A new construction of almost-optimal multiple ZCZ sequence sets for multi-cell QS-CDMA system

In this paper, for the first time, we present a direct construction of multiple zero-correlation zone (ZCZ) sequence sets with inter-set zero-cross correlation zone (ZCCZ) from a generalised Boolean function. Tang et al., in their 2010 paper, proposed an open problem to construct N binary ZCZ sequence sets such that each of these ZCZ sequence sets is optimal and the union of these N sets is again an optimal ZCZ sequence set. The proposed construction partially settles this open problem by presenting a construction of optimal ZCZ sequence sets such that their union is an almost-optimal ZCZ sequence set. The proposed construction is presented by a two-layer graphical representation and compared with the existing state-of-the-art. Moreover, it has been shown that some of the existing constructions are special cases of the proposed construction. Finally, the performance of a novel multi-cell quasi synchronous-code division multiple access (QS-CDMA) system is provided by using the proposed multiple ZCZ sequence sets and it has been compared with a conventional ZCZ-based QS-CDMA system.