Site Surveying and Installation
This domain tests how a WLAN is designed, surveyed, installed, and documented. Questions cover requirement gathering, predictive and on-site surveys, spectrum analysis, AP placement, cabling, mounting, and validation.
Survey and design rules
- Start with requirements: coverage areas, capacity and client density, applications, security, roaming, budget, and aesthetics. Coverage and capacity are different goals; high-density venues need more APs and careful channel reuse.
- A predictive (desktop) survey models walls and attenuation before equipment is installed. A passive survey listens to existing APs; an active survey associates a client and measures throughput, retries, and roaming. A validation survey confirms the installed design.
- Use a spectrum analyzer to find non-Wi-Fi interference. Use survey software with a floor plan to record RSSI, SNR, noise, and data rates. The AP-on-a-stick method tests a proposed AP location before mounting. Document AP locations, channels, power settings, and the bill of materials.
- In 2.4 GHz, use non-overlapping channels 1, 6, and 11 where allowed. In 5 GHz, prefer 20 or 40 MHz channels and avoid DFS problems if clients or radar are present.
- Mount APs below the ceiling or on ceiling tiles, away from metal, elevators, and dense shelving. Keep 60% of the first Fresnel zone clear for long point-to-point links, and account for cable loss and connector loss.
Worked example
A survey shows -67 dBm at the aisle end and a noise floor of -92 dBm. SNR = 25 dB, which meets a common voice target and is strong for data. If a second AP on channel 6 overlaps the first AP's channel 6 coverage, co-channel interference is the issue, not insufficient signal. Validation should include roaming and capacity tests, not only RSSI.
Traps
A heat map from a predictive survey is not proof of performance. A passive survey cannot measure client roaming or uplink. Do not design only for RSSI while ignoring SNR, capacity, and interference.