Wireless Spectrum & Regulation Wireless_Communication_Overview.pptx

Wireless Spectrum, Transmission Impairments, Fading and Channel Correction Mechanisms

1. Overview of Wireless Communication Wireless Spectrum, Transmission Impairments, Fading and Channel Correction Mechanisms

2. Wireless Spectrum & Regulation • Proper choice of frequency spectrum is vital. • Frequencies differ in distance coverage and penetration. • Spectrum is shared among multiple users and regulated. • Key differentiators: Carrier Frequency, Signal Power, Multiple Access Schemes (TDMA, FDMA, CDMA). • Regulatory bodies (e.g., FCC in the US) manage frequency allocations. • Dynamic Spectrum Access and Cognitive Radio are emerging technologies. • ISM bands (e.g., 915 MHz, 2.45 GHz, 5.8 GHz) can be used without licenses under power limits.

3. Transmission Impairments • Signal propagation can experience various impairments. • Key impairments: - Attenuation & Attenuation Distortion - Free Space Loss - Noise (Thermal, Intermodulation, Crosstalk, Impulse) - Atmospheric Absorption - Multipath & Refraction • Free Space Loss Formula: LdB = 20 log(f) + 20 log(d) - 147.56 • Path Loss Exponent (n) affects received power in practical systems.

4. Noise and SNR • Noise limits system performance and can be categorized: - Thermal Noise - Intermodulation Noise - Crosstalk - Impulse Noise • Signal-to-Noise Ratio (SNR) is critical for digital communication. • Eb/N0: Energy per bit to noise density ratio determines BER performance. • Higher Eb/N0 → Lower BER.

5. Fading in Mobile Environment • Fading: Time variation of received signal power. • Causes: Mobile movement, atmospheric changes, obstacles. • Multipath propagation: Reflection, Diffraction, Scattering. • Types of fading: - Large-scale fading (shadowing, distance) - Small-scale fading (rapid variations, Doppler spread, multipath) • Effects: Signal reinforcement, cancellation, intersymbol interference.

6. Channel Correction Mechanisms • Techniques to mitigate fading and improve performance: - Forward Error Correction (FEC) - Adaptive Equalization - Diversity Techniques & MIMO - Adaptive Modulation & Coding (AMC) • OFDM and Spread Spectrum combat frequency selective fading. • Bandwidth Expansion: Carrier aggregation, Frequency reuse, mmWave. • MIMO enables diversity, beam-forming, multi-user MIMO, and multilayer transmission.