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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After some latency, Decoder output bDecodeOut is generated nicely, which can be compared with the output from m-Sequence generator bDataIn. In addition, this chip does have another function, that is to function as a convolutional code encoder.

An Experimental Implementation of Convolution Encoder and Viterbi Decoder by FPGA Emulation

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.

If state h of stage j-1 store minimum path metric PMh,j-1then the minimum path metric PMi,j at state i of stage j is:. Viterbi Algorithm is a recursive optimal solution to the problem estimating the state sequence of a discrete time finite-state Markov process observed in memoryless noise. The output from memory unit is in reverse-order of the received bit stream, so we use a special output unit to generate the decoded bit stream in correct order. The simulated output timing waveform is shown in Figure 3.

A Stage is defined as all states at one time stamp. Based on noise level at a specific instant of time, minimally sufficient hardware resources are allocated to meet the BER requirements of the application while achieving maximum performance. The chip utilization being a low value, some extra circuitry can also be embedded on FPGA board to accomplish greater or bigger tasks in conjunction with the Convolution Encoder and Viterbi decoder.


Here, the shift registers shift to the right for each input. Trellis is defined as state diagram with time stamp, i.

Its benefit lies in the fact that its decoding complexity is virtually not governed by the length of the particular code. The above procedure can be viewed in a finite state machine with transition from the old state to the new state for a given binary input will yield 2 output coded symbols. The ACS unit identifies path with lowest cost metric. The behavioral and timing simulation of the design has been performed and there hvdl are shown in the next two sections. For the purpose of describing the timing waveform, only selected signals of the system are shown in Figure 3.

Bernard Sklar “Digital Communications Fundamentals and applications”,pp. RESET input resets the whole system. They proves to be effective in minimizing forward error in a typical Communication system.

Design and Implementation of Viterbi Decoder Using VHDL – IOPscience

The shift register is initially filled with an all zero sequence convollutional the first binary digit referring to Figure 2. The output of the encoder is sent after some processing before the final transmission through the channel. As illustrated in Figure. This can be easily extricated from Figure 7.

In the register-exchange approach each state has a register to store the survivor path information. To achieve this, the implementafion system utilizes the Convolutional Code Encoder as part of the system. This procedure continues until the last input digit, for the case in Figure 1. This system is divided into two distinct part: The block diagram for this test system is shown previously in Figure 2.

The four technologies face miplementation challenges as mentioned above.

The Viterbi Algorithm removes those trellis paths that could not possibly be candidate for the maximum likelihood choice.

The test system uses the encoder system as described earlier as part of the design to accomplish its objectives as stated above, which is to use convolutional coded signals to test the decoder system. In the traces, Sysclk is the clock for decoding input data stream, which is the rate of generating decoded data.


The constraint length plays an important role in the efficiency of convolution encoder hence, it needs a better understanding. A Viterbi decoder makes use of the Viterbi algorithm to decode the bits stream produced by a convolutional encoder. In the back-trace scheme, only the survivor path information for each state is stored for each code symbol.

A Viterbi encoder includes surplus information in the transmitting signal. The 2 stacks are always in different mode. The code can be recovered significantly even in the presence of noise.

However errors in the received bit sequence may be introduced as the decoder may take wrong decisions for voltages near threshold. Occasionally, this chip can be easily self-tested to make sure the decoder is still functioning properly.

Using these three primary components, the test system had been successful to simulate a ‘soft decision’ test data for the decoder input. 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.

The rightmost digit leaving the 5-stage register is lost. The ACS block generates the survivor path information using the new branch metric and current state metric. In this way a level of correlation between each sample in the signal is automatically obtained. Thereby it becomes necessary to quantize it into several voltage levels so that it can be processed digitally.