GLOSSARY
The vocabulary of
in-building coverage.
Plain definitions for the terms that appear in coverage discussions, proposals and equipment documentation.
Every definition in this glossary is general and vendor-neutral. The terms describe how indoor cellular coverage is discussed and measured; they do not describe a product, a specification or work Aurora Netcom has agreed to carry out. Which of them matter in a given building depends on that building, the carriers in use and the signal available at the site. There are 40 terms below, and each has its own link, so a definition can be quoted directly from any other page.
A
- Active DAS
A distributed antenna system in which the signal is converted, amplified and distributed electronically, typically over fibre or structured cabling to powered remote units placed around the building. Because each remote unit regenerates the signal locally, an active design can serve larger or more spread-out buildings than a passive one, at the cost of power, space and a more involved commissioning process.
- Antenna gain
A measure of how effectively an antenna concentrates radio energy in a particular direction compared with a reference antenna, expressed in decibels (dBi or dBd). Gain does not create power; a higher-gain antenna simply sends and receives more strongly along a narrower beam, which makes aiming and placement more important.
- Attenuation
The loss of signal strength as a radio wave travels through a medium such as air, concrete, glass or coaxial cable, measured in decibels. Attenuation is cumulative: the loss through an exterior wall, an internal partition and a long cable run all subtract from the signal that finally reaches a device.
B
- Benchmark or baseline survey
A structured record of how a building performs before any change is made, taken at identified locations with comparable devices, carriers and tasks. Without a baseline there is nothing to compare later measurements against, so a benchmark is what makes a claim of improvement meaningful rather than anecdotal.
- Bi-directional amplifier (BDA)
An amplifier that boosts signals in both directions: from the mobile network to devices inside the building and from those devices back to the network. A bi-directional amplifier is the active element at the heart of an off-air repeater system; it relays an existing signal and cannot create coverage where no usable donor signal exists.
C
- Carrier aggregation
A technique in which a network combines several frequency blocks, possibly in different bands, to give a single device more total bandwidth. It matters indoors because a system that passes only some of the bands a network uses may leave a device working on fewer aggregated blocks, and therefore at lower throughput, than it would achieve outdoors.
- Coaxial distribution
Distribution of radio signals around a building over coaxial cable, with splitters, couplers and taps feeding each antenna. Coaxial runs are simple and need no power along the way, but loss increases with cable length and with frequency, which practically limits how far a single run can reach.
- Commissioning
The process of bringing an installed system into service: setting gains and levels, verifying that each part behaves as designed, checking that the system does not interfere with the surrounding network, and recording the configuration. Commissioning results, and the conditions under which they were taken, form the record that later maintenance is measured against.
- Coverage versus capacity
Two different problems that produce similar complaints. A coverage problem means the signal is too weak or too noisy to sustain a usable connection. A capacity problem means the signal is adequate but too many devices are contending for the same network resources, so performance falls at busy times. Amplifying a signal addresses coverage; it does not add network capacity.
D
- dBm
A measure of absolute power on a logarithmic scale referenced to one milliwatt. Indoor mobile signal levels are usually negative numbers, and a less negative value is stronger: -75 dBm is considerably stronger than -105 dBm. Because the scale is logarithmic, every 3 dB is roughly a doubling or halving of power and 10 dB is a factor of ten.
- Distributed antenna system (DAS)
A network of antennas distributed through a building, fed from a common source, so that coverage is delivered from many nearby points rather than one distant one. A DAS is defined by how the signal is distributed, not by where the signal comes from: the same distribution network may be fed by an off-air repeater or by a carrier-provided signal source.
- Donor antenna
The outdoor antenna, usually mounted on a roof or facade, that communicates with the mobile network on behalf of an off-air system. Its type, position and aim determine which cell site the system works with and how strong and clean the incoming signal is, so donor placement is one of the most consequential decisions in an off-air design.
- Donor signal
The outdoor network signal that an off-air system captures and relays inside a building. Its strength and quality set the ceiling on what the indoor system can deliver, which is why the donor signal has to be assessed for each carrier before any design is drawn. Where no usable donor signal exists, an off-air approach is not viable and a different signal source is required.
- Downlink
The direction of transmission from the network to the device. Downlink problems typically show up as weak signal indicators, slow downloads or audio that breaks up on the listening end. Downlink and uplink can fail independently, which is why a device may display several bars and still be unable to hold a call.
E
- eNodeB and gNodeB
The base station equipment of a mobile network: eNodeB is the 4G LTE term and gNodeB the 5G NR equivalent. They are the network-side endpoint that a device connects to, whether that base station is on a tower serving a wide area or a small node serving one building.
F
- Femtocell
A very small, low-power cellular access point intended for a limited area, which carries traffic back to the mobile network over a fixed internet connection. A femtocell adds capacity as well as coverage in the space it serves, but its supply, supported carriers and permitted use are determined by the mobile operator rather than by the building owner.
- Fibre distribution
Distribution of signals around a building over optical fibre, with conversion back to radio at each remote unit. Fibre carries the signal long distances with very little loss and is physically small, which suits tall or extended buildings, but it requires powered equipment at each end and a more complex commissioning process than a passive coaxial run.
- Frequency band
A defined range of radio frequencies that a network is licensed to use, identified by band numbers as well as by rough frequency. Different carriers use different bands, and equipment only passes the bands it is designed and approved for, so band support has to be checked against the carriers that actually matter in a given building.
H
- Head-end
The central equipment location where a distributed antenna system takes in its signal source and prepares it for distribution. The head-end typically needs floor or rack space, power, ventilation and a cable route to the rest of the building, so identifying a suitable location early tends to shape the rest of a design.
