U(1) as the Minimal Horizontal Gauge Symmetry

A horizontal U′(1) gauge symmetry is proposed to distinguish two fermionic generations. By extending the notion of generation structure to the Higgs system, and using anomaly-free conditions with the requirements of lepton-number conservation and proper Cabibbo structure, we determine $Y^{\prime }$ associated with U′(1), uniquely. The model can easily be generalized to account for $2^N$ ($N=1,2,\cdots$) generations.