Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-06-11
2002-05-21
Hsu, Alpus H. (Department: 2665)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S342000, C455S069000, C455S522000
Reexamination Certificate
active
06393005
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and a device for controlling the transmitting power of a base station in a mobile communication system based on Code Division Multiple Access (hereinafter abbreviated CDMA).
2. Description of the Related Art
In a CDMA system, transmission is performed by carrying out spread modulation that uses a spread code of high-speed transmission rate after normal information modulation. On the receiving side, normal demodulation is performed after restoring the original information bandwidth by carrying out de-spread modulation that uses the same spread code as the transmitting side. Assignment of an orthogonal spread code sequence to each user allows a plurality of users to communicate simultaneously on the same frequency bandwidth.
In a cellular mobile communication system using CDMA, a plurality of mobile stations share the same frequency band. In communication from a base station to a mobile station, the desired wave signal component and interference wave signal component contained within signals transmitted from the same base station all reach the mobile stations by way of the same propagation path. When a call to mobile station A and a call to mobile station B are made simultaneously from the same base station, for example, mobile station A receives the call to itself as desired wave signal S
A
and receives the transmission signal to mobile station B as interference wave signal S
B
. However, these received signal components S
A
and S
B
have the same fluctuation characteristics because they have been received by way of the same transmission path from the base station to mobile station A, and as a result, Signal-to-Interference power Ratio (ratio of the received power of the desired wave to the received power of the interference wave hereinbelow abbreviated as “SIR”) at the mobile station is constant fixed regardless of the position of the mobile station.
However, when the mobile station receives a desired wave signal from a particular base station X and receives an interference wave signal from another base station Y, the signal component transmitted from base station X and the signal component transmitted from base station Y reach the mobile station by way of different propagation paths. Therefore, the fluctuation characteristics of these signal components also differ, and consequently, a mobile station located near a cell boundary is greatly influenced by the interference wave signal from another base station.
In such cases, degradation of speech quality can be avoided by raising the transmitting power of a base station above the reference power for a mobile station located near a cell boundary. Similarly, degradation in speech quality can also be avoided by increasing the base station transmitting power above the reference power for a mobile station located at a point reached by a plurality of strong multipath signals. On the other hand, the transmitting power of the base station must be reduced below the reference transmitting power for other mobile stations that have good speech quality because the interference wave power received by other mobile stations that are communicating with the base station must be reduced. These factors call for control of the transmitting power of the base station in order to obtain uniform speech quality within a service area.
One example of a method for controlling transmitting power according to the prior art is disclosed in the paper “On the System Design Aspects of Code Division Multiple Access (CDMA) Applied to Digital Cellular and Personal Communication Networks” by A. Salmasi and K. S. Gilhousen and published in IEEE VCT 1991 (pp. 57-62).
FIG. 1
shows a schematic representation of a device for controlling the transmitting power of a base station disclosed in the above-described paper. This device comprises a transmitter, a receiver, and antenna branching filter
108
. The transmitter consists of a number N of communication channel transmitters
101
for communication channels
1
-N, pilot channel transmitter
102
, transmitting power decision unit
106
, and amplifier
107
.
Transmission signals to mobile station
113
(forward transmission signals) are inputted to communication channel transmitters
101
when the signals are speech signals, and to pilot channel transmitter
102
when the signals are pilot signals. After carrying out information modulation and frequency conversion to the radio frequency bandwidth, each individual channel transmitter
101
and
102
spread-modulates the frequency-converted signals using the spread code corresponding to the object mobile station, and outputs the result. The signal generated by adding the output signals of all channels is then outputted to amplifier
107
. The signal amplified by amplifier
107
is then transmitted to mobile station
113
by antenna branching filter
108
. Communication channel transmitters
101
set the communication channel transmitting power based on information notified from transmitting power decision unit
106
(to be described hereinbelow).
The receiver consists of amplifier
109
, a number N of communication channel receivers
110
for communication channels
1
-N, pilot channel receiver
111
, and quality judging unit
112
.
Amplifier
109
amplifies the spread-modulated radio signal received from mobile station
113
by way of antenna and antenna branching filter
108
. Communication channel receiver
110
and pilot channel receiver
111
first subject the radio signal amplified by amplifier
109
to de-spread modulation and extract a radio frequency bandwidth signal, and then frequency-convert the radio frequency signal to a baseband signal, generate an analog signal by demodulation, and output the result. In addition, communication channel receivers
110
each decode quality information attached to radio signals received from mobile station
113
(information indicating the quality of signals transmitted to mobile station
113
from the base station, i.e., SIR as measured at mobile station
113
), and output to quality judging unit
112
. Quality judging unit
112
judges the quality of signals transmitted from the base station to mobile station
113
based on this quality information and notifies transmitting power decision unit
106
. Transmitting power decision unit
106
sets the communication channel transmitting power for the mobile station based on the quality notified from quality judging unit
112
and sets each transmitter
101
to this transmitting power.
In a device for controlling transmitting power of a base station according to this configuration, the transmitting power of a base station is controlled based on the SIR measured at a mobile station. When the SIR measured at the mobile station is lower than a reference value, a request signal to increase the transmitting power is transmitted to the base station. When the measured SIR is greater than the reference value, a request signal to decrease the transmitting power is transmitted to the base station. The base station receives these request signals and either increases or decreases the transmitting power by a prescribed control step power, a small value such as 0.5 dB being used as the control step power. Control is limited to a range of, for example, ±6 dB with respect to the reference power.
In a case in which the total transmitting power of the base station increases and approaches a predetermined maximum transmitting power in the device for controlling transmitting power of a base station of the prior art described hereinabove, the base station is unable to increase the power in accordance with the demand of a mobile station despite the transmission of request signals to increase transmitting power from a mobile station because the total transmitting power would then exceed the maximum transmitting power. In the event of insufficient transmitting power in such a case, there is the problem that the waveform of the transmitting signal of the base station is distorted, thereby preventing corr
Hsu Alpus H.
McGinn & Gibb PLLC
NEC Corporation
Stevens Roberta
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