UCSC's network rewire project has an important component to blanket campus indoor spaces with high quality wireless internet service [WiFi]. In addition to Gigabit Ethernet to the desktop, we have targeted 80 Mb/s for the WiFi service. In all but the smallest buildings multiple radios are needed to provide that service. A rough rule of thumb is that each radio can cover 1000 square feet. That number can change depending on the density of users that are expected.
UCSC and its design firms use computer modeling software to aide us in placing the APs. This is especially important in large buildings because of the high count of APs. Because coverage is affected by user equipment -- think metal cabinets -- even a careful layout may need to be adjusted after it is installed. To accomodate this situation we install more ceiling jacks than we intend to use. We can then adjust coverage by relocating radio assets or deploying an additional radio to fill a dead spot.
At our target radio density one of the things we need to contend with is that our radios can interfere with each other. If too many WiFi access radios are clustered it creates a noise situation where user equipment cannot drive its signal to reach the network. Our design rule is that when APs are within 100 ft, no more than two of them should have a direct sight line. The need to spread radio out in all directions is why we cannot simply run them down the hallway.
ITS works closely with the office of Environmental Health and Safety to make sure that we follow all the rules regarding radio transmitters. The scope of radio systems in use at the University is far broader than the Internet and WiFi. Because WiFi radio run at low power, it is easier to stay on the good side of the limits compared with other systems on our list:
FCC rules permit higher exposure in areas where access is limited to maintenance staff that are expected to control the duration of their exposure. For all WiFi transmitters we follow the lower exposure rules for the general public. This makes sense because WiFi equipment is installed indoors. The limits are based on an assumption of continuous exposure. All radio signals lose strength quickly as the distance from the antenna increases. The minimum safe distance for continuous exposure to UCSC's WiFi APs is 20 cm or about 8 inches. If your distance from the AP is 3 feet your exposure will be about 10 times lower than the limit.
The fine print
There are deliberate simplifications in this write up as regards radio placement design. We have additional information of a more technical nature. If you want additional information open a help desk ticket and request it. Our performance target for the wireless network may not be needed by every user. Achieved speed will depend on user equipment. Likewise, the discussion of radio exposure is necessarily incomplete because users are carrying transmitters in the form of cell phones, tablets and computers. These devices are used in close proximity to their owners which increases personal exposure. UCSC manages radio exposure for the equipment that it installs.
August 1, 2016