Spreading sequences for downlink MC-CDMA transmission

A major drawback of all multicarrier transmission schemes is an increased peak-to-average power ratio (PAPR). In multicarrier code division multiple access (MC-CDMA), this can be avoided by the proper choice of spreading sequences. This paper addresses the problem of spreading sequence selection for the downlink MC-CDMA system with respect to their PAPR properties and the resulting complexity of the transmitter. Both lightly loaded and fully loaded systems are considered. A novel complex-valued orthogonal spreading transform is proposed as an alternative to those frequently encountered in the literature. It is derived from the Vilenkin-Chrestenson orthogonal matrix, as a result of generalizing the relationship, established between the orthogonal sets of Walsh-Hadamard and complementary Golay sequences. The approach, described in the paper, provides a scheme for generating a wide class of spread spectrum sequences which provide low PAPR and allow for an efficient implementation.