SATCOM Glossary: G–L
This section of the glossary covers terms from G through L, including gateway infrastructure, satellite orbit classifications, frequency bands, link performance metrics, and hardware terminology commonly encountered in satellite communication engineering.
Each term includes a concise definition, a note on practical relevance, and cross-links to related pages in the basics and solutions sections of the satcomindex knowledge base.
G
Gateway
A large ground station that serves as the interface between the satellite network and terrestrial infrastructure such as the internet backbone or private networks. Gateways typically use high-gain antennas (7 m to 13 m) and high-power amplifiers to aggregate traffic from many remote terminals.
The gateway is the traffic aggregation point for the satellite system. Gateway location, redundancy, and backhaul capacity directly affect the throughput, latency, and reliability available to all terminals connected through it.
GEO (Geostationary Earth Orbit)
A circular orbit at approximately 35,786 km above the equator where the satellite orbital period matches Earth’s rotation, causing the satellite to appear stationary relative to a ground observer. GEO is used by most traditional communication satellites for fixed coverage over a defined service area.
GEO provides continuous coverage from a single satellite position, eliminating the need for handovers. However, the high altitude introduces approximately 600 ms round-trip latency, which affects real-time applications such as voice and video conferencing.
G/T (Gain-to-Noise Temperature)
A figure of merit for a receiving system, expressed in dB/K, calculated as the antenna gain (dBi) minus the system noise temperature (dB-K). G/T characterizes how well the receive chain can extract signal from noise.
G/T is a key parameter in the downlink budget. A higher G/T means the terminal or gateway can receive weaker signals or support higher data rates. Improving G/T can be achieved by increasing antenna size, reducing feed losses, or using a lower-noise LNB.
Ground Segment
The collective term for all Earth-based infrastructure in a satellite communication system, including gateways, teleport facilities, network operations centers (NOCs), and the terrestrial backhaul that connects gateways to the internet or private networks.
The ground segment determines how satellite capacity is managed, monitored, and distributed. Gateway redundancy, geographic diversity, and backhaul capacity within the ground segment directly affect system-level availability and throughput.
H
Handover (Beam/Gateway/Satellite)
The process of transferring an active communication session from one beam, gateway, or satellite to another without interrupting the service. In LEO constellations, handovers occur frequently as satellites move across the sky; in GEO systems, they typically occur only during planned gateway switches.
Seamless handover is critical for maintaining session continuity in non-geostationary systems. The handover mechanism, speed, and packet loss characteristics directly affect the user experience for latency-sensitive applications such as VoIP and video.
HTS (High Throughput Satellite)
A class of communication satellite that achieves significantly higher total capacity (typically 100+ Gbps) compared to conventional widebeam satellites by using multiple spot beams and extensive frequency reuse. HTS systems operate primarily in Ku-band and Ka-band.
HTS satellites reduce the cost-per-bit of satellite bandwidth by multiplying total system capacity. This makes satellite broadband economically viable for a wider range of applications, from consumer internet access to enterprise connectivity in remote areas.
Hub (VSAT Hub)
The central network equipment at a gateway or teleport that manages all communication with remote VSAT terminals. The hub includes carrier management, bandwidth allocation, protocol acceleration, and network monitoring functions. It controls the outbound TDM carrier and schedules return-link access.
The hub is the intelligence layer of a VSAT network. Its bandwidth allocation algorithms, QoS policies, and acceleration features determine how effectively the satellite capacity is utilized across all connected terminals.
I
IF (Intermediate Frequency)
A standard frequency range (typically 950–2150 MHz for L-band IF) used to carry satellite signals between indoor equipment (modems) and outdoor equipment (BUC/LNB) over coaxial cable. The signal is upconverted to RF for transmission and downconverted from RF on reception.
IF is the interface between the modem and the antenna subsystem. Cable length, connector quality, and signal level at the IF interface affect system performance. Understanding IF signal flow is essential for installation, commissioning, and troubleshooting.
Inmarsat
An operator of GEO satellite constellations providing mobile and fixed communication services globally, particularly in maritime, aviation, and government sectors. Inmarsat operates L-band (for narrowband/safety) and Ka-band (for broadband via Global Xpress) services.
Inmarsat’s L-band services are mandated under the Global Maritime Distress and Safety System (GMDSS) for maritime safety communications. Its Ka-band Global Xpress constellation provides broadband services complementing traditional VSAT in mobility applications.
Interference
Unwanted RF energy that enters the receive path from sources other than the intended signal. In satellite systems, interference can originate from adjacent satellites (ASI), terrestrial emitters, cross-polarization leakage, or other carriers within the same transponder (co-channel interference).
