Pulse or digital communications – Receivers – Particular pulse demodulator or detector
Reexamination Certificate
1999-08-10
2003-05-27
Phu, Phuong (Department: 2631)
Pulse or digital communications
Receivers
Particular pulse demodulator or detector
C375S235000
Reexamination Certificate
active
06570939
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a receiving device applied in a digital radio communication system, and in particular to a receiving device having a demodulating function based on orthogonal detection, and an equalizing function based on maximum likelihood sequence estimation.
DESCRIPTION OF THE RELATED ART
FIG. 1
is a block diagram showing an example of constitution of a conventional radio device. As it is shown in the figure, in general, the receiving device comprises an orthogonal detector
110
, A/D converters
120
,
130
, a maximum likelihood sequence estimating equalizer
150
, and an oscillator
140
. The orthogonal detector
110
is where a signal having gone through an orthogonal demodulation is inputted and two base band signal components orthogonal to each other are generated to be outputted to the A/D converters. The A/D converters
120
and
130
serve to convert each base band signal component inputted from the orthogonal detector
110
to a digital signal, at every sampling period, so as to output the digital signal to the maximum likelihood sequence estimating equalizer
150
. The maximum likelihood sequence estimating equalizer
150
is to output an estimation signal on the basis of the digital signals inputted from the A/D converters
120
and
130
. The oscillator
140
serves to oscillate and output a signal which is to be combined with the signal inputted to the orthogonal detector
110
.
The orthogonal detector
110
includes a mixer
111
for combining the signal having gone through an orthogonal modulation together with the signal outputted from the oscillator
140
, a Π/2 phase shifter
115
for shifting a phase of the signal from the oscillator
140
by Π/2, a mixer
112
inputting a phase-shifted signal from the Π/2 phase shifter
115
where the phase shifted signal is combined with the orthogonal-modulated signal, a filter
113
for letting only predetermined frequency component in the resultant signal from the mixer
111
pass through, so as to output an in-phase component in the base band signal, and a filter
114
for letting only the predetermined component in the resultant signal from the mixer
112
pass through, so as to output an orthogonal component in the base band signal.
The maximum likelihood sequence estimating equalizer
150
has a transmission line estimating section
151
, a replica generator
152
, a branch metric arithmetic section
153
, and a signal sequence estimating section
154
. The transmission line estimating section
151
is to calculate the in-phase component in an impulse response of a transmission line on the basis of the output from the filter
113
having been modulated to a digital signal at the A/D converter
120
. The transmission line estimating section
151
also serves to calculate the orthogonal component in the impulse response of the transmission line on the basis of the output from the filter
114
having been modulated to a digital signal at the A/D converter
130
. The replica generator
152
generates a replica on the basis of the in-phase component and the orthogonal component in the impulse response of the transmission line, that are being calculated at the transmission line estimating section
151
. The branch metric arithmetic section
153
is to calculate a branch metric on the basis of the digitally modulated signals from the A/D converters
120
and
130
having been outputted from the filters
113
and
114
, respectively, and the replica generated at the replica generator
152
. The signal sequence estimating section
154
is to estimate the transmitted signal sequence in accordance with the branch metric calculated at the branch metric arithmetic section
153
. In this case, the replica is a product of a convolution of a candidate signal sequence and the transmission line impulse response, which indicates an estimated value of a reception signal in case when a candidate signal is being transmitted.
In the following, operation of the conventional receiving device as constructed above will be described.
When a signal x(t)=p(t) cos &ohgr;ct−q(t) sin &ohgr;ct is inputted to the orthogonal detector
110
, where &ohgr;c is a carrier wave of angular frequency, the input signal x(t) and the cos &ohgr;ct signal outputted from the oscillator
140
are combined at the mixer
111
, which product passes through the filter
113
, providing the in-phase component p(t) of the base band signal.
Furthermore, a phase of the signal cos &ohgr;ct outputted from the oscillator
140
is shifted by Π/2 resulting in giving out a signal −sin &ohgr;ct to the Π/2 phase shifter
115
. Then at the mixer
112
, the input signal x(t) and the signal −sin &ohgr;ct are combined, which product passes through the filter
114
, providing the orthogonal component q(t) of the base band signal.
The in-phase component p(t) of the base band signal outputted from the orthogonal detector
110
is converted into a digital signal at the A/D converter
120
, at every sampling period T, providing a digital reception signal p(nT). Here, ‘T’ is a transmission rate of the base band signal, and ‘n’ is an integer.
The orthogonal component q(t) of the base band signal outputted from the orthogonal detector
110
is converted into a digital signal at the A/D converter
130
, at every sampling period T, providing a digital reception signal q(nT), n being an integer.
The reception signals p(nT) and q(nT) outputted from the A/D converters
120
and
130
, respectively, are inputted to the maximum likelihood sequence estimating equalizer
150
. Then at the transmission line estimating section
151
provided inside the maximum likelihood sequence estimating equalizer
150
, an in-phase component g(nT) of the impulse response of the transmission line is calculated on the basis of the inputted reception signal p(nT), and an orthogonal component h(nT) of the impulse response of the transmission line is calculated on the basis of the inputted reception signal q(nT).
After that, a replica pR(nT) is calculated at the replica generator
152
on the basis of the in-phase component g(nT) of the impulse response of the transmission line having been calculated by the transmission line estimating section
151
. At the same time, a replica qR(nT) is also calculated at the replica generator
152
on the basis of the orthogonal component h(nT) of the impulse response of the transmission line having been calculated by the transmission line estimating section
151
.
Then at the branch metric arithmetic section
153
, a square of a difference between the reception signal p(nT) outputted from the A/D converter
120
and the replica pR(nT) calculated by the replica generator
152
is added together with a square of a difference between the reception signal q(nT) outputted from the A/D converter
130
and the replica qR(nT) calculated by the replica generator
152
, which resultant represents a branch metric.
Next, the signal sequence estimating section
154
uses the well-known Viterbi algorithm (cf. “WAVEFORM EQUALIZATION TECHNOLOGY FOR DIGITAL MOBILE COMMUNICATION” by Horikoshi et al., pp. 85-89, Triceps Publication) to estimate the transmitted signal sequence on the basis of the branch metric having been calculated by the branch metric arithmetic section
153
.
In such receiving device as discussed above, there are some probable estimation errors in the signal sequence estimation by the equalizer, due to a phase difference between the in-phase component (to be referred to as Ich) and the orthogonal component (to be referred to as Qch), and due to an amplitude difference, DC offset and so forth, caused by the provision of two systems to cope with Ich and Qch respectively, as the orthogonal detector
110
, the filters
113
and
114
, and the A/D converters
120
and
130
are provided. As such estimation error occurs, the transmission characteristic is to deteriorate considerably. Therefore, in this conventional example, the receiving device requires a high-precision phase adjustment, gain adjustment,
Dickstein Shapiro Morin & Oshinsky LLP.
NEC Corporation
Phu Phuong
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