Transmission and reception of reference preamble signals in OFDMA or OFDM communication systems

A method for communications based on OFDM or OFDMA, comprising:

• selecting a CAZAC sequence of a length L in frequency which includes spectral components in first, second and third sequential portions in frequency;
• modifying the CAZAC sequence to produce a first modified sequence by setting amplitudes of spectral components in the first portion of the CAZAC sequence to zeros and adding a first phase shift on spectral components of the second portion of the CAZAC sequence, without changing the third portion;
• modifying the CAZAC sequence to produce a second modified sequence by setting amplitudes of spectral components in the third portion of the CAZAC sequence to zeros and adding a second phase shift spectral components of the second portion of the CAZAC sequence, without changing the first portion;
• combining the first and second modified sequences to form a combined sequence in frequency of a length 2L, wherein the first portion from the first modified sequence is positioned next to the third portion from the second modified sequence in the combined sequence;
• and
• performing an inverse fast Fourier transform on the combined sequence to generate a first preamble sequence in time for OFDM or OFDMA communication.