Towards Systems Beyond 3G Based on Adaptive OFDMA Transmission

Abstract

High data rates, high spectral efficiency, flexibility,and low delays over the air interface will be importantfeatures in next-generation wireless systems. The overallchallenge will be packet scheduling and adaptive radiotransmission for multiple users, via multiple antennas andover frequency-selective wideband channels. This problemneeds to be structured to obtain feasible solutions. The basicsimplifying assumptions used here are clustering of antennasinto cells, orthogonal transmission by use of cyclic-prefixorthogonal frequency-division multiplexing (OFDM) and atime-scale separation view of the total link adaptation,scheduling and intercell coordination problem.Based on these assumptions, we survey techniques that adaptthe transmission to the temporal, frequency, and spatialchannel properties. We provide a systematic overview of thedesign problems, such as the dimensioning of the allocatedtime-frequency resources, the influence of duplexingschemes, adaptation control issues for downlinks and uplinks,timing issues, and their relation to the required performanceof channel predictors. Specific design choices are illustratedby recent research within the Swedish Wireless IP programand the EU IST-WINNER project. The presented resultsindicate that high-performance adaptive OFDM transmissionsystems are indeed feasible, also for challenging scenariosthat involve vehicular velocities, high carrier frequencies, andhigh bandwidths.