Pulse or digital communications – Receivers – Particular pulse demodulator or detector
Reexamination Certificate
1999-10-12
2004-11-30
Chin, Stephen (Department: 2634)
Pulse or digital communications
Receivers
Particular pulse demodulator or detector
C375S341000, C714S701000
Reexamination Certificate
active
06826239
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a modulating method for generating a signal modulated by orthogonal frequency division multiplexing (to be referred to as ‘OFDM’ hereinafter), a modulator utilizing the modulation method, a demodulating method for demodulating the OFDM-modulated signal and a demodulator utilizing the demodulation method. The present invention relates to, in particular, a technique suited for processing an interleaved OFDM modulation signal.
BACKGROUND ART
Conventionally, OFDM modulation has been put to practical use as one of modulation systems in case of radio-transmitting relatively mass storage digital data. As shown in, for example,
FIG. 23
, in a relatively small space such as a home or an office floor, a picture signal (digital picture data) outputted from a picture signal source
1
consisting of a tuner receiving television broadcasting, a reproducing apparatus for reproducing a picture program recorded in a recording medium and the like is supplied to a radio transmitter
2
. The picture signal is modulated to an OFDM modulated signal at a radio transmitter
2
and the modulated signal is radio-transmitted from an antenna
3
in a predetermined frequency band. The radio-transmitted signal is received by a radio receiver
5
connected to an antenna
4
. The received OFDM wave in the frequency band is demodulated and a picture signal is thereby obtained. The received picture signal is supplied to a video recording and reproducing apparatus
6
, in which the signal is recorded in a predetermined recording medium such as a video tape, or supplied to an image receiving machine
7
and subjected to image receiving process. In this case, it is possible to reproduce the picture signal recorded in the video recording and reproducing apparatus
6
and to supply the resultant reproduced signal to the image receiving machine
7
to thereby allow an image to be received by the image receiving machine
7
.
With this system arrangement, it is possible to highly efficiently radio-transmit mass storage digital data by using the OFDM modulated signal for radio transmission between the antenna
3
connected to the radio transmitter
2
and the antenna
4
connected to the radio receiver
5
.
Now, with reference to
FIG. 24
showing an example of the constitution of the radio transmitter
2
for conducting OFDM modulation for transmission, a transmission signal (digital data) obtained at an input terminal
2
a
is supplied to a serial/parallel converter
2
b
and converted to parallel data for each predetermined unit. The parallel data converted at the serial/parallel converter
2
b
is supplied to an interleave memory
2
c
in which interleave processing for changing write and read orders for writing and reading data to/from the memory
2
c
and changing data array. The interleaved parallel data is supplied to an inverse Fourier transform circuit (or IFFT circuit)
2
d
, in which time axis data is orthogonally transformed to frequency axis data by arithmetic operation by means of inverse fast Fourier transform. The orthogonally transformed parallel data is supplied to a parallel/serial converter
2
e
and converted to serial data, which serial data is supplied to an output terminal
2
f
. The data obtained at the output terminal
2
f
is supplied to a transmission processing system to convert the frequency to fall within the range of a predetermined transmission frequency band, thereafter radio-transmitting the data.
Next, with reference to
FIG. 25
showing an example of a constitution in which the signal thus radio-transmitted is received and demodulated by the radio receiver
5
, a signal in a predetermined frequency band is received and a signal frequency-converted to an intermediate frequency signal is obtained at the input terminal
5
a
. The data obtained at the input terminal
5
a
is supplied to a serial/parallel converter
5
b
and converted to parallel data for each predetermined unit. The converted output is supplied to a Fourier transform circuit (FFT circuit)
5
c
, in which orthogonal transform processing for transforming frequency axis data to time axis data by arithmetic operation by means of fast Fourier transform. The orthogonally transformed parallel data is supplied to a de-interleave memory
5
d
, in which de-interleave processing for changing write and read orders for writing and reading data to/from the memory
5
d
, changing data array back to an original data array is conducted. The de-interleaved parallel data is supplied to the parallel/serial converter
5
e
and converted to serial data, which serial data is supplied to the output terminal
5
f.
The demodulation processing for demodulating the OFDM modulation signal conducted with the constitution shown in
FIG. 25
is executed at timing shown in FIG.
26
. That is to say, there are, first, a data input time Ta at which data is inputted to the Fourier transform circuit
5
c
, next a Fourier transform processing time Tb at which Fast Fourier transform is conducted at the Fourier transform circuit
5
c
and then a data output time Tc at which the Fourier-transformed data is outputted. The data outputted at the output time Tc is simultaneously written in the de-interleave memory
5
d
and the data written in the memory
5
d
is read at a read-out time Td. It is noted that transform processing for generating an OFDM modulation signal with the constitution of
FIG. 24
is basically opposite to the demodulation processing and requires the same time as that for the demodulation processing.
Now, description will be given to a case where data is interleaved and transmitted by the transmission processings of
FIGS. 24 and 25
, with reference to
FIGS. 27 and 28
. As shown in
FIG. 27A
, for example, if OFDM modulation for distributing data in 50 units of data numbers of k=0 to 49 to sub-carriers x
0
to x
50
and transmitting them is conducted and this signal is correctly received by a receiver side, then no problem occurs. On the other hand, as shown in
FIG. 27B
, for example, it is assumed that sub-carriers of data numbers k=5, 6 and 7 cannot be correctly received due to multi-pass fading or the like and that the items of data numbered k=5, 6 and 7 are lost.
At this time, if data is transmitted without interleave processing, data items of three consecutive units in one slot, i.e., k=5, 6 and 7 are lost, resulting in burst error as shown in FIG.
28
A. If such a burst error occurs, it is difficult to completely restore data using an error correction code. If data is transmitted after interleave processing, by contrast, data items of three units of k=5, 6 and 7 are arranged in a distributed manner in one slot (the distribution state varies according to interleave conditions) as shown in, for example, FIG.
28
B. Then, a possible error becomes random errors, each of which can be completely corrected by using error correction codes or the like.
By transmitting data after subjecting the data to interleave processing, it is possible to minimize data loss at the receiver side and to ensure a good transmission condition.
Meanwhile, with the constitution shown in
FIG. 25
, interleave processing is conducted using a memory. There is also proposed a constitution in which de-interleave processing is conducted without using a memory.
FIG. 29
shows an example of the latter case. Processing steps shown therein are the same until data obtained at an input terminal
5
a
is supplied to a serial/parallel converter
5
b
and converted to parallel data for each predetermined unit, and the conversion output is supplied to a Fourier transform circuit
5
c
, in which orthogonal transform for transforming frequency axis data to time axis data is conducted by arithmetic operation by means of Fast Fourier transform. The orthogonally transformed parallel data is subjected to processing for changing a data array by wiring change processing
5
d
corresponding to the interleave pattern of the data. The parallel data which data array has been thus changed is supplied to a
Chin Stephen
Maioli Jay H.
Odom Curtis
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