On unequal error protection using convolutional codes

Abstract

This paper demonstrates the inherent unequal error protection (UEP) nature of punctured convolutional codes to develop two UEP schemes. In both schemes, the UEP level of error protection is better than the original error-control coding and modulation scheme employed. The first scheme is based on utilizing the inherent UEP capability within the columns of the puncturing matrix, without a reduction in information throughput. The second scheme reduces the effective code rate b/ v of a punctured convolutional code created from an original rate 1/ v o code. Such a UEP scheme may be of use in a communication system where it is beneficial to briefly reduce the information throughput for a much improved error protection. It is shown that the performance of a simple rate 1/2, constraint length K=3 code, when transformed to an effective rate 1/3 code, provides a coding gain of approximately 5.2 dB with the use of eight level soft-decision decoding over uncoded BPSK. In general, this UEP technique provides a coding gain of slightly greater than 10 log 10(bv o /v) dB over the performance of the original rate 1/ v o code using hard-decision Viterbi decoding. A further coding gain of approximately 1.5 dB can be expected with the use of soft-decision decoding.