Zero-padded OFDM with improved performance over multipath channels

Abstract

It has been proposed recently to replace the cyclic prefix (CP) in OFDM transmission by zero-padding (ZP); this guarantees symbol recovery even when channel nulls are located on a subcarrier. This, though, has the disadvantage that the simple DFT-based receiver does not perform well, but results have shown that if much higher complexity turbo demodulation is used, ZP-OFDM outperforms CP-OFDM. However, by viewing N-carrier OFDM as multicode CDMA with complex spreading codes from the N-PSK alphabet, one can apply to ZP-OFDM the numerous suboptimum multiuser receivers developed for CDMA. The performance of these receivers is dictated by the correlation properties of the IDFT matrix. Therefore, we propose to "modify" the IDFT matrix used to modulate the data in ZP-OFDM so that the resulting matrix possesses better correlation properties, and hence improved performance over multipath channels can be achieved. Simulation results verify the large gains in the uncoded performance of ZP-OFDM with modified IDFT matrix compared to CP-OFDM and ZP-OFDM with the IDFT matrix.