INTERNATIONAL JOURNAL OF ELECTRONICS AND COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)

Transcription

1 INTERNATIONAL JOURNAL OF ELECTRONICS AND COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET) ISSN (Print) ISSN (Online) Volume 4, Issue 6, November - December, 2013, pp IAEME: Journal Impact Factor (2013): (Calculated by GISI) IJECET I A E M E VLSI IMPLEMENTATION OF HUFFMAN DECODER USING BINARY TREE ALGORITHM VIJAYAKUMAR SUVVARI 1, M.V.H. BHASKARA MURTHY 2 1 (M-Tech Student, Department of ECE, AITAM College, Tekkali, Srikakulam Andhra Pradesh, India) 2 (Associate Professor, Department of ECE, AITAM College, Tekkali, Srikakulam Andhra Pradesh, India) ABSTRACT Compression is useful technique in digital system, as it reduces the channel banddths and storage size. This paper presents Huffman decoder based on new binary tree method for improving usage of memory and Banddth. The proposed Huffman decoder is implemented by using ASIC and FPGA design methodologies. To implement the encoder and decoder architectures, 0.6 Micron standard cell library was used for ASIC implementation. Various performance metrics like leakage power, dynamic power, area and number of registers are obtained by using ASIC and FPGA implementations and the results are compared. The simulations are carried out by using Modelsim tool. Keywords: ASIC, Binary tree, Data compression, Decoding algorithm, FPGA. 1. INTRODUCTION The Huffman code is one of the Variable Length Codes (VLC) which compresses the data size. The advantages of this compression algorithm are efficient utilization of channel banddth and storage size. Therefore, Audio and Video standard organizations research on the Huffman code to apply another improved method like MP3 and H.264. Also the Huffman code is adopted in the data compression for a long time. Follong section explains about the significance of the project and implementations. The major disadvantage of array Data Structure is the memory cost spent on storing such a complete binary tree by using an array, which also results in a slow decoding speed. In order to solve the problem, we can use a New Binary tree Algorithm method [1]. The advantage of this method for representing the Huffman decoder is that original data is retrieved easily and requires less memory. 85

2 2. THE PROPOSED METHOD 2.1 The Proposed Huffman Decoder The proposed Huffman decoder ll be implemented on ASIC. The advantage of the algorithm ll be proved by extensive simulations and from prototyping. The performance ll be measured in terms of power dissipation. For power and area calculations, FPGA tools and ASIC development tool ll be used [2]. The customized Huffman hardware decoder s performance ll be compared th different platforms. 2.2 Description of Huffman Coding Given a set of symbols and their weights (usually proportional to probabilities), Find a prefixfree binary code (a set of code words) th minimum expected codeword length (equivalently, a tree th minimum weighted path length from the root) [4]. Formalized description: Input: Alphabet, A={a 1, a 2, a 3,..} which is the symbol of the alphabet of size-n.set, W={w 1,w 2, } which is the set of the (positive) symbol weights (usually proportional to probabilities) i.e. w1= weight (ai), 1 i n. Output. Code C=(A,W), C= {c 1, c 2.} Which is the set of (binary) codeword s, where c i is the codeword for a i, 1 i n. Goal: Let (1) be the weighted path length of code C. n L(C) = L( ci ) length (C i ) (1) i= 1 Condition: L(C) L(T) for any code T(A,W). For any code that is biunique, meaning that the code is uniquely decodable, the sum of the probability budgets across all symbols is always less than or equal to one. In this example, the sum is strictly equal to one as a result, the code is termed a complete code. If this is not the case, you can always derive an equivalent code by adding extra symbols (th associated null probabilities), to make the code complete while keeping it biunique. As defined by Shannon, the information content h (in bits) of each symbol a i th non-null probability is: 1 h i) = log ( ) (2) ( 2 The entropy H (in bits) is the weighted sum, across all symbols a i th non-zero probability w i, of the information content of each symbol: > 0 > 0 w i 1 H ( A) = h( ai ) = log 2 ( ) = log 2 (3) w (Note: A symbol th zero probability has zero contribution to the entropy, since =0. So for simplicity, symbols th zero probability can be left out of the formula above.) i > 0 86

