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Systolic-array based regularized QR-decomposition for IEEE 802.11n compliant soft-MMSE detection

This paper considers the implementation of a soft-output MMSE detector for packet-based MIMO-OFDM transmission. The paper focuses on channel-matrix preprocessing realized with a QR decomposition which needs to be carried out under tight latency constraints. We discuss how the preprocessing algorithm should be selected to meet the specific requirements of the soft-output MMSE detector. Additionally we develop a pipelined systolic-array architecture that is particularly well suited to be combined with low-latency pipelined FFTs. We have implemented the QR decomposition method proposed for an IEEE 802.11n transceiver with 4 spatial streams. In a 0.13 µm 1P8M CMOS technology the corresponding circuit is capable to process 110 complex-valued 4×4-dimensional channel matrices for soft-output MMSE detection per second and gate equivalent and achieves a sustained throughput of 20 million decompositions per second, which is sufficient to meet the stringent latency requirements of IEEE 802.11n.