How to plan a Wi-Fi deployment: Performing a manual site survey
In this series, we are looking at the process of determining what you need in your WLAN network
This blog is the final post in a 3-part series summarizing how to deploy Wi-Fi up to the point where you have gathered network needs and assessed RF environment conditions.
By performing predictive site surveys using a Wi-Fi planning tool, you can develop a good idea of where to place APs and what power levels to set to meet the coverage and capacity requirements learned during the interview stage. However, a predictive site survey, discussed in my last post, cannot cover the existence of neighboring WLANs, which can create adjacent and co-channel interference, and the existence of electromagnetic signals from nearby non-Wi-Fi devices, which can raise the noise floor, affecting the SNR of devices on the WLAN. To learn about these RF signals, you need to perform a manual site survey that includes spectrum analysis.
By going on site and conducting a manual real-time survey, you can verify the accuracy of the predictive survey when applied within the architectural and RF environments where the APs will operate. You can then make whatever adjustments are necessary to realize your WLAN design goals and deliver a wireless solution that meets the level of service required.
Here are a couple of useful points to keep in mind when doing a manual site survey:
For data services, design the WLAN so that the communicating wireless devices have a minimum RSSI (received signal strength indicator) of -70 dBm and an SNR of 20 dB or higher. For a WLAN supporting voice and video, implement a design in which the RSSI is at least -67 dBm with an SNR of 23 dB or higher.
Ideally, a client should be able to detect a signal of -70 dBm or better from one AP and another signal of -75 dBm or better from one or more others. The client connects to the AP with the better signal first, and then if it moves closer to a different one, it can roam to that AP when its signal grows stronger than that of the first one. If a client can detect very strong signals from several APs, too many have been deployed or they are transmitting too powerfully. To correct this situation, you can reduce the number of transmitting APs or lower their Tx power.
The following are some popular tools for conducting manual site surveys and spectrum analysis (they also provide excellent predictive site survey tools as well):
- Ekahau Site Survey and Ekahau Spectrum Analyzer
- AirMagnet Survey - a site survey tool that can integrate with AirMagnet Wi-Fi and spectrum analysis tools; the PRO version includes a built-in planner
- TamoGraph Site Survey - integrates with the MetaGeek Wi-Spy spectrum analyzer
From this point, you have enough information to begin designing the wireless network to meet users’ needs within the RF environment where the devices will be deployed.
All Posts In This Series: