OPU-1
UNIVERSAL POWER-LINE CARRIER SYSTEM TYPE OPU-1
GENERAL DESCRIPTION - Rev 7 (May 2019)
36/67
3.3
MODULATIONS AND DEMODULATIONS
The transposition of a 4 kHz channel to a band of frequencies that extends from 36 to
512 kHz is carried out by means of a modulation process that is completely digital. The type
of modulation used is single side-band with suppressed carrier.
In this way, the analog signal in base band is digitized and delivered to the MOPU where,
by means of digital signal processing, is transposed to the desired channel frequency, with
a resolution of 1 Hz. The resulting digital signal is converted to analog and, before being
transmitted to the high-voltage line, passes through a power stage.
In reception the transposition is carried out in reverse, that is to say, the received analog
signal, after passing through the AGC circuit, is digitized and delivered to the signal
processing unit which carries out the transposition of the signal of each channel in base
band, and extracts the pilot. The digital signal of each channel is then converted to analog.
For the QAM, the data stream proceeding from the digital user interface is encoded and
then modulated at 128-QAM, 16-QAM or 4-QAM according to whether the gross bit rate is
of 81 kbit/s, 40.5 kbit/s or 27 kbit/s, respectively. The data is subjected to the following
processes: scrambling, serial-to-parallel conversion, differential encoding, convolutional
encoding (Trellis encoding), symbol mapping, pulse-shaping filtering and QAM modulation.
The QAM signals obtained in this way are then transposed to the desired frequency band
and, before being transmitted to the high-voltage line, passes through a power stage.
In reception the transposition is carried out in reverse, that is to say, the received analog
signal enters the MQPU module where, once subjected to an AGC process, it is converted
into a digital signal and passes through a band-pass filter which gives the receiver the
selectivity characteristics desired.
In the superimposed-band operation mode, the filtered signal is applied to an
echo-canceller device where the transmit signal that superimposes the received signal is
cancelled, by means of a signal coming from the transmitter and adequately processed.
The obtained signal is demodulated and decoded in order to be sent to the user interface.
In the non-adjacent band operation mode, when an echo canceller is not used, the filtered
signal is directly demodulated and decoded in order to be sent to the user interface.
The input of the OFDM/OQAM modulator is a complex symbol stream for each of the
carriers of the system.
