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A cargo ship in the middle of the Pacific Ocean streams video to its crew. A research station in Antarctica maintains real-time connections to universities worldwide. A rural village hundreds of kilometers from the nearest city accesses the global internet. None of this would be possible without satellite communication—humanity's solution to connecting anything, anywhere on Earth.
Satellite networks represent the ultimate expression of unguided media: signals travel hundreds or thousands of kilometers through space, bounce off relay stations orbiting Earth, and return to connect the most remote locations. Understanding satellite communication is essential for network professionals dealing with global infrastructure, maritime and aviation connectivity, emergency communications, or the rapidly evolving satellite internet services transforming rural and underserved connectivity.
By the end of this page, you will understand satellite orbital mechanics and how orbit choice affects network design, frequency bands and their propagation characteristics, earth station design and link budget analysis, the differences between GEO, MEO, and LEO satellite systems, modern satellite internet constellations like Starlink and OneWeb, and key applications of satellite networking in telecommunications.
Satellite communication relies on placing relay stations in Earth orbit. The characteristics of these orbits—altitude, inclination, and shape—fundamentally determine the satellite system's coverage, latency, and operational complexity. Understanding orbital mechanics is the foundation for understanding satellite network design.
Kepler's Laws and Orbital Periods:
Satellites obey the same laws of motion as planets and moons. Johannes Kepler's laws describe orbital mechanics:
1. First Law (Law of Ellipses): Satellites orbit in elliptical paths with Earth at one focus. Most communication satellites use nearly circular orbits (very low eccentricity), but some specialized applications use highly elliptical orbits (HEO).
2. Second Law (Law of Equal Areas): A satellite in an elliptical orbit moves faster when closer to Earth and slower when farther away. The line from Earth to satellite sweeps equal areas in equal time.
3. Third Law (Period-Distance Relationship): Orbital period increases with altitude. The relationship is:
$$T = 2\pi \sqrt{\frac{a^3}{\mu}}$$
Where:
This law produces a critical result: at an altitude of approximately 35,786 km, the orbital period equals exactly one sidereal day (23 hours, 56 minutes). A satellite at this altitude, in an equatorial orbit, appears stationary from Earth's surface—the geostationary orbit (GEO).
| Orbit Type | Altitude | Orbital Period | Round-Trip Latency | Coverage per Satellite |
|---|---|---|---|---|
| Very Low Earth Orbit (VLEO) | 150–500 km | ~90 minutes | 1–3 ms | ~1,000 km diameter |
| Low Earth Orbit (LEO) | 500–2,000 km | 90–127 minutes | 3–12 ms | 2,000–4,000 km diameter |
| Medium Earth Orbit (MEO) | 2,000–35,786 km | 2–24 hours | 50–200 ms | Quarter to half of visible hemisphere |
| Geostationary Orbit (GEO) | 35,786 km | 24 hours | ~550 ms | ~1/3 of Earth (~120° coverage) |
| Highly Elliptical Orbit (HEO) | Variable (e.g., 500–40,000 km) | 12 hours (Molniya) | Variable | Extended polar coverage during apogee |
Inclination and Coverage:
Orbital inclination is the angle between the orbital plane and Earth's equator:
For global coverage, LEO and MEO constellations typically use multiple orbital planes with inclinations of 50–90° to ensure all latitudes are served.
Ground Track and Revisit Time:
A satellite's ground track is its path projected onto Earth's surface. Non-geostationary satellites continuously move relative to the ground. Key considerations:
GEO provides continuous coverage of a third of Earth with just one satellite, but at the cost of 550+ ms latency. LEO offers low latency (20–50 ms) but requires hundreds or thousands of satellites and complex handoffs. This fundamental trade-off shapes all satellite system architecture decisions.
Orbital Slot Allocation:
Geostationary orbit is a finite resource. Satellites in GEO must maintain spacing (typically 2–3°) to avoid interference—limiting the total number of GEO slots to about 180 operational positions. The International Telecommunication Union (ITU) coordinates orbital slot assignments internationally to prevent conflicts.
LEO and MEO constellations don't have fixed slots but must coordinate to prevent collision risk and radio interference. The rapid proliferation of LEO satellites (Starlink alone has launched thousands) is straining coordination mechanisms and raising concerns about orbital debris and astronomers' access to dark skies.
