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Channel Access Methods
In telecommunications and computer networks, a channel access method or multiple access method allows more than two terminal (telecommunication), terminals connected to the same transmission medium to transmit over it and to share its capacity. Examples of shared physical media are wireless networks, bus networks, ring networks and point-to-point links operating in half-duplex mode. A channel access method is based on multiplexing, which allows several data streams or signals to share the same communication channel or transmission medium. In this context, multiplexing is provided by the physical layer. A channel access method may also be a part of the multiple access protocol and control mechanism, also known as medium access control (MAC). Medium access control deals with issues such as addressing, assigning multiplex channels to different users and avoiding collisions. Media access control is a sub-layer in the data link layer of the OSI model and a component of the link layer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Telecommunications
Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of transmission may be divided into communication channels for multiplexing, allowing for a single medium to transmit several concurrent Session (computer science), communication sessions. Long-distance technologies invented during the 20th and 21st centuries generally use electric power, and include the electrical telegraph, telegraph, telephone, television, and radio. Early telecommunication networks used metal wires as the medium for transmitting signals. These networks were used for telegraphy and telephony for many decades. In the first decade of the 20th century, a revolution in wireless communication began with breakthroughs including those made in radio communications by Guglielmo Marconi, who won the 1909 Nobel Prize in Physics. Othe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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TCP/IP Model
The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suite are the Transmission Control Protocol (TCP), the User Datagram Protocol (UDP), and the Internet Protocol (IP). Early versions of this networking model were known as the Department of Defense (DoD) model because the research and development were funded by the United States Department of Defense through DARPA. The Internet protocol suite provides end-to-end data communication specifying how data should be packetized, addressed, transmitted, routed, and received. This functionality is organized into four abstraction layers, which classify all related protocols according to each protocol's scope of networking. An implementation of the layers for a particular application forms a protocol stack. From lowest to highest, the layers are the link la ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Orthogonal Frequency-division Multiple Access
Orthogonal frequency-division multiple access (OFDMA) is a multi-user version of the popular orthogonal frequency-division multiplexing (OFDM) digital modulation scheme. Multiple access is achieved in OFDMA by assigning subsets of subcarriers to individual users. This allows simultaneous low-data-rate transmission from several users. Comparisons OFDMA is often compared to the combination of OFDM with statistical time-division multiplexing. The advantages and disadvantages summarized below are further discussed in the Characteristics and principles of operation section. See also the list of OFDM key features. Advantages * Allows simultaneous low-data-rate transmission from several users. * Pulsed carrier can be avoided. * Lower maximal transmission power for low-data-rate users * Shorter delay and constant delay * Contention-based multiple access (collision avoidance) is simplified. * Further improves OFDM robustness to fading and interference * Combat narrow-band inter ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Wavelength-division Multiplexing
In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i.e., colors) of laser light. This technique enables bidirectional communications over a single strand of fiber (also called wavelength-division duplexing) as well as multiplication of capacity. The term WDM is commonly applied to an optical carrier, which is typically described by its wavelength, whereas frequency-division multiplexing typically applies to a radio carrier, more often described by frequency. This is purely conventional because wavelength and frequency communicate the same information. Specifically, frequency (in Hertz, which is cycles per second) multiplied by wavelength (the physical length of one cycle) equals velocity of the carrier wave. In a vacuum, this is the speed of light (usually denoted by the lowercase letter, c). In glass fiber, velocity is substan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Carrier Frequency
In telecommunications, a carrier wave, carrier signal, or just carrier, is a periodic waveform (usually sinusoidal) that conveys information through a process called ''modulation''. One or more of the wave's properties, such as amplitude or frequency, are modified by an information bearing signal, called the ''message signal'' or ''modulation signal''. The carrier frequency is usually much higher than the message signal frequency; this is because it is usually impractical to transmit signals with low frequencies over long distances (due to attenuation). The purpose of the carrier is usually either to transmit the information through space as an electromagnetic wave (as in radio communication), or to allow several carriers at different frequencies to share a common physical transmission medium by frequency division multiplexing (as in a cable television system). The term originated in radio communication, where the carrier wave creates the waves which carry the information (mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Modulated
Signal modulation is the process of varying one or more properties of a periodic waveform in electronics and telecommunication for the purpose of transmitting information. The process encodes information in form of the modulation or message signal onto a carrier signal to be transmitted. For example, the message signal might be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal representing a sequence of binary digits, a bitstream from a computer. This carrier wave usually has a much higher frequency than the message signal does. This is because it is impractical to transmit signals with low frequencies. Generally, receiving a radio wave requires a radio antenna with a length that is one-fourth of the wavelength of the transmitted wave. For low frequency radio waves, wavelength is on the scale of kilometers and building such a large antenna is not practical. Another purpose of modulatio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Frequency-division Multiplexing
