Apparatus for removing shared waves

Details Apparatus for removing shared waves Apparatus for removing shared waves

1998-02-13

2001-06-19

Pham, Chi (Department: 2631)

Pulse or digital communications

Spread spectrum

Direct sequence

C375S144000, C375S346000

Reexamination Certificate

active

06249541

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an apparatus for removing shared waves other than a desired wave signal contained in a radio frequency signal.
BACKGROUND ART
FIG. 1
is a block diagram showing a configuration of a conventional apparatus for removing shared waves. For example, U.S. Pat. No. 5,363,403 shows a related configuration. In the drawing, reference numeral
1
means an antenna to receive a radio frequency signal,
2
is an amplifier to amplify the radio frequency signal received by the antenna
1
,
3
is a local oscillator to generate a local oscillation signal, and
4
is a mixer to mix the radio frequency signal amplified by the amplifier
2
with the local oscillation signal, thereby extracting an intermediate frequency signal.
Reference numeral
5
means a CDMA (Code Division Multiple Access) code generator to generate a shared wave identifying code for identifying a CDMA shared wave,
6
is a correlation detector to detect CDMA#2 signal serving as a shared wave signal through code correlation from the intermediate frequency signal depending upon the shared wave identifying code generated from the CDMA code generator
5
,
7
is a demodulator to demodulate information of the CDMA#2 signal serving as the shared wave signal detected by the correlation detector
6
, and
8
is a modulator to modulate the internal-oscillated intermediate frequency signal by the shared wave identifying code and the information of the CDMA#2 signal serving as the shared wave signal demodulated by the demodulator
7
depending upon the shared wave identifying code.
Further, reference numeral
9
means a delay circuit to delay the intermediate frequency signal transformed by the mixer
4
for a predetermined time period,
10
is a subtracter to subtract the CDMA#2 signal serving as the shared wave signal modulated by the modulator
8
from the intermediate frequency signal delayed by the delay circuit
9
,
11
is a CDMA code generator to generate a desired wave identifying code for identifying a desired wave,
12
is a code correlator to detect CDMA#1 signal serving as a shared wave signal through code correlation from output of the subtracter
10
depending upon the desired wave identifying code generated from the CDMA code generator
11
, and
13
is a demodulator to demodulate information of the CDMA#1 signal serving as the shared wave signal detected by the code correlator
12
.
FIG. 2
is a block diagram showing a mobile communication system to which the conventional apparatus for removing shared waves is applied. In the drawing, reference numeral
21
means a mobile station equipped with the apparatus for removing shared waves, such as mobile vehicle communication apparatus, or mobile portable communication apparatus. Reference numeral
22
means a radio base station equipped with the apparatus for removing shared waves to communicate with the mobile station
21
through a radio channel
23
. Reference numeral
24
means a satellite communication apparatus to communicate with the mobile station
21
through a radio channel
25
, and
26
is a satellite communication ground base station equipped with the apparatus for removing shared waves to communicate with the satellite communication apparatus
24
through a satellite line
27
.
Further, reference numeral
28
means a public switched telephone network (hereinafter referred to as PSTN),
29
is a wire telephone connected to the PSTN
28
,
30
is a private system connected to the PSTN
28
,
31
is an exchanger in the private system
30
,
32
is a telephone apparatus connected to the exchanger
31
, and
33
,
34
and
35
are base stations in the private system
30
, which are connected to the exchanger
31
and connected to the mobile station
21
through a radio channel
36
, and are equipped with the apparatus for removing shared waves.
A description will now be given of the operation.
In radio communication between, for example, the mobile station
21
and the radio base station
22
, or the mobile station
21
and the base station
33
, that is, in each radio communication concurrently employing a frequency division multiple access method (hereinafter referred to as FDMA method), a multi-carrier time-division multiple access method (hereinafter referred to as TDMA method), a code division multiple access method (hereinafter referred to as CDMA method), and so forth, various types of radio waves are superimposed at the same frequency. Hence, the radio wave received by, for example, the mobile station
21
contains an unnecessary signal (hereinafter referred to as shared wave signal) in addition to a signal to be received (hereinafter referred to as desired wave signal). It is necessary to remove the shared wave signal from the received radio wave in order to extract the desired wave signal with less noise component due to the shared wave signal.
Thus, the apparatus for removing shared waves as shown in
FIG. 1
is mounted on, for example, the mobile station
21
to extract the desired wave signal by removing the shared wave signal from the received radio wave.
A description will now be given of the operation of the apparatus for removing shared waves.
First, when the antenna
1
receives the radio frequency signal, the amplifier
2
amplifies the radio frequency signal.
After the amplifier
2
amplifies the radio frequency signal, the mixer
4
extracts the intermediate frequency signal by mixing the local oscillation signal generated from the local oscillator
3
with the radio frequency signal. In this illustration, for the sake of simplicity, it must be noted that the intermediate frequency signal contains CDMA#0 signal and the CDMA#2 signal serving as shared wave signals in addition to the CDMA#1 signal serving as the desired wave signal as shown in FIG.
3
. In this connection,
FIG. 9
shows a relationship between a frequency and a time slot in the mobile communication system shared between the TDMA method and a CDMA/TDMA method. For example, it is shown that the TDMA#3 and a partial frequency of the CDMA#3 share a time slot.
After the intermediate frequency signal is extracted by the mixer
4
in the above manner, the correlation detector
6
detects the CDMA#2 signal serving as a shared wave signal through code correlation from the intermediate frequency signal depending upon the shared wave identifying code generated from the CDMA code generator
5
. That is, as shown in
FIG. 4
, the CDMA#2 signal serving as the shared wave signal is correlated by regarding the CDMA#0 signal and the CDMA#1 signal contained in the intermediate frequency signal as the noise components.
After the correlation detector
6
detects the CDMA#2 signal serving as the shared wave signal, the CDMA#0 signal and the CDMA#1 signal serving as the noise components are removed. Thus, the demodulator
7
and the modulator
8
demodulate and thereafter modulate the information of the CDMA#2 signal serving as the shared wave signal to output the information to the subtracter
10
.
On the other hand, when the intermediate frequency signal is extracted by the mixer
4
, the delay circuit
9
delays the intermediate frequency signal for the predetermined time period and thereafter outputs the signal to the subtracter
10
so as to overcome a difference in time between the intermediate frequency signal inputted into the subtracter
10
and the CDMA#2 signal serving as the reproduced shared wave signal.
The subtracter
10
can thereby subtract the CDMA#2 signal serving as the shared wave signal modulated by the modulator
8
from the intermediate frequency signal delayed by the delay circuit
9
, thereby removing a shared wave signal component from the intermediate frequency signal (see FIG.
5
).
After the subtracter
10
subtracts the CDMA#2 signal serving as the shared wave signal from the intermediate frequency signal, the code correlator
12
detects the CDMA#1 signal serving as the desired wave signal through code correlation from the intermed

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