Communication base station system for transmitting data to a movable body

A communication base station system for transmitting data to a movable body includes a plurality of transmission sections, each of the transmission sections receiving a transmission data, modulating this received transmission data, and then converting the frequency of this modulated transmission data to a preset frequency and outputting a result. A control section monitors a status of use of the transmission sections, and if having confirmed at least two transmission sections that do not transmit any data, the control section outputs a specified signal instead of the transmission data to two transmission sections among the confirmed transmission sections. An amplification section collectively amplifies a plurality of output signals from the transmission section and a compensation circuit compensates for intermodulation distortion components generated in the amplification section based on an output of a transmission section that has received the specified signal and its respective transmission frequency. In the present invention configured as above, the two transmission sections that do not transmit any data receive a signal of specified pattern, these transmission sections that have received the signal of specified pattern generate output signals. Using these output signals, intermodulation distortion components caused by non-linearity of an amplifier are compensated for.

BACKGROUND OF THE INVENTION 
The present invention relates to a communication base station system, 
especially a communication base station system that receives transmission 
data, modulates the transmission data, converts the frequency of the 
modulated data to a preset transmission frequency, collectively amplifies 
the converted data and simultaneously compensates for intermodulation 
distortion components generated in this amplification step. 
Conventionally, as shown in FIG. 2, a movable communication base station 
system comprises: orthogonal modulation sections 21.sub.1 to 21.sub.n for 
receiving transmission data X.sub.1 to X.sub.n and outputting modulated 
signals; n units of transmission sections 23.sub.1 to 23.sub.n having 
frequency conversion sections 22.sub.1 to 22.sub.n for receiving the 
modulated signals and performing frequency conversion; a frequency 
instruction section 24 for instructing a frequency to each of frequency 
conversion sections 22.sub.1 to 22.sub.n to determine an output frequency 
of said n transmission sections; and a distortion-compensation-type common 
amplification section 25 for receiving outputs of n transmission sections 
23.sub.1 to 23.sub.n and collectively amplifying the outputs. 
The distortion-compensation-type common amplification section 25 that 
collectively amplifies outputs of n transmission sections 23.sub.1 to 
23.sub.n generates intermodulation distortion components caused by the 
nonlinearity of the amplifier. The level of intermodulation distortion 
components increases in proportion to the square of the number of channels 
and the transmission power output from the transmission sections 23.sub.1 
to 23.sub.n. 
Accordingly, the distortion compensation circuit 26 is provided for 
improving intermodulation distortion components. 
As an art for compensating distortion for the distortion compensation 
circuit 26, an art disclosed in Japanese Patent Laid-Open No.3-109825 
(1991) is known. 
In this art, for compensating distortion without interrupt of transmission, 
the control section 27 calculates a frequency generating distortion based 
on channels in use and the distortion compensation circuit 26 compensates 
for the distortion by using the calculated frequency and an output signal 
of a transmission section among the transmission sections 23.sub.1 to 
23.sub.n corresponding to this frequency. 
However, the above-mentioned art can not provide accurate distortion 
compensation, because it uses a modulated signal that is being transmitted 
and varies irregularly for distortion compensation without interrupt of 
transmission. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a movable body 
communication base station which to accurately compensates for 
intermodulation distortion components caused by non-linearity of an 
amplifier. 
Moreover, the object of the present invention is to provide a movable body 
communication base station which compensates for intermodulation 
distortion components caused by non-linearity of an amplifier without 
interrupt of transmission. 
The present invention is achieved by a communication base station system 
for transmitting data to a movable body including: 
a plurality of transmission sections, each one of the transmission sections 
receiving a transmission data, modulating the received transmission data, 
and then converting the frequency of the modulated transmission data to a 
preset frequency and outputting a result. 
A control sections monitors a status of use of the transmission sections, 
and if having confirmed at least two transmission sections that are not 
transmitting any data, the control section outputs a specified signal 
instead of the transmission data to two of the transmission sections among 
the confirmed transmission sections. 
An amplification section collectively amplifies a plurality of output 
signals from the transmission sections, and 
a compensation circuit compensates for intermodulation distortion 
components generated in the amplification section based on an output of a 
transmission section that has received the specified signal and the 
transmission frequency. 
In the present invention configured as above, the two units of transmission 
sections that are not transmitting any data receive a signal of specified 
pattern, the transmission sections that have received the signal of the 
specified pattern generate output signals. Using the generated output 
signals, intermodulation distortion components caused by non-linearity of 
an amplifier are compensated for. 
Therefore, a signal output from a transmission section is of constant 
amplitude and constant frequency, so accurate compensation is realized.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The preferred embodiment of the present invention are explained, referring 
to the figures. 
FIG.1 is a block diagram of an embodiment of a communication base station 
system according to the present invention. 
A.sub.1 to An are transmission data. 
1.sub.1 to 1.sub.n are orthogonal modulation sections that receive 
transmission data A.sub.1 to A.sub.n, orthogonally modulate the received 
data and output modulated signals. 
2.sub.1 to 2.sub.n are frequency conversion sections that receive the 
modulated signals, convert them to a preset transmission frequency and 
generate output signals B.sub.1 to B.sub.n. Here, the transmission 
frequency is controlled as a channel, the frequency conversion sections 
2.sub.1 to 2.sub.n are assigned a channel by the transmission control 
section 10 described later and convert the frequency of the modulated 
signal to a transmission frequency corresponding to the assigned channel. 
The transmission sections 3.sub.1 to 3.sub.n comprise the orthogonal 
modulation sections 1.sub.1 to 1.sub.n and the frequency conversion 
sections 2.sub.1 to 2.sub.n, respectively. 
