Chapter 4: Feature Description
Innovative Techniques to Boost Capacity and Reduce
Latency
Eleven Working Points
PTP 820S implements ACM with 11 available working points, as shown in the following table:
Table 5 ACM Working Points (Profiles)
Working Point (Profile)
Modulation
Profile 0
QPSK
Profile 1
8 PSK
Profile 2
16 QAM
Profile 3
32 QAM
Profile 4
64 QAM
Profile 5
128 QAM
Profile 6
256 QAM
Profile 7
512 QAM
Profile 8
1024 QAM (Strong FEC)
Profile 9
1024 QAM (Light FEC)
Profile 10
2048 QAM
Figure 13 Adaptive Coding and Modulation with 11 Working Points
Hitless and Errorless Step-by Step Adjustments
ACM works as follows. Assuming a system configured for 128 QAM with ~170 Mbps capacity over
a 28 MHz channel, when the receive signal Bit Error Ratio (BER) level reaches a predetermined
threshold, the system preemptively switches to 64 QAM and the throughput is stepped down to
~140 Mbps. This is an errorless, virtually instantaneous switch. The system continues to operate at
64 QAM until the fading condition either intensifies or disappears. If the fade intensifies, another
switch takes the system down to 32 QAM. If, on the other hand, the weather condition improves,
the modulation is switched back to the next higher step (e.g., 128 QAM) and so on, step by step
.The switching continues automatically and as quickly as needed, and can reach all the way down
to QPSK during extreme conditions.
Page 4-8