How to Perform Site Surveys
Prepare before walking
Gather requirements first: applications, client types and counts, coverage and capacity targets, roaming needs, security and physical constraints. Obtain an accurate, scaled floor plan - an unscaled drawing invalidates a predictive survey.
Survey types
Predictive (simulation) surveys model attenuation and AP placement before hardware exists; their quality depends entirely on the floor plan and the attenuation values entered. Passive surveys listen to existing APs and show coverage and interference. Active surveys associate with the network and measure real throughput, retries and roaming. AP-on-a-stick is a manual, iterative placement method. Validation surveys confirm the deployed design. Spectrum analysis should accompany any survey to find non-802.11 interference.
Executing the walk
Set AP transmit power and channel plan as they will be deployed, then walk a staggered grid at typical client height, recording RSSI, SNR, data rate, channel overlap and secondary coverage for roaming. For high density, survey at peak client load where possible. Outdoors, use GPS to log positions.
Deliverables
A report with floor plans, AP locations and mounting, channel and power plan, predicted versus measured coverage, interference findings, capacity assumptions and remediation items.
Traps
Surveying with maximum AP power and then deploying lower; surveying before the building is furnished; and confusing coverage verification with capacity verification.
Rule of thumb
Design for −65 to −67 dBm RSSI and 25 dB SNR at the cell edge for voice and high-density data, with a second AP visible at about −70 to −75 dBm for roaming.