Adaptive Algorithm for Mapping Channel Quality Information to Modulation and Coding Schemes

In the present and future generation of wireless networks, link adaptation is used for better channel efficiency. With link adaptation the modulation and coding scheme used for transmissions to a particular user is adjusted based on the user´s channel conditions. However, because of delays and measurement errors in the reported channel quality information, the actual transmission may experience a significantly different channel than anticipated. This can either lead to transmission errors (if the channel has deteriorated) or wasted transmission resources (if the channel is actually better than predicted). To avoid the former scenario, a conservative mapping from channel quality information to modulation and coding scheme is used. However, the degree of this conservatism depends on the Doppler Frequency of the channel with higher values requiring a more conservative mapping. In this paper we propose an algorithm for dynamically adjusting the mapping from channel quality reports to the modulation and coding scheme. Hybrid ARQ is assumed and we use the outcome of the first transmission to adjust the mapping. Simulation results are used to illustrate the effectiveness of the approach.