Glossary of Satellite Terms

This page covers the traditional satellite infrastructure terms. If you are looking for terms related to the digital transformation of the ground station, see the glossary page xx.



Advanced Encryption Standard – an encryption algorithm that secures data before it is transmitted over a network. Typically used by US Government Agencies. More on AES can be found on Search Security.


Adaptive Coding and Modulation – an algorithm to dynamically change the coding and modulation scheme to reach to atmospheric conditions and network configurations (Dish size, modem characteristics, BUC size, Satellite power, etc)


Amplitude and phase-shift keying or asymmetric phase-shift keying – a digital modulation scheme that changes the amplitude and phase of the carrier wave. See APSK for more info.

Analog Transmission

A transmission method using a continuous signal for transmitting voice, data, image, signal or video information. This signal varies in amplitude, phase, or some other property in proportion to that of a variable. Further information on Wikipedia.


Equipment that typically transmits and receives electromagnetic waves, usually referred to as the satellite dish



Code Division Multiple Access (CDMA) is a radio communication technology that allows for several transmitters to send information simultaneously over a single communications channel. This shared communications technology often uses spread-spectrum and a special codeing scheme to prevent interference between users.

See Code division multiple access on Wikipedia for additional details.

Carrier to Noise Ratio (C/N)

The ratio of the received carrier power and the noise power in a given bandwidth, expressed in dB. This figure is directly related to G/T and S/N. Typically in a signal, the higher the C/N, the better the quality.


Frequency band with uplink 5.925‐6.425 GHz, downlink 3.7‐4.2 GHz. The C band is primarily used for voice and data communications.

Cellular Backhaul

Transmission of cellular voice and data signals, typically from a base station to a remote site. Includes 3g and LTE.

Circular Polarization

Refers to a method of transmitting signals from a satellite. On some satellites, both right‐hand rotating and left-hand rotating signals can be transmitted simultaneously on the same frequency; thereby doubling the capacity of the satellite to carry communications channels.


Footprint or the area on the earth’s surface that is covered by a satellite’s transmission beam.



Effective Isotropic Radiated Power. This term describes the strength of the satellite signal in dBW and is a result of the transponder output power and the gain of the satellite transmit antenna

Earth Station

Ground equipment that transmits and receives electromagnetic waves, also referred to as an antenna



Geostationary Earth Orbit (GEO) satellites orbit at 35,786 km (22,282 mi) above the equator in the same direction and speed as the earth rotates on its axis, making them appear as fixed in the sky.


Global System for Mobile (GSM) communications is a standard for digital wireless communications to mobile phones.


A figure of merit of an antenna and low noise amplifier combination expressed in dB. “G” is the gain of the system and “T” is the noise temperature. The higher the G/T, the better the system.


A measure of amplification expressed in dB.

Ground Station in the Cloud

A ground station in the cloud is a satellite gateway using virtual and cloud-based architectures to create a flexible, scalable, and cost-effective satellite gateway infrastructure.

Guard Band

Transmission carriers are separated on a transponder by spacing them several kilohertz (kHz) apart. This unused space serves to prevent the adjacent transmission carriers from interfering with each other.



Indoor Unit  (IDU) is network equipment, typically located inside a building, that consists of a modem and router (or hub) connected to the a LAN or terrestrial infrastructure.


Internet Protocol (IP) is a protocol used for data communication across a packet switched network. Typically used with TCP, a higher level protocol.


International Organization for Standardization (ISO) is a standard setting body composed of multiple national standards organizations.


Internet Service Provider is a company that offers Internet access to customers.


See Inbound


In a network an Inbound is typically referred to as the transmission of signal to the satellite from the remote router to a satellite to a hub.



Kilobits per second (Kbps) refers to transmission speed of 1,024 bits per second.


Frequency band with uplink 26.5‐40GHz; downlink 18‐20 GHz, this band is primarily used for two‐way consumer broadband.


