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We propose an iterative extension of the Bell Laboratory Layered Space-Time (BLAST) algorithm and its variant, vertical BLAST (VBLAST). A characteristic feature of the BLAST-type algorithm is that symbol decisions with low reliability are fed back to decode other symbols. Both performance analysis based on Gaussian approximation of residual interference, and simulation results demonstrate that error propagation due to unreliable decision feedback can severely limit system performance. The extended algorithm exploits inherent signal diversity in BLAST to mitigate residual interference, thus overcoming the performance bottleneck due to error propagation. It yields an impressive performance gain over BLAST. In particular, the extension of BLAST with zero-forcing interference ing admits a simple QR implementation and exhibits excellent performance with low complexity.