Communication system may be categorized based on their physical infrastructure and the specifications of the signals they transmit. The physical infrastructure pertains to the type of the channel used and the hardware design of the transmitting and receiving equipment. The signal specifications signify the nature and type of the transmitted signal. The types of communication systems based on their infrastructure and signal specifications are discussed below.
Based on Physical Infrastructure
Based on the physical structure, there are two types of communication systems:
- Line communication systems
- Radio Communication systems
There is physical link, called hardwire channel between the transmitter and the receiver in line communication systems. In a radio communication system, there is no such link and natural resources, such as space and water are used as soft wire channels. A particular communication system can be one of these two types. For example, radio broadcast is purely radio communication system and cannot be categorized as a line communication system. On the other hand, landline telephony is purely a line communication systems and cannot be typed as a radio communication system.
Consider a TV system in which a user can only receive the signals and view available channels. A television receiver cannot transmit the signals. Now consider telephony as another example,. In this case, you can simultaneously send and receive signals. TV transmission is a one way transmission. While telephony is a two way transmission. In technical terms, one way transmission is called simplex, while a two way transmission is called duplex.
The one way or two way transmission feature of a communication system depends on the design of the equipment used on the two sides of the communication system, and is therefore included in the physical structure specifications of the system. As a rule, a communication system can be a simplex or a duplex system, but not both.
Therefore baseband on the physical structure of a communication system, you can define two groups, and only one specification from each group is required to decide the type of communication system. These groups are:
- Line / Radio communication
- Simplex/Duplex communication
For instance, a TV communication system is a combination of the radio and simplex communication systems and landline telephony is a combination of the line and duplex communication systems. A particular communication systems can be implemented as both line and radio communication system. For example, landline telephony is a line communication system. However, overseas or long distance telephony is carried out through satellites and the system is called radio telephony as it makes use of radio waves for transmission and reception. This system is then categorized as a radio communication system.
Based on Signal Specifications
The signal specifications used to decide the type of communication system include:
- Nature of the baseband or information signal.
- Nature of the transmitted signal.
Based on the nature of the baseband signal, there are two types of communication systems.
- Analog communication systems
- Digital communication systems
Based on the nature of transmitted signal, the baseband signal can either be transmitted as it is without modulation, or through a carrier signal with modulation. The two systems can then be categorized as:
- Baseband communication system
- Carrier communication system
Therefore, the four types of communication system categorized based on signal specification are:
- Analog communication systems
- Digital communication systems
- Baseband communication systems
- Carrier communication systems
Of the four, at least two types are required to specify a particular communication system. Thus, two groups are formed consisting each of two types such that at least one of the types from each group is necessarily required to specify a communication system. These groups can be formed as:
- Analog/digital communication systems
- Baseband/carrier communication systems
A particular communication system is either an analog communication system or a digital communication system at a time. For instance , TV transmission is an analog communication system while high definition television (HDTV) is a digital communication system. The internet is another example of a digital communication system.
Similarly, a particular communication system is either a baseband communication system or a carrier communication system. Example of baseband communication system are landline telephony and Fax. Example of carrier communication system are TV transmission, radio broadcast, and cable TV.
Therefore, to completely describe a particular communication system, four of the eight types of communication systems are required. If any one type is missing, then the description of communication system will not be complete. To make things simple and clear, four groups containing these eight types are formed, such that only one choice is possible from each group and the four choices together describe the communication system.
These four groups are:
- Group I: Line/radio communication system
- Group II: Simplex/duplex communication system
- Group III: Analog/digital communication system
- Group IV: Baseband/carrier communication system
Consider the television communication system. It is described as a radio communication system from group I, simplex communication system from group II, analog communication system form group III, and carrier communication system from group IV. That is , a television communication system is a radio-simplex-analog-carrier communication system. This is the description of a television communication system in its totally.
Another example is landline telephony. This is described as line communication system from group I, duplex communication system form group II, analog communication system from group III, and baseband communication system form group IV. Therefore, telephony through landline is a line-duplex-analog-baseband communication system. Similarly, you can completely describe any communication system with these four groups.