Satellite communication uses specific frequency bands allocated by international agreement. Each band has distinct propagation characteristics, equipment requirements, and suitability for different applications. The choice of frequency band is one of the most fundamental decisions in satellite system design.
| Band | Uplink (GHz) | Downlink (GHz) | Bandwidth (MHz) | Characteristics | Primary Applications |
|---|---|---|---|---|---|
| L-band | 1.6–1.66 | 1.5–1.56 | ~60 | Low rain fade; good penetration; limited bandwidth | Mobile satellite, Iridium, GPS |
| S-band | 2.0–2.3 | 1.98–2.20 | ~200 | Low rain fade; moderate bandwidth | Scientific missions, NASA TDRS |
| C-band | 5.9–6.4 | 3.7–4.2 | ~500 | Minimal rain fade; crowded spectrum | Legacy broadcast, tropical regions |
| Ku-band | 14.0–14.5 | 11.7–12.2 | ~500 | Moderate rain fade; smaller dishes | DTH television, VSAT enterprise |
| Ka-band | 27.5–30.0 | 17.7–21.2 | ~3500 | High rain fade; very high throughput | HTS broadband, Starlink, OneWeb |
| V-band | 47.2–50.2 | 37.5–42.0 | ~5000 | Severe rain fade; extreme bandwidth | Next-gen HTS (emerging) |
| Q-band | 42.5–43.5 | 33.0–36.0 | ~3500 | Very high rain fade; gateway links | HTS gateway feeder links |
Uplink vs. Downlink:
Satellite systems use different frequencies for uplink (earth-to-satellite) and downlink (satellite-to-earth), a technique called Frequency Division Duplexing (FDD). This separation:
Propagation Considerations:
Satellite signals traverse the entire atmosphere twice (up and down), encountering various propagation challenges:
Free Space Path Loss: The dominant loss factor, FSPL at satellite distances is enormous:
This 40 dB difference means GEO signals require 10,000× more power (or gain) than LEO signals to achieve the same received power.
Rain Attenuation: As with terrestrial microwave, rain severely attenuates satellite signals above 10 GHz. For Ka-band:
Designers must include link margin or use Adaptive Coding and Modulation (ACM) to maintain connectivity during rain events.
Ionospheric Effects: At frequencies below about 3 GHz, the ionosphere can cause:
These effects diminish rapidly with frequency, making them primarily a concern for L-band and S-band systems.
Modern high-throughput satellites (HTS) use Ka-band for its abundant bandwidth, but rain fade can cause 20+ dB signal loss during heavy storms. HTS systems mitigate this with ACM (falling back to lower data rates during rain), site diversity (routing to unaffected gateway stations), and statistical fade margin. In tropical regions, link availability targets may require significant capacity reduction during monsoon seasons.
Frequency Reuse and Capacity:
Modern satellites maximize capacity through aggressive frequency reuse:
Polarization Reuse: Using two orthogonal polarizations (horizontal/vertical or left/right circular) doubles capacity on the same frequency band. Most satellite systems employ dual polarization.
Spatial (Spot Beam) Reuse: High-throughput satellites (HTS) use multiple narrow spot beams instead of broad regional beams. Non-adjacent beams can reuse the same frequency, dramatically increasing overall capacity. A typical HTS might have 100+ spot beams, reusing the same spectrum 20–50 times.
Color Schemes: The combination of frequency sub-bands and polarizations creates a 'color' scheme (analogous to cellular frequency planning). A common configuration uses 4 colors (2 frequency segments × 2 polarizations), ensuring adjacent beams never share the same color.
An earth station (also called a ground station or terminal) is the terrestrial endpoint of a satellite link. Earth stations range from massive gateway facilities with 10+ meter antennas to handheld mobile terminals. Understanding earth station characteristics and link budget analysis is essential for designing reliable satellite networks.
Earth Station Components:
Antenna Subsystem:
Indoor Equipment:
Antenna Performance Metrics:
| Station Type | Antenna Size | Typical EIRP | Typical G/T | Applications |
|---|---|---|---|---|
| Major Gateway | 7–15 m | 60–70 dBW | 35–45 dB/K | Hub for HTS, broadcast uplink, teleports |
| Enterprise VSAT | 1.2–2.4 m | 45–55 dBW | 20–30 dB/K | Corporate WAN, remote offices, maritime |
| Consumer DTH | 0.45–0.9 m | 35–45 dBW | 12–20 dB/K | Satellite TV reception, consumer broadband |
| Portable/Flyaway | 0.75–1.5 m | 45–50 dBW | 18–25 dB/K | News gathering, military, emergency response |
| Handheld/Terminal | Small patch/helix | 10–20 dBW | <10 dB/K | Satellite phones, IoT devices |
| Flat Panel (Phased Array) | 0.3–0.6 m equivalent | 40–50 dBW | 15–25 dB/K | LEO terminals (Starlink), mobile platforms |
Satellite Link Budget:
A link budget accounts for all gains and losses in the satellite link, determining whether the system will meet performance requirements. The fundamental equation:
$$C/N_0 = EIRP + G/T - L_{path} - L_{atm} - k$$
Where:
Example: GEO Ku-band Downlink
C/N₀ = 52 + 20 - 206 - 0.3 + 228.6 = 94.3 dB-Hz
This C/N₀ is then compared against the required value for the target data rate and modulation scheme to determine if the link closes with adequate margin.
