Efficient distance measurement method for turbo codes that use structured interleavers

This letter presents an efficient and accurate distance measurement method for tail-biting turbo codes that use structured interleavers. This method takes advantage of the structure in the interleaver as well as the circular property of tail-biting. As such, it significantly reduces the computational complexity, which allows the accurate determination of high minimum distance (d(min)) in reasonable time. The efficiency of this method is demonstrated by its ability to determine the true d(min) of 51 and the corresponding true multiplicities for a rate-1/3 turbo code that uses the UNITS 8-state polynomial generators and an MPEG-sized interleaver (1504 information bits) in reasonable time.