What is signal and system? Overview of specific systems.
What is a signal?
Signal constitutes a basic ingredient of our lives. Our daily human communication happens through speech signals and visual signals to form an opinion about the things around us. Even the use of the internet involves information-bearing signals of one kind or the other. A patient’s heartbeat represents signals that help the doctor understand the state of his health.
Formally, a signal is defined as a function of one or more variables that convey information on the nature of a physical phenomenon.
Signals are of various dimensions, when it depends on one variable it is known as one-dimensional signals. For example, speech is a one-dimensional signal. And, when the function depends on more than one variable it is known as a multidimensional signal. For example, an image depends on horizontal and vertical coordinates representing the two dimensions.
What is a system?
Earlier we talked about speech as a signal, in that case, the vocal tract would be a system, as it produces the speech, similarly,, the speech is received and interpreted through our ears, which will also be a part of the system. A system produces and receives signals.
The earlier mentioned example is biological, but the same implications can be made to electronics. Such as, in a speech recognition system, an automated speech is performed and the computer catches our words and phrases.
Formally, a system is defined as an entity that manipulates one or more signals to accomplish a function and hence yields new signals.
Overview of specific systems
We have briefly discussed a few real-life applications of signals and systems. In this section,, we will expand on those examples to get a better understanding of the working of various systems.
Communication systems
There are three basic elements of a communication system: transmitter, channel, and receiver. Every three elements are associated with signals of their own. The transmitter converts the message signal produced by a source of information into a suitable form of transmission over the channel, this channel can be an optical fiber, a coaxial cable, a satellite channel, or a mobile radio channel.
The transmitted signal travels through the channel and may be distorted due to the physical characteristics of the channel, also the noise or other interfering signals contaminate the channel output. This results in the received signal being corrupted.
Here comes the part of the receiver. The receiver operates on the received signal and reconstructs it to be a recognizable form.
The operations performed by the transmitter and the receiver also depend upon the type of communication system. For signal-processing systems, the design followed is that of an analog communication system.
On the other hand in a digital communication system, the signals are converted to a digital form first. The transmitter performs the following operations to convert it:
- Sampling: It converts message signal into a sequence of numbers, with each number representing the amplitude of the message signal at a particular instant of time.
- Quantization: It involves representing each number produced by the sampler to the nearest level selected from a finite number of discrete amplitude levels.
- Coding: It represents each quantized sample by a code word made up of a finite number of symbols.
Control systems
The control of physical systems is a widespread industry of its own, and there are many reasons for using the control systems. But looking at it from an engineering viewpoint, the two most important reasons are the response and the robust performance.
Response: A plant is said to have a satisfactory response when the output follows a specific response input.
Robustness: A plant is said to be robust if it regulates its objects well.
Regulation refers to the plant holding its output as close to the reference input.
Microelectromechanical systems
In addition to purely electrical circuits, our advancement in technology has also made it feasible to build microelectromechanical systems or MEMS. It merges a mechanical system with microelectronic control on a silicon chip, which gives us smaller, more powerful, and less noise, smart sensors, and actuators.
These systems have varied uses and are applied in healthcare, biotechnology, automotive, and navigation systems.
The rapid development of MEMS is highly due to the mentioned two factors:
- An improved understanding of the mechanical properties of thin films.
- The development of reactive ion-etching techniques to define features and spacing precisely in the thin films that are deposited.
One application of MEMS is in a micromachined accelerometer. A basic micromechanical structure used to build an accelerometer can be used to make a gyroscope, a device that can sense the angular motion of the system.
It is very useful for automated flight control systems. A gyroscope works on the principle of the law of conservation of angular momentum, which states that if external torque acts on the system made of different particles then the angular momentum of the system remains constant.
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