We solve optimal symbol dimensions for a recently introduced two-dimensional orthogonal frequency division multiplexing (2D OFDM) scheme with a two-dimensional cyclic prefix (2D CP). The 2D OFDM technique is shown to improve the rate of a wireless relaying system if the channel coherence time is at least nine times longer than the channel impulse response. Furthermore, feasibility and application scenarios of 2D OFDM are discussed using the parameters of terrestrial digital video broadcasting systems (DVB-T/H) as examples.