OPU-1
UNIVERSAL POWER-LINE CARRIER SYSTEM TYPE OPU-1
GENERAL DESCRIPTION - Rev 7 (May 2019)
9/67
1.2
MAIN FEATURES
Some of the most remarkable features of the OPU-1 terminal are the following:
❖
Time synchronization.
The OPU-1 terminal chronologically registers all the alarms produced in the terminal, as
well as the events that refer to the link service. In order to establish the date and time the
alarms and/or events are produced, the OPU-1 terminal has a real time clock, which can
be synchronized with the GPS system or by means of the SNTP protocol.
❖
Two digital modulation schemes
The OPU-1 offers two different modulation schemes to better suit all transmission needs
in terms of the quality of service required by the applications and the transmission line
characteristics. Both QAM and OFDM/OQAM are supported by the OPU-1 and can be
selected from the programming software.
The choice between QAM and OFDM/OQAM depends on the required transmission rate,
required BER and internal latency, on the one hand, and S/N ratio and line attenuation on
the other hand. QAM can work at lower values of S/N and has a lower transmission
latency, whereas OFDM/OQAM increases the transmission rate at the expense of a
higher transmission latency and needs higher values of S/N ratio.
❖
Automatic fall-back/increase rates.
A remarkable feature of the OPU-1 when working with a digital modem unit is the
automatic fall-back rate when there is unfavourable line noise and/or signal reflection
conditions.
In the example for QAM, see FIGURE 3, the transmission rate is automatically reduced to
half or a third of the maximum value if necessary, that is to say, to 40.5 kbit/s and
27 kbit/s respectively. When the line conditions improve, the transmission rate is
automatically re-established.
In OFDM/OQAM, the channel is constantly evaluated in such a way that the carriers
that are affected by noise or interferences can automatically reduce its base modulation
or even disappear. Also the turbo code rate can change to make communications more
reliable. The two mechanisms combined allow the maximum transmission rate to be
dynamically adjusted, ensuring a correct BER in every condition.
For the QAM, this automatic feature can be disabled from the programming software if
necessary.
The link quality measurement is based on the G.821 standard concepts.