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A review of scale factors, fixed-point precision, soft decisions, and hard decisions on the performance of the UMTS (3GPP) turbo codes

Since their introduction in 1993, turbo codes have received a significant amount of attention in the communications theory field due to their Shannon-capacity approaching performance. In recent years, the cellular systems market has embraced turbo code technology and made it part of the latest standards. This paper will review the effects of scale factors, fixed-point precision, soft decisions and hard decisions on the performance of the turbo codes defined in the UMTS third-generation cellular system. In addition, a new scale factor estimation technique which provides improved performance at low signal to noise ratios will be presented.