TL;DR
- Facade penetration loss varies by more than 20 dB between building types, so a single outdoor-to-indoor margin is always wrong somewhere.
- In-building design needs a floor plan and material assignments, not a clutter class.
- Validate indoor coverage with walk testing, not with drive testing outside the building.
Why does outdoor coverage not predict indoor coverage?
Because the dominant loss mechanism changes. Outdoors, path loss is a function of distance and clutter. Indoors, the facade is the controlling term: modern low-emissivity glazing, concrete core walls and metal cladding can each add loss in the tens of decibels, and they vary building by building on the same street.
A planning tool applying one outdoor-to-indoor penetration margin across a city will be optimistic for the office tower with coated glass and pessimistic for the older low-rise next door. The error is not a small correction — it is often larger than the entire design margin.
| Building type | Typical constraint | Usual design response |
|---|---|---|
| Office tower, coated glazing | High facade loss, deep floor plates | In-building antennas per floor, 3D model with glazing loss |
| Shopping mall | Large open volume, high density | DAS with distributed antennas |
| Airport / stadium | Very high peak density | DAS with sectorised head-end |
| Warehouse / industrial | Tall racks, metal structure | Small cells at height, high slab and rack loss |
| Residential high-rise | Many small units, low density each | Repeater or small cell per block |
What do you need to model a building properly?
A floor plan with walls drawn as objects rather than as pixels, and a material assignment per wall type. Concrete, drywall, glass and metal have different loss at different frequencies, and at mmWave the difference between a drywall partition and a concrete core is the difference between coverage and no coverage.
For multi-floor design, the floor slab matters as much as the walls. Vertical leakage between floors is what makes a design either efficient or wasteful: if the slab loss is modelled correctly, one antenna can often serve two floors; if it is not, the design over-provisions and the cost goes up accordingly.
DAS, small cells or repeater — how do you choose?
The decision follows from building size, user density and operator constraints rather than from a general preference. Distributed antenna systems suit large venues with high uniform density — airports, stadiums, large malls — where a single head-end can feed many antennas. Small cells suit medium buildings where capacity per area is high but the venue is not large enough to justify a DAS head-end.
Repeaters are the cheapest option and the most constrained: they amplify what exists outside, so they cannot create coverage where the donor signal is absent, and they amplify interference as readily as signal. In practice the choice is usually between DAS and small cells, with repeaters limited to small single-tenant spaces.
How should indoor coverage be validated?
By walk testing inside the building on the floors that matter. Drive testing outside measures the macro layer, not the indoor experience. A walk test with a smartphone-based tool covers a floor in a fraction of the time a dedicated hardware campaign would take, and produces data that post-processing tools can compare against the design prediction.
The useful comparison is predicted versus measured per floor, not a single building-level average. If the prediction is systematically high on upper floors, the slab loss assumption is wrong; if it is low near the facade, the glazing assumption is wrong. Both are fixable in the model, and both change the next building's design.