G/T (gain-to-noise-temperature ratio) is the single most important receive-side parameter. Higher G/T means better sensitivity: achieved through larger antennas (more gain) and lower-noise electronics (lower T). Upgrading from a 15 dB/K to 20 dB/K terminal provides the same benefit as 5× higher satellite power—often far more economical than building bigger satellites.
Link Margin and Availability:
The difference between actual C/N₀ and required C/N₀ is the link margin. This margin must accommodate:
Typical margin requirements:
Adaptive Coding and Modulation (ACM): Modern satellite systems dynamically adjust modulation and coding based on real-time link conditions. During fair weather, the system uses high-order modulation (32-APSK, 64-APSK) for maximum throughput. During rain fade, it falls back to robust schemes (QPSK, BPSK) to maintain connectivity at reduced speed. ACM enables efficient use of spectrum while maintaining high availability.
Satellite communication systems are architected very differently depending on their orbital regime and application. Understanding these architectural patterns helps network professionals select appropriate services and anticipate operational characteristics.
Geostationary (GEO) Systems:
Characteristics:
Architecture Patterns:
Traditional Bent-Pipe: The satellite acts as a 'mirror in the sky'—receiving uplink signals, frequency-converting, amplifying, and retransmitting on downlink. No onboard processing. Simple, reliable, flexible for changing applications.
Processed Payload (Regenerative): Onboard digital processing demodulates uplink, routes/switches data, and remodulates for downlink. Enables inter-spot-beam routing, mesh connectivity, and better link performance.
High-Throughput Satellite (HTS): Modern GEO satellites with dozens to hundreds of spot beams, frequency reuse, and often regenerative payloads. Capacity: 100–500+ Gbps per satellite. Examples: ViaSat-3 (1+ Tbps), Hughes Jupiter, SES-17.
Applications:
| Parameter | GEO | MEO (O3b) | LEO (Starlink) |
|---|---|---|---|
| Altitude | 35,786 km | 8,000 km | 550 km |
| Round-Trip Latency | ~600 ms | ~150 ms | ~30–50 ms |
| Satellites for Global Coverage | 3 | ~12–20 | ~1,500–4,000 |
| Satellite Lifetime | 15–20 years | 10–15 years | 5–7 years |
| Ground Antenna Tracking | Fixed (GEO pointing) | Tracking required | Phased array (electronic) |
| Launch Cost per Gbps | Low (large satellites) | Medium | Low (mass production) |
| Typical User Dish | 0.6–1.2 m | 0.3–0.6 m | Flat panel (~0.5 m) |
| Best For | Broadcast, backup, wide coverage | Enterprise/maritime low-latency | Consumer broadband, IoT |
Low Earth Orbit (LEO) Constellations:
Characteristics:
Modern LEO Constellations:
Starlink (SpaceX):
OneWeb:
Amazon Kuiper (planned):
Telesat Lightspeed (planned):
LEO constellations represent the biggest change in satellite communications in decades. SpaceX's vertically integrated approach (launching their own satellites on their own rockets) has driven costs down dramatically. Starlink alone now has more satellites in orbit than all previous satellite operators combined. This scale enables consumer pricing ($120/month typical) previously reserved for enterprise services.
Medium Earth Orbit (MEO) Systems:
Characteristics:
Key MEO Systems:
O3b (SES mPOWER):
GPS/GNSS:
Highly Elliptical Orbit (HEO):
HEO orbits provide extended coverage of polar regions not visible from GEO:
Molniya Orbit:
Tundra Orbit:
HEO is used for Arctic/polar coverage where GEO is invisible and LEO coverage is sparse.
Satellite links introduce unique characteristics—high latency, asymmetric bandwidth, and high error rates during fade—that require specialized protocols and techniques. Understanding these adaptations is essential for operating networks that traverse satellite links.
DVB-S2/S2X (Digital Video Broadcasting - Satellite):
The DVB-S2X standard is the dominant physical and data link layer protocol for satellite broadband:
Key Features:
Efficiency: DVB-S2X achieves up to 5.5 bits/Hz spectral efficiency under ideal conditions (256-APSK with minimal coding). ACM allows the system to maintain connectivity during 20+ dB fades by falling back to robust QPSK with heavy coding (~0.5 bits/Hz).
