To achieve a high speed transmission with limited frequency bandwidth, multiple-input multiple-output (MIMO) has been gaining much attention. QR-decomposition based successive interference canceller (SIC) can provide good detection performance with reasonable complexity. In MIMO system, there could be spatial antenna correlation among antennas and this degrades the transmission performance. The performance severely degrades owing to the correlation among transmit antennas in the case of uplink transmission. In this paper, we propose a frequency band allocation in MIMO system based on received power difference among users that each user utilizes several frequency bands that overlap with other users'. At the receiver, QRdecomposition based SIC is performed by utilizing the received power difference. It is shown that the proposed scheme yields superior error rate performance over the conventional scheme by computer simulations.