Frequency band with uplink 14 GHz; downlink 10.9‐12.75 GHz, with more powerful transmission from the satellite more susceptible to rain fade than C‐Band.



Mega bits per second (Mbps) refers to the transmission speed of 1,024,000 bits per second.


Medium Earth Orbit (MEO) satellites are located above LEO and below GEO satellites and typically travel in an elliptical orbit over the North and South Pole 0r in an equatorial orbit.


Multiple‐Frequency Time Division Multiple Access (MF-TDMA) is a broadband access method where different data streams are put into different slots that are separated by both frequency and time.

Mesh Network

Topology whereby a remote VSAT location communicates with another remote location without routing through the hub.


A piece of network equipment containing a modulator and demodulator for receiving or transmitting satellite signals.


The encoding of a carrier wave by amplitude or frequency or phase.


Multicast is a subset of broadcast whereby the signal can be sent to many sites within a defined group, but not necessarily to all sites in that group.


Sending multiple signals or streams of information on a carrier simultaneously transmitting on a single signal.



“Outdoor Unit” – the equipment located outside of a building close to the satellite dish or antenna and typically includes, a low noise block converter (LNB), and a block‐up‐converter (BUC)


Transmission of a signal from the satellite to an antenna. In a network it is typically referred to as the transmission from the hub to a satellite to a remote router



Quality of Service (QoS) provides priority and guarantees a certain level of network response time and other performance factors for each application and user.


Quadrature Phase Key Shifting (QPSK) is a modulation scheme that uses four phases.



Supervisory Control and Data Acquisition (SCADA) is the system that monitors and controls industrial or facility based remote devices.


Single Channel per Carrier (SCPC) is a satellite access method that dedicates one channel to each remote site, sometime used for very high capacity links. See also TDMA.


Communications satellites orbit the earth and transmit and receive radio signals from earth stations.



Border Gateway Protocol – a routing protocol for exchanging route information between gateway hosts in a network of autonomous systems. See BGP on Wikipedia.


Binary Phase Key Shifting – a modulation scheme that uses a change in the phase of a signal to transmit information. The most simple form of PSK, BPSK has only two phases, 180 degrees apart.


A block upconverter (BUC) converts from a lower frequency transmitted by a modem to a higher frequency used by satellites. Most satellite modems output 70-Mhz or L-Band frequencies which must be upconverted to Ku, C, or Ka band frequencies.

More details on BUC can be found on Wikipedia.


Satellite bandwidth is typically expressed in a range of frequencies within a spectrum, expressed in Hertz. It can also be data transfer rate or throughput expressed in bits per second.

A detailed explanation of Bandwidth can be found on Wikipedia.

Bit Rate

Speed of transmission, measured in bits per second (bps)


To transmit to all sites in a given area. In satellite the broadcast area (or domain) is a geographical region covered by the satellite beam.



The ratio of the power to one Watt expressed in decibels. Typically the E.I.R.P of satellite beams are measured in dBW.


Deterministic Time Division Multiple Access (D-TDMA) is iDirect’s patented access technology that provides simultaneous access to shared upstream channels using dynamically assigned time slots.


Digital Video Broadcasting – Satellite – Second Generation (DVB-S2) is the enhanced version of the DVB‐S satellite broadband transmission standard and has forward error correction and modulation specifications.


The time it takes for a signal to go from the sending station through the satellite to the receiving station. This transmission delay for a single hop satellite connection is very close to 240 ms.

Digital IF

Digital IF is the concept of digitizing RF signals into IP.

Digital Satellite Gateway

Satellite gateways typically use an L-Band transport infrastructure to move RF signals between the satellite antenna (outside) and the modem (inside). Modems convert the RF to an IP data stream as well as the opposite. A digital gateway digitizes the RF signal into an IP data stream at the antenna, and the gateway uses standard internetworking (routers and switches) as the transport infrastructure. They are specific to an end-user application while an RF digitizer creates an industry-standard IP data stream (e.g., VITA-49).

