SUMMARYThis paper presents an effective scheduling scheme for sphere decoding (SD) with runtime constraints, targeting the practical multiple-input multiple-output (MIMO) communication systems where neither the interleaving scheme nor its block size cannot be designed freely. The proposed scheme imposes runtime constraints on SD to distribute the errors due to the early termination of SD. Because the distributed errors may be corrected effectively by forward error correction, the error-rate performance can be improved; experimental results show that the performance improvement is approximately 2 dB in terms of the signalto-noise ratio to achieve a bit-error rate of 10 4 in 4 4 16-QAM MIMO systems.