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Thread: Analog or digital signal transmition, what does have better future?

  1. #1 Analog or digital signal transmition, what does have better future? 
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    Why modern Internet and phone providers have analog DSL but not digital T-1 (or similar) as their standard (for copper)?
    What are limitations of both technologies?
    Some sources predict that computers of the future could become analog. Memristor-based, for example. Does it mean they will require no true modem?
    Is there some emerging technology which will allow vastly increase data transmission over copper cables over long distances?


    Last edited by Stanley514; July 31st, 2014 at 09:56 PM.
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    Because they are using telephone lines.
    The internet uses a higher frequency than the telephones do and there has to be filters to prevent the voice transmissions from being seen as noise by the data users.
    If the data signals sent over the telephone lines were digital signal instead of analog the telephone signal would be unable to share the line with the data signal.

    edit: It is also why data users still need to modulate and demodulate the analogue carrier to extract the digital information from it.


    Last edited by dan hunter; August 1st, 2014 at 02:52 AM.
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    The Analog-to-Digital Telephone Transition
    The major carriers have all expressed their desire to convert their networks to all-digital
    technology.
    From a carrier perspective, transitioning a network to all-digital makes sense.
    Digital networks can handle more calls than analog networks, and it’s cheaper to maintain
    and repair those networks.
    So, why don’t the carriers go ahead and switch to digital technology and get rid of the analog
    network? Well, it’s all down to those pesky basic standards we’ve all come to expect. Carriers
    can’t discontinue analog telephone service without the FCC’s permission. The carriers are
    already seeking this permission: AT&T recently filed a petition asking the FCC for permission
    to get rid of its analog networks and replace them with digital technology.
    AT&T and a number of other providers argue that digital networks are superior, that the analog-to-digital
    transition is inevitable, and that companies can’t operate both analog and digital networks and
    still remain profitable.

    http://greenlining.org/wp-content/up...om-to-post.pdf


    Jan 30 (Reuters) - U.S. wireless providers like AT&T Inc and Verizon Communications Inc on Thursday received a nod from regulators to test a transition of the telephone industry away from traditional analog networks to digital ones.

    http://www.reuters.com/article/2014/...0L414G20140130
    Last edited by Stanley514; August 1st, 2014 at 08:29 AM.
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  5. #4  
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    Quote Originally Posted by Stanley514 View Post
    Why modern Internet and phone providers have analog DSL but not digital T-1 (or similar) as their standard (for copper)?
    DSL is digital.
    What are limitations of both technologies?
    They are both just methods of encoding digital data onto a physical medium. DSL uses a standard subscriber twisted pair; T1 uses two pairs of better-quality wiring.
    Some sources predict that computers of the future could become analog. Memristor-based, for example. Does it mean they will require no true modem?
    No; they will always require some kind of modem.
    Is there some emerging technology which will allow vastly increase data transmission over copper cables over long distances?
    Sure. You can get very high rates over a coax for example.
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    DSL is digital.
    There seem to exist some unclarity about that. For example:
    A DSL circuit provides digital service. The underlying technology of transport across DSL facilities uses high-frequency sinusoidal carrier wave modulation, which is an analog signal transmission. A DSL circuit terminates at each end in a modem which modulates patterns of bits into certain high-frequency impulses for transmission to the opposing modem.
    So if believe to Wikipedia regardless its name "digital" it still uses analog signal...
    Digital subscriber line - Wikipedia, the free encyclopedia

    Also, on forums some people claim DSL is analog in fact:
    It is an ANALOG signal on the line between the CPE (MoDem) and the DSLAM. This is why we use a MoDem and why it is, indeed, called a MoDem. It is not, however, as simple a modem as the one you use for dial up. It is quite a complex modem that uses many different channles within the spectrum available on the line.
    DSL runs on digital or analog? - General Questions | DSLReports Forums-

    No; they will always require some kind of modem.
    But not analog to digital conversion? Just some kind of amplifier?

