Basic Signal Theory

Basic Signal Theory
In information and communication technology (ICT), signal theory has to do with basic signal processing as it involves the repsentation and transmission of information. The term ‘signal’ here refers to electromagnetic or electrical signals. 

What are signals?

Signals can be defined as measurable quantities which may be either time-varying or spatial-varying. A signal may be expressed as a function of time and frequency. When a signal is expressed as a function of time, it can be either discrete (discrete-time signal) or continuous (continuous-time signal).While a discrete-time signal is defined only on a discrete set of times, a continuous-time signal varies and the quantities are defined for a continuous set of times.When expressed as a function of frequency, the signal is made up of lots of different range of frequencies.In a more practical sense, there are two basic types of signals:

1. Digital signal
2. Analogue signal

Digital signal

Digital signal can be defined as a discrete signal or discrete-time signal that generates and process data in form of zeroes and ones (0s and 1s). This implies that digital signals can take on only a discrete set of values.  Digital signal is quantized (has finite set of values). The value of a digital signal may be described in terms of voltage pulses that can be sent over transmission medium. As described above, the signal sent is either off (o) or on (1) pluses, repsenting a binary digit. For example, computers use digital signals.

Analogue signal
Analogue signal (unlike digital signal) is not discrete and quantized. Analogue signal is continuous in nature and generates continuous values, leading to continuous wave pattern. Analogue signals can be used over a variety of transmission media. For example, telephone lines use analogue protocols.

What Does Signals Do?

• Signals carry information, in form of data, image, sound or pictures.
• Computers depend on digital signals for data transmission.
• The computer stores data in form of zeros and ones, which are called binary digits.
• A single binary digit is referred to a bit and a set of 8 bits is called a byte. 1024 byte is equal to 1 kilobyte.

A very common coding format for characters repsented in binary digit is ASCII, which stands for ‘standards for American Standard Code for Information Interchange’. ASCII repsents numbers using a combination of 7 bits, with an additional bit called the parity bit. The parity bit is the error-checking bit.

Data can be transferred between computers, using what is called protocol. Either the analogue or digital signals can be used to transmit data or information. However, the type of signal used depends on the communication system and transmission media.

See also

Data transmission

Data communication

Parity Bit and Error checking