3 2.3 Encoder and Decoder for Text The Huffman decoder is implemented for text. The text compression involves its encoding, the text decoder contains the Huffman decoder for obtaining the original text. The Huffman tree used by encoder and decoder is shown Fig 2.1 [3]. The alphabet consists of the uppercase letters and the space. All left branches are labeled 0, and all right branches are labeled 1. This tree is based on the follong assumed frequencies. E 130 T 93 N 78 R 77 I 74 O 74 A 73 S 63 D 44 H 35 L 35 C 30 F 28 P 27 U 27 M 25 Y 19 G 16 W 16 V 13 B 9 X 5 K 3 Q 3 J 2 Z 1 Figure 2.1 binary trees for Text It is assumed that there are 130 Es and 182 spaces for every 1000 letters. The encoder retrieves the code for each symbol from a map, and shifts it out one bit at the time. The decoder is a finite state machine whose state transition graph is obtained from the tree by adding acs(add compare select) from the leaves back to the top of the tree [6]. Each node uses ten bits for its encoding. The code of the root is 0. If a state is not a leaf of the tree, and its encoding is n, then the encodings of its two children are 2n+1 and 2n The Hardware Implementation of Algorithm Encoder: Figure 2.2 Block diagram of Encoder 87

4 The fig 2.2 shows the block diagram of Encoder and Code for each character which comes from the tree shown in Fig 2.1 is stored in LUT (LOOK UP TABLE). Character input which is given to the encoder acts as input to the LUT which gives corresponding encoded word on the data bus which is given to a shift register so as to serially shift the data out. As it is a variable length coding, in order to determine the end of the code word for each character while shifting out, one more bit is added to the end of the code word in the LUT is made as 1. The code word is logically shifted out till it contains only 1 at its LSB. Then next character is loaded from the ROM. Apart from this, the encoder should generate an enable signal to the decoder so that the decoder knows when the valid data is presented to it. Decoder: Both encoding and decoding should be done th respect to the same tree. So, same data which is stored in the encoder LUT is stored in the decoder LUT in a different way. The Fig.2.3 below shows the block diagram of Huffman Decoder and clearly explains the operation. Fig 2.3 Block diagram of Huffman Decoder There ll be a LUT which consists of the mapping from encoded data stream to the regular characters. Initial state starts th 0. Based on state value some character comes out of LUT which ll be either 0 or valid character. Comparator output ll be either 0 or 1 depending on the contents. If it is 0, the state ll be left shifted and given as input to adder if not 0 ll be fed to the adder meaning that an encoded value is decoded. Depending on the serial cipher input either 1 or 2 is given as input to adder. Both the inputs are added and registered to get the state which is fed to the LUT. This process is continuous for the serial cipher input. 88

5 3. SIMULATION AND RESULTS 3.1 ASIC & FPGA Implementation Figure 3.1 Implementation Flow using Xilinx13.1 ISE tool Figure 3.1 shows the flow that is followed in implementing a design on Xilinx FPGA using the tool Xilinx13.1 ISE. 3.2 Power & Area Analysis The leakage power (static) and dynamic power analysis of the design can be done by using Xilinx13.1 Power Analyzer. To analyze the dynamic power, the design file imported from Place and Route (i.e.,.ncd file ) and physical constraint file (i.e.,.pcf file ) are required. Along th these files, a value change dump (.vcd ) file is required [5]. Hence to estimate the stching power, the design has to be synthesized to target FPGA. Now, by using the XPower Analyzer, the three files,.ncd file,.pcf file and.vcd file, are included to determine, static and dynamic power consumption of the design. Table 3.1. Power and Area Analysis Report Performance Metric ASIC Implementation (0.6Micron CMOS Digital library) FPGA Implementation (Xilinx Spartan 2s) Leakage power nw 1.3 W Dynamic Power mw 91 mw Area 1800 Logic cells 1602 Logic cells Total no of registers Table 3.1 compares ASIC and FPGA Implementations of Huffman decoder. It gives the Power and area analysis of the design, using Synopsys Design compiler logic synthesizer. The design has been mapped to 0.6 Micron CMOS Technology. ASIC design methodology adopted for Huffman decoder design, yields low power dissipation and relatively higher performance. 89

6 3.3 Simulation Results for Text The functional simulations [7] for the Huffman decoder are carried out using Modelsim tool. In case of text both encoder and decoder are presented. The decoder requires for decoding the Huffman encoded data[8]. Fig 3.2 Huffman Encoder output for HELLO Fig 3.2 shows the simulation results for Huffman encoder. In Fig 3.2, address is the input to LUT, character is the output from the LUT which is to be encoded. Encoding for the character starts when the enable signal goes high. Cipher is the encoded serial output from the Huffman encoder. Fig 3.3 Huffman Decoder output for HELLO Fig 3.3 shows the simulation results for Huffman decoder. The encoded data for the text is input to the decoder, which is applied to the decoder in the form of serial bits. Cipher is the serial encoder data input. en is the enable signal to enable decoding. plain is the decoded character symbol. Fig 3.4 shows the simulation results of the combined unit th both encoder and decoder. 90

