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high density bipolar (HDB)

HDB (High Density Bipolar) coding is a further development of the pseudoternary AMI coding, Alternate Mark Inversion (AMI), and originates from the simple bipolar method. The pseudoternary code recognizes three signal levels: positive level, zero level and negative level (+1, 0, -1).

The line coding corresponds essentially to the AMI coding. In HDB coding, a binary "0" is represented by the zero level. A binary 1 is represented by an alternating pulse, where the first 1 has a negative level (-1), the following 1 is represented by +1. The duration of the states is 50% of the clock time, in the other 50% the state is reset to 0. In order to avoid the transmission of long sequences of zeros, which makes the clock recovery more difficult, a special bit combination, the so-called violation, is inserted when more than n consecutive zeros are transmitted.

Coding according to the HDB3 method

Coding according to the HDB3 method

With the HDB2 method, no more than two zeros may follow each other (n=2). Then the Violation bit (V bit) is inserted. With the HDB method, the level of this bit has the same polarity as the last 1. If the last 1 was represented with +1, then the violation level is also +1.

In the HDB3 procedure with n = 3, the Violation bit (V bit) is added after three zeros, either as +1 or as -1. If an even number of binary ones are transmitted between two Violation states, then the first 0 is represented with a pulse. This state corresponds to an A-state, an AMI-compliant rule violation. The HDB code is used for the transmission of pulse code modulated signals; among others it is used for the transmission interfaces E1 and E3.

Informations:
Englisch: high density bipolar - HDB
Updated at: 18.02.2014
#Words: 267
Links: home data base (Tetra) (HDB), coding, advanced metering infrastructure (smart metering) (AMI), bipolar method, code
Translations: DE
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