Multiplex communications – Duplex – Communication over free space
Reexamination Certificate
1998-04-27
2001-10-30
Jung, Min (Department: 2663)
Multiplex communications
Duplex
Communication over free space
C370S295000, C370S480000, C455S176100
Reexamination Certificate
active
06310863
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a dual-band data communication device which can transmit and receive either one of two frequency bands while switching the two, and particularly relates to a dual-band data communication device which can be used with any high/low relationship between a transmission/reception frequency and a local oscillation frequency.
Basically, a data communication device performs transmission and reception by using only one frequency band. With only one frequency band, however, a data communication device might fail in communication when another device uses the same frequency band or when the frequency band cannot be used because of noise or the like. Therefore, dual-band data communication devices which can use two frequency bands selectively by switching these two bands have been used.
FIG. 10
is a block diagram of a conventional dual-band data communication device. In
FIG. 10
, the dual-band data communication device is constituted by: an antenna
101
for transmitting/receiving a transmission/reception wave efficiently; a duplexer
102
for separating the transmission/reception wave into a transmission wave and a reception wave; a receiver
103
for converting the reception wave into two orthogonal base-band reception signals RX-I and RX-Q, the former one of which is an in-phase component and the latter one of which is a quadrature component; a transmitter
104
for converting two orthogonal base-band transmission signals TX-I and TX-Q, the former one of which is an in-phase component and the latter one of which is a quadrature component, into a transmission wave; a first local oscillator
105
for a first band used for frequency-conversion in the transmitter and the receiver; a first local oscillator
106
for a second band used for the same purpose as the first local oscillator
105
; a reception second local oscillator
107
used for orthogonal detection in the receiver; a transmission second local oscillator
108
used for orthogonal modulation in the transmitter; A/D converters
109
for converting the orthogonal base-band reception signals RX-I and RX-Q into digital orthogonal base-band reception signals respectively; a digital demodulation processing means
201
for demodulating the digital orthogonal base-band reception signals into reception data; D/A converters
111
for converting digital orthogonal base-band transmission signals into orthogonal base-band transmission signals TX-I and TX-Q respectively; a digital modulation processing means
601
for modulating transmission data into digital orthogonal base-band transmission signals; and a band selection control means
113
for controlling the mode as to which one of the first and second bands is used. The band selection control means
113
performs control for selection between the first local oscillator
105
for the first band and the first local oscillator
106
for the second band by using a band selection control signal
114
to thereby make it possible to perform control of selection as to which one of the first and second bands is to be used.
However, in such a conventional dual-band data communication device, it is necessary to fix the direction of phase rotation of the orthogonal base-band reception signals supplied into the digital demodulation processing means. This is because, if the direction of phase rotation changes so that the high/low relationship of frequency is inverted in frequency conversion, the data are inverted.
Let in-phase and quadrature components of digital orthogonal base-band signals be i(t) and q(t), respectively. The reception signals orthogonally modulated by cos(&ohgr;t) and sin(&ohgr;t) are frequency-converted with a local oscillation signal cos(&ohgr;
0
t) as follows.
2
cos
(
ω
0
t
)
·
{
i
(
t
)
·
cos
(
ω
t
)
-
q
(
t
)
·
sin
(
ω
t
)
}
=
i
(
t
)
·
{
cos
(
ω
0
+
ω
)
t
+
cos
(
ω
0
-
ω
)
t
}
-
q
(
t
)
·
{
sin
(
ω
0
+
ω
)
t
-
sin
(
ω
0
-
ω
)
t
}
=
{
i
(
t
)
·
cos
(
ω
0
+
ω
)
t
-
q
(
t
)
·
sin
(
ω
0
+
ω
)
t
}
+
{
i
(
t
)
·
cos
(
ω
0
-
ω
)
t
+
q
(
t
)
·
sin
(
ω
0
-
ω
)
t
}
In the case of frequency conversion, the phase is not changed if the local oscillation frequency is made lower than the reception frequency, but the phase of the quadrature component is inverted if the local oscillation frequency is made higher than the reception frequency. If the local oscillation frequency is set to have a high/low relationship which is difference between the first and second bands, the phase of the quadrature component is inverted between the two bands, and the direction of rotation of the phase is reversed. Accordingly, in differential phase modulation, logic
1
and logic
0
are replaced by each other.
Therefore, there arose such a constraint condition that it was necessary to set the high/low relationship between the reception frequency and the local oscillation frequency in common between the first and second bands. Accordingly, there was a problem that the degree of freedom in designing the first-band local oscillator and the second-band local oscillator was reduced.
In the same manner, the phase is not changed if the local oscillation frequency is made lower than the reception frequency and signals the frequency of which is increased by addition are made transmission signals. However, the phase of the quadrature component is inverted if the local oscillation frequency is made higher than the reception frequency and signals the frequency of which is decreased by substraction are made transmission signals. If the local oscillation frequency is set to have a high/low relationship which is different between the first and second bands, the phase of the quadrature component is inverted between the two bands, and the direction of rotation of the phase is reversed. Accordingly, in differential phase modulation, logic
1
and logic
0
are replaced by each other.
Therefore, since the direction of rotation of the phase of the digital orthogonal base-band transmission signals outputted from the digital modulation processing means was fixed, there arose such a constraint condition that it was necessary to set the high/low relationship between the transmission frequency and the local oscillation frequency in common between the first and second bands. Accordingly, there was a problem that the degree of freedom in designing the first-band local oscillator and the second-band local oscillator was reduced.
SUMMARY OF THE INVENTION
In order to solve the foregoing conventional problems, an object of the present invention is to provide a dual-band data communication device in which the degree of freedom in designing a first-band local oscillator and a second-band local oscillator can be increased.
In order to solve the foregoing problems, according to the present invention, a dual-band data communication device comprises a dual-band digital demodulation processing means and a dual-band digital modulation processing means for performing demodulation and modulation properly, respectively, in use for a first band or a second band in response to selection control by a band selection control means for performing the control as to which one of a first-band local oscillator and a second-band local oscillator is used.
With such a configuration, modulation and demodulation can be performed properly in use of the first band or the second band regardless of the manner of setting the high/low relationship between the transmission/reception frequency and the local oscillation frequency. Accordingly, the degree of freedom in designing the first-band local oscillation frequency and the second-band local oscillatio
Jung Min
Matsushita Electric - Industrial Co., Ltd.
Pearne & Gordon LLP
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