Performance analysis andEnhancement of forward errorCorrection techniques for Broadband wireless technology

Abstract

newlineTurbo coding is a very powerful error correction technique that has newlinemade a tremendous impact on channel coding in the last few years It newlineoutperforms all previously known coding schemes by achieving near Shannon newlinelimit in error correction using simple component codes This technique can newlinealso be used to provide a robust error correction solution to combat channel newlinefadingTurbo codes are recommended for increased capacity at high newlinetransmission rates due to their superior performance when compared to newlineconvolutional codes Soft Output Viterbi Algorithm SOVA and log newlineMaximum aposteriori Probability log MAP algorithm are the two prime newlinecandidates for decoding Turbo codes newlineThe limitations of SOVA and log MAP are observed in the form of newlinetwo distortions namely over optimistic soft outputs and correlation between newlinethe intrinsic and extrinsic information The performance will degrade newlinesubstantially due to former and only mildly due to the latter The former type newlineof distortion depends on i the ratio of energy per bit Eb to noise power newlinespectral density N0 and ii extrinsic information while the latter type newlinedepends on intrinsic information The respective compensation coefficients newlineare calculated The compensations for extrinsic information and intrinsic newlineinformation are possible with a common scaling factor which is constant and newlineindependent of the energy per bit to noise power spectral density ratio Eb N0 newlineiteration and interleaver length newline