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Computer Engineering Articles
Page 33 of 35
Infrared 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 ...
Read MoreFirst-Generation (1G) Mobile Phones
Wireless cellular technology or mobile communications started with first generation mobile phones, popularly known as 1G. It was an analog telecommunications system, introduced in 1979 and continued to mid of the 1980s. History 1G mobile communication system was introduced in Japan in 1979 by Nippon Telegraph and Telephone (NTT). Initially, it started in Tokyo and within next five years expanded to cover the whole of Japan. In 1981, Nordic Mobile Telephone (NMT) was launched in European countries. In 1983, Ameritech launched 1G mobiles in the USA using Motorola mobile phones. Use of mobile communication system was then followed by several ...
Read MoreImproved Mobile Telephone System
Improved Mobile Telephone System (IMTS) was a radio system that linked to public switched telephone networks (PSTN) before the era of cellular mobiles. It was introduced in 1964 and was the wireless equivalent of landline dial up telephones. Features IMTS was a radio system for mobile telephones that was an improvement over the previous Mobile Telephone System (MTS). MTS supported half duplex communication. So, the communicating parties could not communicate simultaneously. IMTS supported full duplex communication, thus allowing both the user to talk and hear simultaneously. IMTS required a high power transmitter to be installed, preferably on the ...
Read MoreFrequency Division Duplex
Frequency division duplex (FDD) is a communication technique where the connected parties can communicate with each other in both directions through use of separate frequency bands for transmitting and receiving. Since FDD uses different frequency bands for upstream data and downstream data, the sending and the receiving signals do not interfere with each other. FDD in Cellular Networks Cellular networks use FDD to separate the channels. One block of the electromagnetic spectrum is allocated for uplink, which carries data from mobile phones to a base station. A different block of the spectrum is allocated to downlink, carrying data ...
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