4.sub.1 to 4.sub.n are specified signal generation sections corresponding 
to the transmission sections 3.sub.1 to 3.sub.n and generate signals of 
respective specified patterns C.sub.1 to C.sub.n that make the respective 
corresponding transmission sections having received the specified signals 
among the transmission sections 3.sub.1 to 3.sub.n transmit a signal of 
constant amplitude and constant frequency. 
5.sub.1 to 5.sub.n are switching sections, corresponding to the 
transmission sections 3.sub.1 to 3.sub.n, which receive the transmission 
data A.sub.1 to A.sub.n and the signals of specified pattern C.sub.1 to 
C.sub.n, usually output the transmission data A.sub.1 to A.sub.n, but 
switch to output the signals of specified pattern C.sub.1 to C.sub.n to 
the transmission sections 3.sub.1 to 3.sub.n when the instruction signal 
described later has been supplied. 
Distortion-compensation-type amplification section 6 collectively amplifies 
the output signals B.sub.1 to B.sub.n and compensates intermodulation 
distortion components generated in the amplification step using the 
distortion compensation circuit 7. 
Control section 8 and comprises the transmission monitoring section 9, the 
transmission control section 10 and the distortion compensation control 
section 11. 
The transmission monitoring section 9 stores information corresponding to 
the transmission sections in use among the transmission sections 3.sub.1 
to 3.sub.n and a channel in use and transmits this information to the 
transmission control section 10. 
Receiving a request of transmission from outside, the transmission section 
10 assigns a channel to the frequency conversion sections 2.sub.1 to 
2.sub.n based on the information from the transmission monitoring section 
9. Also, receiving a request for distortion compensation from the 
distortion compensation control section 11 and confirming two units of 
transmission sections not in use, it assigns a channel for distortion 
compensation to the confirmed two units of transmission sections based on 
the information from the transmission monitoring section 9, and 
simultaneously outputs an instruction signal to the switching sections 
corresponding to the two confirmed transmission sections. Moreover, it 
calculates a frequency at which distortion is generated and instructs a 
result to the distortion compensation circuit 7 based on the channel for 
distortion compensation assigned by the transmission control section 10. 
Here, the frequency at which distortion is generated is expressed by the 
following equation. 
EQU f=2*f.sub.k .+-.f.sub.j (1) 
Where, f.sub.k is the transmission frequency of the transmission section 
3.sub.k and f.sub.j is the transmission frequency of the transmission 
section 3.sub.j. 
Next, the operation of a movable communication base station system 
configured as above is explained. 
First, the transmission control section 10 having received a request for 
transmission from outside confirms information on a status of used 
channels and use of the transmission sections 3.sub.1 to 3.sub.n stored in 
the transmission monitoring section 9. Then, it assigns channels not in 
use to the frequency conversion sections not in use among the frequency 
conversion sections 2.sub.1 to 2.sub.n, and lets them carry out 
transmission. 
Where, when receiving a request for distortion compensation from the 
distortion compensation control section 11, the transmission control 
section 10 analyzes information of the transmission monitoring section 9. 
If having confirmed two or more units not in use, it assigns a channel for 
distortion compensation to two arbitrary transmission sections, and 
simultaneously outputs an instruction signal to two switching sections 
corresponding to the two arbitrary transmission sections. In addition, it 
informs the distortion compensation control section 11 of the channel 
assigned for distortion compensation. 
The distortion compensation control section 11 calculates a frequency at 
which distortion is generated based on the channel assigned for distortion 
compensation from the transmission control section 10, informs the 
distortion compensation circuit 7 of the calculated frequency. 
The distortion compensation circuit 7 performs distortion compensation 
based on the frequency of the distortion compensation control section 11 
and outputs of the transmission sections that have received specified 
signals. 
For example, let suppose that the transmission sections 3.sub.k 
(1.ltoreq.k.ltoreq.n) and the transmission sections 3.sub.j 
(1.ltoreq.j.ltoreq.n) do not transmit any data. 
When having received a request for distortion compensation from the 
distortion compensation control section 11, the transmission control 
section 10 confirms that the transmission sections 3.sub.k and 3.sub.j do 
not transmit any data based on a status information of use of the 
transmission sections 3.sub.1 to 3.sub.n stored in the transmission 
monitoring section 9. Then it assigns a channel for distortion 
compensation to the frequency conversion section 2.sub.k in the 
transmission section 3.sub.k and the frequency conversion section 2.sub.j 
in the transmission section 3.sub.j and simultaneously outputs an 
instruction signal to the switching section 5.sub.k and 5.sub.j. 
By this operation, the signals of specified pattern C.sub.k and C.sub.j are 
supplied from the specified signal generation sections 4.sub.k and 4.sub.j 
to the transmission sections 3.sub.k and 3.sub.j, and the output signals 
B.sub.k and B.sub.j become signals of constant amplitude and constant 
frequency. Then, the output signals B.sub.k and B.sub.j are supplied to 
the distortion-compensation-type common amplification section 6. 
On the other hand, the transmission control section 10 assigns a channel 
for distortion compensation to the distortion compensation control section 
11. The distortion compensation control section 11 calculates the 
frequency f at which distortion is generated based on the above-mentioned 
equation (1) and supplies the valve of this frequency to the distortion 
compensation circuit 7. 
Next, the distortion compensation circuit 7 compensates for intermodulation 
distortion components based on the frequency f at which distortion is 
generated and the output signals B.sub.k and B.sub.j. 
Like this, the control section 8 makes two transmission sections that do 
not transmit any data receive signals of a specified pattern and the 
distortion compensation circuit 7 compensates distortion using a signal of 
constant amplitude and constant frequency, so intermodulation distortion 
caused by non-linearity of amplifier can be accurately compensated for.