In telecommunication, a paired disparity code is a line code in which at least one of the data characters are represented by two codewords of opposite disparity that are used in sequence 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.
The simplest paired disparity code is alternate mark inversion signal. Other paired disparity codes include 8B10B, the modified AMI codes, coded mark inversion, 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.
Famous quotes containing the words paired, disparity and/or code:
“The paired butterflies are already yellow with August
Over the grass in the West garden;
They hurt me. I grow older.”
—Li Po (701–762)
“I find it a great and fatal difference whether I court the Muse, or the Muse courts me. That is the ugly disparity between age and youth.”
—Ralph Waldo Emerson (1803–1882)
“Hollywood keeps before its child audiences a string of glorified young heroes, everyone of whom is an unhesitating and violent Anarchist. His one answer to everything that annoys him or disparages his country or his parents or his young lady or his personal code of manly conduct is to give the offender a “sock” in the jaw.... My observation leads me to believe that it is not the virtuous people who are good at socking jaws.”
—George Bernard Shaw (1856–1950)