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Mobile radio transmission is affected by the time and frequency dispersion of the channel. The well-known Orthogonal Frequency Division Multiplexing (OFDM) modulation constitutes an efficient and simple mean to avoid the first, i.e. time dispersion, impairment. Furthermore, if properly dimensioned, i.e. selecting an appropriate number of subcarriers and Cyclic Prefix (CP) length, up to a certain point, CPOFDM can also support mobility, i.e. time selectivity. It is why CP-OFDM has been adopted in various standardized air interfaces, as for instance in DAB, DVB-T, IEEE 802.11, 802.16. OFDM is also a simple way to share the radio resource in frequency and it is why OFDMA has also been retained for downlink 3GPP/LTE transmission.
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