Physical Layer - Transmission Impairments
Attenuation
The received signal must be sufficiently higher than noise to be received without error.
- Signal amplitude decreases with distance.
- Depends on the medium.
- Attenuation is an increasing function of frequency.
Delay Distortion
This occurs as the velocity of propagation of a signal through a guided medium varies with frequency:
- Only in guided media.
- Propagation velocity varies with frequency.
- Different parts of the spectrum arrive at different times.
Noise
This is additional signals inserted between the transmitter and receiver. It could be due to:
- Thermal
- Due to the thermal agitation of elections.
- Uniformly distributed
- White noise.
- Inter-modulation
- Signals that are the sum and difference of the original frequencies sharing a medium.
- Cross-talk
- A signal from one line is picked up on another.
- Impulse
- Irregular pulses or spikes caused by external electromagnetic interference.
- Short Duration
- High Amplitude