Abstract
AbstractThis paper presents a performance evaluation of the multimode Fast Variable Rate CELP coder developed by CSELT S.p.A. in the UMTS Code Division Testbed (CODIT) Project [1] for applications involving channels with time‐varying error characteristics. The radio channel is statistically modelled by one Rician or Rayleigh‐distributed desired signal and several uncorrelated Rayleigh plus log‐normally shadowed interfering signals, propagating according to two different laws: a dual path loss law with a turning point (microcellular environment) and a single path loss law (macrocellular environment). For channels with these error characteristics, each mode of the Fast Variable Rate CELP coder has a particular allocation of bits between source and channel coding stages, leading to an unequal error protection code tailored to suit the different error sensitivities of the source bits. It is shown that, on the basis of the sensitivity evaluation of source bits to errors, according to two different error sensitivity measures. Forward Error Correction whose power is matched to the error sensitivity of the source bits can be used. Increased robustness of source bits to errors can thus be obtained while satisfying bandwidth requirements.
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