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Determining the best channel using AirView

This guide will explain how to determine the best channel configuration for your wireless network using the built-in AirOS v5.2.AirView Spectrum Analyzer utility.

Traditionally, when users or installers select which channel to use, they run a Site Survey utility. Indeed, it is very useful, but has various limitations, including, but not limited to, these ones: a) Site Surveys don’t offer graphs for easy and quick analysis of spectrum crowdedness. b) Only other 802.11bgn (for 2.4GHz devices) or 802.11an (for 5GHz devices) networks appear in the Site Survey, excluding cordless phones, Bluetooth, and proprietary protocols using these bands and any other source of interference from non-802.11 devices. When using a spectrum analyzer, you may determine with much more information, which is the best channel and width to be selected in your existing or new wireless deployments, avoiding interference and improving data throughput and reliability.

The examples and pictures are based on a NanoStation M2 and M5; in any case, the procedure is the nearly the same for all M-series devices.

Requirements:

• Ubiquiti M-series device running AirOS v5.2 or higher
• Java VM version 6 or higher installed.
• PC or Laptop configured to access the unit (check this external link)

Steps

• To access the AirView utility, login to the device. You can do that by entering your device’s IP address in your Web Brower’s address bar. (By default, the IP address is 192.168.1.20).
• Go into the “Tools” menu and select “AirView”.
• A Pop-up window will appear, it alerts that when launching AirView, all wireless connections will be terminated for as long as the program runs. To agree, press the “Launch AirView” button.

Note: It’s extremely recommended not to run AirView in Access Points with stations associated, because all your clients will be disconnected for as long as AirView is running. It takes up to 30 seconds to switch into the previous Wireless mode, once AirView is closed. AirView cannot be run in a wirelessly accessed Station (or Station WDS), since the program will terminate the device’s wireless connections.

• Open and run the “airview.jnlp” file.
• Inside AirView, you have the following charts: a) Waterfall or Channel Usage chart, b) Waveform chart and c) Real-time chart.

Waterfall chart: 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 chart: 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 an AirView session.

Waveform chart: Like the Waterfall chart, this 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 chart: 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 - this trace will update and hold maximum power levels across the frequency since the start of an 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.

• Allow AirView to gather sufficient information from the radio spectrum (the beam to be analyzed depends of the type of the device’s antenna(e), 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”, it is the beam width of the antenna. Let pass at least some minutes, 5 minutes is a good time for usual situations, to recover data before doing the analysis.

• Now you should analyze the information shown in the graphs. In my personal opinion, for a basic analysis, the more important information 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 with more crowdedness, with a signal strength of approximately between -84 and -70dBm), than in the average spectrum. Actually, this band isn’t very crowded; it simply means you could use any of these frequencies, solely limited by the restrictions of 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, there is a zone between 2425MHz and 2450MHz that is extremely crowded, with energy levels of up to -23dBm. In this scenario, if planning to deploy a 2.4GHz network, you should avoid using channel 6, or channels near to 6. You should use channel numbers 1 or 6 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 are 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 prefer the ones with a lesser number of hits.

• Finally, once you have decided which frequency and channel width to use, close AirView, wait some seconds while the device comes back into standard Wireless mode. Then go to the Wireless tab. Specify the channel width to use. Enable channel shifting only if it is needed, and select the frequency to use. Subsequently, press the Change button. After a few seconds, an alert on the top of the page will appear. Finally press the Apply button to apply the changes.

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.