CWDP 305 Chapter 4 Site Surveys

I cannot recall the exact number of surveys I have performed, but I have visited a variety of places, including hotels, offices, schools, hospitals, care facilities, car dealerships, factories, and an airport, along with all their respective facilities.

Let's explore Chapter 4 of the CWDP-305: Certified Wireless Design Professional Study Guide by Tom Carpenter, which I have enjoyed so far.

Importance of Personal Protective Equipment (PPE)

Safety is paramount during site surveys, necessitating the use of appropriate personal protective equipment (PPE). In busy warehouses, wearing steel-toed boots and reflective vests prevents injuries from machinery. Hard hats protect against falling objects, while safety glasses guard against eye injuries. Hearing protection prevents long-term damage from noise, and gloves and protective clothing shield against cuts and airborne particles

I have visited places where I was required to wear a Geiger counter around my neck as a precaution. If it beeped excessively, I needed to leave the area immediately. In the food industry, it is necessary to be fully dressed in protective clothing, including shoe covers, a hairnet, and a mask. Don't forget the refrigerators, thick jackets, and gloves, which make handling a tablet challenging. You must work quickly because the equipment can freeze.

The Wi-Fi Survey toolkit: For a proper Wi-Fi survey you’ll need a few different Access Point models to test signal propagation, plus at least two main antenna types: omnidirectional and directional. A laptop or tablet with enough power and interchangeable batteries is a must for running survey software. Wi-Fi adapters make sure everything is compatible, and client devices like Wi-Fi phones can come in handy.

Nowadays, tools like the Ekahau Sidekick with integrated antennas and a handy NIC shoulder belt make life so much easier. I remember lugging around a heavy laptop, USB dongles, and separate wireless antennas. Gladly, times have changed.

Other essentials include a laser range finder for measuring distances and a camera to document AP locations or anything unusual. Flashlights are great for dark corners, flagging tape helps mark locations, and a tripod or mobile stand lets you adjust AP height. Battery packs are lifesavers for portable power. I remember surveys where I relied on a PoE switch and 15 meters of UTP cable, plus the heavy weight of those old battery packs.

A survey cart is perfect for a mobile workspace while a power injector and extension cord are handy backups. A laser temperature sensor is useful for spotting hot spots, and simple things like clipboards, pens, and highlighters make note-taking easy. Long Ethernet cables power survey APs and communication devices keep the team coordinated. GPS help map outdoor locations, and zip ties or duct tape secure cables.

In addition to the necessary hardware, having a combination of software tools to detect, diagnose, and analyze existing radio frequencies is crucial for effective site surveys.

• Spectrum Analyzer: This tool is vital for locating existing RF sources in coverage areas before designing a WLAN. It detects energy emitted within a frequency range, identifying interference from devices such as wireless phones, Bluetooth devices, microwave ovens, and more. Spectrum analyzers provide RF signature samples and display the duty cycle of signals, helping determine if a source can be removed or needs to be designed around.
• Protocol Analyzer: This tool captures WLAN frames traversing specific channels and decodes their contents, supporting the latest 802.11 protocols. It displays information such as signal strength and noise floor, often in a more understandable format than raw data. Protocol analyzers can filter for specific frame types, display performance statistics, and work with remote sensors to monitor the entire wireless network. They are used to identify WLANs, discover areas with high frame retries, determine packet types, find improperly configured APs, track client connections, and locate active clients.

Systems analysis is crucial after initial customer discussions to clarify expectations for the new WLAN design. It evaluates the existing infrastructure for compatibility, focusing on outdated Ethernet cabling and switches with insufficient Power over Ethernet (PoE). We love the freedom of going wireless, but every access point still needs its own dedicated PoE port in a switch.

It's important to look at what applications are being used by examining client usage and data transmission to determine the necessary throughput and Quality of Service (QoS) requirements.

While systems analysis takes time upfront, it ultimately saves time and money by providing a well-informed plan. The site survey ensures that the current setup can support the new WLAN, and if an onsite visit isn't possible, proper documentation of the existing infrastructure and architecture is a must.

Gathering attenuation measurements is super important for figuring out how much RF signals lose strength when passing through walls and other objects. You can't just guess what materials are in a wall based on how it looks. Well in the years I have done the surveys, sometimes a look or just a knock on the wall I could predict pretty accurate. 5 GHz signals can act differently than 2.4 GHz.

Doing an active site survey lets you see how much signal loss happens due to both free space and building materials. Higher frequencies, like those in the 6 GHz band, have shorter wavelengths, which means you'll notice bigger differences in signal loss between channels.

When you're surveying, it's a good idea to pick a channel in the middle of the band for more accurate results. Understanding how RF signals behave is key to designing a solid WLAN.

To measure attenuation, place the access point close to the wall and record the signal strength on both sides. This method helps to figure out how much signal loss different materials cause, and you can use that info to create facility floor plans in your WLAN design software for the best AP placement.

Predictive Design

In predictive design, you start by loading a floor plan into your survey software and scaling it for accurate dimensions. You’ll draw in walls if needed and assign attenuation values to walls, windows, doors, and other objects. However, floor plans are often an issue; they can be outdated or even nonexistent, and sometimes you have to settle for a low-quality picture of the fire escape route. The use of CAD-based floor plans with pre-drawn walls and doors to simplify the setup process, as they can be directly imported into design software. If CAD files aren't available, you may need to spend significant time manually drawing details.

Once that’s set, you can simulate access points and see how RF signals will spread. You choose the AP’s brand, model, antenna type, and power settings, then place it on the floor plan to visualize coverage. You can move the AP around to find the best spot before adding more.

