In this paper, we analyze the domination of either Rayleigh fading or Doppler spread effects in the fifth telecommunication generation and beyond (5G&B) high-speed railway for speeds beyond 500 km/h. We use the Doppler spread compensator (DSC) technique and combine it with a multiple-input multiple-output (MIMO-DSC) system to compensate for the Doppler effects and to obtain a higher capacity. We perform a series of computer simulations to evaluate the dominance of either Rayleigh fading or Doppler effects on the error-floor of the 5G&B high-speed railway system. The results show that the domination of Rayleigh fading and the Doppler effects depends on the number of antenna elements. When the number of antenna elements is large, Rayleigh fading dominates; however, when the number of antenna elements is small, the Doppler effect dominates causing worse bit-error-rate (BER) performances. These results indicate that further optimization is required to perform best against both Rayleigh fading and Doppler effects.