Error correction code and apparatus for the correction of differentially encoded quadrature phase shift keyed data (DQPSK)

Claim 1

In error correction apparatus for correcting errors in binary information that has been transmitted using apparatus encoding and decoding the data as differentially encoded quadrature phase shift keyed data and using an (mn 0 , mk 0 ) convolutional code with the truncated parity check matrix: H= (D,TD,T.sup. 2 D, . . . , T.sup.m1 D) where D is an (N.sub. 0 -K 0 )m× n 0 binary matrix and T is the shift matrix defined by ##STR1## where m(i.sub. j) is a submatrix of H deleting all rows in which the i th bit is zero, the i j th column of M(i.sub. j) has a weight four and every other column of M(i.sub. j) has weight zero or one, the improvement comprising: first shift register means, coupled to the input of apparatus for encoding the data as differentially encoded quadrature phase shift keyed data, for dividing a sequence of said data bits into a plurality of sets and generating parity bits for each set of the binary information bits in the sequence in accordance with the submatrix (Mi.sub. j) where the EXclusive OR columns i, i+1, i+2i+3 of M(i.sub. j) has a weight zero or one if i j < i or i j > i+3, and the EXclusive OR of columns i, i+1, i+2, i+3 of M(i.sub. j) has weight three or four if i j - i=0, 1, 2 or 3; second shift register means, at the output of the apparatus decoding differentially encoded quadrature phase shift keyed data, for dividing a sequence of decoded data bits into a number of sets including the information bits and parity bits of encoded sets, and; third shift register means, coupled to the output of the second shift register means, for receiving said generated syndromes of the sequence and the data bits of the sequences to correct said data bits.