Applications of Communication Systems

Communication systems form the backbone of modern civilization, enabling everything from personal conversations to global financial transactions. This chapter explores the diverse applications across industries and daily life.

Telecommunications

Telephone Networks

The Public Switched Telephone Network (PSTN) remains one of the largest communication systems ever built:

Specifications:

• Voice bandwidth: 300 Hz – 3.4 kHz
• Sampling rate: 8 kHz (Nyquist for 4 kHz)
• Quantization: 8 bits/sample (PCM)
• Bit rate: 64 kbps per voice channel
• Signaling: SS7 (Signaling System 7)

Mobile Communication

Broadcasting

Radio Broadcasting

AM Radio:

• Frequency: 530–1700 kHz (MW band)
• Bandwidth: 10 kHz per channel
• Modulation: Double sideband AM
• Range: Hundreds of kilometers (ground wave)
• Audio quality: Moderate (5 kHz audio)

FM Radio:

• Frequency: 88–108 MHz (VHF band)
• Bandwidth: 200 kHz per channel
• Modulation: Wideband FM (Δf = 75 kHz)
• Range: 50–100 km (line of sight)
• Audio quality: High fidelity (15 kHz audio)

Television Broadcasting

Satellite Communication

Applications:

• Direct-to-Home (DTH) television
• Global telephone backhaul
• GPS navigation
• Weather monitoring
• Military surveillance
• Internet access in remote areas

Link Budget Example:

• Satellite altitude: 35,786 km (GEO)
• Free space path loss at 12 GHz: ~206 dB
• Typical EIRP: 50–55 dBW
• Required C/N: 10–15 dB
• Rain margin: 3–6 dB

Internet and Data Communication

Fiber Optic Networks

Wireless Data Networks

• Wi-Fi 6 (802.11ax): Up to 9.6 Gbps, OFDMA, 2.4/5/6 GHz
• 5G NR: Up to 20 Gbps downlink, mmWave + sub-6GHz
• LoRa: Long range IoT, 0.3–50 kbps, 10+ km range
• Zigbee: Short range sensor networks, 250 kbps, mesh topology

Medical Communication Systems

• Telemedicine: Real-time video consultation (requires low latency <150ms)
• Remote surgery: Haptic feedback communication (requires <1ms latency)
• Patient monitoring: ECG/EEG telemetry (continuous low-bandwidth streams)
• Medical imaging: DICOM image transfer (high bandwidth, lossless)
• Emergency services: Priority communication with QoS guarantees

Military and Defense

• Secure voice: Encrypted radio communication (frequency hopping)
• Radar systems: Target detection and tracking
• Electronic warfare: Jamming and counter-jamming
• Tactical networks: MANET (Mobile Ad-hoc Networks)
• Satellite reconnaissance: High-resolution imaging downlinks

Internet of Things (IoT)

IoT Communication Technologies:

Space Communication

• Deep space: NASA DSN, extremely weak signals (~10⁻²² W received)
• Near-earth: LEO constellation communication (Starlink, OneWeb)
• Interplanetary: Light-speed delays (Mars: 4–24 minutes one-way)
• Modulation: Coherent PSK with turbo/LDPC coding

Solved Example

Problem: A satellite TV system operates at 12 GHz with free-space path loss. Calculate the path loss for a GEO satellite at 35,786 km altitude.

Solution:

Free Space Path Loss (FSPL):

FSPL(dB) = 20×log₁₀(d) + 20×log₁₀(f) + 20×log₁₀(4π/c)

Where:

• d = 35,786 × 10³ m = 3.5786 × 10⁷ m
• f = 12 × 10⁹ Hz
• c = 3 × 10⁸ m/s

FSPL = 20×log₁₀(4π×d×f/c) FSPL = 20×log₁₀(4π × 3.5786×10⁷ × 12×10⁹ / 3×10⁸) FSPL = 20×log₁₀(4π × 1.4314×10⁹) FSPL = 20×log₁₀(1.8 × 10¹⁰) FSPL = 20 × 10.255 FSPL ≈ 205.1 dB

This enormous path loss explains why satellite earth stations need large dish antennas (high gain) and satellites need high-power transponders.

Interview Questions

Q1: Why is fiber optic communication preferred for long-distance high-speed links?

Fiber optics offer extremely high bandwidth (tens of THz), very low attenuation (0.2 dB/km at 1550nm), immunity to electromagnetic interference, high security (difficult to tap), small size and weight, and no ground loop problems. These advantages make it superior to copper for backbone networks.

Q2: What are the main challenges in deep space communication?

Challenges include extreme signal attenuation (inverse square law over millions of km), very long propagation delays (minutes to hours), limited power on spacecraft, Doppler shifts due to relative motion, and atmospheric effects during earth-station reception. Solutions include very large ground antennas, ultra-sensitive receivers, and powerful error-correcting codes.

Q3: How does 5G enable new applications that 4G cannot support?

5G provides three key capabilities: enhanced Mobile Broadband (eMBB) with 10+ Gbps for AR/VR, Ultra-Reliable Low-Latency Communication (URLLC) with <1ms latency for autonomous vehicles and remote surgery, and massive Machine-Type Communication (mMTC) supporting 1 million devices/km² for IoT.

Q4: What communication technology is most suitable for a smart agriculture sensor network covering 10 km² with 1000 sensors?

LoRaWAN is ideal: it provides 10-15 km range, ultra-low power consumption (years on batteries), supports thousands of devices per gateway, and the low data rates (sufficient for periodic sensor readings) reduce bandwidth costs. The star-of-stars topology with a few gateways covers the area efficiently.