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In this paper, the authors describe two complementary link adaptation strategies for OFDM-based multi-user systems, which have found their way into a proposal for a 4G wireless communication system. The first link adaptation scheme makes use of frequency diversity and spreads the transmit signal over the whole system bandwidth, while the other strategy concentrates its transmission in selected sub-bands. Although based on distinct philosophies, both strategies are well justified in wireless systems with a great variety of deployment conditions and user mobility. The results obtained in this paper show that frequency-adaptive transmission is particularly effective when both subcarrier allocation and adaptive coding and modulation are used.
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