Spreading sequences for multi-carrier CDMA systems

The paper contains an analysis of the basic criteria for the selection of spreading sequences for the multi-carrier CDMA (MC-CDMA) systems with spectrum spreading in the frequency domain. It is shown that the time-domain crosscorrelation function between the spreading sequences is not a proper interference measure for the asynchronous MC-CDMA users. Therefore the spectral correlation function is introduced and, together with the peak-to-average power ratio (PAPR) and the dynamic range of the corresponding multi-carrier waveforms, is used for the evaluation of MC-CDMA sequences. Some well-known classes of sequences, such as Walsh and Gold sequences, as well as orthogonal Gold and Zadoff-Chu (1972) sequences, are evaluated with respect to the aforementioned basic criteria. It is also shown that the multi-carrier spread spectrum waveforms based on the (multilevel) Huffman sequences have the lower PAPR than a single sine wave.