To facilitate ranging between mobile terminals and a base station in a wireless communication network employing orthogonal frequency division multiplexing (OFDM) for uplink data communications, a periodic ranging channel for use by a mobile terminal is defined. The channel specifies a plurality N of blocks of sub-carrier frequencies of an OFDM frequency band which are non-contiguous within the OFDM frequency band. The channel also specifies a time slot within an OFDM subframe which spans one or more OFDM symbol periods. A ranging transmission is periodically sent as a spread signal across the specified N blocks of sub-carrier frequencies within the specified time slot. The duration of the ranging transmission may be less than a duration of the OFDM subframe. A notional grid of tiles representing time and frequency resources associated with the subframe may facilitate channel definition. A similar approach may be used to define an initial access channel for initial access transmissions.