Vhdl Implementation of Turbo Encoder and Decoder Using Log-map Based Iterative Decoding

— In order to have reliable communication, channel coding is often employed. Turbo code as a powerful coding technique has been widely studied and used in communication systems. Turbo coding is an advanced forward error correction algorithm. A standard component in third generation (3G) wireless communication systems. Third generation (3G) mobile communication systems aim to provide a variety of different services including multimedia communication. This requires digital data transmission with low bit error rates. Due to the limitation of the battery life of wireless devices, transmitted power should remain as low as possible, which makes the system more susceptible to noise and interference. Error control coding is thus used to increase the noise immunity of the communication systems. A New coding scheme called “turbo coding", which stems from convolution coding, has been adopted in the 3G mobile communication system due to its high coding gain and reasonable computation complexity. Turbo coding was initially introduced by Berrou, Glavieux and Thitimasjshima in 1993.Ultimate Performance that approaches the Shannon limit requires a new approach using iteratively run soft in/soft out (SISO) decoders called turbo decoders. Two key innovations in turbo coding: Parallel concatenated encoding and iterative decoding. Parallel concatenated encoders consist of two or more component encoders for convolution codes. Decoding is performed iteratively. The output of the first decoder is permutated and fed to the second decoder to form one cycle of the iteration. Each systematic code is decoded using a soft-in soft-out (SISO) decoder. A SISO decoder can be implemented using the various decoding algorithm Turbo code decoder algorithm is studied in detail in this paper. The performance of Turbo code used in Code Division Multiple Access (CDMA) under Additive White Gaussian Noise (AWGN) channel is evaluated. The bit error rates (BER) of Turbo code at low signal-to-noise ratio (SNR) are obtained by simulations. Tools used: Xilinx 9.2i,Altera,Synopsys.Matlab,Libero IDE Language:VHDL