Wireless Design and Site Survey Concepts
Start with the requirement
Design begins with a business requirement, and the first fork is coverage-driven versus capacity-driven. Coverage designs (warehouses, outdoor yards, sparse IoT) use fewer APs at higher power. Capacity designs (offices, lecture halls, auditoriums) use more APs at lower power so cells stay small and airtime is reused. For high density, plan roughly 25–30 clients per radio for data, fewer where voice or video dominates.
Survey types and what each proves
- Predictive (virtual): software model from floor plans and attenuation values; no hardware on site.
- Passive: a listening adapter records RF coverage; it proves nothing about client behavior, throughput, or roaming.
- Active: a real client associates and measures throughput, DHCP, authentication, and roaming.
- AP-on-a-stick: a temporary AP is placed at candidate locations and validated before permanent mounting.
- Validation (post-deployment): confirms the installed network meets the design.
Traps: a passive survey cannot validate roaming or application performance; a predictive survey never replaces validation; AP-on-a-stick is a survey technique, not an AP operating mode.
Design targets
- −67 dBm RSSI for data and voice coverage; −65 to −60 dBm where real-time voice matters.
- 25 dB SNR minimum; 20 dB is marginal.
- 15–20% cell overlap for data, more for voice and fast roaming.
- Prefer 5 GHz/6 GHz as the primary band; keep 2.4 GHz at 20 MHz for IoT and legacy.
Rule of thumb: if you remember only two numbers, remember −67 dBm coverage and 25 dB SNR as the design floor, with 20 MHz channels at 5 GHz.