known sequences to determine which information bits were originally put into the shift register 24 an important aspect of the arrangement shown in fig5 and 6 is that the particular selection of the baseband voltages serves to improve the minimum voltage distance possible between any two of the code paths which can exist for the various sequences of t 1 and t 2 the distance structure of the code of fig5 is such that the minimum distance between any two of the possible transmitted code paths involves two antipodal code branches and one orthogonal code branch with the grey code encoding of t 1 and t 2 onto the 4 ary pam as shown in fig6 this produces a minimum distance between the paths of at least equ7 for binary psk as a standard for comparison the minimum distance is equ8 comparing equations 6 and 7 shows that the simple coding scheme has a 2 5 db advantage over binary psk even though both schemes are 1 bit transmitted symbol schemes and would require essentially the same channel bandwidth the coded scheme shown in fig5 and 6 would require a constraint length 3 viterbi decoder in the receiver 22 with the four branch metrics computed by correlating each received symbol against each of the four possible pam levels it should be noted that.