Techniques for implementing non-uniform constraints in modulation encoded data

DETAILED DESCRIPTION The present invention provides techniques for implementing non-uniform constraints on data that is modulation encoded in order to achieve uniform constraints on the overall stream containing encoded and unconstrained data.
In some reverse concatenation architectures unconstrained error control code parity is inserted into the data stream after modulation encoding.
The present invention prevents these parity bits which are not modulation encoded from degrading the overall modulation constraint of the resulting data stream.
Specifically the present invention prevents a situation in which a data stream that consists of both modulation encoded data and unconstrained data contains bit sequences that tend to cause errors during read back, such as too many consecutive zeros.
Stricter modulation constraints are enforced on modulation encoded data bits that are next to the unconstrained data bits, relative to the remaining modulation encoded data bits.
By enforcing stricter modulation constraints on the bits that are next to the unconstrained bits, an entire stream of data can be confined to a desired modulation constraint.
Other objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed description and the accompanying drawings, in which like reference designations represent like features throughout the figures.