The recently suggested Generalized Prefix-Orthogonal Frequency Division Multiplexing (GP-OFDM) uses an optimal non-zero guard interval (GI). A GI consisting of all zeros is also known, and the technique is referred to as Zero Padding (ZP-OFDM). ZP-OFDM performs very well, but suffers from a complexity problem. This paper provides two improved and low-complexity receiver designs for ZP-OFDM, which make the convolutions between the transmitted signal and the channel skew-cyclic. The channel matrix becomes phi-circulant. Both designs require a one-dimensional optimization. The first new design requires the result of the optimization to be available at the transmitter. The second new design eliminates completely the feedback to the transmitter. Simulation results indicate that proposed ZP-OFDM receivers have significant performance advantages compared with existing ZP-OFDM receivers such as ZP-OFDM-OLA and ZP-OFDM-FAST. The performance advantages are maintained in the presence of channel estimation errors and error-correction coding. (C) 2016 Elsevier Inc. All rights reserved.