  Generalized spatial modulation (GSM) is a novel multiple-antenna technique
offering flexibility among spectral efficiency, energy efficiency, and the cost
of RF chains. In this paper, a novel class of sequence sets, called enhanced
cross Zcomplementary set (E-CZCS), is proposed for efficient training sequence
design in broadband GSM systems. Specifically, an E-CZCS consists of multiple
CZCSs possessing front-end and tail-end zero-correlation zones (ZCZs), whereby
any two distinct CZCSs have a tail-end ZCZ when a novel type of cross-channel
aperiodic correlation sums is considered. The theoretical upper bound on the
ZCZ width is first derived, upon which optimal E-CZCSs with flexible parameters
are constructed. For optimal channel estimation over frequency-selective
channels, we introduce and evaluate a novel GSM training framework employing
the proposed E-CZCSs.