I
- Isolation
The degree of separation between the outdoor donor antenna and the indoor antennas of a repeater system, expressed in decibels. Adequate isolation prevents the amplified indoor signal from being picked up again by the donor antenna. Insufficient isolation limits usable gain and can cause the system to oscillate.
L
- Link budget
An accounting of every gain and loss along a signal path, from the source through cables, splitters and antennas to the device, used to predict the level that will arrive at a given point. A link budget is how a designer decides how many antennas are needed and where, and it is a calculation rather than a measurement.
- Low-emissivity (low-E) glazing
Glass with a thin metallic coating applied to improve thermal performance. The same coating that reflects heat also reflects radio waves, so modern energy-efficient glazing can attenuate mobile signals far more than plain glass. This is a common reason a newly built or recently refurbished building has weaker indoor reception than an older one.
M
- MIMO
Multiple-input, multiple-output: the use of several antennas at each end of a link so that more than one data stream can be carried at the same time. MIMO can raise throughput considerably where conditions allow, but it depends on having genuinely separate signal paths, which constrains how indoor antennas are arranged and cabled.
N
- Noise floor
The level of background radio noise present in a band, below which a wanted signal cannot be distinguished. Amplification raises the wanted signal and the noise together, so a system that adds gain without regard to noise can increase the measured signal level while making the connection no more usable.
O
- Off-air repeater
A system that captures an existing outdoor network signal through a donor antenna, amplifies it and re-radiates it inside a building, and relays the return path back out. It is called off-air because the source is the live network rather than a direct carrier connection, and its performance is therefore bounded by the donor signal available at the site.
- Oscillation or feedback
The unstable condition that arises when a repeater's amplified output is received again by its own input, in the same way an audio system howls when a microphone hears its own loudspeaker. Oscillation degrades the connection and can disturb the surrounding network, so systems monitor for it and reduce gain or shut down when it is detected.
P
- Passive DAS
A distributed antenna system in which the signal is carried from a single source to the antennas entirely through coaxial cable, splitters and couplers, with no powered equipment in between. Passive designs are simpler and need no power at the antenna, but cable loss grows with distance and frequency, which limits practical reach.
- Passive intermodulation (PIM)
Unwanted signals generated when strong radio signals meet a non-linear junction in supposedly passive hardware, such as a corroded connector, a loose fitting or dissimilar metals in contact. The resulting products can land on a receive frequency and raise the noise floor, degrading the uplink even though every component is nominally passive.
- Path loss
The reduction in signal strength that occurs simply from a radio wave spreading out as it travels, before any obstruction is considered. Path loss increases with distance and with frequency, which is one reason higher-frequency bands tend to cover a shorter distance indoors than lower-frequency ones.
- Penetration loss
The specific loss a signal suffers passing through a building element such as a wall, floor, roof or window, measured in decibels. Concrete, dense masonry, metal cladding, foil-backed insulation and coated glazing all attenuate strongly, so penetration loss usually explains why outdoor coverage does not translate into indoor coverage.
R
- Remote unit
A powered unit placed away from the head-end in an active distributed antenna system, which converts the distributed signal back to radio and feeds one or more local antennas. Remote units need power, a mounting location and access for maintenance, so their placement affects both coverage and the practicality of the installation.
- Riser
The vertical pathway through a building, usually a stacked shaft or cupboard, through which cabling travels between floors. Riser availability, existing occupancy, fire-stopping requirements and access arrangements often determine what distribution design is realistic in an occupied building.
- RSRP
Reference Signal Received Power: the average power a device measures from a network's reference signals, expressed in dBm. RSRP describes how strong the wanted signal is, but not how clean it is, so a strong RSRP accompanied by poor quality measurements still indicates a problem.
- RSRQ
Reference Signal Received Quality: a ratio that relates the wanted reference signal to the total received power in the band, expressed in decibels. Because it accounts for interference and load as well as strength, RSRQ often falls at busy times even when RSRP is unchanged.
S
- SINR
Signal-to-interference-plus-noise ratio: how far the wanted signal stands above everything else the receiver hears, expressed in decibels. SINR is usually the best single indicator of whether a connection will actually work well, because networks select higher data rates only when the ratio supports them.
- Small cell
A compact, low-power base station that serves a limited area and connects back to the mobile network over a fixed link. Unlike a repeater, a small cell is part of the network itself, so it adds capacity as well as coverage. Deployment involves the mobile operator, because the equipment forms part of a licensed network.
U
- Uplink
The direction of transmission from the device to the network. Uplink is usually the weaker direction, because a handheld device transmits at far lower power than a base station. Uplink problems often appear as a call that connects but is inaudible at the far end, or as messages that fail to send from a location where the signal indicator looks healthy.
V
- VSWR
Voltage standing wave ratio: a measure of how well an antenna and its feed line are matched, derived from how much transmitted power is reflected back instead of radiated. A poor ratio wastes power and points to a physical fault such as a damaged cable, a bad connector or a water-ingress problem.
W
- Walk test
A survey carried out by walking a defined route through a building while recording measurements and observations at identified points. A walk test captures how a space actually behaves, including variation between floors, corridors and interior rooms, in a way that a calculation alone cannot.
- Wi-Fi calling
A feature that carries mobile voice calls and messages over a Wi-Fi connection instead of the cellular network. Where it is supported by the carrier, the device and the local network, it can relieve voice problems in a specific area, but it depends on the quality of the Wi-Fi and the internet connection behind it and does not help data sessions that remain on the cellular network.
Measurement names and units follow common industry usage. Where a carrier, a manufacturer or a specification defines a term more narrowly, that definition governs the work in question.
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