Download Parts of Communication System Channel

Communication System
Dr inż. Zdzisław Pólkowski
Badea George-Cosmin
CONTENTS
• Definition;
• Characteristic of communication system;
• Parts of Communication system;
• Pulse code modulation;
• Modes of channel operation.
Definition
• Electronic Communication System- defined as the whole mechanism
of sending and receiving as well as processing of information
electronically from source to destination;
• Communication System- to produce an accurate replica of the
transmitted information that is to transfer information between two or
more points through a communication channel, with minimum error;
•A system or facility for transferring data between persons and
equipment. The system usually consists of a collection of individual
communication networks, transmission systems, relay stations,
tributary stations and terminal equipment capable of interconnection
and interoperation so as to form an integrated whole.
• Example – Radiotelephony, broadcasting, point-to-point, mobile
communications, computer communications, radar and satellite
systems.
http://dictionary.reference.com/browse/communication+system
Characteristic of Communication System
• Must be a Sender and Receiver;
• A protocol is a set of rules which governs the transfer of data between
computers. Protocols allow communication between computers and
networks.
• Handshaking is used to establish which protocols to use. Handshaking
controls the flow of data between computers;
• Protocols will determine the speed of transmission , error checking
method, size of bytes, and whether synchronous or asynchronous;
•Examples of protocols are : token ring, CSMA/CD, X.25, TCP/IP;
http://www.boredofstudies.org/wiki/Characteristics_of_communication_systems
Parts of Communication
System
Parts of Communication System
• Communication systems consist of five parts:
 Source;
Transmitter;
 Channel;
 Receiver;
 Destination.
Input
Signal
Received
Output
Transmitted
Signal Receiver Signal
Signal
Transmitter
Communication
(RX)
(TX)
Channel
http://comutronics.blogspot.com/p/communication-q_8.html
Parts of Communication System
 Source (input signal) :
• The source originates a message, such as: human voice, the television
picture, data.
• If the data is non-electrical (analogue) it must be converted by an input
transducer (microphone, camera) into an electrical waveform (baseband
modulation) referred to as the baseband signal or message signal.
Input
Signal
Received
Output
Transmitted
Signal Receiver Signal
Signal
Transmitter
Communication
(RX)
(TX)
Channel
http://comutronics.blogspot.com/p/communication-q_8.html
Parts of Communication System
Transmitter (TX):
• The transmitter modifies the base-band signal for efficient transmission.
• Characteristics: Modulation, amplification, transmission frequency (TX),
transmission power, coding;
•MW modem, WiFi Card, Bluetooth Card, RF transmitter.
Input
Signal
Received
Output
Transmitted
Signal Receiver Signal
Signal
Transmitter
Communication
(RX)
(TX)
Channel
http://comutronics.blogspot.com/p/communication-q_8.html
Parts of Communication System
 Channel:
•The Channel is a medium , such as wire, coaxial cable, a waveguide, an
optical fiber or a radio link, through which the transmitter output is sent;
• Channel characteristics, ability for transmission, noise, interference,
power needed, fading, multipath.
Input
Signal
Received
Transmitted
Signal Receiver
Signal
Transmitter
Communication
(RX)
(TX)
Channel
Output
Signal
http://comutronics.blogspot.com/p/communication-q_8.html
Parts of Communication System
 Receiver (RX):
• The receiver reprocesses the signal received from the channel by
undoing the signal modifications made at the transmitter and the channel;
• Characteristics: demodulation, receiver frequency (RX), Receiving power,
decoding;
•MW modem, WiFi Card, Bluetooth Card, RF receiver.
Input
Signal
Received
Output
Transmitted
Signal Receiver Signal
Signal
Transmitter
Communication
(RX)
(TX)
Channel
http://comutronics.blogspot.com/p/communication-q_8.html
Parts of Communication System

Destination (output signal):
• The destination is the unit to which the message is communicated;
• The receiver output is fed to the output transducer, which converts the
electrical signal to its original form.
Input
Signal
Received
Output
Transmitted
Signal Receiver Signal
Signal
Transmitter
Communication
(RX)
(TX)
Channel
http://comutronics.blogspot.com/p/communication-q_8.html
Pulse code modulation
Pulse code modulation (PCM)
• Analog transmission is not particularly efficient. When the signal-to-noise
ratio of an analog signal deteriorates due to attenuation, amplifying the
signal also amplifies noise.
• Digital signals are more easily separated from noise and can be
regenerated in their original state. The conversion of analogue signals to
digital signals therefore eliminates the problems caused by attenuation.
•Pulse Code Modulation (PCM) is the simplest form of waveform coding.
Waveform coding is used to encode analogue signals (for example speech)
into a digital signal.
•The combined encoder/decoder is known as acodec. A PCM encoder
performs three functions:
 Sampling;
 Quantising;
 Encoding
http://www.technologyuk.net/telecommunications/telecom_principles/pulse_code_modulation.shtml
Pulse code modulation (PCM)
 Sampling:
• Sampling is the process of reading the values of the filtered analogue
signal at discrete time intervals.
• A scientist called Harry Nyquist discovered that the original analogue
signal could be reconstructed if enough samples were taken.
• He found that if the sampling frequency is at least twice the highest
frequency of the input analogue signal, the signal could be reconstructed
using a low-pass filter at the destination.
http://www.technologyuk.net/telecommunications/telecom_principles/pulse_code_modulation.shtml
Pulse code modulation (PCM)
 Quantising:
• Quantisation is the process of assigning a discrete value from a range of
possible values to each sample obtained. The number of possible values
will depend on the number of bits used to represent each sample.
•Quantisation can be achieved by either rounding the signal up or down to
the nears available value, or truncating the signal to the nearest value
which is lower than the actual sample.
• Quantisation noise can be reduced by increasing the number of
quantisation intervals, because the difference between the input signal
amplitude and the quantization interval decreases as the number of
quantization intervals increases.
http://www.technologyuk.net/telecommunications/telecom_principles/pulse_code_modulation.shtml
Pulse code modulation (PCM)
 Encoding :
• Encoding is the process of representing the sampled values as a binary
number in the range 0 to n. The value of n is chosen as a power of 2,
depending on the accuracy required.
•Increasing nreduces the step size between adjacent quantisation levels
and hence reduces the quantisation noise. The down side of this is that the
amount of digital data required to represent the analogue signal increases.
http://www.technologyuk.net/telecommunications/telecom_principles/pulse_code_modulation.shtml
Models of channel
operation
Models of channel operation
1.
Simplex:
•Simplex is one direction of communication, it requires only one line of
communication;
• Simplex channels are not often used in communication system because it
is not possible to send back error or control signals to the transmit end;
• A good example would be TV or Radio.
http://uva.ulb.ac.be/cit_courseware/datacomm/dc_014.htm
Models of channel operation
2.
Half-Duplex:
• Two directions of communication but only one direction is allowed through
at a time;
• Only one end transmits at a time, the other end receives;
• An advantage is that the single lane is cheaper then the double lane;
• Example of half-duplex is talk-back radio, and CB Radio.
http://uva.ulb.ac.be/cit_courseware/datacomm/dc_014.htm
Models of channel operation
3.
Full Duplex
• Two ways of communication with data can travel in both directions
simultan cously;
• It can perform feedback. The most expensive;
• Example., is mobile phone line.
http://uva.ulb.ac.be/cit_courseware/datacomm/dc_014.htm