  In this paper, for the first time, we present a direct and new construction
of multiple zero-correlation zone (ZCZ) sequence sets with inter-set zero-cross
correlation zone (ZCCZ) from generalised Boolean function. Tang \emph{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 if the
union of these $N$ sets is taken then that union 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
a near-optimal ZCZ sequence set. Further, the performance parameter of each
binary ZCZ sequence set in the proposed construction is $1$ and tends to $1$
for their union. The proposed construction is presented by a two-layer
graphical representation and compared with the existing state-of-the-art.
Finally, novel multi-cluster quasi synchronous-code division multiple access
(QS-CDMA) system model is provided by using the proposed multiple ZCZ sequence
sets.
