ABSTRACT

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Now the 3^rd generation cellular system called IMT-2000 is being actively researched and developed for standardization. WCDMA TDD has become one of IMT-2000 standards. Convolutional coding is a coding scheme proposed in the standard of WCDMA TDD. Viterbi decoders are used to decode convolutional codes. We designed a convolutional encoder and a Viterbi decoder for WCDMA TDD specification.
A Viterbi decoder consists of several major building blocks, branch metric computation block, Add-Compare-Select (ACS) block, survivor path storage block and the output sequence generator block. The branch metric computation block computes the branch metrics for each branch. The ACS block generates the survivor path information using the new branch metric and current state metric. The output sequence generator block estimates the original input sequence applied to the encoder.
In this paper, a complete process of designing a convolutional encoder and a Viterbi decoder is presented. An integrated design environment with simulation and synthesis tools are used to verify and optimize the design. The final design is targeted for Xilinx Virtex FPGAs.