Site Survey Tool - TamoGraph

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System Requirements
Driver Installation
Licensing and Trial Version Limitations
Interface Overview
Access Point List
Floor Plan / Site Map
Plans and Surveys, Properties, and Options Panel
Main Menu
Performing a Site Survey
New Project Wizard
Data Collection
Understanding Survey Types: Passive, Active, and Predictive
Active Survey Configuration
Best Practices, Tips, and Tricks
Survey Job Splitting
Predictive Surveys
Drawing Walls and Other Obstructions
Drawing Attenuation Zones
Placing and Configuring Virtual APs
Working with Presets
Applying Visualizations
Working with Multi-floor Sites
Mixing Real and Virtual Data
Best Practices, Tips, and Tricks
Analyzing Data – Passive and Predictive Surveys
Selecting Data for Analysis
Adjusting AP Locations After Passive Surveys
Splitting an AP into Multiple Unique APs
Working with Multi-SSID APs
Visualization Types
Signal Level
Signal-to-Noise Ratio
Signal-to-Interference Ratio
AP Coverage Areas
Number of APs
Expected PHY Rate
Frame Format
Channel Bandwidth
Channel Map
Analyzing Data – Active Surveys
Selecting Data for Analysis
Visualization Types
Actual PHY Rate
TCP Upstream and Downstream Rate
UDP Upstream and Downstream Rate
UDP Upstream and Downstream Loss
Round-trip Time
Associated AP
Spectrum Analysis
Hardware Requirements
Spectrum Data Graphs
Performing Spectrum Analysis Surveys
Viewing Collected Spectrum Data
Exporting Spectrum Data
Reporting and Printing
Customizing Reports
Google Earth Integration
Configuring TamoGraph
Plans and Surveys
Plan / Map
Client Capabilities
Colors and Value Ranges
AP Detection and Placement
Visualization Settings
Configuring GPS Receiver
Using GPS Configuration Dialog
Finding the GPS Receiver Port Number
Taking Photographs
Voice Control
Using TamoGraph in a Virtual Machine
Frequently Asked Questions
Sales and Support

Signal-to-Interference Ratio

This visualization shows the signal-to-interference ratio (SIR) measured in dB. SIR is a measure to quantify by how much the signal level of an AP (interfered AP) exceeds the interference level. The interfering signal is the signal being transmitted by other APs (interfering APs) that may or may not belong to your WLAN and that use the same or one of the adjacent 802.11 channels. In low SIR zones, client devices may experience low throughput. SIR is shown for the AP that experiences the worst interference in the given map area among the APs selected for analysis. You can deselect one or several of the selected APs to see SIR values for the APs that experience less interference.

Selecting one AP at a time for SIR analysis is recommended because this produces a clearer picture. You should isolate AP-specific problem zones by selecting your APs one by one. Working with a cumulative picture, displayed when multiple APs are selected, is more difficult.

SIR is best illustrated with an example. Consider an area where the AP signal strength is -50 dBm, and the AP works on channel 1. In the same area, a -70 dBm signal from another AP that works on the same channel can be seen. If WLAN utilization is 100% (i.e., if the APs send radio waves all the time), the SIR value would be 20 dB. However, real-world WLAN utilization is almost never that high, which decreases the interference and increases SIR. If the interfered and interfering APs have the same signal strength, the SIR value would be 0 dB. In classical, non-digital radios, a SIR value of 0 dB makes signal reception impossible, but 802.11 devices use a technology that allows them to operate despite a zero or even negative SIR value, which sounds counterintuitive.

Simply put, if an AP is not heavily loaded, it transmits just a few hundred packets per second. If a nearby AP working on the same channel also transmits a few hundred packets per second, the transmissions “collide” very infrequently, thus resulting in virtually zero interference. The average network utilization that is used for SIR computations is a configurable option (see below).

Interference is highest when the interfered and interfering APs work on the same channel. In the 2.4 GHz band, where channel frequencies overlap, adjacent channel interference is still substantial when the interfered and interfering APs are one and two channels apart and becomes virtually non-existent when they are five channels apart. In the 5 GHz band, there is no adjacent channel interference. Many 802.11n and 802.11ac devices use channel bonding, i.e., two 20 MHz channels for 802.11n and up to eight 20 MHz channels for 802.11ac at the same time. For example, channel 11 might be used as the primary channel and channel 6 as the secondary one. In these cases, TamoGraph factors in interference on non-primary 802.11n or 802.11ac channels, if any. It should also be noted that when visualizing SIR, the application takes into consideration interfering signals from all APs, regardless of whether they are selected in the AP list. The application also detects multi-SSID APs and does not consider separate different SSIDs with different MAC addresses of the same AP as sources of interference with each other (see Working with Multi-SSID APs for more information).

The following options on the Visualization Settings panel (located on the Options tab of the right-side panel) affect the way SIR is analyzed:

· Area is considered covered if signal strength is at least – This setting defines the AP coverage area based on the minimum signal strength. If the signal strength is below the specified level, the area is considered to be not covered, and no SIR values will be computed for the area (such areas will appear as white spots). This improves the SIR visualization clarity: In low signal areas, SIR is almost always very low, but such areas should not distract your attention, as they cannot ensure good connectivity or throughput anyway.
· Average network utilization – This setting defines how heavy the interference is from the interfering APs. If the interfering signal strength is high, but the network utilization is low, the interfering AP does not create much interference. A typical office WLAN has a network utilization of between 10% and 25%. Adjust this setting to match the actual value for your WLAN.

Double-clicking on the SIR legend on the status bar allows you to configure the color scheme and change its value range.

Suggested Solutions

Low SIR areas are not uncommon in WLANs. The presence of such areas does not necessarily mean that the WLAN will suffer from low throughput. However, if such zones cover most of your site and are located close to APs, corrective actions should be taken. When low SIR areas are discovered, the following solutions are suggested:

· Change the channel selection. APs working in close proximity should never use overlapping channels. Consider the classical “honeycomb” AP placement, if possible. Note that in some 802.11n equipment, the position of the secondary channel (below or above the primary one) is a user-configurable option, which gives you an additional degree of freedom.
· If you experience low SIR values in the 2.4 GHz band, consider switching your APs to the 5 GHz band, where there are more non-overlapping channels from which to choose. If you use an 802.11n AP with 40 MHz bandwidth in the 2.4 GHz band, you have virtually no way of avoiding interference. For example, if the primary channel is set to 1, the secondary channel is set to 5. In the United States, where there are eleven channels in the 2.4 GHz band, all you can do is configure the next AP to work on the primary channel 11, the secondary being 6. As a result, the secondary channels would be only one channel apart, which may result in high interference. If channel bonding is not used (i.e., a single 20 MHz channel), you have three non-overlapping channels from which to choose: 1, 6, and 11. This is illustrated in the image below.