Wireless Communication

Introduction to Wireless Communication

Wireless communication transmits information through electromagnetic waves without physical connections. From Wi-Fi and Bluetooth to cellular networks and satellite links, wireless technology enables our connected world.

Electromagnetic Wave Fundamentals

Wavelength-Frequency Relationship

Where λ is wavelength (m), c is speed of light (3×108 m/s), f is frequency (Hz)

Example: 2.4GHz Wi-Fi: λ = 3×108/2.4×109 = 0.125m (12.5cm)

Frequency Spectrum

  • RF (Radio Frequency): 3kHz - 300GHz
  • LF/MF: AM radio (530-1710kHz)
  • HF: Shortwave, amateur radio (3-30MHz)
  • VHF: FM radio, TV (30-300MHz)
  • UHF: Cellular, Wi-Fi, GPS (300MHz-3GHz)
  • Microwave: 5G, satellite (3-30GHz)

Signal Propagation & Path Loss

Friis Transmission Equation

Where Pr is received power, Pt is transmitted power, Gt and Gr are antenna gains, d is distance

Free Space Path Loss (dB)

Simplified: FSPL(dB) = 20log10(d) + 20log10(f) - 147.55

Example: 2.4GHz at 10m: FSPL ≈ 40dB loss

Signal Strength (RSSI)

Typical values: -30dBm (excellent), -67dBm (good), -80dBm (weak), -90dBm (minimum)

Modulation Techniques

Modulation encodes information onto carrier waves by varying amplitude, frequency, or phase.

Amplitude Modulation (AM)

Varies carrier amplitude. Simple but susceptible to noise. Used in AM radio.

Frequency Modulation (FM)

Varies carrier frequency. Better noise immunity. Used in FM radio, Bluetooth.

Phase Modulation (PM)

Varies carrier phase. Efficient for digital data. Used in Wi-Fi (PSK, QAM).

Spread Spectrum

Spreads signal across wide bandwidth. Excellent noise immunity and security. Used in GPS, LoRa, CDMA.

Wireless Protocols & Standards

Wi-Fi (802.11): 2.4GHz/5GHz, 10-100m range, 54Mbps-10Gbps
Bluetooth: 2.4GHz, 10-100m range, 1-3Mbps, low power
Zigbee: 2.4GHz, 10-100m range, 250kbps, mesh network, ultra-low power
LoRa/LoRaWAN: 868/915MHz, 2-15km range, 0.3-50kbps, long range IoT
Cellular (4G/5G): 700MHz-39GHz, km range, Mbps-Gbps speeds
NFC: 13.56MHz, less than 10cm range, 424kbps, contactless payments

Applications

  • •IoT Sensors: Temperature, humidity, motion monitoring (Zigbee, LoRa)
  • •Smart Home: Lighting, thermostats, security (Wi-Fi, Zigbee)
  • •Wearables: Fitness trackers, smartwatches (Bluetooth LE)
  • •Agriculture: Soil monitoring, livestock tracking (LoRaWAN)
  • •Industrial: Machine monitoring, asset tracking (5G, Wi-Fi 6)
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