Is there any documentation that outlines what signal levels the various modulation schemes switch at when ACM is enabled. Are these levels user settable, or are they fixed by Cambium in the firmware of the radios?
Thanks in advance.
Hello, these are fixed values based off of BER (bit error rate) levels. More detailed information is available in the technical description (page 81 of the PTP820G v10.9 Technical Description). The best places to find information on the PTP820 are: the technical description, user guide and installation guide. Here is an excerpt from the technical description.
Hitless and Errorless Step-by Step Adjustments
ACM works as follows. Assuming a system configured for 128 QAM with ~170 Mbps capacity over a 30 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.
ACM Benefits
The advantages of PTP 820G’s dynamic ACM include:
• Maximized spectrum usage
• Increased capacity over a given bandwidth
• 11 working points, with~3 dB system gain for each point change
• Hitless and errorless modulation/coding changes, based on signal quality
• Adaptive Radio Tx Power per modulation for maximum system gain per working point
• An integrated QoS mechanism that enables intelligent congestion management to ensure that high priority traffic is not affected during link fading conditions.
Thank you Chris.
Reason I am interested in these switch point levels is that I am trying to model a link with PathLoss 5.1, where I am evaluating the ACM feature. However, the radio data files I can find on the Cambium site only has single files for each modulation code. That is, one for 64QAM, a separate one for 128QAM...and so on. For me to make an "ACM" file for simulation in PL5.1, I need to specify the specific step up and step down signal levels for each modulation scheme.
Can Cambium provide such an ACM simulaton file for PL5.1?
Alternatively, if I can get the details on the specific signal level switch points (note the technical documentation does not specify these levels), I can make the simulation file myself.
Thanks in advance
I'm not sure if ACM is going to be available in Pathloss. I would have to defer to another engineer that works with Pathloss in order to answer that. Our available pathloss files are available here: https://support.cambiumnetworks.com/files/ptp820/#r4
I'm also not sure if we can provide the exact values in order to generate the file manually. I will forward this request to our Pathloss expert and get his thoughts on the best approach.