Tip of the Week – 25 Sep 2013

Tip of the Week – Baud Rate and Transmission Rate

For 40G, 100G and higher equipment using new modulation schemes, you may be interested in knowing what the actual signal Baud Rate is in your fiber. The Baud Rate can simply be defined as the rate the optical light (LED or Laser) turns on and off in the fiber, ie the number of light pulses per second. It is also referred to as the Symbol Rate. This rate determines how wide the DWDM channel needs to be to accommodate the optical signal.

The Transmission Rate is defined as the rate digital information is transferred in the channel inclusive of all coding bits. This rate is commonly used when specifying any communication system, for example 10Gig or 1Gig, which refers to the Transmission Rate. The Transmission Rate is also sometimes called the Bit Rate.

In classic optical transmission systems using 1Gig and 10Gig transceivers, the Baud Rate is the same as the Transmission Rate, BaudRate = TransmissionRate. They use a signal modulation scheme called on-off keying OOK, light turns on and off which represents 1 bit of information.

For the new exotic modulation systems for Transmission Rates of 40G and higher, the Transmission Rate is a multiple “n” of the Baud Rate. This is required to fit higher transmission rate systems into existing DWDM (100GHz and 50GHz) spaced channels.

BaudRate = TransmissionRate / n

Where, n is the number of bits that can be encoded in a Baud symbol.

Very popular for 100G is the DP-QPSK modulation scheme with coherent signal detection. This modulation rate has a Baud Rate of only 28 Mbps which can be used with many DWDM systems. Most manufacturers will be more than happy to provide you with the equipment Baud Rate along with the Transmission Rate.

Pertinent Products/Services:

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Benefits

  • Accurately measure optical power loss over all 18 CWDM channels 1270nm to 1610nm (CWDM Power Meter also required).
  • Determine if high loss channels at fiber water peak wavelengths can be used for communication.
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Applications

  • CWDM networks
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