Orthogonal time-frequency-space (OTFS) modulation, which demonstrates the superior robustness against time-frequency-selective fading over the orthogonal frequency-division multiplexing (OFDM) modulation, has been deemed to be a promising two-dimensional transmission technique for high-mobility wireless communications. Unfortunately, OTFS systems would suffer frominter-frame interference(IFI),inter-Doppler interference(IDoI), andinter-delay interference(IDeI). In this paper, a novel generalized channel model involving IFI, IDoI, and IDeI for wireless OTFS systems has been derived by considering practical factors such as Doppler effect, carrier-frequency drift of local oscillators, multi-path fading, and cyclic prefix coding. Meanwhile, the symbol-error-rate (SER) performance of the PSK-OTFS system is theoretically investigated accordingly. Monte Carlo simulation results demonstrate that our proposed new theoretical SER performance analysis can lead to more accurate results than the existing theoretical analysis involving IDoI only. Moreover, the detailed quantitative analysis of the dominant interference (IFI/IDoI/IDeI) under different conditions is also conducted in this work. Our proposed new interference analysis can be adopted easily to evaluate the reception quality of the future wireless OTFS transceivers.