Small improvements in half-rate convolutional codes with popular constraint lengths for applications in satellite communications

Half-rate convolutional coding with constraint length 7 and Viterbi decoding has been widely used on satellite data links for a long time because of the substantial savings in satellite transponder power through the 4-5 dB in coding gain. A variant of the standard convolutional encoder consisting of a parallel- and serial-shift register combination is described which leads to small improvements in coding gains for popular constraint lengths and code rates. For example, it is shown that there is a memory-7 half-rate code, with a d_free of 11 in comparison with the best conventional memory-7 half-rate code which has a d_free of only 10. The parallel- and serial-shift register combination can be used to generate a wide class of k/n rate codes in a straightforward manner and can lead to improved performance in concatenated coding arrangements