wireless networks

Wireless Networks
Lecture 4

Frequency Spectrum
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Terms Regarding Channels
• • • • • CAI FVC RVC FCC RCC

Revision

Lecture 4

Medium Property
• Guided Medium • Unguided Medium
▫ Air

• Information Travels using some signals • Signals are Electromagnetic Signals.

Antennas
• Antenna couple electromagnetic energy to and from space from a wire or coaxial cable. • Antenna is the radiator point that radiates signals in every direction with equal power. • That Radiation pattern is symmetric in all directions.

Hertzian Antenna or Dipole Antenna

Directional Antennas

Signal Propagation
• Line of Sight (LOS). • Ground Waves • Sky wave

Inverse Square Law
• Power of the transmitted signal is inversely proportional to square of the distance between them. (Inverse Square Law).

Multipath Propagation
• Delay Spread

Inter Symbol Interference
• Bit Stream can be represented in Digital form • They may superimpose on each other. • Higher the Symbol rate lower the ISI. • This can be removed by performing these functions at receiver end. • Training Sequence • Equalizer

Fading
• In wireless communications, fading is deviation of the attenuation affecting a signal over certain propagation media. The fading may vary with time, geographical position or radio frequency, and is often modeled as a random process.

Types of Fading
• Multipath Fading • Signal reaches receiver after following various paths hence its overall power decreases with the passage of time.