International Journal of Advances in Engineering & Technology, Sept 2012. ©IJAET ISSN: 2231-1963 148 Vol. 4, Issue 2, pp. 148-155 COMPARATIVE ANALYSIS OF MODIFIED REGISTER EXCHANGE METHOD AND TRACE BACK METHOD OF VITERBI DECODER FOR WIRELESS COMMUNICATION H. Singh 1 , R. K. Vyas 2 and Deepak Raghuvanshi 3 1 Student of Digital Communication Engineering, RTU University, Kota, India 2 Department of Electronics & Comm. Engineering, RTU University, Kota, India 3 Student of Digital Communication Engineering, RGPV University, Bhopal, India ABSTRACT The Objective of this paper is to describe the comparative analysis of the two different method of implementation for Viterbi decoder based on the modified Register Exchange and Trace Back Method. The base of the comparison is simulation result. Both the technologies are simulated with Xilinx software9.1i. The simulation result in the form of HDL synthesis report, Timing analysis and Power estimation. The Modified Register Exchange Method is Simpler than the Trace Back (TB) Method but its disadvantage is that every bit in the memory must be read and rewritten for each bit decoded .Using the ‘pointer concept; a pointer is assigned to each register with the help of this concept copying the contents of one register to another, the pointers are modified. Power dissipation, Performance, memory size is analyzed for both the modified Register Exchange method and TB method. The new Register Exchange Method shows an average power reduction of 45 percent. The memory is reduced by half. KEYWORDS: Hardware description language (HDL), Register Exchange (RE), Viterbi Decoder (VD), Trace Back (TB) I. INTRODUCTION Code Division Multiple Access (CDMA) spread spectrum technology was introduced in the second generation of mobile systems. The Viterbi Decoder (VD) consumes about one third of the power dissipation of the CDMA mobile modem [3]. The VD is used to optimal decode convolutional codes. In this paper, we are focus on the technique which are beneficial for designing a [4][5]low power VD for wireless communication, with the focus on minimizing the number of operations. This paper presents a new Modified RE method, which enables it to be Used for large constraint length VD’s, in addition to being simpler and lower in power dissipation than the TB method. The RE method is based on successive register –exchange operations among states (two origin states and two destination states), which construct a butterfly unit as shown in Fig. 3 [l2].The left shifting of the current state and appending the decoded bit (the bit that causes the transition) to the LSB of the current state, results in the destination state. The TB approach is acceptable for trellises with a large number of states. This paper is divided into three sections. First section describes the background of the VD and gives the basic introduction of the TB and Modified RE method. The second section describes the comparative analysis of both techniques based on the experimental result generated by Xilinxbsoftware9.1i.The third section shows the simulation result of Modified RE method and TB method. This paper divided into three main sections. First section describes the background of