Modulation Rate Calculation

Morning All.

I am working with one of our RSP installers to explain how the modulation calculation works. Trying to get the best modulation rate. Currently the connection is sitting at -66V/-76H with a 450b High Gain to a 450i AP. Currently getting 8x/3x MIMO-A

I have recommended that they tune the horizontal chain to be within at least 5 of the Vertical chain.

My question is, how is the overall modulation calculated? Does it go off of the lower chain’s rate, or is it some combination of the 2 levels?

Side note, we have limited control of how these devices are installer as we are a wholesale provider to the ISP in this instance. I am looking for a little more detail to implore the provider to improve the signal rather than just telling them to fix it.

Here is some info that might help:

Understanding Modulation Calculation

Modulation rates in wireless communication systems, like the one you described (8x/3x MIMO-A), depend on several factors including signal strength, signal quality, and the capabilities of the hardware involved. In your case, with the 450b High Gain connected to a 450i AP, the modulation rate is crucial for determining the overall data throughput and efficiency of the link.

Factors Affecting Modulation Rates

  1. Signal Strength and Quality: The received signal strength (RSSI) and Signal-to-Noise Ratio (SNR) are primary factors that influence the modulation rates. Higher signal strength and better signal quality generally allow for higher modulation schemes, which translate into better data rates.
  2. MIMO Configuration: MIMO (Multiple Input Multiple Output) technology improves link reliability and throughput by using multiple antennas at both the transmitter and receiver ends. The notation 8x/3x MIMO-A indicates the number of spatial streams being used.
  3. Balancing Vertical and Horizontal Chains: Ensuring that the signal levels on both vertical and horizontal chains are balanced (within 5 dB as you suggested) can help in maintaining optimal modulation rates. Imbalance between these chains can lead to suboptimal performance and lower modulation rates.

Modulation Calculation

In MIMO systems, the overall modulation rate is often determined by the weaker signal chain. This means that if one of the chains (vertical or horizontal) has a lower modulation rate due to poorer signal quality or strength, the overall modulation rate for the link might be reduced to match the weaker chain to maintain reliability.

For instance:

  • If the vertical chain is receiving at a higher modulation rate (e.g., 8x) and the horizontal chain is receiving at a lower modulation rate (e.g., 3x), the system might default to the lower rate to ensure consistent and reliable communication.

Recommendations for Optimization

  1. Antenna Alignment: Fine-tuning the alignment of the antennas can significantly improve signal strength and quality, thereby improving modulation rates. Ensure that both the vertical and horizontal chains are as closely matched in signal strength as possible.
  2. Environment Check: Assess the surrounding environment for potential sources of interference that could affect signal quality. This includes physical obstructions, other electronic devices, or competing wireless signals.
  3. Firmware and Configuration: Ensure that the firmware of both the AP and the client devices are up-to-date and configured optimally. This includes setting appropriate power levels and selecting the best channels to minimize interference.
  4. Use of Link Planning Tools: Cambium Networks offers tools like LINKPlanner and cnHeat, which can help in modeling and optimizing the network performance based on geographic and environmental data​​​​.

Final Note

For precise modulation calculations and optimization, using Cambium Networks’ tools and ensuring proper alignment and configuration will yield the best results. If further assistance is needed, reaching out to Cambium Networks’ technical support can provide more tailored solutions.

Hope this helps!

Best Regards

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Thank you Kinan. The line that says “The overall modulation rate is often determined by the weaker chain” should help me drive this home with our providers.

Thank you for the info. I will be using a fair amount of this in a training document for them.

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@Tandr06 fyi there are some faulty 450i APs out there, with 10-15 db signal down on one of the chains.

With such a big signal difference, I’d be investigating the installation further and also checking you don’t have chain imbalances on other SMs installed to that AP.