Hybrid ternary code

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In telecommunications, the hybrid (H-) ternary line code is a

non-return-to-zero-level (NRZL) and the polar return-to-zero
(RZ) codes.

The H-ternary code has three levels for signal representation; these are positive (+), zero (0), and negative (−). These three levels are represented by three states. The state of the line code could be in any one of these three states. A transition takes place to the next state as a result of a binary input 1 or 0 and the encoder's present output state. The encoding procedure is as follows.[1]

Input bit Prior output Output level
0 + −
0
− 0
1 +
0 +
−
  1. In general, the encoder outputs + level for a binary 1 input and a − level for a binary 0 input.
  2. However, if this would result in the same output level as the previous bit time, a 0 level is output instead.
  3. Initially, the encoder output present state is assumed at 0 level when the first bit arrives at the encoder input.

The new line-coding scheme violates the encoding rule of NRZ-L when a sequence of 1s or 0s arrives and hence, it overcomes some of their deficiencies. During the violation period for a run of 1s or 0s, it operates on the same encoding rule of the polar RZ but with pulse occupancy of full period.

NRZ-L and polar RZ codes have deficiencies compared to the proposed H-ternary encoding scheme. NRZ-L code lacks sufficient timing information when the binary signal remains at one level in of either 1 or 0. This has direct influence on synchronising the receiver clock with that of the transmitter and, as a result, has impact on the detection of the received digital signal.

The H-ternary code has also timing superiority compared to similar ternary codes. Other ternary line code such as

HDB3
).

On the other hand, the new code has a smaller bandwidth in comparison with the polar RZ code. The latter has its frequency spectral components concentrated at twice the original binary data rate because the polar RZ code has a pulse duty cycle of 50 percent.

See also

Other line codes that have three states:

References

  1. S2CID 62247348.{{cite book}}: CS1 maint: date and year (link
    )
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