Siksha Sarovar

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3.1 Wireless Medium Access Issues in IoT Networks

Lesson 15 of 31 in the free Internet of Things (IoT) notes on Siksha Sarovar, written by Rohit Jangra.

3.1.1 The Nature of the Wireless Medium: Unbounded Propagation

Communication in IoT occurs over the shared Radio Frequency (RF) spectrum. Unlike wired networks (Ethernet), the wireless medium is "Unbounded," leading to complex physics-based challenges that require advanced MAC and physical layer engineering.

3.1.2 Comprehensive Medium Access Challenges (Academic Deep-Dive)

Issue NameTechnical DefinitionEngineering Mitigation StrategyImpact on Network
Hidden TerminalNode A sees B, C sees B, but A/C are invisible to each other.Use RTS/CTS (Request/Clear to Send) handshake.High collision rate
Exposed TerminalNode is blocked because a neighbor is busy.Use directional antennas or power control.Low throughput
Path LossSignal power decay over distance ($P_r propto 1/d^n$).Use high-gain antennas or multi-hop relay.Limited range
Multi-path FadingSignals reflect off walls and cancel out at the receiver.OFDM (Orthogonal Frequency Div Multiplexing).Signal drops
InterferenceCrowded 2.4GHz band (Wi-Fi vs Zigbee vs Microwaves).Frequency Hopping Spread Spectrum (FHSS).Retransmissions
ShadowingObstacles like buildings blocking the signal path.Deploy nodes at higher elevations or use mesh.Connectivity gaps

3.1.3 Spectral Efficiency and Resource Management

Most IoT protocols operate in the ISM (Industrial, Scientific, and Medical) bands:

  • 2.4 GHz Band: High bandwidth, global availability, but poor penetration through concrete and highly congested.
  • Sub-GHz Bands (868/915 MHz): Superior range (10km+), better penetration through walls and foliage. Used by LoRa and Sigfox.
  • mmWave (5G NR): Gigabits per second bandwidth, but requires direct line-of-sight and has zero wall penetration.