A new class of two-dimensional RLL recording codes

The benefits of using modulation codes in two dimensions in multichannel recording include improved clocking and improved ratios of user bits to recorded bits. Recent work has described a class of d _x, k_y codes in two dimensions which satisfy the d_x constraint in one dimension and the k_y constraint in the other. In tape systems this method is extremely vulnerable to dropouts. A new class of two-dimensional run-length codes that operate using the usual d _x, k_y constraint along the track is proposed, with an additional k_y constraint across the tracks. In this approach the horizontal d_x, k_x code is allowed a much larger k_x constraint since it is no longer the sole carrier of clocking information. Capacities are calculated for a range of codes and number of channels, and an example of the construction of one such code is given. An extension of the codes that preserves clocking during channel loss is described