Wi-Fi Channel Analysis
Traditionally, tools such as RF spectrum analyzers have been used to diagnose wireless network performance issues. These tools help identify the amount of noise in an RF band, the physical sources of these undesirable emissions, and assist in the configuration of a WiFi network for optimal performance. However, historically these tools are expensive, require highly trained technicians to operate effectively, and are not optimized for the particular requirements of packet data-oriented 802.11 networks. Additionally, removing the source of interference is not realistic in most office or home environments; users are neither willing to give up their mobile phones, office microwave, nor their wireless security system for network management purposes.
Nuts About Nets realized the challenges of WiFi network performance required a new approach. Rather than build on traditional RF-based tools, the company invested research and development efforts pioneering native solutions using the 802.11 protocol itself. The company felt that focusing on channel selection, an intrinsic and essential component of managing a WiFi installation, was the right area to analyze and optimize — hence, WiFi channel analysis was born.
|WifiEagle Channel Analyzer|
The technology behind WiFi channel analysis is called Indirect Measurement of Microwave Interference, or IMMI for short. This set of algorithms and analysis techniques uses the best features of traditional RF spectrum analysis in that it jumps directly to the end-game of performance tuning, i.e. how to choose the best 802.11 channel for an optimum user experience. The key insight for IMMI is it can use the features of the 802.11 protocol and the underlying 2.4/5Gz physical radio to gather RF data from the ambient environment, and correlate this information with the performance of the wireless device. This approach eliminates the need for a separate device to conduct spectrum analysis, and properly moves the domain of analysis from complex RF energy issues to the area where the 802.11 administrator can effect: choosing the best available bandwidth slice — that is, the best WiFi channel.
IMMI computes the available bandwidth of each 802.11 channel by measuring the amount of interfering RF energy on each channel’s underlying 2.4/5Gz frequency spectrum. These measurements are carried out indirectly using the available 802.11 radio on a device (wireless laptop, access point, WiFi-enabled mobile phone), rather than a separate probe. The algorithm utilizes the CSMA/CA layer from the 802.11 standard to measure the time delay a packet is subjected to on a given channel. This delay is a direct, 802.11 centric view of the congestion of the underlying RF spectrum, whether from other 802.11 traffic or general noise on the 2.4/5Gz environment. IMMI does not require additional computations to quantify the type of RF noise and its potential impact; rather, it jumps right to the answer.
A WiFi channel analyzer is the only product on the market that can rank 802.11 channels using a performance metric. This is because it employs an 802.11 device to make the measurements. By virtue of the fact a channel analyzer views the RF world through the eyes of an 802.11 device, then the diagnostic information it provides more closely mirrors the performance you can expect from your own 802.11 devices.
|Spectrogram chart from WifiEagle Channel Analyzer. The RF signal is generated by AirHORN.||Spectrum trace from AirSleuth 2.4 GHz RF spectrum analyzer. The RF signal is generated by AirHORN.|
The two charts above help to illustrate the difference between IMMI and spectrum analysis. Using AirHORN as a source of RF transmission, snapshots of the acquired data were then taken from WifiEagle and AirSleuth. WifiEagle uses IMMI technology, whereas AirSleuth is an RF spectrum analyzer. The data presented by the IMMI tool displays available throughput performance, channel-by-channel. We clearly see which channels are affected by the RF interference generated by AirHORN. Furthermore, the difference between channels is quantifiable. The spectrum trace on the right is also informative — it tells us there is a spike of RF interference centering around the frequency of 2437 MHz. However, we have no way of translating this RF measurement to something meaningful and quantifiable in the 802.11 world. And, again, that's because an instrument that only measures RF energy operates at a level below the 802.11 standard.
Optimal Channel Selection vs Tracking Sources of Interference
If your goal is to hunt down interfering wireless devices, then an RF spectrum analyzer is still the tool of choice. But consider this — it turns out in practice most WiFi problems are solved by changing to a better channel. This is because: (a) the interfering device may belong to someone else and you have no control over it; (b) the interfering device may be perfectly legitimate in its own right (e.g. a wireless security system); (c) it is time-consuming and challenging to track down the source of interference — RF waves bounce off of walls and objects, making it difficult to determine from which direction the source actually emanates. When your goal is reformed to one of simply determining the best WiFi channel under the current conditions, then a WiFi channel analyzer is a better choice.