Figure 2. Constraint length (K)=7, code rate (r)=1/2 convolutional. encoder. Implementation of Convolutional Encoder and Viterbi Decoder using Verilog HDL . Implementation of Convolutional Encoder and Viterbi Decoder using VHDL. Conference Paper (PDF Available) ยท December with 2, Reads. Request PDF on ResearchGate | Paper: VHDL Implementation of Convolutional Encoder and Viterbi Decoder | In digital communication the.

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Once the complete code word is received, a trace-back block extracts the decoded output sequence using the survivor path information [17]. Current state is the state of memory bank 5. This is possible due to the fact that unlike a microprocessor which deploys its code to be executed sequentially, FPGA executes the whole code at once.

The output contains redundant bits to reduce probability of error introduced by additive white Gaussian noise. Based on noise level at a specific instant of time, minimally sufficient hardware resources are vierbi to meet the BER requirements of the application while achieving maximum performance.

The off decoding algorithms for independent noise memoryless channels have been developed and refined, namely Viterbi Decoding for Convolutional Codes. Since the received signal is a voltage, therefore it can be analog. The survival is encoded as 1 bit, which is stored into memory.

A comparison can then be made by comparing the bits obtained from the Decoder Output and the M-Sequence Generator.

To get the right order of output bit stream, 2 stacks is used to push-pop the decoded bits from traceback. The design flow followed to accomplish the designing process is similar to the one used in industry. This technique improves encodeg error protection of the information symbols at the end of encoded message.


This is the essence of the encoder system which is shown in block diagram in Figure 2. The overall design is carried out using VHDL code. Even though their results are suboptimal, but they are used to decode very long codes, wherever it becomes difficult to apply any other algorithm. To decode a convolution code some algorithm must be adopted at the receiver side. Using these three primary components, the test system had been successful to simulate a ‘soft decision’ test data for the decoder input.

These stores the best path obtained from back-tracing procedure applied to the trellis structure. Immplementation happens due to the fact that there is no need to activate the registers after updating hence the switching activity reduces decreasing power dissipation.

Without loss of generality, it is assumed to be 1 sample per bit.

For a constraint length of 3, the possible state transition and outputs have been calculated and tabulated in Table 1. During the data transmission, suppose three of the received symbols got corrupted underlined, bold red.

RESET input resets the whole system.

Design and Implementation of Viterbi Decoder Using VHDL

VHDL is convolutionwl for the whole design. However, it is not an optimal choice [10]. This process was followed by the synthesis of the description of design to generate a gate level circuit. All the modulo-2 adders can be implemented using XOR gates. A Stage is defined as all states at one time stamp. Thereby it becomes necessary to quantize it into several voltage levels so that it can be processed digitally.

Design and Implementation of Viterbi Decoder Using VHDL – IOPscience

This can benefit for low power design of Forward error control approach. Hence, the chip generated in this project functions as a decoder, specifically Viterbi decoder, for digital communications over noisy channels.

However, traditional implementation of Viterbi decoding using software cannot keep up with the speed requirements for digital data transmission. After some latency, Decoder output bDecodeOut is generated nicely, which can be compared with the output from m-Sequence generator bDataIn.


From the synthesis report Fig. The decoder system is the kernal of our project. In shift update method, the survivor path information is shifted in to the registers. The satellite and space communication channels are likely candidates for the cost-effective use of coding to improve communication efficiency. A Viterbi decoder was developed by Andrew Viterbi in to decode convolutionally encoded messages [3].

Constraint length is the number of memory elements used in the shift register, to add redundant bits along with the arriving single bit input. Translating implemrntation diagram in Figure 2.

Viterbi algorithm is a special case of Bellman Ford shortest distance algorithm. First, We give a brief introduction about Viterbi algorithm.

The shift register is initially filled with an all zero sequence and the first binary digit referring to Figure 2. Observing bvdataout0 and bvdataout1 in Figure 2.

Convolution coding scheme can be applied to both continuously running data stream as well as to blocks of data, whereas block codes are suited only for the latter. Convolution codes were first introduced in by Elias as FEC coding scheme [4]. The Viterbi algorithm has a high complexity for computation, but it does xonvolutional maximum likelihood decoding.

The algorithm is used to estimate a measure of similarity through the hamming distance between the received signal, at time implementatioon and all the possible trellis paths entering each state at time ti.