Communication Systems (Comm-01630) : Slides Credits: Dr. Uzma Nawaz University of Engineering and Technology, Peshawar
Communication Systems (Comm-01630) : Slides Credits: Dr. Uzma Nawaz University of Engineering and Technology, Peshawar
Communication Systems (Comm-01630) : Slides Credits: Dr. Uzma Nawaz University of Engineering and Technology, Peshawar
• Communication System
• Analog Communication System
• Digital Communication System
• Advantages & Disadvantages of Analog and Digital
Communication
• Noise in Communication System
• SNR
• Communication Channels
• Channel BW (channel capacity) & Rate of Communication
Data
o Cross talk ~ when one channel is being used by two persons i.e. two channels are closed enough that they
interfere with each other. To separate them, guard band is used. This interference is classified as noise.
o Lose connection also accounts to noise.
o Sunlight is also a noise (different types of waves are involved).
Dr. Uzma Nawaz 5/27/2020
Cont..
iii. Receiver ~ reprocess the received signal i.e. reverses the process done by the
transmitter on the signal.
It is also called destination. It removes the distortion & noise.
It consists of:
Demodulator
DAC (digital to analog converter)
Decoder
The output transducer converts the electrical signal into its original form. The
destination is the unit to which the message is communicated.
Channel capacity/Max data rate ~ The max rate (bits/sec) at which data can be
transmitted over a given communication channel.
Two criterion are used for measuring channel capacity;
i. Nyquist criterion that’s is used for noiseless channel/medium.
𝑪 = 𝟐𝑩𝒍𝒐𝒈2𝑴;
B is channel bandwidth, M = 2m ; m= no. of bits/symbol, M= no. of signaling
values or symbols.
ii. Shannon's Criterion that is used for noisy channel/medium.
𝑪 = 𝑩𝒍𝒐𝒈𝟐 (𝟏 + 𝑺𝑵𝑹)
Dr. Uzma Nawaz 5/27/2020
Analog Communication System
An analog communication system is a communication system where the information signal sent from
point A to point B can only be described as an analog signal.
An analog signal is any continuous time signal that change with time period.
The sine wave is the representation of time-varying feature of analog signal.
The analog and Digital signal characteristics mainly include adaptability, continuity,
representation, data type, signal type, medium of transmission, type of values, security,
bandwidth, hardware, data storage, portability, data transmission, impedance, power
consumption, recording data, use, rate of data transmission, examples and applications.
Adaptability: Analog signals are less adjustable for a range of use, whereas digital signals are
more adjustable for a range of use.
Continuity: Analog signals use a continuous variety of amplitude values whereas digital signal
takes a limited set of distinct values at consistently spaced spots in the time.
Type of Data: Analog signals are continuous in nature, whereas digital signals are discrete.
Type of Waves: Analog signal wave type is sinusoidal, whereas a digital signal is a square
wave.
An analog signal signifies a continuous signal that A digital signal signifies a discrete signal that carries
keeps changes with a time period. binary data and has discrete values.
Analog signals are continuous sine waves. Digital signals are square waves.
Analog signal range will not be set. Digital signal is limited as well as ranges from 0 to 1.
Analog signal is further horizontal toward distortion A digital signal has resistance in response toward the
during the response to noise. noise, therefore, it does not often face distortion.
An analog signal broadcasts the information in the A digital signal broadcasts the information in the form
signal form. of binary that is bits.
The bandwidth B of a channel is the range of frequencies that it can transmit with reasonable accuracy and
precision.
For example, if a channel can transmit a signal with proper accuracy having frequency ranging from 0 Hz to 5000 Hz,
the channel bandwidth is 5k Hz.
The rate of information transmission is directly proportional to bandwidth B.
If channel bandwidth B can transmit N pulses per second then to transmit KN pulses per second, channel bandwidth
should be KB.
For example, consider the possibility of increasing the speed of information transmission by time compression of
signal. If the signal is compressed in time by factor of 2, it can be transmitted in half time, speed of transmission is
doubled. Transmitting this signal without distortion, channel bandwidth must also be doubled.
The quality of information transmission is related to signal power i.e. increasing the signal power can reduce the
effect of channel noise resulting in accuracy of transmission.
To maintain a given rate & accuracy of information transmission, signal power and channel bandwidth are
exchangeable i.e. reducing B to increase signal power and vice versa.
Dr. Uzma Nawaz 5/27/2020
Cont..
The two primary communication resources are Signal power & bandwidth B.
The design of communication scheme having B and signal power depends on the
application. E.g. Telephone channel has limited bandwidth of 3kHz but transmitted power
is high, whereas space vehicles have infinite bandwidth but power is limited.
SNR is proportional to signal power, SNR and bandwidth are exchangeable.
If a given rate of information transmission requires a channel bandwidth B1 and signal-
noise-ratio SNR1, then it is possible to transmit the same information over a channel
bandwidth B2 and signal-noise ratio SNR2,
𝐵1
𝐵2
𝑆𝑁𝑅1 ≈ 𝑆𝑁𝑅2