Title :
Parallel lookahead algorithms for pruned interleavers
Author_Institution :
Algorithms & Archit. R&D Group, Qualcomm Flarion Technol., Bridgewater, NJ, USA
Abstract :
In this letter, the design of efficient parallel pruned channel and turbo interleavers for ultra mobile broadband (UMB) physical layer standard is addressed. Channel interleaving is based on a bit-reversal algorithm in which addresses are mapped from linear order into bit-reversed order. Turbo interleaving is based on filling a 2D array row by row, interleaving each row independently using a linear congruential sequence (LCS), bit-reversing the order of the rows, and then reading the interleaved addresses column by column. To accommodate for flexible codeword lengths L, interleaving is done using a mother interleaver of length M = 2n, where n is the smallest integer such that L les M, such that outlier interleaved addresses greater than L - 1 get pruned away. This pruning operation creates a serial bottleneck since the interleaved address of a linear address x is now a function of the interleaving operation as well as the number of pruned addresses up to x. A generic parallel lookahead pruned interleaving scheme that breaks this dependency is proposed. The efficiency of the proposed scheme is demonstrated in the context of both UMB interleavers. An iterative pruned bit-reversal algorithm that interleaves any address in O(log L) steps is presented. Moreover, an iterative pruned turbo interleaving algorithm based on LCSs that interleaves any address in O(log2 L) steps is presented.
Keywords :
computational complexity; interleaved codes; iterative methods; mobile radio; turbo codes; channel interleaving; flexible codeword lengths; iterative pruned bit-reversal algorithm; linear congruential sequence; parallel lookahead algorithms; pruned interleavers; turbo interleavers; ultra mobile broadband physical layer standard; Communications Society; Computer architecture; Filling; Interleaved codes; Iterative algorithms; Noise reduction; Physical layer; Protection; Research and development; Turbo codes; Channel interleavers, pruned interleavers, turbo interleavers, linear congruential sequences, turbo codes;
Journal_Title :
Communications, IEEE Transactions on
DOI :
10.1109/TCOMM.2009.11.070661