UCHT complex sequences for downlink multi-carrier DS-CDMA systems

Downlink multi-carrier direct sequence code-division multiple-access (MC-DS-CDMA) often makes use of Walsh-Hadamard (WH) sequences to channelize different users and increase diversity gain. The recently introduced unified complex Hadamard transform (UCHT) sequences are, for the first time, applied as spreading sequences in MC-DS-CDMA. The quadri-phase UCHT complex sequences are orthogonal and easy to generate. Some of UCHT sequences provide better autocorrelation properties than orthogonal WH sequences. It is found that the system spread by UCHT sequences outperforms that spread by WH sequences in frequency selective fading channels.