An MMSE interference estimator for Turbo BLAST systems

Turbo BLAST(Bell LAb's Layered Space Time) [1] detection and decoding has demonstrated promising performance for coded BLAST systems. In Turbo BLAST system, an iterative interference cancellation and decoding approach is adopted to simplify processing. The interference is estimated using the extrinsic information from the decoder, which we refer as extrinsic estimator. In this paper, we propose an optimal Minimum Mean Square Error (MMSE) interference estimator for Turbo BLAST system. We show that the mean square error of interference estimation is improved using the proposed estimator. As a result, for QPSK system, the Turbo BLAST system using the MMSE estimator achieves superior performance compared to extrinsic estimator at low and medium SNR regions. At high SNR's, performance of both systems converges to the performance lower bound. For Turbo BLAST system with 16QAM modulation, using the extrinsic estimator leads to divergence of the bit error rate (BER) performance, while using the proposed estimator, the BER still converges to the lower bound.