Codes for improved timing recovery in PR4 and EPR4 magnetic recording

We consider an alternative to the widely-used (0,G/I) constraint in partial response digital magnetic recording systems. The new one-pairs constraint is an upper bound on the maximum number of symbols between pairs of ones in a coded sequence. Codes for the one-pairs constraint can be used to limit quasi-catastrophic error propagation and improve timing recovery in Class-IV partial response (PR4) and Extended PR4 (EPR4) magnetic recording systems. Rate 4:5, 8:9, 16:17, and 24:25 block and finite state codes are discussed and compared with well-known rate 8:9 and 16:17 block codes. The new codes have improved one pairs statistics, low complexity, and for the 24:25 code, reduced error propagation.