Wireless in buildings

Maya Okonkwo starts her eighth term at Cobalt Line Systems on the wireless crew. Over seven terms she has pulled and certified copper, spliced fibre, commissioned switches and access points, installed card readers and cameras, and tuned a school gym. Every one of those systems ended at a jack, a panel or a loudspeaker she could see. Wireless work is different: the product is invisible. A building owner pays for radio signal that fills the right spaces at the right level, and the only way to know it is there is to measure it. Her new lead, Frank Delisle, has designed and tested in-building wireless systems for twenty years, first for a cellular carrier and then for integrators. On her first morning he hands her a spectrum analyzer, a survey tablet and a stack of floor plans, and says that by the end of the term she will be able to look at a drawing and tell where the radio will struggle before anyone has hung an antenna.

This course covers the wireless systems an installer meets inside buildings, the physics that decides how well they work, and the work of designing, surveying, installing and testing them. It builds on the access point mounting and powering in LVT-220 and the fibre and copper skills of LVT-130 and LVT-210, and it leads into the code rules for communication cabling in LVT-330. This first lesson maps the territory: what wireless systems a modern building holds, why buildings are hard on radio, who owns and regulates each system, and how a wireless project runs.

The wireless systems in a building

Walk through St. Brendan's Hospital's new east wing, the project that will run through this course, and count the radios. Staff laptops, workstations on wheels and tablets use Wi-Fi. Nurses carry hands-free badges that also use Wi-Fi, so a call that drops in a stairwell is a patient safety issue. Infusion pumps, patient monitors and portable X-ray machines send data over Wi-Fi or over dedicated medical telemetry radios. Real-time location tags on wheelchairs and pumps report their positions. Visitors and patients expect their phones to work, which means cellular coverage from three or four carriers. Security officers and maintenance staff carry two-way radios. And when the fire department arrives, firefighters need their portable radios to reach their dispatch centre and each other from the basement to the roof.

The table matters because the owner of the spectrum decides what an installer may do. Wi-Fi uses bands that anyone may use, as long as the equipment is certified and follows power limits, so the building owner can design and install it freely. Cellular spectrum belongs to the carriers, who paid billions for it; nobody may retransmit a carrier's signal without that carrier's consent. Public safety spectrum belongs to the agency that holds the licence, and in-building systems for it are regulated by fire codes as well as by the radio regulator. In Canada the regulator is Innovation, Science and Economic Development Canada, ISED; in the United States it is the Federal Communications Commission, the FCC. Both certify radio equipment, and both treat an unauthorized amplifier on a licensed band as a serious matter.

Why buildings are hard on radio

Radio signals travel well through air and poorly through dense materials. A signal from a cell tower a kilometre away arrives at the outside of St. Brendan's at a usable level, then loses a few decibels through each window, ten or more through each concrete wall, and much more through floors, elevator shafts and the lead-lined walls around the imaging suite. Modern energy-efficient glass carries a thin metal coating that reflects heat and also reflects radio, so a tower that worked fine through old windows can disappear when the windows are replaced. Basements, parking garages and interior stairwells, which have the thickest walls and no windows, are often the worst spots in a building, and they are exactly where firefighters operate.

Inside, the problem changes. Wi-Fi access points sit a few rooms away from their users, not a kilometre away, so the challenge is less about getting enough signal and more about controlling it: enough signal in every room, not so much that access points interfere with each other, and enough capacity for the number of devices. A hospital floor might have two hundred devices on Wi-Fi at once; Brightwater's insurance office, which Maya commissioned last term, can have four hundred during an all-hands meeting. Lessons 4, 6 and 7 deal with these problems.

Three ways to bring radio indoors

Every in-building wireless system does one of three things. It can put the transmitter indoors: Wi-Fi access points, small cells and private radio repeaters are complete radios placed inside the building, near their users. It can capture a signal from outside and repeat it indoors: a bi-directional amplifier, or BDA, takes the signal from a donor antenna on the roof aimed at a distant tower, amplifies it and sends it through antennas inside, and amplifies the replies on the way back. Or it can bring a signal source into the building by cable: a distributed antenna system, or DAS, takes signals from carrier base station equipment installed in the building, or from a BDA, and spreads them over coax or fibre to many small antennas. Lesson 8 covers DAS and lesson 9 covers public safety BDAs.

The choice is the designer's, but the installer must understand it, because each approach has its own failure modes. An access point that fails affects one area. A BDA that oscillates, feeding its own output back into its input, can jam the radio system it is meant to help across a whole neighbourhood. A DAS with a bad connector can add passive intermodulation, a kind of interference created when strong signals meet a corroded or loose joint, that degrades every carrier on it. Workmanship that is invisible in a cabling job shows up as interference in a radio job.

