Look ahead length L is given by m+1 where m is the preselected positive integer.

The feedback decoder makes hard decision on data bits.

The soft decision algorithm has limited resolution than hard decision algorithm and thus it cannot use hamming distance metric.

As soft decision decoding algorithm has limited resolution it cannot use hamming distance metric. Instead it uses Euclidean and monotonic metric such as Euclidean distance squared.

While using Euclidean distance squared metric, maximum correlation is desirable rather than minimum distance.

Minimum distance between all pair of code words is related to the error correcting capability of the code.

The error correcting capability of a code scheme increases as the number of channel symbols n per information bit k increases or the rate k/n decreases. As n increases bandwidth and complexity also increases.

Soft decisions require more storage and it also increases the complexity. For this reason soft decisions are preferred less when compared to hard decisions.

Generally code’s are selected based on the free distance property. The criteria for selecting code is that it should not have catastrophic error propagation and it should have maximum free distance.

A catastrophic error is defined as an event whereby a finite number of code symbols error causes an infinite number of decoded data bit errors.