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Auto TX Power

Auto TX (Transmit) Power is part of the Cisco Meraki Auto RF feature set which is designed to provide zero-touch optimization of wireless networks for high density environments. Specifically, Auto TX leverages the Cisco Meraki Cloud to manage radio transmit power on AP's in order to optimize coverage cells for roaming. As the wireless environment changes, radios on the AP's can adapt accordingly without the need for an onsite wireless controller. 

Auto TX Overview

Each AP (Access Point) samples the signal-to-noise (SNR) of neighboring AP's which reside in the same Dashboard network. All radios on an AP can perform the sampling. The SNR readings are compiled into neighbor reports which are sent to the Cloud for processing. The Cloud aggregates neighbor reports from each AP. Using the aggregated data, the Cloud can determine AP's direct neighbors (neighbors that a client might directly roam too) and how much each AP should adjust radio transmit power so coverage cells are optimized. Once calculations are complete, the Cloud instructs each AP to decrease, or in some instances increase, transit power to reach an optimal power level. The Auto TX process is performed every 20 minutes for each AP in the Dashboard network on both 2.4GHz and 5GHz radios.  

Real-time Auto TX Process

This example demonstrates the process, with a Dashboard network containing 4 APs with overlapping coverage.

 

  1.  Each AP will sample the SNR of its neighbors and compile the readings into a neighbor report to be sent to the Cloud.
  2. The Cloud requests the neighbor report from each AP in the Dashboard network.
  3. Once the Cloud has the neighbors reports from each AP, it aggregates these reports and determines each AP's direct neighbor(s) and how much each AP should adjust their transmit power to achieve optimal coverage overlap. If necessary, the Auto TX algorithm will lower the transmit power of each AP within a range of 1dB-3dB or increase the transmit power 1dB per iteration. The target being 30 SNR for an AP's strongest direct neighbor but never less than 17dB SNR for an AP's weakest direct neighbor. Reducing transmit power too much with weak neighbors present could cause a hole in coverage.
  4. Once transmit power levels have been calculated, the Cloud iterates through each AP in the Dashboard network, instructing them to decrease or increase their transmit power. If the target SNR is already met, no transmit power adjustment is needed.
  5. This process is repeated every 20 minutes on each AP in the Dashboard network.

Opportunistic Auto TX

At this time the new Auto TX algorithm is available only to devices with a 3rd radio (Ex. MR18, MR34, etc.), other devices will use the opportunistic Auto TX algorithm. This algorithm uses a different metric set to determine the appropriate power level, given that the AP does not have real-time visibility of neighboring APs. Because information is collected over a longer time period and there is limited visibility to other APs, the resulting power level may be higher than optimal.

Mesh awareness

The steady state algorithm is mesh aware and will not adjust the power of a AP's radio that is serving mesh repeaters. Radios on an AP that are acting as a gateway for an active mesh repeater will not change TX power. 

 

Determining Auto TX Effectiveness

It is possible to determine if the Auto TX algorithm has adjusted the transmit power of APs by looking at the transmit power values on the Radio settings page. If an adjustment has been made, an AP's radio will show the current transmit power in the form of XdBm(Auto). In order to determine the effect Auto TX is having on the wireless network, a base line site survey needs to be compared to a site survey taken after Auto TX is enabled. Prior to enabling Auto TX, take a site survey of the entire wireless network. Once Auto TX is enabled, wait 24 hours and perform another site survey. Compare the signal strength, coverage areas, and channel overlap of both surveys to determine the effect Auto TX makes on the wireless environment.

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Last modified
15:29, 30 Mar 2017

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ID: 1562

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