why Time Division Multiplexing is used in digital  technology?
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Really, you don't know and have to ask, this is basic primary school stuff.....good god fella, you have a lot of catchin up to do.
304534
Well... that's kind of a broad question, but here's the basics both signals. \n\nDigital Signal\n----------------------------\nA digital signal is like an electronic representation of bianary.  it has 2 states, high and low.  It depends on the logic being used (CMOS, TTL, or ECL), but the lows can run anywhere from -5.2 VDC in ECL Logic, and the highs up to +5.2VDC in TTL Logic.  in the o'scope, all you will see looks a little like:\n_-_--____--_--__--_--_____-__-----_       <==== where you can see definate highs and lows.\n\n__--__--__--__--__--__--__--__--__--__ <== A typical digital clocking signal, like in your computer\n\nAnalog Signal\n------------------------\nAn analog signal is like what you see in your windows media player when you turn on the o'scope visualisation (do it, it's a good example of an analog signal).  The pure definition of an analog signal is a variable signal that is continuous in both time and amplitude.  It could be a perfect Sine, triangle, square, or sawtooth Wave ( http://en.wikipedia.org/wiki/Image:Waveforms.png ), a straight DC level, or what you see in the Media Player Example.
1010922
Not at all, RS232 is one of the oldest interface still used (it dates back to 1969!).\n\nIn the most "advanced" variant it can carry a maximum of 215 000 bits per second, which is way too low for a decent video signal.\n\nTo give you a comparison point, HDMI - which is the connector of choice for transmitting digital video signal - has a data rate of up to 5 000 000 000 bits per second...\n\nIn the case of the Sky Digibox, the RS232 port is here just to allow an upgrade of the internal software, to perform diagnosis without opening up the box, or to connect a gamepad.
644807
The serial digital interface or SDI as it is known is the standard for transmitting video data over a coax cable. It allows transmission at a rate of about 270Mbps or so, but can get up higher to around 540 Mbps or so.\n\nMost noise or interference that run through SDI and ruin the data transmission can be detected and corrected using a code called Hamming Code. Not only does it support video but can also carry four digital audio signals along with the one video channel, making it great for HD type quality sound.\n\nI have included a link for hamming code in case you were curious about data correction using this method.\n\nI hope this helps you out. Enjoy
1168745
MULTIPLEXER is a combinational circuit which can select any one of the inputs and route it to the output\n       DECODER is  used 2 distribute the data on a line to any one of the output line according to the binary code on data select lines\n \n  i thnk dis will do
765317
Well, this really borders on electrical engineering. The conversion between a binary stream of unmodified digital data and the transmitted signal occurs through modulation to more fault tolerant and/or less error prone signals. We'll take ethernet as an example. Ethernet uses an inverted version of Manchester encoding. Manchester encoding is used for a multitude of reasons. For example, Manchester encoding is easily synchronised, and is less susceptible to losing the established synchronisation, since there are no long periods between voltage changes on the wire.\n\nManchester encoding features two voltage states per bit. It is the second voltage stage that carries the data. When the bit stream changes states, such as from binary 0 to binary 1, the second voltage stage stays identical to the first, that is, voltage is not changed for the second bit period. When the bit stream keeps the same state from bit to bit, such as a binary 1 followed by another binary 1, the second voltage stage changes to opposite of the first voltage state, signifying the change of state. An example binary string and conversion could be something like\n\nBinary\n\n   1      1      0      1      0      0       1      0\n---------------------------------------------------------------\n lo/hi  lo/hi hi/lo  lo/hi  hi/lo  hi/lo  lo/hi  hi/lo\n\nManchester\n\nThis is how the voltage is put on the wire. As you can see, when two consecutive identical states, such as a 1 followed by a 1 is transmitted, the second stage voltage state is opposite of the following first stage voltage state, while when the bit stream changes states, the second stage voltage state is identical to the following first stage voltage state, and the second stage of that bit is opposite of the first.\n\nEncoding is used in everything from wire transmissions to optical media, such as CDs, where encoding is done on a 1:2 basis. That is, one byte of binary data is encoded to a two byte number sequence to facilitate the varying quality of CD readers and the inevitable wear and tear.\n\nFor radio and cellular use, modulation occurs as well, though this is done by frequency modulation, which is done by the same concept as voltage modulation.\n\nFor more information, you can google (or Wikipedia, there should be articles about these) "Manchester encoding", "Frequency modulation" and "Eight-to-fourteen modulation".
269494
Your question is too vague to properly answer.  However, I can suggest looking at mosix for a distributed system.  Types of sensors and what is the ultimate goal of the project will help me to better answer you.
427113
Currently the world's communication systems are dependent upon the Trans-Pacific and the Trans-Atlantic Fiber optic cables.  Satellite traffic does not carry near as much information as these two cables.
357712
modulation is simply affecting a frequency by altering its waveshape such as with a microphone. Multiplexing is dividing a frequency between 2 or more input signals...I.E. having 2 or more microphones riding on the same frequency but totally independant of each other. Phone lines are multiplexed to contain more than one phone conversation.
27846
Modulation is used in communications because the frequency of the signal must be high enough to travel through the air over great distances.  The power necessary to send a low frequency signal, such as your voice, hundreds of meters away would be too much.  Increasing the frequency by modulating onto a carrier frequency allows us engineers to decrease the required power to send that same message.  Hope this helps.
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Digital to digital conversion occurs when an analog system is used to convert between two digital signals.  The process involves first changing a digital signal to analog form, then the analog form is re-encoded digitally.  This process is often used to allow analog filtering techniques to be applied to digital signals.
