ISSN: 2277-3754 ISO 9001:2008 Certified International Journal of Engineering and Innovative Technology (IJEIT) Volume 2, Issue 2, August 2012 12 Abstract —This paper investigates the Viterbi Algorithm for decoding convolutionally coded messages for forward error correction. A new power saving strategy that may enable mobile receivers to decode convolutionally coded transmissions with lower energy utilization using soft decision decoding techniques is developed. The idea behind the work is the selective use of the Viterbi decoder only when error is present in the transmitted message. When there is no error, a simple decoder is used. The analysis of the proposed method was done using the profiler tool in MATLAB®. Results obtained by MATLAB® simulation demonstrate that, there are no increases in bit-error probability as a result of the proposed method. The MATLAB processing time (and hence energy) shows that, in comparison to that obtained with a standard Viterbi decoder, the proposed method uses less energy at EbNo above 3dB. Index Terms— Convolution Codes, Error Dependent, Viterbi Algorithm, Power Saving, Soft Decision. I. INTRODUCTION The Viterbi algorithm which was proposed by Andrew J. Viterbi [13] in 1967 is a maximum likelihood decoder used in decoding convolutionally coded messages. Because of the complexity of the algorithm, it is energy intensive irrespective of whether the received signal contains errors or not. As a result of globalisation, there has been proliferation of mobile receivers/devices especially handsets, wireless sensor networks (WSN) and Mobile Adhoc Networks (MANET). These devices consume a lot of energy especially in decoding the encoded signals. Energy is a scarce and economic commodity the world over. There is therefore the need to design a decoder that conserves energy in mobile devices. Many researchers have been researching and reporting on ways of minimising energy used in the decoding [5, 2, 3, 10, 11, 12, 14, 16, 17, 18, 19]. Olaf J. Joeressen and H. Meyr [17] based their design on the two steps soft out Viterbi algorithm proposed by [19]. In their design, instead of constructing competing paths for all states and performing the update operation along the paths for all the states, they output only the information along the single decoded state transition sequence (the final survivor). Oh and Hwang [12] proposed a trace back scheme to cut down the switching activities incurred while tracing back. Their scheme is designed for a decoder, where the trace back starts before the end of the code word. The key idea is to reuse the information from the previous trace to shorten the trace back. [19] Used clock gating – In clock gating, the clock of each register is enabled only when the register updates it survivor path information. Their simulations showed a 30% reduction in dynamic power dissipation which gives a good indication of power reduction on implementation. [5] Investigated the use of an algorithm proposed by Barry Cheetham for selective use of Viterbi decoder in decoding codes when there is error and the use of a simple decoder when there is no error. He employed hard decision decoding and concluded that the new algorithm gives better performance above 5dB when compared to the standard Viterbi decoder. The purpose of this paper is to propose a new and adaptive error dependent power saving Viterbi decoder based on the work done by [5] using soft-decision decoding. In a conventional Viterbi decoder, the complex and energy consuming Viterbi decoder is always used to decode a message irrespective of whether the message contains error or not. In this approach, an error dependent version of the algorithm is proposed. It consists of two parts, one simple decoder and the second a normal Viterbi decoder. The simple decoder is used when there is no error in the transmission and the Viterbi decoder is used only when the transmission contains errors. II. DESIGN METHODS FOR THE VITERBI ALGORITHM This research will involve the study of energy saving in communications system through observation and evaluation of performance of the new algorithm in comparison with conventional systems, the simulation/empirical approach is employed [4, 6, and 9]. This is achieved by modelling a communications system in Matlab and modifying the decoding section to minimize energy consumption. The Viterbi Algorithm was developed by Andrew J. Viterbi and first published in the IEEE transactions journal on Information theory in 1967 [13]. It is a maximum likelihood decoding algorithm for convolutional codes. This algorithm provides a method of finding the branch in the trellis diagram that has the highest probability of matching the actual transmitted sequence of bits. Since being discovered, it has become one of the most popular algorithms in use for convolutional decoding. 1. The Branch Metric Unit (BMU) which calculates the BMs; 2. The Path Metric Unit (PMU) includes a number of Add Compare Select Units (ACSU) which add the BMs to the corresponding PMs, compares the new PMs, and select the PMs indicating the most likely path; at the same time, the Error Dependent Soft-Decision Power Saving Viterbi Decoder for Mobile Devices Offor K. J., Mbachu C. B., Okonkwo I. I.