In this work, the effect of a radio-over-fibre (RoF) subsystem on the bit error rate (BER), total degradation (TD) and system capacity performances of downlink multiple-input multiple-output (MIMO) wideband code division multiple access (WCDMA) are assessed. The research investigates the use of maximal ratio combining (MRC) in single-input multiple-output (SIMO) schemes and Alamouti space-time block coding (STBC) in MIMO systems to compensate for the collective effects of the optical subsystem and the radio channel for different channel conditions and number of users. Results show that the aforementioned techniques are effective methods to compensate for both the non-linearity of the optical subsystem and the time-varying wireless radio frequency (RF) channel. It is also demonstrated that by increasing the number of users for severe non-linearity conditions, the BER performance of the system is significantly affected. Also, an appropriate quiescent point can always be found for the optical subsystem which improves the system performance irrespective of different conditions.