Review: TamoGraph Site Survey 2.0 - Page 3

By Lisa Phifer

February 14, 2011

After APs are selected, TamoGraph displays its analysis in the center panel. Given sufficient signal and data, TamoGraph can auto-place APs on the floorplan or map. Alternatively, you can drag APs to their actual location to improve analysis. The more data we collected, the better TamoGraph was at auto-placement - although it put one high-powered neighbor in the middle of our building. (In general, neighbor APs should be deselected to focus analysis on your own APs.)

TamoGraph then generates color-coded heatmaps, corresponding to selected "visualizations."

  • Signal Level (Coverage) Heatmap: Depicts measured/extrapolated signal strength. By default, TamoGraph considers anything above -60 dBm excellent; below -85 dBm marginal. But you can click on the status bar to change nearly any map's range or color scheme.
  • Signal to Noise (SNR) Heatmap: Quantifies the extent to which signal exceeds background noise. For example, if RF noise measured at a given point is -90 dBm and signal is -50 dBm, SNR is an excellent 40 dB. Low SNR can be caused by RF interferers. Some common interferers are easily guessed, but tough cases may require spectrum analysis.
  • Signal to Interference (SIR) Heatmap: Quantifies the extent to which an AP's signal exceeds co-channel interference generated by nearby Wi-Fi APs. TamoGraph offers two parameters to tweak this map: the minimum signal which defines each AP's coverage (determines area of overlap) and average utilization (determines low SIR impact).
  • AP Coverage Areas: Depicts the RF footprint of each selected AP, based on configurable minimum signal strength. This makes it easy to visualize overlap, although we found it helpful to select just a few APs at a time (e.g., by choosing one SSID for APs that beacon many SSIDs). TamoGraph can also display a count of the APs covering each area.
  • Expected PHY Rate Map: Uses AP capabilities and SNR to estimate the PHY rate of the strongest AP in each mapped area. We found this map misleading because it assumes that AP and client capabilities are equal. In reality, clients are often less capable, reducing negotiated upstream/downstream PHY rates. Furthermore, survey adapter selection can artificially cap measured PHY rates far below an AP's maximum.
  • Frame Format and Channel Bandwidth Maps: Shows whether Non-HT, HT-Mixed, or HT-Greenfield frames and 20/40 MHz wide channels are used by the strongest AP in each mapped area. We found this useful to spot areas impacted by neighboring legacy APs.

Finally, the single-most insightful map produced by TamoGraph is called Requirements (below). This visualization highlights any mapped area that fails to meet project specs. Although we skipped right over this earlier, every project is actually created with default minimum requirements for signal, SNR, SIR, PHY rate, AP count, channel width, and frame format.

TamoGraph offers three predefined specs - basic, medium, and advanced - that can be customized and saved to reflect your site's needs. For example, "advanced" requires redundant, high-throughput connectivity - any area with low PHY rate or less than two APs will be shaded to reflect this shortfall. The Requirements map is effectively a "roll up" of all other TamoGraph maps, which we found useful to spot problem areas to be investigated with other heatmaps.

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