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), which 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 multi-user 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.

Zero-tail DFT-spread-OFDM signals

“…This leads to the possibility of setting the overhead represented by the low power samples according to the estimated channel without compromising the numerology. Note that the proposed solution is different from known zeropadded approaches (e.g., [5], [6]), which replace the CP with zeros with the aim of improving robustness to the channel fades with a penalty in receiver complexity, since cyclicity at the receiver is partly lost. We aim instead at a solution which preserves the orthogonality of the data subcarriers at the receiver.…”

Generalized DFT-s-OFDM Waveforms Without Cyclic Prefix

“…(28) is meant at emulating a cyclic signal over the useful N samples. This operation is known in signal processing as overlapp-and-add (OLA) [31] and shown in Figure 8; it allows transforming the linear convolution with the fading channel with a cyclic convolution and has been used, for instance, for the detection of Zero-Padded OFDM signals [32]. With respect to traditional cyclicity as introduced VOLUME 6, 2018 by CP, OLA slightly colors the noise term [33].…”

A Performance Improvement of COFDM System with Pseudorandom Sequence Processing Technique

“…(2) ZP-OFDM is recently proposed to replace CP-OFDM I( [6], [7], [8]. The replacement of the cyclic prefix withl where %k DW 1)eoe h at lmnso h zero-padding has the advantage that the symbol recovery vector V'c, and for the ZP-OFDM the guard period is is guaranteed even when channel nulls are located on a zr-adn 6,ie subcarrier.…”