Interference degrades the carrier-to-interference ratio (C/I), reducing the effective C/N and potentially causing demodulation errors. Identifying and mitigating interference sources is a key operational task for satellite network operators, requiring spectrum monitoring and coordination with adjacent networks.
J
Jitter
The variation in packet arrival time (delay variation) over a network connection, measured in milliseconds. In satellite links, jitter results from variable queuing delays at the hub and terminal, encapsulation overhead, and access scheme timing.
Excessive jitter disrupts real-time applications such as VoIP and video conferencing, causing audio distortion and video artifacts. QoS mechanisms at the satellite hub use jitter buffers and traffic prioritization to keep jitter within acceptable bounds for real-time traffic classes.
K
Ka-band
A satellite frequency band operating at approximately 26.5–40 GHz (downlink 17.7–21.2 GHz, uplink 27.5–31 GHz). Ka-band supports high bandwidth per beam and is the primary band for HTS broadband services.
Ka-band enables high-capacity spot beams with smaller terminal antennas (as small as 60 cm for consumer services). However, Ka-band is more susceptible to rain attenuation than Ku-band or C-band, requiring larger fade margins or ACM to maintain availability in tropical regions.
Keying (Phase-Shift Keying)
A digital modulation method that encodes data by varying the phase of the carrier signal. Common PSK variants in satellite communications include QPSK (4 phase states), 8PSK (8 states), and 16APSK/32APSK (combined amplitude and phase modulation) as defined in DVB-S2/S2X standards.
The choice of keying scheme determines the spectral efficiency and the required C/N for reliable demodulation. Higher-order PSK variants carry more bits per symbol but require a cleaner link. ACM systems switch between keying schemes dynamically based on real-time link quality.
Ku-band
A satellite frequency band operating at approximately 12–18 GHz (downlink 10.7–12.75 GHz, uplink 13.75–14.5 GHz). Ku-band is the most widely deployed band for VSAT services, direct broadcast television, and enterprise satellite networks.
Ku-band offers a practical balance between antenna size (typically 0.75 m to 2.4 m for remote terminals), bandwidth availability, and rain-fade resilience. It is the default band for most commercial VSAT deployments in temperate and maritime environments.
L
Latency
The time delay between sending and receiving data across the satellite link, typically measured as round-trip time (RTT). GEO satellite links exhibit approximately 550–650 ms RTT due to the 35,786 km orbital altitude; LEO systems achieve 20–50 ms RTT.
Latency is the primary performance differentiator between GEO and LEO satellite systems. High latency affects TCP throughput, interactive applications, and real-time communication quality. Protocol acceleration and local caching at the terminal mitigate some latency effects on GEO links.
LEO (Low Earth Orbit)
An orbital altitude range between approximately 300 km and 2,000 km above Earth. LEO constellations such as Starlink and OneWeb use hundreds or thousands of satellites to provide global or near-global coverage with low-latency broadband service.
LEO reduces round-trip latency to 20–50 ms, comparable to terrestrial networks, making it suitable for real-time applications. However, LEO requires large constellations, frequent satellite handovers, and complex ground segment orchestration to maintain continuous coverage.
Link Budget
A systematic accounting of all power gains and losses in a satellite communication path, from the transmitter through the uplink, satellite transponder, downlink, and receiver. The link budget calculates whether the received signal power meets the minimum C/N required for the target modulation and coding scheme.
The link budget is the fundamental engineering tool for satellite system design. It determines the required antenna sizes, amplifier power levels, and bandwidth allocations. An accurate link budget ensures the system meets availability targets under worst-case conditions such as rain fade.
Link Margin
The difference between the actual received C/N and the minimum C/N required for demodulation, expressed in dB. Link margin provides a buffer against signal degradation from atmospheric attenuation, antenna mispointing, equipment aging, and other variable losses.
Sufficient link margin ensures that the satellite link remains operational during adverse conditions. Operators typically design for 2–4 dB of clear-sky margin on Ku-band links and 4–8 dB on Ka-band links in tropical regions. The relationship between link margin and fade margin determines overall service availability.
LNB (Low Noise Block Downconverter)
An outdoor RF component mounted at the antenna feed that amplifies the received satellite signal and downconverts it from the receive frequency band (e.g., Ku-band or Ka-band) to the intermediate frequency (IF/L-band) for transmission to the indoor modem over coaxial cable.
The LNB’s noise temperature is a major contributor to the system G/T. A lower-noise LNB improves receive sensitivity, enabling smaller antennas or higher data rates. LNB selection must match the polarization and frequency plan of the target satellite.