Chapter 4.5 4.5 received data packets, is therefore useful. This can be seen as a mechanism for handling variations in the instantaneous radio-link quality after transmission and nicely complements channel-dependent scheduling and Scheduling, link adaptation and hybrid ARQ Erik Dahlman, Stefan Parkvall, Johan Skold and Per Beming One key characteristic of mobile radio communication is the typically rapid and significant variations in the in- stantaneous channel conditions. There are several reasons for these variations. Frequency-selective fading will