Double Hop

Transmission of information from one terminal to another terminal in two stages, first from a remote site VSAT up to the satellite to the network hub or from the network hub up to the satellite then to another remote site.


Transmission of a signal from the satellite to the earth. In a network it is typically referred to the link between a network hub over the satellite to a remote site.



Frequency Division Multiple Access (FDMA) is a channel access method that allocates each application or user a different frequency band.


Forward Error Correction (FEC) is the system for error control that has the sender include redundant data so errors can be detected and corrected at the receiver.


The area on the earth’s surface that is covered by a satellite’s transmission beam.


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Low-Density Parity-Check (LDPC) is a forward error correction code that is currently the most efficient scheme for transmitting data over a noisy transmission channel. It is used with DVB‐S2.

Further details on LDPC on Wikipedia.


Low Earth Orbit (LEO) is a satellite orbit from 160‐2000km above the earth. These satellites orbit the earth and take about 127 minutes to make a full orbit.


Frequency band from 1 to 2 GHz, this band is the result of the down‐conversion of the received downlink satellite signal from the LNB.

Low Noise Amplifier (LNA)

This is the preamplifier between the antenna and the earth station receiver. For maximum effectiveness, it must be located as near the antenna as possible, and is usually attached directly to the antenna receive port.

Low Noise Block Downconverter (LNB)

A combination Low Noise Amplifier and downconverter built into one device attached to the feed. It is used for the downlink satellite transmission by converting a band from a higher frequency to a lower frequency.


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Paired Carrier Multiple Access (PCMA) is a satellite signal canceller that maximizes the capacity of satellite networks by using ViaSat’s patented PCMA technology to reduce satellite bandwidth as much as 50 percent.


proliferated Low Earth Orbit Satellite Constellation – This is a constellation of LEO satellites (orbit less than 2000 km) that is in the hundreds or thousands of satellites.


Phase Shift Key (PSK) is a digital modulation scheme that changes the phase of the carrier wave.


A technique used by satellite operators to reuse the satellite transponder frequencies when transmitting these signals to Earth. Two methods are possible: linear and circular. To successfully receive and decode these signals on earth, the antenna must be outfitted with a properly polarized linear or circular feedhorn to select the signals as desired



Radio Frequency Interference – A disruption to desired radio communications that enters through the receiving antenna along with the desired communication signals.


Radio Frequency (RF) is the electromagnetic frequencies for wireless transmission that is above the audio range and below infrared light.

Rain Fade

Decrease of satellite signal strength due to rainfall. This occurs typically at Ku Band frequencies due to its increased sensitivity to noise temperature.



Transmission Control Protocol (TCP) is a core Internet protocol that is a higher level protocol often combined with IP.


Time Division Multiple Access (TDMA) is a channel access method that allows applications or users to share the same frequency by dividing the full bandwidth into specific timeslots.


Receives outbound signal, from an earth station, at the satellite and amplifies the signal before retransmitting it to an earth station

U – Z


Wide Area Network (WAN) is a computer network that covers a broad area that connects multiple remote locations.


Transmission of a signal from the remote router to a satellite to a hub.


Virtual LAN (VLAN) is a group of hosts that simulates a LAN although they are not located locally on the same network switch.


The VmE bus International trade Association created VITA-49 to create a standard method for packaging digitized RF signals into an IP packet. VITA-49 created the ability to deploy IP based, digital gateway architectures.


Very Small Aperture Terminal (VSAT) is an antenna that is typically less than 3 meters in diameter.


Wideband Global Satcom (WGS) a satellite communication system used by the U.S. Department of Defense.


Frequency band with uplink 7.9‐ 8.4 GHz, downlink 7.25 – 7.75 GHz, this band is primarily used for military communications and Wideband Global Satcom (WGS) systems.