- Hybrid ternary code
The hybrid (H-) ternary line code operates on a hybrid principle that combines the binary non-return-to-zero-level (NRZ-L) and the polar
return-to-zero(RZ) codes and thus it is called H-ternary.
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 codecould 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 (Glass and Bastaki 2001, Glass et al. 2001).
# The encoder produces + level when the input is a binary 1 whether the encoder output present state is at 0 or – level.
# The encoder produces – level when the input is a binary 0 whether the encoder output present state is at 0 or + level.
# The encoder produces 0 level when the input is binary 1 and the encoder present state is + level or when the input is binary 0 and the encoder present state is – level.
# 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-Lwhen 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.
It is evident that 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
alternate mark inversion(AMI) also lacks the timing information when a run of zeros needs to be transmitted. This drawback is partly overcome by its modified version the high density bipolar with three zeros substitution ( 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.
Concept by: Dr. Abdullatif Glass, Dr. Nedhal Abdulaziz & [http://www.bastaki.net/ Dr. Eesa Bastaki]
line codes that have 3 states:
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