Wireless Site Surveys: Planning WiFi Coverage the Right Way
Deploying WiFi without a site survey is like wiring a building without a floor plan — you might get lucky, but you will probably end up with dead spots, interference, and frustrated users. A proper wireless site survey measures the radio environment, identifies obstacles, and produces a data-driven AP placement plan. This guide walks through the types of surveys, the tools you need, and the most common mistakes to avoid.
Why Site Surveys Matter
WiFi operates in shared, unlicensed radio spectrum. Unlike a wired Ethernet port that delivers a dedicated connection, a wireless access point shares its airtime with every client in range. The radio environment is affected by building materials, neighbouring networks, microwave ovens, Bluetooth devices, and even the number of people in a room. A site survey measures all of these factors so you can design a wireless network based on evidence rather than guesswork.
Without a survey, common problems include dead spots where signal does not reach, co-channel interference where too many APs on the same channel compete for airtime, capacity bottlenecks where a single AP is overwhelmed by too many clients, and roaming issues where devices cling to a distant AP instead of handing off to a closer one. A properly executed survey prevents all of these issues.
Types of Wireless Site Surveys
A predictive (virtual) survey is performed in software before any hardware is installed. You import a floor plan, draw walls and assign material types (plasterboard, concrete, glass), place virtual APs, and the software simulates RF propagation to produce estimated heat maps. Predictive surveys are excellent for new construction or fit-outs where physical access is not yet possible. However, they are only as accurate as the wall material data you provide — real-world validation is still recommended after installation.
A passive on-site survey involves walking through the physical space with a laptop or tablet running survey software while it listens to all WiFi signals in the area. The surveyor walks a predefined path, marking their position on a floor plan at regular intervals. The software records signal strength (RSSI), noise floor, signal-to-noise ratio (SNR), channel utilisation, and the number of detected SSIDs on each channel. This approach reveals the actual RF environment, including interference from neighbouring networks that a predictive survey cannot account for.
An active on-site survey goes a step further. The survey device associates with the target SSID and measures real throughput, latency, packet loss, and roaming behaviour as the surveyor walks the site. Active surveys are essential for validating that the deployed network meets performance requirements — for example, confirming that a warehouse WiFi network can sustain the throughput needed for handheld barcode scanners or voice-over-WiFi handsets without dropouts.
For the most accurate results, perform your active survey during normal business hours when the building is occupied. WiFi performance can change significantly between an empty building and one full of people, devices, and moving objects.
Tools of the Trade
Ekahau AI Pro (formerly Ekahau Site Survey) is the industry standard for enterprise wireless surveys. It supports predictive design, passive and active surveys, and produces detailed heat maps and reports. NetSpot is a more affordable alternative suitable for small-to-medium deployments, available on macOS and Windows. For on-site surveys of spaces where APs have not yet been installed, engineers use an AP-on-a-stick — a temporary access point mounted on a tripod or pole, powered by a battery pack. The AP is placed at each proposed mounting location, and the surveyor walks the coverage area to measure real-world signal propagation.
What to Measure
Several key metrics determine whether your WiFi design will succeed. RSSI (Received Signal Strength Indicator) measures the signal level at the client — a minimum of -67 dBm is recommended for reliable data, and -65 dBm or better for voice-over-WiFi. SNR (Signal-to-Noise Ratio) compares the signal to the background noise floor; aim for at least 25 dB for data and 30 dB for voice. Channel utilisation shows how busy each channel is — anything above 50% indicates congestion. Co-channel interference (CCI) occurs when multiple APs on the same channel overlap, forcing them to share airtime and reducing overall throughput.
Remember that RSSI values are negative numbers measured in dBm. A value of -50 dBm is a much stronger signal than -75 dBm. When reading heat maps, green and blue typically indicate good coverage, while yellow, orange, and red indicate weak or marginal signal.
AP Placement Principles
Access points should be ceiling-mounted wherever possible, as this provides the best downward radiation pattern for most omnidirectional antennas. Mount APs in the centre of the coverage area they serve, not against exterior walls where half the signal radiates outside the building. Consider the attenuation of building materials: plasterboard walls may only reduce signal by 3–5 dB, but concrete, brick, and metal stud walls can attenuate 12–20 dB or more. Lift shafts, fire-rated walls, and tinted glass are particularly hostile to WiFi signals.
For density planning, consider not just coverage area but client count per AP. A single AP may cover a large open-plan office in terms of signal, but if 60 users are connected to it, performance will suffer. In high-density environments such as lecture theatres, conference rooms, and call centres, deploy more APs at lower power to create smaller cells, each serving fewer clients. A common guideline is no more than 25–30 clients per radio for reliable performance.
Avoid the temptation to simply increase AP transmit power to fill dead spots. The client device (laptop or phone) transmits at a much lower power than the AP, creating an asymmetric link — the client can hear the AP, but the AP cannot hear the client. The result is a connection that appears strong but performs poorly.
Outdoor Considerations
Outdoor WiFi introduces additional challenges. APs must be housed in weatherproof enclosures (IP67-rated or better), mounted securely to withstand wind, and connected via shielded cabling or fibre. Signal propagation outdoors is more predictable (fewer walls), but range can be affected by rain, foliage, and multipath reflections off buildings. Directional antennas are often used to focus coverage where it is needed — for example, across a car park or courtyard — rather than broadcasting in all directions.
Heat Maps and Documentation
The final deliverable of a site survey is a heat map overlaid on the floor plan, showing signal strength, SNR, and channel utilisation across the entire space. This documentation serves as both the design blueprint and the post-installation validation record. It should be archived and updated whenever significant changes occur — new walls, additional APs, or changes in the RF environment. Good documentation makes troubleshooting future WiFi complaints dramatically faster.
Common Mistakes to Avoid
The most frequent mistake is deploying too few APs and cranking up the power to compensate. This creates the asymmetric link problem described above and leads to poor client experience. Another common error is using wide channel widths (80 or 160 MHz) in dense environments — wider channels provide more throughput per client but reduce the number of non-overlapping channels available, increasing co-channel interference. In most enterprise environments, 20 or 40 MHz channels on 5 GHz and 20 MHz on 2.4 GHz are preferred. Finally, many deployments ignore the 2.4 GHz band entirely or fail to plan for it. While 5 GHz (and now 6 GHz with WiFi 6E) offers more channels and less interference, 2.4 GHz remains essential for IoT devices, older laptops, and longer-range coverage. With only three non-overlapping channels (1, 6, and 11) in the 2.4 GHz band, careful channel planning is critical to avoid self-interference.
Frequently Asked Questions
A predictive survey for a single floor can be completed in a few hours. A passive on-site survey typically takes half a day to a full day per floor, depending on the size and complexity of the space. Active surveys take longer as they require associating with the network and measuring throughput at each location.
With tools like NetSpot or Ekahau and some training, an experienced IT professional can perform a basic survey. However, for large or complex environments — multi-storey buildings, warehouses, hospitals, or outdoor areas — engaging a wireless specialist is recommended. They bring experience interpreting RF data and designing for edge cases that are easy to overlook.
Yes. A post-installation validation survey confirms that the real-world deployment matches the design. It catches issues such as APs mounted in slightly different positions, unexpected interference sources, or building materials that attenuate more than predicted. This step is essential for ensuring the network performs as designed.
Re-survey whenever there are significant changes: office renovations, new walls or partitions, a large increase in the number of wireless clients, or the introduction of new interference sources. As a general guideline, a validation survey every two to three years helps ensure the network continues to meet performance requirements.
