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Binary Convolutional Codes (BCC)


Instructions


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Viterbi Workshop

Instructions

  • Getting Started
    • If you have no background in binary convolutional codes, you may want to read the background information on BCCs.
    • If you are ready to learn about how the Viterbi Algorithm works, read on.
  • Using the Viterbi Algorithm Workshop
    • Stepping Through the Algorithm
      The workshop applet is designed so that you don't have to know anything about the Viterbi algorithm to operate it. When you start the workshop applet, it starts up a default simulation. All you need to do is press the STEP button in the middle panel. It will automatically take you through every step in the decoding process. To understand what is happening at each step, read the message displayed in the Message Box in the middle panel above the step button.
    • The Default Simulation
      The parameters for the default simulation can be viewed in the right panel. The default binary convolutional code used for the initial simulation can be viewed by pressing the Edit Transfer Function button.
    • The Long Trellis Diagram
      A Trellis is an extension of a code's state diagram that shows the passage of time. Every branch between two states represents a possible state change in the encoder. Associated with each branch is the input message word and the resultant codeword generated from the current state and this message word. The workshop displays two active diagrams of the trellis. The one in the bottom panel displays a stretch of the trellis that is as long as it takes for one full decoding operation.
    • The Small Trellis Diagram
      The diagram in the left panel shows a close-up of one section of the trellis at a time. Each trellis section displayed here corresponds to one moment in time, another way to think about it is one state change of the encoder.
    • The Color Scheme Conveys Information
      The color scheme used in both the small and long trellis diagrams indicates the current status of the Viterbi algorithm and the values associated with the trellis.
    • Shifting Along the Trellis
      You can view the detailed information for a single trellis section that is not currently being visited by the algorithm in one of two ways. First, you can use the "<<" and ">>" buttons to shift left or right one trellis section or trellis block at time. Secondly, you can simply click in the long trellis diagram on the trellis section you want to view. To shift to the previous or next blocks in the trellis by clicking, just click to the left or the right of the trellis in the long trellis diagram. Note that you can shift around the trellis at any time and this will not affect the progression of the algorithm. To jump back to the current trellis section being visited by the algorithm, press the "Recenter" button. However, you do not need to do this because the diagrams will shift back to the proper place when you next press the STEP button.
  • Starting a New Simulation
    • To restart the simulation with the same parameters but a new message sequence, simply press Restart.
    • To run a different simulation, enter new parameters in the setup panel on the right and then press Restart. Note that no changes take effect until you press Restart.



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