DVB-RCS2 (Return Channel via Satellite): Companion standard for the return link (user to hub):
| Layer | Standard/Protocol | Function | Satellite Adaptations |
|---|---|---|---|
| Physical | DVB-S2X (forward), DVB-RCS2 (return) | Modulation, FEC, framing | ACM, high-efficiency codes, fade management |
| Data Link | DVB-S2 GSE, MPEG-TS | Encapsulation, multiplexing | Generic Stream Encapsulation for IP-native operation |
| Network | IP (v4/v6) | Routing, addressing | TCP/IP optimization, PEPs, header compression |
| Transport | TCP, UDP, QUIC | End-to-end delivery | PEP acceleration for TCP over high-latency links |
| Application | HTTP, MPEG streams | User applications | Prefetching, compression, caching |
TCP Performance Enhancement:
TCP's congestion control algorithms were designed for terrestrial networks with latency of a few tens of milliseconds. GEO satellite links with 600 ms round-trip expose fundamental TCP limitations:
Problem: Slow Start and Congestion Window: TCP's slow start algorithm takes many round trips to reach full throughput. With 600 ms RTT, ramping up to full speed takes tens of seconds—devastating for web browsing and interactive applications.
Problem: Congestion Detection: TCP interprets packet loss as congestion. On satellite links, corruption-based losses (from fade) are misinterpreted as congestion, causing unnecessary throughput reduction.
Solution: Performance Enhancing Proxies (PEPs): PEPs are transparent middleboxes at each end of the satellite link that:
Modern Approach: End-to-End Optimization: Newer protocols like QUIC and BBR congestion control are more satellite-friendly:
PEPs work by intercepting and modifying TCP connections—which conflicts with end-to-end encryption. TLS-encrypted flows can be accelerated if the PEP has certificate access, but this breaks the end-to-end security model. With increasing encryption adoption, satellite operators are shifting focus to transport-layer optimizations that don't require breaking end-to-end encryption.
Multiple Access Schemes:
Forward Link (Hub to Terminals): Typically TDM (Time Division Multiplexing)—the hub transmits a continuous stream, and terminals filter out their packets. DVB-S2X carries multiple streams, with terminals decoding relevant ones.
Return Link (Terminals to Hub): Multiple terminals share uplink capacity using:
Inter-Satellite Links (ISLs): Modern LEO constellations use optical ISLs to route traffic between satellites:
Satellite networks serve applications where terrestrial connectivity is unavailable, insufficient, or needs backup. Understanding the application landscape helps network professionals identify where satellite solutions add value and what requirements they must meet.
| Requirement | Recommended Approach | Rationale |
|---|---|---|
| Low latency (<100 ms) | LEO constellation (Starlink) | GEO latency is fundamentally ~600 ms |
| Remote fixed installation | GEO HTS or LEO | Simple fixed antenna; capacity available |
| Maritime/mobile platform | LEO or Ku-band GEO with tracking | Requires motion-tolerant antenna |
| Polar region coverage | LEO (polar inclined) or MEO | GEO doesn't cover high latitudes |
| Mission-critical backup | GEO VSAT with SLA | Mature, proven, contractual guarantees |
| Low-bandwidth IoT | Satellite IoT (Swarm, Orbcomm) | Cost-optimized for small data volumes |
| Broadcast distribution | GEO | One satellite covers 1/3 of Earth continuously |
Many enterprises use satellite as part of hybrid architectures: primary terrestrial connectivity (fiber, LTE) with satellite backup that activates automatically during outages. For retail, banking, and healthcare, this ensures business continuity when primary links fail. Modern SD-WAN platforms integrate satellite seamlessly alongside terrestrial links.
The Convergence Trend:
The satellite industry is converging with terrestrial networking:
Cloud Integration: Major cloud providers (AWS Ground Station, Azure Orbital, Google Cloud) offer ground station-as-a-service, enabling satellite operators to process data directly in the cloud without building their own ground infrastructure.
5G and Satellite: 3GPP standards now include Non-Terrestrial Networks (NTN), defining how 5G radios can operate over satellite links. This enables seamless handoff between terrestrial 5G and satellite, unified device connectivity, and satellite as a legitimate backhaul for 5G base stations.
Software-Defined Satellites: Modern satellites increasingly feature software-defined payloads that can reconfigure frequency plans, beam patterns, and protocols via software update—adapting to changing market needs over their 15+ year lifetimes.
The vision: satellites become transparent parts of global network infrastructure, accessed through the same APIs and management tools as any other network link, with users unaware of whether their packets traverse fiber, microwave, or space.
Satellite communication enables connectivity where no other technology can reach—from remote villages to transoceanic ships to aircraft at 40,000 feet. The emergence of LEO constellations is transforming what was once an expensive, high-latency last resort into a competitive broadband option.
What's Next:
In the final page of this module, we'll synthesize everything we've learned about unguided media to explore wireless characteristics comprehensively—examining the common challenges and design principles that apply across radio, microwave, infrared, and satellite communication, and how modern wireless networks address them.
You now have a comprehensive understanding of satellite communication—from orbital mechanics through frequency allocation, link budgets, system architectures, networking protocols, and applications. This knowledge is essential for designing global network architectures, understanding connectivity options for remote locations, and anticipating how satellite is converging with terrestrial networking.