Predictive design also helps create a Bill of Materials (BoM) and budget for the project, giving you a good estimate of how many AP's you’ll need before visiting the site. Although I really like to visit the site beforehand to refine the predictive model, I often have questions after the design to confirm details, like whether the walls are as thick as they seem or if the office interior is mostly glass and plants. It’s also important to consider if the building is monumental or if there are restrictions on running cabling along the roof. This approach makes planning for cabling and switch locations easier and provides a solid starting point for your site survey.

Traditional Design while Surveying Methods

In the early days of Wi-Fi, WLAN designs relied on APoS surveys to test signal strength by moving access points (APs) around, focusing on coverage and later on capacity in busy areas.

The design process involved selecting AP locations, testing signals, and auditing setups. Initially, APs were placed in hallways, but moving them into rooms improved performance as device numbers grew. Manual site surveys are still effective for accurate RF readings, providing valuable data despite being time-consuming. Hybrid site surveys combine manual and predictive modeling for efficiency, with modern tools enhancing the process. Accurate data from these surveys is essential for reliable WLAN designs.

AI-assisted design is becoming a game-changer, using algorithms to optimize network layouts based on various factors, but there is still a need to validate the designs to ensure they meet all the requirements.

Surveying for Applications and Architectures

Surveying for specific applications and architectures means understanding the unique network requirements for each use case.

VoIP requires strong, consistent coverage with minimum signal strength of –67 dBm, adequate AP overlap, high SNR (25 dB or higher), and minimal packet loss. The design should account for client transmit power and noise levels to maintain call quality.

Video is high-bandwidth and can be live (requiring low latency and multicast support) or streaming (using buffering to handle delays).

Data networks are easier to design but still need to meet throughput requirements and accommodate QoS for real-time applications like Skype or FaceTime.

Location services need multiple APs (at least three, ideally four) to see each client location with –75 dBm or better. APs near corners and walls may operate in “listen only” mode to reduce interference.

Single-Channel Architecture (SCA) focuses on density, determining AP numbers based on client count and application types.

Outdoor surveys for wireless bridges require point-to-point or point-to-multipoint designs, clear line of sight, and at least 60% Fresnel Zone clearance. Designers must gather terrain and weather information, determine optimal AP heights, calculate link budgets and EIRP, and comply with FCC transmit power limits.

Gaining Access and Clearance

Before starting a site survey, it’s important to secure access to all required areas. Some locations may need special badges, an escort, or even training and background checks, which can take days or weeks to arrange. Planning this ahead of time helps avoid delays during both the survey and the later implementation phase.

Once the survey is complete, thorough documentation ensures the design can be implemented smoothly, even without your direct involvement. This typically includes floor plans showing AP locations, interference sources, and switch details, along with photographs of AP placements, potential issues, and unique site conditions. For AP-on-a-stick or design-as-you-go surveys, the documentation also guides precise AP placement and configuration decisions.

Implementation Plan is created after the site survey and marks the final step of the design process. It addresses obstacles such as insufficient switch ports, switch locations, IP addresses, or rack space., validation Survey to verify after implementing a WLAN, the design by testing coverage, throughput, and other requirements, documenting results to ensure the project meets all specifications.

These subjects are discussed at chapter 5-9.

Defining and Documenting Metrics

Metrics are data collected during a WLAN survey to assess network performance and set minimum expectations for data rates and operations. Key metrics include:

• RSSI – Received Signal Strength Indicator is a measure of the signal strength at a particular location. Devices need a minimum signal to receive transmissions at a given data rate. RSSI is relative because each vendor calculates it differently, but higher numbers generally mean a stronger signal and lower numbers mean a weaker signal.
• Noise Floor – This is the level of background RF energy in an environment, essentially all signals other than the one you care about. It’s usually measured in dBm; for example, –94 dBm is a common reading.
• SNR – Signal-to-noise ratio isn’t really a ratio but the difference between your signal and the noise floor. For example, a –53 dBm signal with a –94 dBm noise floor gives an SNR of 41 dB. Higher SNR allows more complex modulation and higher data rates. Unlike RSSI, SNR is an actual measurement of signal quality.
• Interference Levels – Some channels can have more interference than others, depending on nearby devices like cameras. You can think of interference on a channel as its effective noise floor, considering signal strength and duty cycle.
• Cell Coverage – This refers to how much area a single AP covers. Coverage is usually defined by signal strength and AP output power, such as 10 mW for high-density areas, 25 mW for standard density, or 50 mW for low-density deployments.
• Cell Overlap – The overlap between cells helps clients roam smoothly. While vendors may suggest 25% overlap, it’s more practical to ensure that at least two APs are visible to a client at any given location, especially in 5 GHz WLANs. For 2.4 GHz, coverage for 20–40 feet is usually sufficient.
• Data Rates – The speed at which bits are sent over the RF medium. Data rate depends on signal strength, channel width, modulation, coding, and guard intervals.
• Throughput – The actual usable data transmitted across the network. Throughput is always lower than the data rate, so it’s the better metric for testing if applications will perform properly.
• Latency – The time it takes for data to travel from one point to another. For VoIP, one-way latency should be under 150 ms.
• Jitter – Variations in latency. If packets take inconsistent times to arrive, it can disrupt VoIP. Jitter buffers help smooth this out.
• Loss – Packets that don’t reach their destination, typically measured as a percentage.
• Retries – When packets are lost or corrupted, they are resent. High retry rates indicate potential WLAN problems.

Until next time, keep the signal strong!

Source(s):

Carpenter, T., et al. (2024). CWDP-305: Certified Wireless Design Professional Study Guide (1st ed.). Durham NC, USA: Certitrek Publishing