WiFi Installer Handbook

Do not design WiFi from floor area alone

Square metres can help with a budgetary starting point, but they do not describe walls, shelving, ceiling height, device capability, user density, application requirements, interference or the RF behaviour of the building. A reliable design begins with requirements and a survey model, not an AP-per-area formula.

Requirements before RF design

• Applications: ordinary data, voice, scanners, real-time systems, guest access or location services.
• Client types and their supported bands, channel widths and transmit power.
• User/device density and expected concurrency.
• Coverage areas, roaming paths and areas that deliberately do not require service.
• Available Ethernet uplinks and PoE at proposed AP positions.
• Mounting restrictions, ceiling construction and environmental requirements.

RSSI, noise floor and SNR

RSSI describes received signal level. Noise floor describes background energy seen by the receiver. SNR is the difference between useful signal and noise, so a strong RSSI can still produce poor service if the noise floor is also high. The correct target depends on the client and application.

Cisco's site-survey guidance gives a voice example of -67 dBm minimum RSSI and 25 dB minimum SNR for the referenced voice deployment. That is an application-specific design example, not a universal WiFi rule for every network.

Detailed guide: RSSI, SNR and noise floor.

Channel utilisation matters even when your AP is quiet

A channel is shared airtime. Cisco notes that channel utilisation can be high even when a particular AP has few clients because neighbouring networks and non-WiFi interference also consume or block airtime. This is why a speed complaint cannot be diagnosed from RSSI alone.

Channel width is a design trade-off

Wider channels can provide more PHY capacity when spectrum is clean and clients support them, but they consume more spectrum and reduce the number of non-overlapping channel choices. In dense deployments, narrow channels can provide better frequency reuse. The correct choice depends on band, regulatory domain, density, interference and client requirements.

Predictive survey, AP-on-a-stick and validation

Transmit power and client asymmetry

An AP can often transmit more strongly than a handheld client. Cisco specifically warns that a survey can appear to have good downlink coverage while clients struggle to transmit back if the AP power is higher than the client can support. Design should therefore consider the client side of the RF link.

Roaming

Roaming behaviour is influenced by the client. Network features can assist roaming, but the installer should validate the actual device types and applications that matter to the project. Check coverage overlap along real movement paths rather than assuming that two AP circles touching on a plan will produce acceptable roaming.

Wired dependencies

Every AP is also an Ethernet endpoint. Confirm switch-port speed, PoE requirement, VLAN configuration, DHCP/DNS reachability and uplink capacity. A WiFi complaint can originate from the wired network behind the AP, so collect both RF and switch-side evidence.

Post-installation evidence

• Final AP position and mounting orientation.
• AP model, radio configuration and firmware version.
• Channel and transmit power state at commissioning.
• Coverage, SNR and channel-utilisation survey evidence for critical areas.
• Roaming checks for required paths and client classes.
• Switch port, VLAN and PoE mapping for each AP.
• Known interference, coverage exceptions and unresolved defects.

Related resources

Site Survey Centre | Troubleshooting Centre | Wireless products at Server Warehouse | PoE switches