In telecommunications, frequency-division multiplexing (FDM) is a technique by which the total bandwidth (signal processing), bandwidth available in a communication channel, communication medium is divided into a series of non-overlapping frequency bands, each of which is used to carry a separate signal. This allows a single transmission medium such as a microwave radio link, cable or optical fiber to be shared by multiple independent signals. Another use is to carry separate serial bits or segments of a higher rate signal in Parallel communication, parallel. The most common example of frequency-division multiplexing is radio and television broadcasting, in which multiple radio signals at different frequencies pass through the air at the same time. Another example is cable television, in which many television channels are carried simultaneously on a single cable. FDM is also used by telephone systems to transmit multiple telephone calls through high capacity trunklines, communi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Frequency-division Multiple Access
Frequency-division multiple access (FDMA) is a channel access method used in some multiple-access protocols. FDMA allows multiple users to send data through a single communication channel, such as a coaxial cable or microwave beam, by dividing the bandwidth of the channel into separate non-overlapping frequency sub-channels and allocating each sub-channel to a separate user. Users can send data through a subchannel by modulating it on a carrier wave at the subchannel's frequency. It is used in satellite communication systems and telephone trunklines. FDMA splits the total bandwidth into multiple channels. Each ground station on the earth is allocated a particular frequency group (or a range of frequencies). Within each group, the ground station can allocate different frequencies to individual channels, which are used by different stations connected to that ground station. Before the transmission begins, the transmitting ground station looks for an empty channel within the fr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Moshe Sidi
Moshe Sidi (; born 1953) is a professor emeritus in the Faculty of Electrical and Computer Engineering at the Technion - Israel Institute of Technology. Sidi served as the Senior Executive Vice President and Executive Vice President for Academic Affairs of the Technion, and as Executive Director of the Neaman Institute for National Policy Research. Early life and education Moshe Sidi was born in Ramla, Israel. He graduated from the Ramla-Lod high school. He began his academic studies in Electrical Engineering at the Technion, and received his B.Sc. in 1975, and M.Sc. in 1979. He continued his Ph.D. studies at the Technion until 1982. His thesis on ''Interfering Queues in Packet Radio Networks'' was supervised by Prof. Adrian Segall. Career Sidi joined the Faculty of Electrical and Computer Engineering at the Technion in 1982 as a lecturer. He became a senior lecturer in 1986, and an associate professor in 1990. He was promoted to full professor in 1997. In 2001 he ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Raphael Rom
Raphael "Raphi" Rom () is an Israeli computer scientist working at Technion – Israel Institute of Technology. Rom earned his Ph.D. in 1975 from the University of Utah, under the supervision of Thomas Stockham. He is known for his contribution to the development of the Catmull–Rom spline, and for his research on computer network A computer network is a collection of communicating computers and other devices, such as printers and smart phones. In order to communicate, the computers and devices must be connected by wired media like copper cables, optical fibers, or b ...s. Selected publications *. *.Review of ''Multiple Access Protocols'' by Apple van de Liefvoort (1993), ''ACM SIGMETRICS Performance Evaluation Review'' 20 (3): 5–6, . *. *. *. *. References External linksHome page Living people Academic staff of Technion – Israel Institute of Technology Israeli computer scientists University of Utah alumni Year of birth missing (living people) {{co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Random Access
Random access (also called direct access) is the ability to access an arbitrary element of a sequence in equal time or any datum from a population of addressable elements roughly as easily and efficiently as any other, no matter how many elements may be in the set. In computer science it is typically contrasted to sequential access which requires data to be retrieved in the order it was stored. For example, data might be stored notionally in a single sequence like a row, in two dimensions like rows and columns on a surface, or in multiple dimensions. However, given all the coordinates, a program can access each record about as quickly and easily as any other. In this sense, the choice of datum is arbitrary in the sense that no matter which item is sought, all that is needed to find it is its address, i.e. the coordinates at which it is located, such as its row and column (or its track and record number on a magnetic drum). At first, the term "random access" was used because th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Space-division Multiple Access
Space-division multiple access (SDMA) is a channel access method based on creating parallel spatial pipes (focused signal beams) using advanced antenna technology next to higher capacity pipes through spatial multiplexing and/or diversity, by which it is able to offer superior performance in radio multiple access communication systems (where multiple users may need to use the communication media simultaneously). In traditional mobile cellular network systems, the base station has no information on the position of the mobile units within the cell and radiates the signal in all directions within the cell in order to provide radio coverage. This method results in wasting power on transmissions when there are no mobile units to reach, in addition to causing interference for adjacent cells using the same frequency (so-called co-channel cells). Likewise, in reception, the antenna receives signals coming from all directions including noise and interference signals. By using smart ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |