By Cal Calamari, Global Solutions Lead for Enterprise Networks and Connections, Motorola Solutions
Wi-Fi wireless networks are ubiquitous these days: changing the way we work, the way we communicate, and our expectations of how we access the information we need, wherever we are. Wi-Fi is pervasive in all things mobile — the devices we carry to communicate — and can be found almost everywhere, e.g., home, work, cafés, fast food restaurants, hotels, schools, hospitals, retail stores, manufacturing, subways, trains, and airplanes.
Even as prevalent as Wi-Fi is, the user experience connected to these networks can vary. The user can experience dropped connections, poor performance, or decent data service but poor voice or video. Variances in user experience can be directly attributed to “Plan, Design and Deploy” attributes of a wireless site survey.
To help you achieve a better overall wireless network design and end user experience, below are Motorola Solutions’ Top 10 Site Survey Tips you can take to ensure a successful wireless site survey.
- Thoroughly prepare for the site survey.
- Obtain scaled floor plans of the building(s) and of the areas with physical attributes that are to be covered. Be sure to note any special data rate or device density areas.
- Format drawings and organize for the walk through. When surveying large buildings, pages of floors can get out of sequence. Mistakenly marking up floor 5 when you were on floor 7 will create problems later.
- Make sure you understand both technical and business requirements. Does the customer have specific coverage requirements (e.g., -65 dbm?) Do they want to support voice? Video? How many streams and at what data rate? Do their business requirements restrict access point placement to hide them which could mean non-optimal locations or limitations in running cables?
- Check density requirements? For example, areas where large numbers of people congregate such as auditoriums, lobbies, nurse stations, cafeterias, conference rooms, etc.
- Walk the property first for an understanding of the space and possible sources of radio frequency (RF) interference.
- You’ll want to note if the floor plans are consistent with the physical space. Changes such as new walls, large shelves, partitions, etc. could have been made that were never updated on the floor plans or drawings. You’ll want the floor plans to match the actual physical space for coverage planning, but also for future reference.
- What are the construction materials? Solid concrete? Any reflective surfaces such as metal, glass, or lead-paned glass? What about absorption materials such as books, cloth, water, sound deadening materials? All of these will affect the RF transmissions, possibly reflecting or attenuating the signal or absorbing RF energy before it finds its way to the client device. How about hidden materials such as lead lined walls in radiology for hospitals?
- How high are the ceilings? The 30- to 40-foot ceilings in auditoriums and warehouses can create challenges for today’s mobile client connectivity.
- Are there any sources of possible RF interference such as microwave ovens or large motors? Many times, microwaves have been overlooked because they were not operational when a scan was performed, but then later create havoc at lunch time, disrupting service and productivity. Are there other Wi-Fi networks nearby or other commercial RF transmitters that operate in the 2.5 GHz and 5 GHz bands in the area? These bands are open, public bands; so many consumer products also use these bands.
- Are there plenum vs. non-plenum environments for above ceiling deployments?
- Check each proposed mounting location for cable access. You will need to determine if there will be difficulty running CAT 6 cable to the access point or physically mounting the access point. There will be times when the ideal location for the access point is not practical. Either the access point cannot be secured or hidden, or if it can be, you may not be able to route a cable to that location. The business also may have a requirement to hide the wireless infrastructure and cabling due to aesthetics requirements.
- Verify the wired network infrastructure to ensure it can support the wireless access points. Does it have the available Ethernet 10/100/1000 ports with Power over Ethernet (PoE)? Can the Ethernet switch support the access point power type, either 802.3 -af or –at, and have enough total power budget? Is redundant power required? One commonly overlooked specification is if there will be enough wired bandwidth for the network. As access points are added, if they support the new 802.11ac standard, the client data rates can climb significantly. Particular attention needs to be given to uplink and downlink to ensure the customer’s requirements are going to be met, which may mean additional WAN bandwidth or 10GbE ports on the Ethernet switch.
- Identify coverage areas. Determine if there are particularly difficult areas to provide coverage, where spot coverage may be required or use of directional antennas or even using a mesh connection to place an access point at a remote area where you cannot run a cable.
- You’ll need to understand the true application of the Wi-Fi network. Are there specific business applications? Will users be using latency sensitive applications such as video or voice? If so, what quality of video stream is required— standard definition or high definition? Voice is not bandwidth intensive but is highly sensitive to mobile client roaming and latency. Particular attention to the specific client’s characteristics will be required, along with ensuring the Ethernet switch is capable of supporting quality of service. Consider a warehouse deployment. In warehouse environments, often you can get away with fewer APs and use higher gain antennas because coverage is the desired metric, rather than throughput or capacity. Bottom line, understanding the applications and the number and type of client devices is critical.
- Know the client devices that are going to be used and survey accordingly. All the common survey apps have a feature that allows you to modify for client power or antenna gain. The difference between your typical laptop and most mobile devices is approximately 5dBm (15dBm vs. 10dBm); a mobile device will not only transmit more “quietly” than a laptop, but also cannot “hear” as well. If a survey is done with the default settings, and the surveyor wants to plan coverage of -65dBm everywhere, then they’ve really only planned for having laptops as clients and will likely fall short for mobile devices. Mobile device users will experience spotty coverage and dropped connections, along with less than expected data rates. When surveying, keep your survey client around the same height at which the users would be connecting for a more realistic survey. Lastly, a common mistake is not checking the noise floor and taking it into account for your survey. The noise floor will erode your signal quality. Failing to take this into account will impact weaker clients.
- Use less than full power on both radios for surveying to allow for coverage-hole mitigation. Most modern Wireless LAN systems have automatic RF management capabilities. These systems will automatically adjust the channels and power of each radio to minimize co-channel interference and adjacent channel interference to achieve optimal performance. However, by only using 50 percent of the radio power, you will safeguard your network in the event of an access point or radio failure, allowing the adjacent radios to increase their power and still provide coverage in that area until the problem can be rectified. One common mistake is trying to cut cost and provide coverage with fewer access points. This could fail to place access points close enough so they can hear each other. When this happens, the automatic RF management could be rendered useless for making the automatic adjustments and being able to provide coverage in the event of a failure.
- Disable Dynamic Chain Selection (DCS) in order to maintain both chains are in operation during surveys. When surveying, if DCS is enabled, it will power down a chain because the only traffic being passed is beacon traffic. This will result in about a 3dB drop. If you disable DCS when surveying, there will be increase in the signal strength.
- Document your findings. Take copious notes and markup the floor plans and drawings with actual deployment information. You will need to know each physical location of each access point and what the physical environment was when it was planned and installed. This information helps when you have to debug an issue remotely or if the customer wants to run security apps or use locationing. Also, if coverage has changed, you might discover a new wall was added or that someone brought in a large book rack.
Wi-Fi networks have evolved from convenient network access in a conference room to the primary network access. However, unlike wired networks which could be considered nearly appliance-like today, wireless networks face unique and unpredictable challenges: operating in unlicensed RF bands that can be affected by sources of RF interference, physical environmental attributes, and large variances in mobile device characteristics.
A successful site survey will be thorough and methodical, collecting sufficient information to minimize the number of variables to make the unpredictable, predictable.
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