Commercial Cellular DAS and In-Building Cellular Coverage

What a commercial cellular DAS scope includes#

Telelink Business Services is a licensed C-7 Low Voltage Systems Contractor, CSLB License #472017. We install in-building cellular coverage systems for offices, campuses, healthcare buildings, warehouses, parking structures and public agency facilities across California.

This page covers carrier cellular coverage only. A commercial cellular DAS does not satisfy an emergency responder radio coverage requirement. That system, required under the California Fire Code and usually called ERRCS or BDA, runs on different frequencies with different equipment listings, a different approving authority and a separate submittal.

A cellular coverage scope from us covers:

• An RF survey of the existing carrier signal in the building, by carrier and by band
• A system type recommendation: off-air repeater, passive DAS, active DAS or hybrid
• Coordination of the carrier consent required under 47 CFR Section 20.21
• Head end layout, rack space, grounding coordination and the electrical handoff
• Coax or fiber distribution with the loss budget calculated run by run
• Antenna layout floor by floor, including stairwells, elevators and below grade levels
• Commissioning, a walk test against the design target, and an as-built package

Why cellular coverage fails inside modern buildings#

Carriers build their networks for outdoor coverage. What happens indoors is a byproduct, and it has gotten worse as buildings have gotten tighter.

Low-emissivity glass carries a thin metallic coating that reflects heat and attenuates radio energy at the same time. A modern curtain wall can take a usable outdoor signal down to nothing two rooms in. Concrete with rebar, precast panels, metal stud framing, foil-faced insulation and metal roof decks each do the same to a weaker degree, and they combine. Below grade there is no exterior wall at all, so basements, subterranean parking and loading docks start from zero. On a large floor plate the core sits far enough from any window that distance alone does the damage.

Spectrum adds to it. Carriers have moved traffic onto mid-band spectrum, which carries more data than the low-band spectrum it displaced and penetrates building materials less well. Renovation can create the problem where none existed: a re-glazing project or a new metal panel skin takes a building that worked to a building that does not.

Off-air repeaters, passive DAS and active DAS#

Three architectures cover almost every commercial job. The choice follows building size and where the signal comes from.

An off-air repeater takes its signal from the macro network. A directional donor antenna on the roof is aimed at a carrier cell site, coax carries that signal to a bidirectional amplifier, and the amplified signal is distributed inside. No carrier equipment enters the building. It is the least expensive path, and it works only where the roof has usable donor signal and there is enough isolation between the donor and indoor antennas to keep the amplifier from oscillating.

A passive DAS is passive after the signal source. Coax, splitters, couplers and taps carry signal to the antennas. Every foot of coax and every split costs signal, so the loss budget is calculated per run in design and sets a hard limit on how far the system reaches.

An active DAS converts the signal at a head end and distributes it over fiber to remote units placed through the building. Each remote amplifies locally and feeds short coax runs to nearby antennas. Fiber removes the distance penalty, so an active system scales to towers, campuses and large floor plates and handles several carriers and bands on one distribution. It costs more, takes more head end space, and needs power at every remote.

System	Signal source	Distribution	Where it fits
Off-air repeater	Roof donor antenna	Coax	Smaller buildings with usable roof signal, one or two carriers
Passive DAS	Off-air or a carrier source	Coax with splitters and taps	Compact buildings where the loss budget closes
Active DAS	Carrier base station or small cell	Fiber to remote units, short coax tails	Towers, campuses, large floor plates, multiple carriers
Hybrid	Either	Fiber to remotes, then passive coax	Most large buildings end up here

Single carrier, multi carrier and who funds the system#

A single carrier system is the cheapest version of every architecture above. It covers the carrier the donor is aimed at, which works when the building is one tenant on one carrier fleet and leaves a standing tenant complaint everywhere else.

Multi carrier means either a band-selective amplifier and a donor path per carrier on an off-air system, or a neutral host active DAS with a signal source per carrier. Cost rises with head end space, power and equipment; the schedule rises with the number of separate carrier approvals. Plan around approvals rather than installation labor.

Carriers sometimes fund and own coverage inside a building where the traffic justifies it, which in practice means large venues, transit facilities and very high occupancy buildings. A carrier-provided small cell is a compact base station that backhauls over the building’s internet connection; the owner provides space, power and backhaul, and the carrier decides whether to deploy it. It can fix coverage in one suite. It does not scale to a tower.

