International Journal of Engineering Trends and Technology (IJETT) – Volume 8 Number 2- Feb 2014 ISSN: 2231-2803 www.internationaljournalssrg.org Page 73 Implementation of Turbo Encoder and Decoder Mrs.K.M.Bogawar, Assistant Professor, Ms.Sharda Mungale Dr.Manish Chavan, Dept. of Electronics,Priyadarshini College of Engineering Nagpur, Dept. of Electronics &Tele. R.T.M.Nagpur University,India Ramdeobaba College of Engg.& Technology,Nagpur,India ABSTRACT :Turbo code has become the coding technique of choice in many communication and storage systems due to its near Shannon limit error correction capability. With requirement on increasing data rates for deep space mission, it is required to have efficient encoder and decoder. Turbo codes provide up to 0.8 dB improvement in Eb/No over the current best codes used by deep space missions. The total number of decoder iterations depends on the physical channel characteristics. In this paper, we proposed a turbo encoder with the 1/3,1/4,1/6 rate and turbo decoder. Keywords:-Turbo coding, forward error correction, interleaving, puncturing, iterative decoding, MAP decoding I. INTRODUCTION In 1948, Shannon proved that every noisy channel has a maximum rate at which information may be transferred through it and that it is possible to design error-correcting codes that approach this capacity, or Shannon limit, provided that the codes may be unbounded in length. For the last six decades, coding theorists have been looking for practical codes capable of closely approaching the Shannon limit. Turbo codes, a new technique of error correction coding developed in the 1990s.In 1993, a concatenated forward error correction (FEC) scheme, turbo coding was introduced by Berrou.Turbo coding is a very powerful error correction technique that has made a tremendous impact on channel coding in the last few years. It outperforms all previously known coding schemes by achieving near Shannon limit error correction using simple component codes and large interleavers. Turbo codes have become a 3G standard The iterative decoding mechanism, recursive systematic encoders and use of interleavers are the characteristic features of turbo codes. The use of turbo codes enhances the data transmission efficiency in digital communications systems. Turbo code development proceeded from theoretical analyses of polynomial selection, weight distributions imposed by interleaver designs, decoder error floors, and iterative decoding thresholds. A family of turbo codes was standardized and implemented and is currently in use by several spacecraft. JPL’s LDPC codes are built from protographs and circulants Turbo codes enable reliable communication over power- constrained communication channels at close to Shannon’s limit. However, a significant number of iterations are required to produce this result leading to higher latency. The task of channel coding is to encode the information sent over a communication channel in such a way that in the presence of channel noise, errors can be detected and/or corrected. Thus efficient implementation of turbo codes in order to meet real-time constraints is an active area of research. Designing a channel code is always a tradeoff between energy efficiency and bandwidth efficiency. Codes with lower rate (i.e. bigger redundancy) can usually correct more errors. If more errors can be corrected, the communication system can operate with a lower transmit power, transmit over longer distances, tolerate more interference, use smaller antennas and transmit at a higher data rate. These properties make the code energy efficient. On the other hand, low-rate codes have a large overhead and are hence heavier on bandwidth consumption. Also, decoding complexity grows exponentially with code length, and long (low-rate) codes set high computational requirements to conventional decoders. According to Viterbi, this is the central problem of channel coding: encoding is easy but decoding is hard.The