airMAX - Guide to Channel Scanning with airView
This guide will explain how to determine the best channel configuration for your wireless network using the built-in airOS airView Spectrum Analyzer utility.
Notes: This article only applies to airMAX M devices. All latest generation devices (airMAX AC, LTU, etc.) include the built-in airMagic tool for suggesting the best channel (i.e. achievable bits/Hz capacity) based on all aggregate Stations associated with the AP radio. Read more about airMagic in this Community Story.
Introduction
To optimize the performance of a wireless network, the network designer should seek the best SNR (Signal‑to‑Noise Ratio) possible. Signal level can be predicted and planned based on the transmit power, antenna gain, distance, and frequency band. However, a common problem with unlicensed wireless bands (2.4 GHz, 5 GHz, etc.) is that noise cannot be predicted, and clean spectrum is not guaranteed on any certain frequencies. Previously, an off‑the‑shelf spectrum analyzer (which may cost upwards of $10,000) was required to conduct a site survey or spectrum analysis at the installation site of the wireless equipment. Now integrated on all Ubiquiti Networks™ airMAX™ M products, airView™ provides powerful spectrum analyzer functionality, removing the need to rent or purchase additional equipment for doing site surveys.
Requirements
- Ubiquiti M-series device running airOS v5.2 or higher. We recommend staying with the current version, downloadable here.
- Java VM version 6 or higher installed. (Java 7 recommended).
- PC or Laptop configured to access the unit.
How to Use airView to Find the Best Channel
1. To access the airView utility, log in to the device in question. Do so by entering the device's IP address in the browser bar. By default, the IP address is 192.168.1.20.
2. Click the Tools dropdown menu and select airView.
3. A pop-up window will appear, with a warning that states that by launching airView, all wireless connections will be terminated for as long as the program runs. To agree, press the Launch airView button. If you do not see this window, make sure you have pop-ups enabled on the browser and try again.
It is not recommended to run airView on airMAX M-series Access Points with connected Stations, since any all connections will be dropped as long as airView is active. Unlike with AC & later devices, M-series devices do not have a dedicated airView chipset, and therefore must use the same data radio to analyze the spectrum. Furthermore, it may take up to 30 seconds to switch to the previous wireless mode once airView is closed.
Note: You cannot run airView remotely on a wirelessly-connected radio, since the program will terminate the device’s wireless connections.
4. Open and run the airview.jnlp file.
5. Inside airView, you will see three charts which are explained in more detail in the airView Graphs section below.
6. Allow airView to gather sufficient information from the radio spectrum (the beam to be analyzed depends on the type of antenna the device has. For example, if you are using a Bullet M2HP with an Omni-directional antenna, then airView will gather and show energy levels from all directions. On the other hand, if you are using a NanoBridge M5 or NanoStation M2, then airView will only gather data from zone that the antenna can "hear"—the beam width of the antenna. Wait for at least 5 minutes for the data gathering before continuing with the analysis.
7. Analyze the graphs provided. What graphs are analyzed will vary from scenario to scenario and will also depend on the personal preference of each user. In general, for basic analysis, the more commonly used graphs are the Waterfall and Waveform charts. The key parameter in the Waterfall chart is the power (dBm) across the frequency spectrum; in the Waveform chart, the key is the relation between Power Level and number of hits.
For better understanding, see this screenshot of airView in bands 4.9GHz to 6.4GHz: 
As you can see in the first chart (Waterfall), there is a zone between the 5400MHz and 5500MHz that appears to be more crowded, with a signal strength approximately between -84 and -70dBm. In reality, this band isn't very crowded; the information on this chart simply means you could use any of these frequencies (respecting any restrictions set by your local authority).
Note: Usually, frequencies between 5180MHz and 5320MHz, 5745MHz and 5825MHz are allowed for unlicensed use. However, you should check the regulatory information for your country.
Now let’s take a look at this frequency: 2405MHz to 2475MHz.
As you can see in the screenshot above, the frequency range between 2425MHz and 2450MHz has peak energy (noise) reaching levels as high as -23dBm. When planning a 2.4GHz WLAN in this area, you should avoid using channel 6. You should use channel numbers 1 or 11 in case of 20MHz channel width. Should you have a crowded spectrum with only a small, less noisy area, like for example 2455MHz to 2470MHz, to avoid interferences you may select a channel width of 10MHz for your network.
Note: Standard Wi-Fi devices only operate in 20MHz channel width, without channel shifting.
Let’s take a look again at the previous screenshot, with frequencies between 4.9GHz and 6.4GHz; in the Waveform view you can see two significant zones with higher energy levels near 5GHz and between 5400MHz and 5500MHz. Even though in 5400-5500MHz there is a lesser number of hits, these hits are very strong. If you want to use this band, try to select a frequency (you legally are allowed to) with lesser energy levels. Should you have frequencies with nearly the same power level, then give preference to those with a lesser number of hits.
Note: Make sure the AP and all the Stations use the same Channel width and Channel Shifting parameters. Otherwise, no connection between AP and Stations can be established.
airView Graphs
Waterfall View
This is a time-based graph showing the aggregate energy collected over time for each frequency while airView has been running. The color of energy designates its amplitude: colder colors stand for lower energy levels (with blue representing the lowest levels) at that frequency bin, whereas warmer colors (like yellow, orange or red) mean higher energy levels at that frequency bin.
The Waterfall View's legend (top-right corner) provides a numerical guide associating the various colors to power levels (dBm). The low end of that legend (left) is always adjusted to the calculated noise floor, and the high end (right) is set to the highest detected power level since the start of the session.
Channel Usage View
In this graph, each 2.4GHz (or 5GHz for M5-serie devices) Wi-Fi channel is represented by a bar displaying a percentage showing the relative "crowdedness" of that specific channel. This percentage is calculated by analyzing both the popularity and the strength of RF energy in that channel since the start of the airView session.
Waveform View
Like the Waterfall view, this is a time-based graph showing the aggregate energy collected for each frequency over time while airView has been running. The color of the energy designates its amplitude: colder colors stand for lower energy levels (with blue representing the lowest levels) at that frequency bin, whereas warmer colors (like yellow, orange or red) mean higher energy levels at that frequency bin.
The spectral view over time will essentially display the steady-state RF energy signature of a given environment.
Real-time View
This graph displays a traditional Spectrum Analyzer in which energy (in dBm) is shown in real time as a function of frequency. There are three traces in this view:
- Max Hold: updates and holds maximum power levels across the frequency since the start of the airView session.
- Average: shows the running average energy across frequency.
- Real-time: shows the real-time energy seen by the airView device as a function of frequency.