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Wireless information sending and baud rate

  1. Feb 18, 2009 #1
    I understand how a baud rate can be set by a clock and the data can be shifted through a line. Both sides need a clock to keep in sync. How would this be achieved if you are using wireless. Would both sides need to communicate back and forth because I can't see how a clock could be set on both sides if both sides can't communicate.

    I am only interested in moving information in one direction.
     
  2. jcsd
  3. Feb 18, 2009 #2

    MATLABdude

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    Well, it really depends on the communications protocol you're using. If you're using an asynchronous protocol (like RS-232 serial, or USB, or Ethernet--IEEE802.3) you know that you won't maintain perfect time synchronization, but you can keep it close enough for short bursts (a few hundred KB, for instance). As long as you know when a transmission happens (say, with a really long high pulse), and the transmission speed (say, 9600 baud) and you've got a decent clock crystal, you can receive packets of data without having to transmit a clock.

    If, on the other hand, you're using a synchronous protocol (e.g. I2C or SPI), you rely on a clock being generated by the bus master.

    Generally, most wireless protocols are asynchronous. If you needed to wirelessly transmit a clock, and have multiple channels available, and your wireless transmission speed was much faster than your wired protocol, you can use one channel to transmit the clock and one to transmit the data. Or you can come up with some way of transmitting both on the same channel.

    But it's probably easier to change synchronous data to asynchronous (say, with a micro) transmit it wirelessly, and then convert it back from asynchronous to synchronous on the receiver end. Or just not use synchronous in the first place.
     
  4. Feb 18, 2009 #3
    Still a little out of my league! But thanks for the information.
     
  5. Feb 18, 2009 #4

    mgb_phys

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    Wifi (802.11) uses a more complex scheme but simple wireless (or infrared) datalinks use Manchester coding http://en.wikipedia.org/wiki/Manchester_code to embed a clock in the data stream.
    It costs you in terms of bandwidth but is very reliable and simple to implement.
     
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