// reference · site survey · cwna ch.12
WLAN Site Survey Methodology
A site survey is the process of gathering RF data to plan or validate a WLAN deployment. Done properly, it prevents coverage gaps, co-channel interference, and surprise failures. Skipped, and you're fixing the same problem after the users complain. Source: Cisco site survey guidelines, Ekahau methodology, CWNA-109 study guide.
// three survey types
Passive Survey Pre- or post-deployment
The survey client is in listen-only (monitor) mode. It never associates to any AP. It simply captures beacons and any 802.11 frames it can hear. Records RSSI, channel, SSID, BSSID, noise floor.
Measures
✓ AP discovery (who is broadcasting where)
✓ RF coverage heatmap from AP beacons
✓ Rogue AP detection (unexpected BSSIDs)
✓ Co-channel interference mapping
✓ Noise floor measurement per channel
Cannot measure
✗ PHY rate negotiation (no association = no data frames)
✗ Uplink performance (cannot measure client-to-AP signal)
✗ Retransmission rate
✗ Actual TCP/UDP throughput
When to use
Pre-deployment assessment of existing RF environment. Rogue AP hunting. Verifying coverage footprint after deployment. No disruption to users.
Active Survey Pre- or post-deployment
The survey client associates to each AP as it moves through the area. It generates actual 802.11 data traffic (ICMP pings, UDP probes) and measures real link performance. The most comprehensive survey type.
Measures
✓ Everything passive gives you
✓ Actual PHY rate boundaries per location
✓ Uplink and downlink performance
✓ Retransmission rates under real load
✓ SNR measurement (not just RSSI)
✓ TCP/UDP throughput tests
Cannot measure
✗ Work without APs deployed (need something to associate to)
✗ Assess RF environment before any APs exist
When to use
Post-deployment validation. Troubleshooting complaints. Vendor comparison testing. Certifying a deployment meets SLA requirements.
Predictive Survey Pre-deployment
Software-based simulation. Import a floor plan, specify wall materials and thickness, place virtual APs, and the tool models expected RF coverage using propagation algorithms. No walking required. No APs needed.
Measures
✓ AP placement planning before APs are purchased
✓ Coverage estimation for buildings under construction
✓ Fast design iteration without physical changes
✓ Multi-floor propagation modeling
Cannot measure
✗ Account for unknown RF absorbers (furniture, people, equipment)
✗ Replace active validation after deployment
✗ Accurately model metal elevator doors, glass with metallic coating, unusual materials
When to use
New building deployments. Pre-deployment AP count estimation. Customer proposal RF design. Always follow with active validation after deployment.
// coverage design thresholds - cell edge targets
| Application | Min RSSI | Min SNR | Cell overlap | Notes |
|---|---|---|---|---|
| VoIP / Voice over Wi-Fi | -67 dBm | >25 dB | 20% | Tightest requirement. Cell overlap needed for BTM/FT roaming without call drop. |
| Video streaming / Zoom | -70 dBm | >20 dB | 15-20% | Similar to voice. Jitter-sensitive - SNR matters more than raw RSSI. |
| Data / General enterprise | -70 dBm | >20 dB | 15% | Standard office coverage design target. MCS 6+ capable at cell edge. |
| IoT / sensors / scanners | -72 dBm | >15 dB | 10-15% | Lower throughput requirement. May tolerate -75 dBm if retry-tolerant. |
| Minimum viable signal | -82 dBm | >10 dB | N/A | BSS floor - below this = no association. -82 dBm = BPSK MCS 0 sensitivity. |
// ap on a stick (apos)
A pre-deployment active survey technique. Mount a temporary AP on a tripod at proposed AP locations (cable drops). Walk the intended coverage area while associated to the temporary AP. Measure actual RF propagation with real AP hardware before committing to AP placement.
When to use:
New building with cable drops already run. Validating a predictive design before purchasing APs. When material attenuation is unknown and predictive tools would be unreliable.
// site survey workflow
1. Customer briefing
Understand application requirements (voice, data, IoT). Confirm coverage areas. Gather floor plans.
2. Pre-survey passive
Map existing RF environment. Find rogues. Identify interference sources.
3. Predictive design
Model AP placement in Ekahau or similar. Estimate AP count.
4. APoS validation
Physical test at proposed AP locations. Confirm coverage before final cable runs.
5. Deployment
Install APs at confirmed locations. Configure channels and power.
6. Post-deployment active
Walk the space with APs deployed. Confirm RSSI/SNR at cell edge. Fix gaps.
Validate survey findings with your PCAP
WiFi Analyser shows per-client RSSI, retry rate, and roaming events - the PCAP view of what your site survey predicts.