telecommunications Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of ...

, a paired disparity code is a

line code In telecommunications, a line code is a pattern of voltage, current, or photons used to represent digital data transmission (telecommunications), transmitted down a communication channel or written to a storage medium. This repertoire of signal ...

in which at least one of the data characters is represented by two codewords of opposite disparity that are used in

sequence In mathematics, a sequence is an enumerated collection of objects in which repetitions are allowed and order matters. Like a set, it contains members (also called ''elements'', or ''terms''). The number of elements (possibly infinite) is cal ...

so as to minimize the total disparity of a longer sequence of digits. A particular codeword of any line code can either have no disparity (the average weight of the codeword is zero), negative disparity (the average weight of the codeword is negative), or positive disparity (the average weight of the codeword is positive). In a paired disparity code, every codeword that averages to a negative level (negative disparity) is paired with some other codeword that averages to a positive level (positive disparity). In a system that uses a paired disparity code, the transmitter must keep track of the running DC buildup the running disparity and always pick the codeword that pushes the DC level back towards zero. The receiver is designed so that either codeword of the pair decodes to the same data bits. Most line codes use either a paired disparity code or a

constant-weight code In coding theory, a constant-weight code, also called an ''m''-of-''n'' code or ''m''-out-of-''n'' code, is an error detection and correction code where all codewords share the same Hamming weight. The one-hot code and the balanced code are two ...

. The simplest paired disparity code is alternate mark inversion signal. Other paired disparity codes include 8b/10b, 8B12B, the

modified AMI code Modified AMI codes are a digital telecommunications technique to maintain system synchronization. Alternate mark inversion (AMI) line codes are modified by deliberate insertion of bipolar violations. There are several types of modified AMI codes, ...

coded mark inversion file:Cmi.gif, frame, CMI line coding In telecommunication, coded mark inversion (CMI) is a non-return-to-zero (NRZ) line code. It encodes ''zero'' bits as a half bit time of zero followed by a half bit time of one, and while ''one'' bits are encod ...

, and 4B3T. The digits may be represented by disparate physical quantities, such as two different frequencies, phases, voltage levels, magnetic polarities, or electrical polarities, each one of the pair representing a 0 or a 1.

References

*{{FS1037C MS188 Line codes