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Improving Network Performance with airPRISM


A lot of WISPs are familiar with network slowdown. You set up your network and go about your business, until calls start coming in that the internet is slow; or maybe your own internal network management system sends you some alerts. Everything was fine earlier, what’s changed now?

The sudden onset of poor network performance has two typical causes, both of which we’ve addressed through innovative features in airMAX® AC. They’re different types of interference, and understanding each of them a little better will help you troubleshoot any network issues.

In many ways, radios process the signals they receive much like we humans do. To make sense of the incoming transmission that we want to hear, we need it to be a certain amount louder than all of the background noise. Just like when we’re trying to hear someone talk from across a loud and noisy room, radio receivers need a sufficient Signal-to-Noise Ratio (SNR) to decode data.

External Interference

When a radio system that is not your own interferes with your network, that is referred to as external interference. It may be on the same channel as you are operating on, or it may be on an adjacent channel. Either way, there’s not usually a way you can prevent the interferer from transmitting, so you need to find a way to protect your network against that interference.

If the interferer is operating on the same channel as you are, the easiest thing to do typically is move your network to a different channel. However, in cases where there are a limited number of clear channels available, or the external interferer is especially strong, there’s a good chance your network will still suffer due to adjacent channel interference. This occurs when you cannot move to a channel far enough away from the interferer, and your radio still hears its noise loudly.

This issue most often occurs at the tower, where multiple APs are co-located. To combat this, airMAX AC APs incorporate our proprietary airPrism® filtering technology. This combination of hardware and software real-time filtering works to block out adjacent channel interference, by tightening the range of frequencies your radio will listen for to just those in your chosen channel.

Think of airPrism filtering like a pair of noise-cancelling headphones. With airPrism, your AP can focus on what it wants to be able to hear – the transmissions from your CPEs – and ignore all of the noise around it that would otherwise create interference. This feature is exclusive to airMAX AC APs, and makes a huge difference to your overall wireless network performance.


Unlike external interference, self-interference is caused by your own radio equipment. As a network expands, it’s easy to accidentally create crippling self interference that can create plenty of problems for your network performance. Typically there are two causes of this:

1. CPE to AP Self-Interference

When deploying any radio device, it’s easy to think that the higher the transmit power, the better. After all, we want to give our gear the best chance at receiving the strongest possible signal, so why would we go with anything less than the maximum power? The answer is that because the airwaves we use to transmit wireless data are a shared medium, we can easily create self-interference when a CPE is transmitting too strongly, causing its signal to be received loudly by another AP. This causes issues where the inadvertently receiving AP can’t hear its own CPEs.

The ideal solution to this is ATPC, or Automatic Transmit Power Control. With this key feature in airMAX AC, the airMAX AC AP dynamically controls the transmit power of each of its connected CPEs. The transmit power each of them uses is adjusted to stay at a level that will give each of them a high-performance connection, but without transmitting any unnecessary excess power.

2. AP to AP Self-Interference

In many cases, multiple APs are deployed at a tower. They are deployed in such close proximity to each other that when one AP transmits, another AP hears that transmission at a time when it is expecting to hear its own CPEs. This causes network performance issues, as the AP cannot hear its CPEs clearly while the other AP next to it is transmitting. The key to avoiding this is GPS Sync.

With GPS Sync, all of the APs on a particular tower site can be synchronized together. This means that they all transmit at the same time, and expect to receive data from their CPEs at the same time. This eliminates the problem created by AP to AP self-interference, because the AP is never waiting to receive a radio signal while another AP on the same tower is transmitting.

Optimizing Network Performance

By understanding a little more about both external and self-interference, we can see how they both impact our network performance and what we can do to combat them. Powerful features in airMAX AC such as airPrism filtering, ATPC, and GPS Sync do a great job at keeping your network operating at the optimal level of performance, even in the presence of interference.