During a first time interval, an access point transmits orthogonal frequency division multiplexing (OFDM) signals using a first cyclic prefix length. The access point receives a plurality of signal reports, such as Channel Quality Indicators (CQIs), from user devices being served by the access point. Based on the signal reports, the access point determines a distribution of signal qualities experienced by the user devices. The access point selects a second cyclic prefix length based, at least in part, on the distribution of signal qualities. The access point transmits OFDM signals using the second cyclic prefix length during a second time interval.