apparatus performing communication with the same station at the same time.
This object is achieved by having this base station apparatus set the transmission rate of a communication terminal apparatus based on the reception quality of that communication terminal apparatus, and perform transmission to that communication terminal apparatus using a minimum transmission power value at which the characteristics of a received signal in that communication terminal apparatus meet a desired quality. Also, the above object is achieved by having this base station apparatus set a transmission power value according to whether or not reception quality in a communication terminal apparatus is excessive, and performing transmission to that communication terminal apparatus using that transmission power value.
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Aoyama Takahisa
Hiramatsu Katsuhiko
Kato Osamu
Miyoshi Ken'ichi
Sumasu Atsushi
Stevens Davis Miller & Mosher LLP
Tran Congvan
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