2. Telecommunications

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CSS GSA — Paper 7, Part-I, Section V, Sub-topic 2: Telecommunications (Mobile, Satellite, Surveillance, GPS, Fiber Optic)

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Past-paper weightage: high. Fibre optics and GPS are two of the most consistently repeated IT questions (asked in 2016, 2018, 2019, 2020, 2022, 2023, 2024, 2025).

1. Mobile (Cellular) Communication

• The service area is split into cells, each served by a base station/tower
• Principle: the phone sends radio waves to the nearest tower, which routes the call/data through the wider network; as you move, the call is handed off from tower to tower

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5G in Pakistan: the PTA held Pakistan's first 5G spectrum auction on 10 March 2026. Jazz, Zong and Ufone bought 480 MHz of the 597 MHz offered for about US$507 million (Jazz 190 MHz, Ufone 180 MHz, Zong 110 MHz). 5G services were due to start in Islamabad and provincial capitals within months, with 4G quality improving first.

• Parts of a cell phone: processor, memory, radio transceiver, antenna, battery, display, microphone/speaker, SIM card

2. Satellite Communication

• Signals are relayed through orbiting satellites (broadcasting, GPS, remote-area links)

• Natural vs artificial satellite: natural (Moon) is not made by humans; artificial (ISS, communication satellites) is human-made
• Communication satellite: a transponder receives a signal from a ground station, amplifies it and sends it back to another place

3. Surveillance Systems

• CCTV, radar, satellite imaging for monitoring, security and tracking
• Uses: law enforcement, border security, traffic, disaster response

4. GPS (Global Positioning System)

• Satellite navigation giving location and time; the US system is called Navstar GPS
• At least 24 satellites (about 30 working today) in medium Earth orbit
• How it works
  1. Each satellite broadcasts its position and the exact time sent
  2. The receiver measures the delay of signals from at least four satellites
  3. Delay × speed of light = distance from each satellite
  4. Trilateration from four distances gives latitude, longitude, altitude, and corrects the clock
• Other global systems: GLONASS (Russia), Galileo (EU), BeiDou (China)
• Uses: navigation, mapping and surveying, timing, smartphone location services

5. Fibre Optics

• Data is sent as pulses of light through thin glass or plastic fibres
• Construction: core (light travels here) → cladding (lower refractive index) → protective jacket
• Principle: total internal reflection; because the core has a higher refractive index, light keeps bouncing inside the core
• Communication chain: electrical signal → light (laser/LED) → fibre → photodetector → electrical signal

6. MCQ Traps

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• GEO satellites stay fixed over a point; LEO orbit closer and faster
• Fibre sends light pulses, not electrical signals
• GPS needs at least 4 satellites for a 3D position plus time

7. Self-Test Questions

1. Write short notes on fibre optics and the Global Positioning System.
2. How is an 'Optical Fibre' constructed? How is it helpful in transmitting electromagnetic radiations?
3. Give a brief account of Optic Fibres. What is their importance in the present-day telecom system?
4. Where and how are Fibre Optics used? Also write down their advantages and disadvantages.
5. What is GPS? How does it work?
6. Explain the basic principles of how a cellular phone works.
7. How does a satellite work? Also explain what satellites are used for.

8. Past-Paper MCQs (FPSC)

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Taken from the FPSC papers you shared (2015–2025). FPSC does not publish MCQ keys, so the answers are worked out by me.

1. (CSS 2025, Q1.11) The amount of data transmitted for a given amount of time is called: (A) Noise (B) Bandwidth (C) Frequency (D) None of these
2. (CSS 2025, Q1.14) In the structure of fiber, the light is guided through the core due to total internal: (A) Reflection (B) Refraction (C) Diffraction (D) None of these
3. (CSS 2025, Q1.20) The waves which are used for line of sight (LOS) communication are called: (A) Space waves (B) Cable waves (C) Antenna waves (D) None of these

• ✅ Answer key
  1. (B) Bandwidth
  2. (A) Reflection (total internal reflection)
  3. (A) Space waves (they travel in a straight line, so antennas must see each other)

9. Past-Paper Long Questions with Answers (FPSC)

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Every question below appeared in the FPSC papers you shared; the year and question number are in each title. Answers are model outlines written by me, ready to expand.

• CSS 2025 Q5(d), 2024 Q2(b), 2022 Q5(b), 2018 Q5(b): How is an optical fibre constructed and how does light propagate through it? What are its advantages? Draw its basic structure. (5)
  • Draw: a long thin cylinder labelled core, cladding, jacket
  • Construction: section 5
  • Propagation: light enters the core at an angle larger than the critical angle, so it reflects fully at the core–cladding boundary again and again (total internal reflection) down the fibre
  • Advantages: high bandwidth, low loss, no interference, secure, light and thin, made from abundant silica
  • Transmission: electrical → light → fibre → photodetector → electrical
• CSS 2020 Q3(d), 2019 Q3(b), 2016 Q3(b): Where and how are fibre optics used? Write their advantages and disadvantages. Give a brief account and importance in telecom. (5)
  • Uses
    • Telecom backbone and internet cables (including undersea cables)
    • Cable TV and broadband to homes
    • Medicine: endoscopes and surgery
    • Industry and military communication
    • Sensors and lighting
  • Importance: carries almost all international internet traffic with huge capacity
  • Advantages and disadvantages: use the table in section 5
• CSS 2023 Q5(c), 2020 Q5(d), 2016 Q3(b): What is GPS? How does the Navstar GPS system work for different applications? (5)
  • GPS and its working steps: section 4 (24+ satellites, signal delay, four satellites, trilateration)
  • Applications: car, aircraft and ship navigation; mapping and surveying; precise time for banks and networks; smartphone maps and ride apps; farming; disaster rescue; military
• CSS 2022 Q5(c): Briefly explain the working and structure of a cell phone. (5)
  • Use section 1: cells, base stations, radio waves, handoff
  • Structure: processor (CPU), memory, radio transceiver, antenna, battery, display, microphone and speaker, SIM card (identifies the subscriber)
  • Steps of a call: voice → digital signal → radio wave to the tower → mobile network → destination
• CSS 2021 Q5(d): Differentiate between natural and artificial satellites. Briefly describe the working of communication satellites with some applications. (5)
  • Natural satellite: formed in nature, orbits a planet (the Moon)
  • Artificial satellite: human-made and launched (ISS, weather, GPS, communication satellites)
  • Working of a communication satellite: ground station sends an uplink signal; the transponder amplifies it and changes its frequency; it sends a downlink signal to receivers; usually in GEO so dishes need not move
  • Applications: TV broadcasting, telephony, internet, weather forecasting, navigation, remote sensing
  • Pakistan: PakSat-1R (2011) and PakSat-MM1 (2024)
• CSS 2015 Q4(a): Working principle of television, microwave oven, RADAR (two of three) (5)
  • Microwave oven and RADAR are answered in the Atomic Structure chapter
  • Television: a camera turns the picture into electrical signals; a transmitter sends them as radio waves; the TV receiver converts them back into a picture on the screen (pixels lit by LEDs/LCD panels today)

10. CSS Exam Perspective

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• Most repeated areas: fibre optics (almost every year), GPS, satellites, cell phone working
• Short-question style: 'How is… constructed?', 'Where and how is… used?', 'What is GPS? How does it work?'
• Tip: draw the fibre diagram and write the four GPS steps; both are fast marks