7 Fig 3.4 Huffman Encoder and Decoder combined results for HELLO text In Fig 3.4, addr signal is a 5-bit input signal which acts as the address to the LUT in the encoder stage which gives corresponding alphabetical outputs. Encode is the serial output stream which given as input to the decoder. decchar is the decoded character output from the decoder. The encoding and decoding [9] [10] operations are performed for the text HELLO. The simulation results for HELLO text reveal that only 22 bits are required to store it whereas 40 bits are required for the original text. Hence original data can be retrieved easily and requires less memory by using the new binary tree algorithm. 4. CONCLUSION Huffman decoder using Binary tree algorithm was implemented on ASIC and FPGA platforms. The Architecture implemented by ASIC Design, using 0.6Micron CMOS technology, yields leakage power dissipation of 33.25nW, dynamic power of 28.36mW, and area containing 1800 logic cells. For FPGA Design (Spartan 2E), the above said parameters are 1.3W, 91mW, and 1602 logic cells respectively. Hence the ASIC Implementation results an architecture that consumes low power than FPGA design methodology. Future works needs to be carried out to improve the area. REFERENCES [1] Seunghyun Beak, et.al, A New Binary tree Algorithm Implementation th Huffman decoder on FPGA, IEEE August [2] Z.Aspar, et.al, Parallel Huffman Decoder th an Optimized Look UP Table Option on FPGA, TENCON Proceedings of TESCON, vol.1, pp , Sept [3] K. L. Chung and J. G. Wu, Level-Compressed Huffman Decoding, IEEE Transactions on communication, vol. 47, NO. 10, October, [4] E. Hashemian, et.al, Fundamentals of Data Structures in C New York, 1993, pp.201. [5] T. Jeong, Implementation of low power adder design and analysis based on power reduction technique, Microelectronics Journal, vol. 39, pp , Nov [6] K.K.Parhi, High-Speed VLSI Architectures for Huffman and Viterbi Decoders, Circuits and Systems II: Analog and Digital Signal Processing, IEEE Transactions, vol.39, pp , June,

8 [7] Md. Ajmal Sadiq, T.Naga Raju and Kumar. Keshamoni, Modeling And Simulation of Test Data Compression using Verilog, International Journal of Electronics and Communication Engineering &Technology (IJECET), Volume 4, Issue 5, 2013, pp , ISSN Print: , ISSN Online: [8] Riyadh A. Abdulhussein And Abdulkareem S. Abdallah, A Comparison Study of Non-Binary Tcm-Aided Pam, Qam, Psk Schemes-Based Novel Decoding Algorithm, International Journal of Electronics and Communication Engineering &Technology (IJECET), Volume 4, Issue 5, 2013, pp , ISSN Print: , ISSN Online: [9] P. Prasanth Babu, L.Rangaiah And D.Maruthi Kumar, Comparison And Improvement of Image Compression Using DCT, DWT & Huffman Encoding Techniques, International Journal of Computer Engineering & Technology (IJCET), Volume 4, Issue 1, 2013, pp , ISSN Print: , ISSN Online: [10] S.Anandanarayanan and Dr.S.K.Srivatsa, A High Performance Novel Image Compression Technique Using Huffman Coding With Edge Dection, International Journal of Computer Engineering & Technology (IJCET), Volume 4, Issue 2, 2013, pp , ISSN Print: , ISSN Online: AUTHORS DETAIL VIJAYAKUMAR SUVVARI completed his U.G from SISTAM Engineering College, Srikakulam Affiliated to JNTUK, in the year 2007 and he is pursuing M.tech (VLSI System Design) in AITAM College, Tekkali. His research interests are VLSI Design, DSP etc. M.V.H. BHASKARA MURTHY received his M.Tech from JNTUH, Hyderabad in 2006 and B.E from Andhra University, Visakhapatnam in the year He is pursuing his Ph.D., in the area of Wireless Communications from JNTUK, Kakinada, India. He is a member of IE (India). He had 20 years of experience includes both Industrial and teaching. At present he is working as a Associate Professor in the department of Electronics and Communication Engineering, AITAM College, Tekkali, Andhra Pradesh, India. He has published and presented both national and International Conferences and Journals. His areas of interests are VLSI Design, Wireless Communications etc. 92