Communication Systems
Communication:
The
term ‘communication’ refers to sending, receiving and processing of
information by
electronic means.
Electronic communications started with wire
telegraphy in the 1940s, developing into telephony some decades later. It used
radio technology at the beginning of the past century after the invention of
the triode tube. It subsequently became even more widely used and refined
through the invention and use of transistors, integrated circuits (ICs) and
other semiconductor devices.
Communication
System:
- Message and Signal
- Information Source
- Transmitter
- Channel-Noise
- Receiver
- Destination
The massage is the information to be communicated. It can be sound, text, numbers, pictures or videos or any combination of these. On the other hand, signals are the electrical representation of messages.
Information source:
Communication system exist to convey a massage. the massage comes from the information source. i.e. information source generates the massage. The amount of information contained in any given massage can be measured in bits.
Transmitter:
Usually, the information generated by a source system is not transmitted directly in the from in which they are generated. Rather, a transmitter transforms and encodes the information in such a way as to produce electromagnetic signals that can be transmitted across some sort of transmission system.
Channel-noise:
It is inevitable that the signal will deteriorate during the process of transmission and reception as a result of some distortion in the system, or because of the introduction of noise, which is unwanted energy, usually a random character, present in a transmission system.
Receiver:
The receiver accept the signal from the transmission system and converts it into a from that can be handled by the destination device.
Destination:
Destination takes the incoming information from the receiver. Example: Loud speaker, video display unit, teletypewriter, various radar displays, television picture tube etc.
Block diagram of a communication system:
Modulation:
There are three main hurdles in the process of
such direct transmission of audio-frequency signals:
Regulatory Agencies:
Standards Organizations:
Figure : Block diagram of a communication system
Modulation is the process of putting
information onto high-frequency carrier for
transmission.
In
essence, the transmission takes place at the high frequency (the carrier) which
has been
modified to carry the lower frequency information. The low frequency
information is often
called the intelligence signal or modulating signal.
It
follows that once this information is received the signal must be removed from
the high
frequency carrier- a process called demodulation.
Need for Modulation:
1. The
signal range is relatively short.
2. If
everybody started transmitting the low frequency signals directly, mutual
interference will render all of them ineffective.
3. Size
of the antenna required for efficient radiation of source signal would be
large
(i.e. about 75 km) as explained below.
Types of modulation:
Figure : Types of modulation
Regulatory Agencies:
- All communications technology is subject to regulation by government agencies such as the Bangladesh Telecommunications Regulatory Commission (BTRC) in Bangladesh.
- The purpose of these agencies is to protect the public interest by regulating radio, television, and wire/cable communications.
- Institute of Electrical and Electronics Engineers (IEEE)
- International Telecommunication Union - Telecommunication Standardization Sector(ITU-T)
- International Organization for Standardization (ISO)
- American National Standards Institute (ANSI)
- Electronic Industries Association (EIA)