| Convolutional encoding is a coding scheme often employed in deep space communications, wireless communications and broadcasting communications. The optimal decoding of convolutional encoding is Viterbi decoding with the characteristic of excellent decoding performance and the simple decoder structure. Viterbi decoder has obtained rapid development in all kinds of data transmission systems, especially in wireless communications and satellite communications. The Viterbi decoder used in In-Band On-Channel Digital Audio Broadcasting (IBOC DAB) receiver is designed, which can meet requirement of audio transmission service and data transmission service in IBOC DAB system. The main research of this paper is summarized as follows:(1) By simulation, analysis and comparision of the performance of Viterbi decoding under the condition of different constrain length, quantification series and traceback length, Viterbi decoder scheme of 8-level quantification and soft decision, which meets (2,1,7) convolutional coding is presented. (2) A simple distance computing method of faster and less hardware consumption is adopted in Branch Metric Generator (BMG). A parallel add compare select (ACS) structure is proposed in the design of Viterbi decoder. In the meantime, the path overflow control unit that reduces the circuit scale is presented. A pipelining ahead carry adder is adopted in the design of adder. The comparison unit is described in detailed RTL level verilog HDL language. The solutions both increase the speed and save the hardware consumption of ACS module.(3) The functional simulation and logic synthesis of Viterbi decoder are finished by Modesim6.1 of Mentor company and Synplify Pro8.1 of synplicity company. The timing simulation and place and route are accomplished by Xilinx ISE8.1. And the design of Viterbi decoder is tested by Xilinx Spartan3 xc3s200. The maximal data output speed of this decoder is 55Mbps under the premise of meeting the power. |
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