Commonly used protocols involving J cooperating communicators are based on repetition encoding and achieve diversity of order J with bandwidth efficiency 1/J. We introduce a protocol capable of achieving the same diversity with bandwidth efficiency essentially equal to 1/2. The protocol is based on linear complex-field coded (LCFC) relay transmissions over orthogonal frequency division multiplexed (OFDM) subcarriers. Cooperators provide diversity by repeating delayed versions of the original packet, thereby generating a frequency-selective multipath channel. The so enabled diversity is collected by standard LCFC-OFDM decoders. Analysis and corroborating simulations establish that the novel protocol achieves diversity order equal to the number of users.