Impairments in the physical layer
Impairments a factors
or conditions that degrade the quality of the signal during travel in the
physical medium.
Some common
impairments in the physical layer include:
1. Attenuation:
Attenuation is a reduction in signal strength in a medium(cable).
Measured in
decibels (dB).
2. Distortion:
Distortion is an alteration or deformation of the signal waveform in
transmission media.
3. Noise:
Noise is unwanted and
random signals that create disturbance in a communication channel.
It degrades the
quality of the transmitted signal and creates errors.
different forms of
noise are:-
A.
Thermal Noise:
Also known as
Johnson-Nyquist noise, arises from the random motion of electrons in conductors
due to their thermal energy.
B. Shot Noise:
Discrete noise of
electric current, particularly in devices like semiconductor diodes or vacuum
tubes.
C. Interference:
Interference noise
is caused by external electromagnetic signals.
D. Crosstalk:
Crosstalk noise
occurs when signals from one channel interfere with signals in another channel.
E. Impulse Noise:
Impulse noise
consists of short-duration bursts of interference by external factors.
F. Quantization
Noise:
Quantization noise
occurs in analog-to-digital (ADC) and digital-to-analog (DAC) conversion
processes,
G. Phase Noise:
Phase noise can
degrade the performance of communication systems in high-frequency and
high-speed applications.
4. Jitter:
It is a variation
in the timing of signal transitions relative to a reference clock.
It degrades the
accuracy of data transmission.
It can be caused
by several factors, including Clock, Noise, Interference, Signal Reflections, and Clock
Skew.
5. Interference:
- Interference occurs by an undesired signal
that disrupts the transmission or reception of data over a communication
channel. Different forms and have different causes, including Electromagnetic
Interference (EMI), Crosstalk, Impulse Noise, Signal Reflections, Cross-Modulation, and Thermal Noise.
6. Delay:
Delay refers to the time it takes for a
signal to travel from the transmitter to the receiver through the communication
medium.
There are two main
types of delay in the physical layer:
A. Propagation
Delay:
The time it takes for
a signal to travel from the transmitter to the receiver.
B. Transmission
Delay:
The time it takes to
transmit the entire signal from the transmitter to the receiver.
Delays have several implications for communication systems:
Latency:
Timing
Constraints:
Interference with
Real-Time Communication:
Bandwidth-Delay
Product:
7. Dispersion:
- Dispersion is the spreading of a signal as
it travels through a transmission medium.
Several types of dispersion can occur in the physical layer:
A. Modal
Dispersion:
occurs in multimode Fiber optic cables.
B. Chromatic
Dispersion:
occurs in both multimode, different wavelengths (colors)
C. Polarization
Mode Dispersion (PMD): occurs as the polarization of the light traveling
through the Fiber.
Dispersion can
have significant effects on the performance of communication systems:
Signal
Degradation:
overlapping symbols and distortion of the signal waveform.
Limitation on Data
Rates and Distances:
limits the maximum data rates and transmission distances.
Interference with
Advanced Modulation Schemes: used to increase data rates in Fiber optic
communication systems, such as coherent detection and quadrature amplitude
modulation (QAM).
8. Bit Error Rate
(BER):
The ratio of erroneous bits or number of
bits received in error compared to the total number of transmitted bits during
a given time.
High BER can
result from various impairments.
Expressed as a
fraction or a percentage, representing the proportion of bits that are received
incorrectly relative to the total number of transmitted bits.
Techniques for
reducing the Bit Error Rate include:
A. Error
Correction Coding:
B. Modulation
Schemes:
C. Equalization:
D. Signal
Processing:
E. Power Control:
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