Who is involved

A wireless project has more parties than a cabling job. The owner, here St. Brendan's, sets the requirements: which systems, which areas, what performance. The RF designer, often a specialist engineer or the integrator's own designer, produces the design: antenna locations, equipment, cable routes and predicted coverage. Cobalt Line's Sanjay Iyer is the designer of record for structured cabling; for the east wing's radio systems, Frank and an outside RF engineer share the design. Carriers must approve any cellular system that carries their signal. The public safety agency, through its radio system manager, must consent before anyone amplifies its channels. The authority having jurisdiction, usually the fire department or building official, enforces the coverage code and witnesses acceptance tests. The general contractor schedules access, and other trades, electricians, ceiling installers and fire alarm contractors, all touch the work.

Maya will spend more time than she expects on paperwork. Before a public safety BDA can be switched on, the agency's written consent and the regulator's registration or licence must be in place. Before a carrier system goes live, the carrier must accept the design and test results. Before a Wi-Fi system is handed over, the owner's network team must accept the survey. The installer's part is to do the work exactly as designed, document every change, and never transmit on a licensed band without authorization.

How a wireless project runs

Most in-building wireless projects follow the same path. First comes a needs assessment and, often, a site survey of the existing signal: the designer measures what the outside networks already deliver inside, floor by floor, so the design adds only what is missing. Next comes the design, usually with predictive modelling in survey software from floor plans and wall types. Then the installation: cable, antennas, equipment, power and grounding. Then optimization, adjusting antenna positions, gains and power levels. Then acceptance testing, measured on a grid and witnessed where the code requires. Finally, documentation and handover, followed by annual tests for public safety systems.

The east wing schedule, which Frank shows Maya on the first day, follows this path over nine months. The existing-signal survey of the shell building happens now, while walls are still open, because once the lead lining, the energy-efficient glass and the drywall are in, the numbers will be worse, and the designer wants to know how much worse. Antenna and cable installation follows the ceiling grid. Acceptance testing waits until the building is finished, because a coverage test in a building with no doors, ceilings or furniture measures a different building.

Safety on wireless jobs

Wireless work adds a few hazards to the ones Maya already manages. Roof work for donor antennas means fall protection and, near other antennas, attention to radio frequency exposure, which lesson 10 covers. Antenna mounting at height uses ladders and lifts, under the same rules as LVT-110. Lithium and lead-acid batteries for public safety systems store a great deal of energy. Spectrum analyzers and signal generators are test transmitters only when used as designed; transmitting a test signal on a licensed band without authorization can disrupt emergency communications, so test transmissions on public safety or carrier bands are made only with the licensee's coordination. Frank's rule is simple: on someone else's frequency, listen freely, transmit only with permission.

# Wireless inventory for a building: which system serves each device, and who must approve it
systems = {
    "Wi-Fi":               {"bands": "2.4/5/6 GHz", "approval": "owner (licence-exempt)"},
    "Cellular DAS":        {"bands": "carrier bands", "approval": "each carrier"},
    "Public safety ERRCS": {"bands": "700/800 MHz", "approval": "agency licensee + fire code official"},
    "Two-way radio":       {"bands": "VHF/UHF", "approval": "owner's licence"},
}
devices = [("staff laptop", "Wi-Fi"), ("nurse badge", "Wi-Fi"), ("visitor phone", "Cellular DAS"),
           ("firefighter portable", "Public safety ERRCS"), ("security radio", "Two-way radio"),
           ("infusion pump", "Wi-Fi"), ("paramedic radio", "Public safety ERRCS")]
by_system = {}
for dev, sys_name in devices:
    by_system.setdefault(sys_name, []).append(dev)
for name, info in systems.items():
    devs = ", ".join(by_system.get(name, [])) or "none"
    print(f"{name:20s} {info['bands']:12s} approval: {info['approval']}")
    print(f"{'':20s} serves: {devs}")

Wi-Fi                2.4/5/6 GHz  approval: owner (licence-exempt)
                     serves: staff laptop, nurse badge, infusion pump
Cellular DAS         carrier bands approval: each carrier
                     serves: visitor phone
Public safety ERRCS  700/800 MHz  approval: agency licensee + fire code official
                     serves: firefighter portable, paramedic radio
Two-way radio        VHF/UHF      approval: owner's licence
                     serves: security radio

The inventory looks simple, but it is the first document Frank asks for on any job. It tells the crew who has to sign off before anything transmits, and it reminds everyone that the nurse badge and the infusion pump share the same Wi-Fi as the laptops, so a Wi-Fi design that is fine for email can still fail the devices that matter most.