ty bits is not appropriate code rates while at lower initial coding rates, Chase as a retransmission of (some of) the systematic bits combining is almost as good as IR. Furthermore, the provides better performance. Incremental redundancy performance gain of incremental redundancy compared with Turbo codes can therefore benefit from multiple to Chase combining can also depend on the relative levels of feedback, for example by using two different power difference between the transmission attempts. negative acknowledgments - NAK to request additional With incremental redundancy, the code used for the parity bits and LOST to request a retransmission of the first transmission should provide good performance not systematic bits. In general, the problem of determining only when used alone, but also when used in combination the amount of systematic and parity bits in a retrans- with the code for the second transmission. The same holds mission based on the signal quality of previous trans- for subsequent retransmissions. Thus, as the different mission attempts is non-trivial. redundancy versions typically are generated through Hybrid ARQ with soft combining, regardless of puncturing of a low-rate mother code, the puncturing whether Chase or incremental redundancy is used, leads patterns should be defined such that all the code bits used to an implicit reduction of the data rate by means of by a high-rate code should also be part of any lower-rate retransmissions and can thus be seen as implicit link ad- codes. In other words, the resulting code rate R after aptation. However, in contrast to link adaptation based transmission attempt i, consisting of the coded bits from on explicit estimates of the instantaneous channel con- redundancy versions RVk, k = 1, i, should have similar ditions, hybrid ARQ with soft combining implicitly ad- performance as a good code designed directly for rate R justs the coding rate based on the result of the decoding. Examples of this for convolutional codes are the so-called In terms of overall