Chase Decoding of Linear Z4 Codes at Low to Moderate Rates

A free Z
₄
code C may be decoded by decoding its canonical image C macr over Z
₂
twice in succession. Hence, a Chase decoder for C could employ as its hard-decision (HD) decoder, a two-stage decoder which performs HD decoding on C macr in each stage. Alternatively, one could have a two-stage soft-decision decoder by employing a Chase decoder for C macr in each stage. We demonstrate that the latter approach can offer a significant reduction in complexity over the other, with little or no price to pay in terms of word error rate performance, particularly at low to moderate code rates.