--- title: "Short note: Satellite communication system" subject: "Communication Systems" chapter: 5 key: "semester_6/communication_systems:short-note-satellite-communication" source: https://www.bctengineer.com/q/semester_6/communication_systems/short-note-satellite-communication site: BCT Engineering --- # Short note: Satellite communication system Communication Systems · Chapter 5: Multiplexing Techniques - Asked in: 2072 Asoj (CS I), 4 marks; 2068 Bhadra (CS I), 4 marks (asked 2 times) - Video: [How do Satellites work? | ICT #10](https://www.youtube.com/watch?v=ror4P1UAv_g) — Sabin Civil Engineering - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/communication_systems/short-note-satellite-communication - Whole chapter: https://www.bctengineer.com/md/semester_6/communication_systems/chapter-5 ## Question Write a short note on satellite communication system. ## Short answer Satellite communication uses orbiting satellite as repeater: receives uplink, amplifies, frequency converts, retransmits downlink. Space segment: transponders, antennas, power, attitude control. Ground segment: earth stations with dishes, amplifiers, modems, TT&C. GEO at 35,786 km appears fixed; bands: C (6/4 GHz), Ku (14/12 GHz), Ka (30/20 GHz). Delay ~240-270 ms. Advantages: wide coverage, broadcast, distance-independent cost. Disadvantages: high launch cost, delay, rain fade, limited life. ## Answer A **satellite communication system** uses an artificial satellite in orbit as a **repeater in space**: it receives signals from an earth station, amplifies them, changes their frequency and retransmits them to other earth stations over a wide area. ```text [Satellite: transponder] ^ uplink \ downlink / (6 / 14 GHz) v (4 / 12 GHz) [Earth station A] [Earth station B] ``` **Main parts** - **Space segment:** satellite with transponders (receive antenna, LNA, frequency down-converter, power amplifier such as TWTA/SSPA, transmit antenna), solar panels, batteries, and attitude/orbit control. - **Ground segment:** earth stations with large dish antennas, high-power amplifiers (uplink), low-noise amplifiers (downlink), modems and multiplexers; plus telemetry, tracking and command (TT&C) stations. **Key features** - **Geostationary orbit (GEO)** at about 35 786 km above the equator; the satellite appears fixed, so antennas need not track. Three GEO satellites can cover almost the whole Earth. - Different uplink and downlink frequencies avoid interference: **C-band 6/4 GHz**, **Ku-band 14/12 GHz**, Ka-band 30/20 GHz. - Typical transponder bandwidth: 36 MHz. - **Multiple access:** FDMA, TDMA, CDMA. - One-way earth–satellite–earth delay about 240–270 ms for GEO. - LEO and MEO constellations give lower delay (used for mobile broadband, GPS). **Advantages:** wide coverage, broadcast capability, distance-independent cost, quick setup in remote and hilly areas (useful in Nepal). **Disadvantages:** high launch cost, propagation delay and echo, rain fade at high frequencies, limited lifetime (about 15 years). **Applications:** TV broadcasting (DTH), telephony and VSAT networks, navigation (GPS), weather and remote sensing, internet. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What does a communication satellite essentially do? A. Acts as a repeater in space: receives, amplifies, changes frequency and retransmits B. Stores messages and forwards them later without amplification C. Only reflects the signal passively without changing frequency D. Generates the original message for earth stations Answer: A. The satellite is a repeater: it amplifies the received uplink signal, shifts its frequency and retransmits it on the downlink. (Key point: Role of satellite) 2. Why are the uplink and downlink frequencies different? A. To increase the transponder bandwidth B. To avoid interference between the received and transmitted signals C. To reduce the launch cost D. To make the satellite appear stationary Answer: B. Using different frequencies (e.g. 6/4 GHz) stops the strong transmitted signal from interfering with the weak received one. (Key point: Uplink/downlink frequencies) 3. Which statement about a geostationary (GEO) satellite is correct? A. It orbits at about 500 km and needs tracking antennas B. It is at about 35 786 km above the equator, appears fixed, and three satellites cover almost the whole Earth C. It has the lowest delay of all orbits D. It is at 35 786 km but must be tracked continuously Answer: B. GEO satellites sit above the equator at about 35 786 km, appear fixed so antennas need not track, and three give near-global coverage. (Key point: GEO properties) 4. Which is a disadvantage of GEO satellite communication? A. Cost increases with distance B. Propagation delay (about 240-270 ms one way) and echo C. Cannot broadcast to many stations D. Cannot work in remote areas Answer: B. The long path gives large delay and echo; the cost is distance-independent and coverage is wide. (Key point: Disadvantages) ## Related in Communication Systems - [Short note: FDMA in satellite communications](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Ashort-note-fdma-satellite) — Communication Systems, chapter 5, asked 2× - [Modulation; analog communication system block diagram](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Amodulation-analog-block-diagram) — Communication Systems, chapter 1, asked 3× - [Short note: M-ary baseband communication system](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Ashort-note-mary-baseband) — Communication Systems, chapter 6, asked 3× - [Block diagram of analog communication system](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aanalog-comm-block-diagram) — Communication Systems, chapter 1, asked 2× - [Duplex digital communication system vs analog](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Adigital-comm-duplex-vs-analog) — Communication Systems, chapter 1 - [Communication system block diagram; need for modulation](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Acomm-block-diagram-needs-modulation) — Communication Systems, chapter 1 ## Related in other subjects - [Communication via satellite as unguided scheme](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Asatellite-unguided) — Instrumentation II, chapter 5 - [Data logging system for optical, satellite, Bluetooth](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Adata-logging-three-schemes) — Instrumentation II, chapter 5 - [Lead compensator for satellite position control](https://www.bctengineer.com/question.md?key=semester_6%2Fdigital_control_system%3Alead-compensator-satellite) — Digital Control System, chapter 4 - [Optical fiber vs satellite transmission](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aoptical-fiber-vs-satellite) — Data Communication, chapter 4