Concatenative Complete Complementary Code Division Multiple Access and its Fast Transform

Over multipath channels, \textit{complete complementary code division multiple access} (CC-CDMA) and \textit{convolutional spreading code division multiple access} (CS-CDMA) provide {\it inter-channel interference} (ICI) free transmission with an enhanced {\it spectral efficiency} (SE). However, the {\it convolutional spreading} (CS) operation of the systems is computationally complex and involves a high \textit{peak-to-average power ratio} (PAPR). Address such issues, we propose the \textit{concatenative complete complementary code division multiple access} (CCC-CDMA). Since the CCCCs can be generated from the rows of the Walsh-Hadamard or \textit{discrete Fourier transform} (DFT) matrices, the CS operation can be implemented using corresponding {\it fast transforms} (FTs) to reduce computational complexity. Simulation results shown that enlargement of {\it spreading factor} (SF) strengthens the robustness against clipping noise and the binary CCCC generated by Walsh-Hadamard matrix has excellent robustness against Doppler frequency shifts.