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Adaptive modulation improves system throughput considerably by matching transmitter parameters to time-varying wireless fading channels. Crucial to adaptive modulation is the quality of channel state information (CSI) at the transmitter. We consider a channel predictor based on pilot symbol assisted modulation (PSAM) for multi-input multi-output (MIMO) Rayleigh fading channels. We analyze the impact of the channel prediction error on the bit error rate (BER) performance of an adaptive system assuming perfect CSI. Our numerical results reveal the critical value of the normalized prediction error, below which the predicted channels can be treated as perfect by the adaptive modulator; otherwise, explicit consideration of the channel imperfection must be accounted for at the transmitter.