We develop a new construction criterioin for BSPK space-time codes. Based on this criterion, we propose a new method of improving the performance of space-time codes, namely bit interleaving. Then, we provide a computationally effective, iterative way of decoding bit interleaved space-time codes. At the end, we note the 2dB gain due to the new approach. A proposed 16 state bit interleaved code operates close to 3dB from the outage probability.