On the Design of Cyclic Prefix Length for Time-Reversed OFDM

Time-reversed orthogonal frequency division multiplexing (TR-OFDM) has recently received attention as a promising scheme for supporting single-input multiple-output communications over time-dispersive fading channels with high bandwidth efficiency. In TR-OFDM, the use of passive time reversal processing offers a simple means of reducing channel time dispersion. Consequently, a cyclic prefix (CP) with a length shorter than the channel order can be used without inducing much inter-block interference (IBI). This paper tackles a technical challenge critical to the success of TR-OFDM, that is, how to minimize the CP length while satisfying certain performance requirements. Based on a data model derived for TR-OFDM, a quantitative relationship between the CP length and error performance is first established and a design procedure is then proposed. Our design reveals that the optimal CP length depends on the power delay profiles of underlying channels. Our design also leads to new insight in the time reversal operation and helps identify channel situations where TR-OFDM might not work effectively. The merits of our design are confirmed by both theoretical analysis and numerical simulations.