# IMPLEMENTATION OF CONVOLUTIONAL ENCODER AND VITERBI DECODER USING VHDL PDF

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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When updating the survivor path matrix, the key issue is that the content of each register does not change as soon as it is updated.

## Design and Implementation of Viterbi Decoder Using VHDL

The satellite and space communication channels are likely candidates for the cost-effective use of coding to improve communication efficiency. If the voltage samples are directly decodes before digitizing the received bit sequence then we term such kind of process as soft decision decoding[15]. 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.

In designing the whole system, the targeted specification for both the decoder system and the test system are set as follows: Here, VHDL is used throughout the whole system as well as this project. We generate decoded data from calculated survival in ACS using traceback scheme.

There are two approaches for generation of decoded output sequence, register-exchange and back-trace[16].

Each stack will be run in pop mode or push mode in turn. A Branch is defined as one step state transition. Reset0 is encder reset. In shift update method, the survivor path information is shifted in to the registers.

Viterbi Decoding for Convolutional Codes is presented here as an efficient system for reliable communication over noisy digital communication channels. Few categories of algorithms that already exist for such purpose are listed below:.

The effective decoding algorithms for independent noise memoryless channels have been developed and refined, namely Viterbi Decoding for Convolutional Codes. The operation of Viterbi decoder is simulated under Mentor Graphics. In maximum likelihood sense this is the most optimal algorithm for decoding of a convolution code.

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

By using a FPGA a massive parallel execution of the code can be employed, hence an increased throughput. The survivals are passed to memory unit, which will carry out traceback decoding. The 2 stacks are always in different mode. This can be realized by applying clock gating-scheme [18]. The encoder system is an essential part of the test system in which will be discussed later.

The output contains redundant bits to reduce probability of error introduced by additive white Gaussian implmeentation.

The output sequence generator block estimates the original input sequence applied to the encoder. A matched decoding scheme for convolutionally encoded transmission is cnvolutional at the receiving end. Hence, it can be employed only for relatively short codes.

The overall design is carried out using VHDL code. Convolution Encoding with Viterbi decoding is a powerful Forward Error Control FEC technique that is a proven mechanism in which the transmitted signal remains uncorrupted mainly by Additive white Gaussian Noise residing enxoder a channel.

They proves to be effective in minimizing forward error in a typical Communication system. The Viterbi decoder is consisted of 4 sub-units: From the synthesis report Fig.

Entity encoder is a top level entity for entity shiftadd and mux The schematic diagram for output unit is shown as below. Memory is organized as 6 16×10 memory banks. For the purpose of describing the timing waveform, only selected signals of the system are shown in Figure 3.

Thus, the results here verified that the test system works as expected. The test system functions as an off-line testability with minimum sharing of decoder resources.

### Design and Implementation of Viterbi Decoder Using VHDL – IOPscience

However, traditional implementation implementwtion Viterbi decoding using software cannot keep up with the speed requirements for digital data transmission. The trellis diagram Fig 2 represents the state diagram of Figure 4. First, We give a brief introduction about Viterbi algorithm. We show the selected traces in the next two pages, Figure 3. The test system implements the convolutional code signals to test the decoder system which is generated by the convolutional fecoder encoder.

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. Simple Block Diagram of the Encoder System. Decoding With Viterbi Algorithm: The simulated output timing waveform is shown in Figure 3. 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.

Thereby it becomes necessary to quantize it into several voltage levels so that it can be processed digitally. The ACS unit is used to calculate the path metrics for each state in current stage from path metrics of its 2 previous states and the associated state-transition branch metric, then the path with least path metric is selected as survival path for the state in current stage. Also it is useful only when the constraint length is large.