Every other building is owner funded. The owner buys, owns and maintains the system, and still needs each carrier’s express consent under 47 CFR Section 20.21 to carry its signal. We prepare and carry that approval, and the decision sits with the carrier.

Before funding any of it, check whether Wi-Fi calling over a properly designed wireless network answers the actual complaint. It carries voice on handsets that support it and needs no carrier consent. It does nothing for a device that must stay on the cellular network, or for a garage with no Wi-Fi in it, so it is a partial answer rather than a substitute.

The RF survey that has to happen first#

No design starts without one. We walk the building with a scanning receiver and measure, floor by floor, received signal level and signal quality for each carrier on each band in use. The roof is surveyed separately to establish whether there is a donor signal worth using and which direction it arrives from. We note the construction that will attenuate the finished design and identify the areas with no path to the outside at all.

The survey produces four things: floor by floor heat maps of what exists today, a design target agreed with the owner and expressed as a minimum received signal level in dBm at the edge of coverage, a system type recommendation, and an antenna count. A proposal written without a survey is a guess about how much signal the walls take out, and that guess is what changes in the field.

Head end, distribution and antenna layout by floor#

The head end needs a conditioned space with rack space, a coax or fiber path to the roof, and a path to every riser. Distance from the head end to the donor antenna is straight loss, so room selection is a design decision rather than whatever space is left over. Dedicated line voltage circuits serving DAS head end equipment are installed by a licensed C-10 electrical contractor, and we show that handoff on submittals. The rack, grounding busbar, pathway and labeling in that room fall under our network room buildout scope. Head end and distribution equipment from CommScope, Corning, JMA Wireless, SOLiD and ADRF is commonly specified for this scope in California, and what we install is what the RF design and the carrier approval settle on.

Passive distribution uses low-loss plenum rated coax sized per run against the loss budget, with splitters and taps selected so the last antenna on the run still meets the target. Active distribution uses singlemode or multimode fiber from the head end to the remote units, pulled, terminated and tested like any other fiber backbone. Riser sleeves, firestopping and pathway are coordinated with the general contractor.

Antennas go in at the spacing the link budget supports for the construction in that area, which is why an open office takes fewer antennas than a corridor of hard-walled offices at the same square footage. Stairwells and hoistways are designed on their own: a stairwell typically takes an antenna every few floors, and elevator coverage takes a hoistway or cab antenna, coordinated with the elevator contractor. Below grade parking is its own zone.

Roof penetrations and donor antenna mounting are carried by the general contractor and the structural scope. We give the GC the penetration location, the mast loading and the pathway requirement, and we set and aim the donor antenna once the curb and flashing are in.

Commissioning, the walk test, and design by building type#

Commissioning starts with setting gains and confirming the system is not oscillating and not raising the uplink noise floor at the donor site. Then the walk test: a defined grid on every floor, walked with a test receiver, recording level and quality for each carrier against the design target. Where a point misses, we adjust gain, move an antenna or add one, and walk it again. The commissioning report, the as-built antenna schedule, the loss budget calculations and the carrier approval correspondence go into the closeout package.

Three building types change the design enough to call out.

Parking structures are long, low and open sided with heavy concrete decks between levels. Coverage runs linearly, equipment sits in weather-rated enclosures, cable is protected from vehicle traffic, and each below grade level gets its own antennas because nothing reaches it from outside. Core drilling between decks is coordinated with the structural scope.

Hospitals are small rooms and dense walls, with shielded imaging suites that will not be covered and should not be, and clinical areas where work is scheduled around patient care and infection control. Hospitals also carry public safety radio requirements, a separate system with its own approvals, coordinated with this one for pathway and head end space and kept apart otherwise. Our healthcare and clinics page covers work in occupied clinical space.

Warehouses are high bays with metal roof decks and foil-faced insulation, and racking that changes the RF picture once loaded. Antennas go in at height with lifts during a window the operator can give up, and the walk test is repeated after the racks are full, because a survey of an empty warehouse describes a building that will not stay that way. See industrial and warehouse.

Next step#

Send floor plans, the construction type, the carriers your tenants use and whether anyone has surveyed the building, through request a bid. We return a survey scope first, then a design and a price written against the results. General contractors bidding a Division 27 package can start at for general contractors.