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Computer Engineering Articles
Page 33 of 36
Passband Transmission
In passband transmission, the amplitude, phase or frequency of the carrier signal is regulated to transmit the bits. The incoming data stream is modulated onto a carrier and then transmitted over a band-pass channel. The types of passband transmission are illustrated as − Amplitude Shift Keying (ASK) In ASK, the amplitude of the signal is varied to represent the signal levels, while frequency and phase remains constant. In order to represent 0 and 1, two different amplitudes are used. Frequency Shift Keying (FSK) In FSK, the frequency of the signal is modulated to represent the signal levels, while ...
Read MoreThe Electromagnetic Spectrum
The electromagnetic spectrum is the entire range of electromagnetic radiation according to the wavelength or frequencies. It has a range of frequencies from 1Hz to Hz. The waves in order of increasing frequencies are radio waves, microwaves, infrared rays, visible light, UV rays, X-rays and gamma rays.Among these range, the frequencies between Hz to Hz are used for communication. The following diagram shows the electromagnetic spectrum. The first figure gives the full range of frequency spectrum while the second figure elaborates that part of the spectrum which can be used for data communication − The ...
Read MoreRadio Transmission
In the electromagnetic spectrum, all omnidirectional waves in the frequencies 3KHz to 1GHz are called radio waves. They are widely used for communications since they are easy to generate, can travel long distances and can penetrate buildings. Radio waves have omnidirectional antennas, i.e. antennas that can send signals in all directions. The properties of radios waves vary according to their frequencies. However, radio waves at all frequencies are prone to interference from electrical equipments like motors etc. Low and Medium Frequency Radio Waves Low and medium frequency radio waves can pass through obstacles and have ground propagation. However, the ...
Read MoreInfrared Transmission
Infrared waves are those between the frequencies 300GHz and 400THz in the electromagnetic spectrum. Their wavelengths are shorter than microwaves but longer than visible light. Infrared propagation is line of sight. They cannot penetrate walls and sun’s infrared rays interfere with these rays. So cannot be used for long – range communication. As their usage is confined within closed space, they do not need any government permissions for their applications. Applications of Infrared Waves in Communications Remote controls for television, stereos and other home appliances. Wireless LANs Wireless modem, keyboard, mouse, printer etc Fire detectors Night vision ...
Read MoreLight Transmission
Electromagnetic waves within the frequency range of 400 THz – 790 THz are detected by the human eye. Light transmission is line of sight propagation and is blocked by obstacles. Laser Signals Optical signalling can be obtained by laser signals. For example, the LANs in two buildings can be connected by installing laser signalling system on the rooftops. Laser rays are unidirectional. So both the transmitter and the receiver need perfectly aligned photo-emitter and photo-detector. Visual Light Communication A more used variant of light transmission is visual light communication (VLC). VLC refers to data communication using visible ...
Read MoreTelephone Modems
Modem is an abbreviation of “modulator demodulator”. It is a network device that modulates digital information or bits into analog signals for transmission at the sending end, and demodulates the analog signals to bits at the receiving end. Telephone modems enables data communication between two computers over voice – grade telephone lines. Purpose and Usage The computers are digital devices that are connected via analog local loops of the telephone networks. So, there is a need to convert the bits to analog signals so that they can be transmitted via the physical channels; and conversely convert analog signals in the ...
Read MoreLayered Operating System
The operating system is split into various layers In the layered operating system and each of the layers have different functionalities. This type of operating system was created as an improvement over the early monolithic systems. Why Layering in Operating System? Layering provides a distinct advantage in an operating system. All the layers can be defined separately and interact with each other as required. Also, it is easier to create, maintain and update the system if it is done in the form of layers. Change in one layer specification does not affect the rest of the layers. Each of ...
Read MoreTrunks and Multiplexing
Trunks Definition Trunks are a large-bandwidth communication channels connecting switching centres, forming the core of the telephone network. A trunk comprises of a cluster of broadcast frequencies that are suitable for long haul communication of many voice and data signals simultaneously. Features The characteristic features of a trunk are − They carry digital information as opposed to analog signals carried by local loops. They are designed for both voice and data transmission. They can carry millions of calls simultaneously over long distances. They have very high bandwidth. They generally comprise of a cluster of fiber optic cables bundled together ...
Read MoreDigitizing Voice Signals
Analog Telephone Cores The early telephone networks had analog cores. Frequency division multiplexing (FDM) was used to transmit a number of voice signals over the single line. Twelve calls were multiplexed into a group. Five groups were multiplexed into a supergroup. Digital Telephone Cores The present telephone networks have digital cores. This requires that the analog signals in the local loops are converted to digital signals that are transmitted via the trunks. This is done by codec (coder decoder). Time division multiplexing (TDM) is used to multiplex digital signals in the trunks, since it can be entirely handled by digital ...
Read MorePulse Code Modulation
Pulse code modulation (PCM) is a technique of digitally representing analog signals. It takes samples of the amplitude of the analog signal and changes it to binary data. PCM technique is used by codecs in telephone networks to convert analog signals in local loops to digital signals in the trunks, and reverse conversion at the receivers’ end. Operations in Pulse Code Modulation The operations in PCM technique involves operations at the transmitting end and the operations at the receiving end. Transmitting End − In the transmitting end, the analog signals are sampled, quantized and encoded. The codec samples the analog ...
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