Communication Systems: When we try to find definition
These are the systems used to provide the information transfer between persons and equipments. Usually these consist of collection of individual communication networks, transmission systems, relay stations, tributary stations, terminal equipments for interconnection and interoperation. A telephone, telegraph, teletypewriter, television, data transmission are the common systems used by normal people.
Communication Systems are of two types:
Analog Communication systems and Digital Communication Systems
Here we will discuss each type briefly.
Analog communication systems, amplitude modulation (AM) radio being a typifying example, can inexpensively communicate a band limited analog signal from one location to another (point-to-point communication) or from one point to many (broadcast). Although it is not shown here, the coherent receiver provides the largest possible signal-to-noise ratio for the demodulated message. An analysis of this receiver thus indicates that some residual error will always be present in an analog system's output.
Examples of Analog communication Systems are:
Base mobile radios: VX4204HF Radios or Man Pack Radios: systems 600M, VX-1210Repeater: VXR 7000VHF and UHF Hand Held: VX829, Alpha, VX160, VX424
Digital Communication Systems:
Although analog systems are less expensive in many cases than digital ones for the same application, digital systems offer much more efficiency, better performance, and much greater flexibility.
In digital communications, binary encoded information (i.e. a sequence of 1s and 0s) is sent from a transmitter to one or more receivers. The transmission medium between the transmitter and receiver (the channel) may be copper cable, optical fiber, free space, etc. Major design goals of most digital communication systems include maximizing bandwidth efficiency and minimizing bit error ratio (BER).
A basic characteristic of digital communications systems is the need for synchronization between the binary encoded data and the various circuit elements in the transmitter and receiver. Bit synchronization information is generally conveyed by the bit clock, which is a square wave signal that has a frequency equal to the data rate (in bits per second).
The bit stream can be encoded into a voltage waveform in a variety of ways. One of the most commonly used binary encoding schemes is non-return-to-zero. In NRZ encoding, a binary one is represented by a high voltage (or optical power) level and a binary zero is represented by a low voltage (or optical power) level. The time duration for a single bit (the bit period) is called the unit interval (UI). The UI is the same for each bit in the bit stream and it is equal to the reciprocal of the data rate.
Examples of Digital Communication Systems:
Base Mobile Radios: Vx-2500, Vx - 7100 seriesHF and Man Pack Radios: 2050HF, PRC2090VHF and UHF Hand Held: Vx - 920 seriesTetra: MT680, PT580H, TC700FM