6 ICT Applications – Satellite Systems (IGCSE 0417 Section 6.11)
1. What the syllabus expects
The Cambridge IGCSE 0417 ICT syllabus requires knowledge of exactly five satellite‑based services. These are the only systems you need to master for the exam:
- Global Positioning System (GPS)
- Other satellite‑navigation constellations (GLONASS, Galileo, BeiDou)
- Geographic Information Systems (GIS) that use satellite data
- Satellite television (direct‑to‑home broadcasting)
- Satellite telephone services
2. Global Positioning System (GPS)
GPS is a US‑operated constellation of at least 24 Medium‑Earth‑Orbit (MEO) satellites that broadcast precise timing signals. Receivers calculate position by measuring the travel‑time of these signals.
| Aspect | Key Points |
|---|
| Characteristics | - ≥ 24 satellites in MEO (≈ 20 000 km altitude)
- Provides latitude, longitude & altitude
- Civilian accuracy ≈ 5–10 m; military accuracy < 1 m
- Frequency: L‑band (1.575 GHz) – civilian C/A signal & encrypted military P‑Y signal
|
| Typical Uses | - Navigation for cars, aircraft and ships
- Mapping, surveying and land‑management
- Location‑based services – e‑commerce deliveries, emergency dispatch, fitness trackers
|
| Advantages | - Global coverage – works anywhere on Earth
- Real‑time positioning, no subscription fee for civilian users
- Highly reliable; built into virtually all smartphones, tablets and vehicle navigation units
|
| Disadvantages | - Signal blocked by tall buildings, dense foliage or indoor environments
- Accuracy reduced by ionospheric/atmospheric disturbances
- Vulnerable to intentional jamming or spoofing attacks
|
3. Other Satellite‑Navigation Constellations
Other nations run compatible navigation systems. They use the same time‑of‑flight principle but differ in orbital layout, frequency bands and service features.
| System | Key Features | Advantages | Disadvantages |
|---|
| GLONASS (Russia) | 24 satellites, MEO (≈ 19 500 km), global coverage | Slightly better accuracy at high latitudes; provides an independent backup to GPS | Overall civilian accuracy a little lower than modern GPS; older civilian signal unencrypted and more easily jammed |
| Galileo (European Union) | 30 satellites (incl. 6 spares), MEO (≈ 23 200 km), civilian‑controlled | Civilian accuracy ≈ 1 m; built‑in authentication reduces spoofing; free for civilian use | Full constellation still being completed – performance not yet uniform worldwide; best results need a Galileo‑compatible receiver |
| BeiDou (China) | 35 satellites (regional + global phases); mix of GEO, IGSO and MEO orbits | Provides a short‑message service (up to 120 bytes) directly to users; strong coverage in Asia‑Pacific | Limited civilian receiver support outside China; accuracy comparable to GPS but less widely adopted |
4. Geographic Information Systems (GIS) Using Satellite Data
GIS integrates spatial data (e.g., satellite imagery, GPS points) with attribute data to store, query, analyse and visualise geographic information.
| Aspect | Key Points |
|---|
| Characteristics | - Layered model – raster (satellite images) + vector (points, lines, polygons)
- Supports spatial queries, modelling, map production and real‑time updates
- Common software: ArcGIS, QGIS, Google Earth Engine
|
| Typical Uses | - Urban planning and infrastructure design
- Environmental monitoring – deforestation, flood mapping, climate change
- Disaster management – damage assessment, relief coordination
- Precision agriculture – soil moisture, crop health, yield prediction
- Transport routing and logistics optimisation
|
| Advantages | - Provides a visual, comprehensive picture of geographic phenomena
- Facilitates data‑driven decision making
- Near‑real‑time updates possible with modern satellite feeds
|
| Disadvantages | - High‑resolution satellite imagery can be expensive
- Requires specialised software and trained personnel
- Large data volumes demand substantial storage and processing power
|
5. Satellite Television (Direct‑to‑Home Broadcasting)
Satellite TV sends television signals from an uplink earth station to a geostationary satellite, which then beams the signal back to a dish antenna at the viewer’s premises.
| Aspect | Key Points |
|---|
| Characteristics | - Geostationary satellites at ≈ 35 786 km altitude
- Typical frequency bands: Ku‑band (12–18 GHz) or Ka‑band (26.5–40 GHz)
- Digital compression (MPEG‑2, MPEG‑4) allows many channels per transponder
|
| Typical Uses | - Free‑to‑air and pay‑per‑view TV channels
- Direct‑to‑home (DTH) service for rural or remote areas
- Interactive services – video‑on‑demand, electronic programme guides
|
| Advantages | - Wide coverage – reaches locations where cable or terrestrial broadcast is unavailable
- High‑definition picture quality; supports 4K/HD‑R
- Quick deployment – only a dish, LNB and set‑top box required
|
| Disadvantages | - Signal attenuation (“rain fade”) in heavy precipitation
- Initial cost of dish, LNB and receiver
- Higher latency than terrestrial broadcast (not noticeable for linear TV, but relevant for interactive services)
|
6. Satellite Telephone Services
Satellite phones communicate directly with orbiting satellites, bypassing terrestrial mobile networks. They are essential for voice and low‑rate data in locations without cellular coverage.
| Aspect | Key Points |
|---|
| Characteristics | - Operates in L‑band (1.5–1.6 GHz) or Ku‑band (12–14 GHz)
- Uses Low‑Earth‑Orbit constellations (e.g., Iridium) or Medium‑Earth‑Orbit constellations (e.g., Inmarsat)
- Handset size ≈ 200 mm × 100 mm; external antenna often required for best signal
|
| Typical Uses | - Emergency and disaster response where ground networks are down
- Maritime and aviation communication in remote oceanic regions
- Field work in mining, oil‑gas, scientific expeditions
- Humanitarian aid and remote community outreach
|
| Advantages | - Global reach – works virtually anywhere on the planet
- Reliable when terrestrial infrastructure is damaged or absent
- Supports voice and low‑rate data (text, GPS tracking)
|
| Disadvantages | - Higher cost per minute compared with standard mobile phones
- Handset and external antenna are bulkier than a typical mobile phone
- Signal quality can be degraded by deep valleys, dense urban canyons or heavy foliage
|
7. Suggested Diagram
Include a simple orbit diagram that shows:
- GPS constellation in MEO (≈ 20 000 km)
- A geostationary satellite used for TV broadcasting (≈ 35 786 km)
- LEO/ME0 satellites used for satellite phones (Iridium, Inmarsat)
8. Action‑Oriented Review Checklist (Exam‑Focused)
- State that the five satellite services listed in Section 1 are the *only* ones required by the IGCSE 0417 syllabus.
- For each service, be able to name at least two key characteristics (e.g., orbit type, number of satellites, frequency band).
- Give two practical uses for each service and explain why the service is valuable in those contexts.
- Compare at least one advantage and one disadvantage for every system, focusing on coverage, cost, reliability and technical limitations.
- Explain how GIS integrates satellite imagery and GPS data to produce layered maps and support spatial analysis.
- Remember the specific frequency band for GPS (L‑band) and the distinction between civilian (C/A) and military (P‑Y) signals.
- When discussing other navigation constellations, mention each system’s unique strength (e.g., Galileo authentication, GLONASS high‑latitude performance, BeiDou short‑message service) and any current limitation.
- Be prepared to sketch a simple orbit diagram and label the three orbit types (LEO, MEO, GEO) used by the services above.