    Also I have question: does radiation produced by digital signal in a cable differs from that produced by analog signal? I mean if it could be produced by pulsed direct current, it doesn't suppose to produce radiofrequency waves? But it still produces some white noise or what?
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    Quote Originally Posted by Stanley514 View Post
    So if believe to Wikipedia regardless its name "digital" it still uses analog signal...
    All physical layers transmit signals via physical (and therefore analog) means. Even a fiber optic OOK (on off keying) scheme, about as "digital" as you can get, uses 'sinusoidal' light waves. In general digital transmission refers to the data that is carried, not the physical layer doing the carrying.
    But not analog to digital conversion? Just some kind of amplifier?
    You will always need a physical (i.e. analog) to digital conversion stage. It might be as simple as a gate; it might be as complex as a phase locked loop driving an I/Q discriminator and a Viterbi decoder.

    Also note the way you are currently defining "analog" (i.e. anything that can be represented as a physical signal with some uncertainty as to frequency, voltage, phase etc) all computers are analog. Saying they are digital is a simplification because MOST of the time you can abstract the analog voltages to a simpler digital representation.

    Also I have question: does radiation produced by digital signal in a cable differs from that produced by analog signal? I mean if it could be produced by pulsed direct current, it doesn't suppose to produce radiofrequency waves? But it still produces some white noise or what?
    No, there is no difference. All signals are the same.
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    All physical layers transmit signals via physical (and therefore analog) means.
    Do you claim we cannot transfer data by DC pulses?
    Last edited by Stanley514; August 2nd, 2014 at 12:12 AM.
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    Quote Originally Posted by Stanley514 View Post
    All physical layers transmit signals via physical (and therefore analog) means.
    Do you claim we cannot transfer data by DC pulses?
    Sure we can. And since DC pulses have characteristic voltages, currents, durations etc they are inherently analog. You can interpret them as digital (i.e. say "anything over 2 volts is a 1, and anything under .8 volts is a 0") but that's an abstraction rather than reality, and that abstraction breaks down very quickly over long distances.
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    and that abstraction breaks down very quickly over long distances.
    What do you mean by that? And what if they would by truly digital?
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    In a digital signal the information is represented by 2 distinct amplitudes.
    In other words you are transmitting voltage spikes.
    Digital signals are square waves instead of sine waves.
    Digital signals are not very sensitive to noise since they are basically on or off signals.
    Analog signals are more sensitive to noise.
    A digital signal sent over a line shared with an analog signal is seen as a series of volyage spikes by the analoge devices.
    (unfiltered phone lines crackle or howl when digital signals are being transmitted)
    Digital signals consume less power during transmission. (usually much less)
    Digital signals are high impedance while analog signals are usually low impedance. (makes filtering fairly easy)
    Digital signals usually require some form of time synchonization but analog signals usually don't.
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    In a digital signal the information is represented by 2 distinct amplitudes.
    In other words you are transmitting voltage spikes.
    Digital signals are square waves instead of sine waves.
    Digital signals are not very sensitive to noise since they are basically on or off signals.
    Analog signals are more sensitive to noise.
    A digital signal sent over a line shared with an analog signal is seen as a series of volyage spikes by the analoge devices.
    (unfiltered phone lines crackle or howl when digital signals are being transmitted)
    Digital signals consume less power during transmission. (usually much less)
    Digital signals are high impedance while analog signals are usually low impedance. (makes filtering fairly easy)
    Digital signals usually require some form of time synchonization but analog signals usually don't.
    Does modern technology allows to create truly digital signals in a copper cable? And if yes, will people gain if communication companies will switch to
    all true digital communications? Including phone, internet and TV?
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  13. #12  
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    Quote Originally Posted by Stanley514 View Post
    Does modern technology allows to create truly digital signals in a copper cable? And if yes, will people gain if communication companies will switch to
    all true digital communications? Including phone, internet and TV?
    The answer to the first question is, "Yes."
    The answer to the second question is "I don't know."

    edit. If you were just using digital signals fiber optics would be a far better choice than copper wire.
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    Which electric signals are more susceptible to attenuation and require more repeaters, digital or analog? I've read quite opposite minds on this account.
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    Quote Originally Posted by Stanley514 View Post
    Which electric signals are more susceptible to attenuation and require more repeaters, digital or analog? I've read quite opposite minds on this account.
    All signals that are intended for long distance high bandwidth transmission are processed to match the physical channel they are using. And again there are no such things as purely digital signals in data transmission - or indeed even in modern PC motherboard design.

