A Study of Asymmetric ZCZ Sequence Sets

The present paper proposes two methods for constructing new asymmetric ZCZ sequence sets. ZCZ sequence sets are used as spreading sequences for AS-CDMA systems. An asymmetric ZCZ sequence set is a type of ZCZ sequence set and consists of multiple sequence subsets. Compared with conventional ZCZ sequence sets, the most important property of the proposed asymmetric ZCZ sequence sets is that the cross-correlation function between arbitrary sequences that belong to different sequence subsets has quite a large zero-cross-correlation zone. This property is useful for application to the AS-CDMA systems. If a cell is divided into concentric circles and each sequence subset is assigned to users existing in each area between two circles, then the proposed asymmetric ZCZ sequence sets can achieve much larger zero-cross-correlation zones than the conventional ZCZ sequence sets. The proposed asymmetric ZCZ sequence sets are expected to be useful for designing spreading sequences for AS-CDMA systems. Key-Words: Asymmetric ZCZ sequence sets, AS-CDMA, Spreading sequences, Spread spectrum communications, Perfect sequences, Orthogonal codes