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Because up to a few years ago it was always the easiest and cheapest method to transmit and receive broadcasts with.  The first system invented (discovered ?) by Marconi was an analogue system and it has stayed that way since.  \n\nActually, the terms 'analogue' and 'digital' only apply to the modulation methods used;  once the modulated signal leaves the radiating antenna it travels as an analogue electro-magnetic wave through space regardless of which type of modulation is used.
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Multiplexors, Digital Cross-Connect Systems.
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In fibre optic telecommunications, wavelength-division multiplexing (WDM) is a technology which multiplexes multiple optical carrier signals on a single optical fibre by using different wavelengths (colours) of laser light to carry different signals. This allows for a multiplication in capacity, in addition to making it possible to perform bidirectional communications over one strand of fibre.\n\nThe term wavelength-division multiplexing is commonly applied to an optical carrier (which is typically described by its wavelength), whereas frequency-division multiplexing typically applies to a radio carrier (which is more often described by frequency). However, since wavelength and frequency are inversely proportional, and since radio and light are both forms of electromagnetic radiation, the two terms are closely analogous.\n\nWDM systems are divided into two market segments, dense and coarse WDM. Systems with more than 8 active wavelengths per fibre are generally considered Dense WDM (DWDM) systems, while those with fewer than eight active wavelengths are classed as coarse WDM (CWDM).\n\nCWDM and DWDM technology are based on the same concept of using multiple wavelengths of light on a single fibre, but the two technologies differ in the spacing of the wavelengths, number of channels, and the ability to amplify signals in the optical space.\n\nThe Ethernet LX-4 physical layer standard is an example of a CWDM system in which four wavelengths near 1310 nm, each carrying a 3.125 gigabit-per-second data stream, are used to carry 10 gigabits per second of aggregate data.\n\nCWDM is also been used in cable television networks, where different wavelengths are used for the downstream and upstream signals. In these systems, the wavelengths used are often widely separated, for example the downstream signal might be at 1310 nm while the upstream signal is at 1550 nm.\n\nAn interesting and relatively recent development relating Coarse WDM is the creation of Small Form Factor Pluggable (SFP) transceivers utilizing standardized CWDM wavelengths. SFP Optics allow for something very close to a seemless upgrade in even legacy systems that support SFP interfaces. Thus, a legacy ethernet switch can be easily "converted" into a multiwavelength switch simply by judicious choice of transceiver wavelengths, combined with an inexpensive passive optical multiplexing device. This is in contrast to Dense WDM systems which, though Optically Amplifiable and far more efficient (in terms of bandwidth) are orders of magnitude more expensive. Thus it would seem that CWDM would be poised to find a solid market share in metropolitan systems as well as high-end enterprise.
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To answer the question properly, need to know more about the nature of the signal.\n\nWhat is the signal bandwidth (what is the fastest that the signal is changing?)\n\nWhat is the dynamic range of the signal? (What is the ratio of the are the maximum-to-minimum values expected)\n\nWhat amount (%) of error can you tolerate in each measurement?\n\nFlash conversion is very fast, but is power hungry and limited in its number of bits. I'd probably choose this one only if there were no other alternatives. Considering that seismic events are relatively slow with respect to the typical speeds of electronics, I might expect that a flash converter may not be necessary.\n\nThere are several very fast successive-approximation ADCs that could probably do the job. And they are cheap!\n\nSigma-delta converters are relatively slow, but have a very wide dynamic range. Useful for high precision across a wide range.\n\nCheck out www.analog.com. They make a lot of converters, you can probably find some application notes on the topic.
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A modulator is used to impress the information from a single source upon a radio wave or other system carrier, such as the process that happens when you play a VCR through channel three of your TV. The audio and video program are modulated onto a high frequency radio wave which can be received by your TV (demodulated). A radio wave can easily pass through space unlike the baseband video and audio signals.\n\n   A multiplexer may be thought of as a time sharing system in which several program sources are alternately routed to an output. An example of this would be in security systems where the pictures from several cameras are combined to be seen on one monitor screen.\n\n   Modulation has a 'one to one' relationship, as well as does its inverse, 'demodulation'. Multiplexing has a 'many to one' relationship. Its inverse, demultiplexing, has a 'one to many' relationship useful for extracting the various original signals.\n\nWK
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Programming a DSP is similar to programming any other type of microcontroller, except that it is designed with signal processing in mind. As such it is designed with extra multipliers and pipelines to allow faster signal processing. They also (some do) come with software libraries to implemented tested signal processing functions such as the fourier transform, and convolution.\n\nAn FPGA is exactly what the name suggests: a programmable gate array. You program it as a piece of hardware. The FPGA basically implements look up tables and as such is good for doing complex logic very fast. Using languages such as VHDL and Verilog you can create complex logic structures. Many pre-writen FPGA cores exist that allow you to implement processors, multipliers, video/audio converters, network protocols... just about anything. So an FPGA is extremely flexible. If you are looking to implement a complex system, then an FPGA is what you want.\n\nIf you are using signal processing, and are testing an algorithm then a DSP would be best, as reprogramming an FPGA for signal processing tasks isnt as easy as it is for a DSP. You could how ever develop a DSP like FPGA core, but this would require extensive effort... and unless you understood your algorithm well would waste development time.\n\nIn the past I have with ease used an FPGA to build a system containing a processor, ethernet, serial ports, and 100s of digital I/Os... this is exactly what they are suited for.\nWhere as if i were building a digital equaliser for example, a DSP would be best.