Wi-Fi design for SMEs: why more access points make it worse

Wi-Fi is a shared, half-duplex medium governed by contention. Adding radios on overlapping channels does not add capacity — it adds interference. Most SME wireless problems we are called in for are self-inflicted by well-meaning expansion.

Design for capacity, not coverage bars

Start from device count and application profile, not floor area. Thirty laptops on video calls in an open-plan office is a capacity problem; a warehouse with ten handheld scanners across 4 000 m² is a coverage and roaming problem. The two designs look nothing alike.

The numbers that matter

• Target -65 dBm RSSI at the client for reliable data, -67 dBm for voice
• Keep co-channel interference below -85 dBm on the primary channel
• Signal-to-noise ratio of 25 dB or better in every working area
• Aim for one primary 5 GHz cell per working zone — not per ceiling tile

Turn the power down

Access points shipped at maximum transmit power create huge cells that all hear each other. Reduce 2.4 GHz power hard (or disable the band where legacy devices allow), keep 5 GHz cells tight, and let clients roam between smaller, cleaner cells.

Channel planning beats auto-RF

Automatic channel selection is a fallback, not a design. Use 20 MHz channels in dense environments, 40 MHz where you have spectrum to spare, and reserve 80 MHz for low-density executive areas. In 2.4 GHz there are only three non-overlapping channels: 1, 6 and 11.

The wired side decides the wireless experience

• Cat6/6A cabling, certified and labelled — untested cable is a future outage
• PoE budget headroom on switches, with UPS backing
• A VLAN per purpose: staff, guest, IoT, CCTV, voice
• Firewall policy between those VLANs, not just between LAN and WAN

Validate, then document

A predictive design is a hypothesis. Walk the site after installation with a survey tool, confirm RSSI, SNR and roaming behaviour under load, then hand over heat maps and an AP placement map. When something changes six months later, that document is what stops the guesswork.

• #Wi-Fi
• #SME
• #Site Survey
• #Design