    Simple example. Let's use RS232 as an example, a protocol you might consider "digital" because it only has two states - high voltage (+3 to +15 volts) for a 0 and low voltage (-3 to -15 volts) for a 1. Over short distances this is easy; send a +12 volt signal to represent a 0, and you get a +11.9 volt signal. It's still a 1.

    Now you use that to transmit over a long distance. And due to leakage and resistance, at the far end of the line, rather than a high voltage or a low voltage you see +0.8 volts. Is it a 1 or a 0? How can you not be sure if it's a digital signal?
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    Quote Originally Posted by Stanley514 View Post
    Does modern technology allows to create truly digital signals in a copper cable?
    Yes, but they are not digital signals as you think of them; they are analog waveforms that are processed at the receiving end to recreate the digital symbols you want to send. Indeed, the more accurate the recovery of the digital signal, the more analog processing goes on. For simple digital signals (like NRZ or Manchester encoding) you have transmission lines with analog source impedance control and analog termination at the far end, as well as phase locked loops to do clock recovery and line drivers/receivers to better recover the original symbols from a noisy analog line.

    The bigger issue (and maybe this is what you are getting at) is that the encoding is much more complex than a simple analog encoding scheme. The simplest scheme is direct voltage representation; a microphone changes pressure waves into a voltage and this voltage is sent directly down the line. More complex systems also use all-analog signal chains (like AM or FM modulation) and systems even more complex use a digital representation of that analog waveform (PCM.)
    And if yes, will people gain if communication companies will switch to all true digital communications? Including phone, internet and TV?
    Most companies have already done so, although again the line itself carries a complex analog waveform that encodes a digital signal.
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    edit. If you were just using digital signals fiber optics would be a far better choice than copper wire.
    Isn't fiber too expensive?
    If you know so much, maybe you could tell me, could non-linear copper line with electrical soliton transmission signal
    be cheaper than fiber optic and rival them in speed? How many repeaters will they need?
    Circuits at the Nanoscale: Communications, Imaging, and Sensing - Google Books
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  18. #17  
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    Quote Originally Posted by Stanley514 View Post
    edit. If you were just using digital signals fiber optics would be a far better choice than copper wire.
    Isn't fiber too expensive?
    If you know so much, maybe you could tell me, could non-linear copper line with electrical soliton transmission signal
    be cheaper than fiber optic and rival them in speed? How many repeaters will they need?
    Circuits at the Nanoscale: Communications, Imaging, and Sensing - Google Books
    But I don't "know so much" and am not shy to admit it, as the response to the second part of your 2 part question in post #12 shows.

    The reason fiber optiics would be a better choice is that light is a very high frequency carrier and gives a wide relative bandwith so you can carry a lot of differnet channels on it.

    Data and Computer Communications: Networking and Internetworking - Gurdeep S. Hura, Mukesh Singhal - Google Books
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    Quote Originally Posted by Stanley514 View Post
    could non-linear copper line
    Non-linearity in any communications medium is, in general, a very bad thing, and tends to reduce overall bandwidth.
    with electrical soliton transmission signal
    Well, you'd have to design the system and compare the throughput to a commercial method. For example, with a fairly standard twisted pair (cat 7A) you can get speeds up to a gigabit per second.
    be cheaper than fiber optic and rival them in speed?
    You are going to be very, very hard pressed to find anything that rivals fiber in speed and cost. The fiber itself is very cheap; far cheaper than copper wire. In general the terminations are the problem.
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  20. #19  
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    From what I know, fiber cable is still regarded as a backbone cable, but not as a user-end residential cable. It would be to fragile and inconvenient, not only expensive, as a such.
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    Quote Originally Posted by Stanley514 View Post
    From what I know, fiber cable is still regarded as a backbone cable, but not as a user-end residential cable. It would be to fragile and inconvenient, not only expensive, as a such.
    It is often used as residential cable. Here cable TV (AT+T uVerse) is delivered via FTTN (fiber to the node.) Coax then goes the last hundred yards. Verizon Fios is a FTTH service - fiber all the way to the home.
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    You are going to be very, very hard pressed to find anything that rivals fiber in speed and cost.
    I think electrical soliton line may require much fewer repeaters than typical copper line.
    They mention copper soliton line should be accompanied by lot of varactors. How much such varactors could cost?
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