4.1 Introduction4.2 IQRD‐RLS Algorithm4.3 IQRD‐Based Receivers with Fixed Constraints4.4 IQRD‐based Receiver with Optimized Constraints4.5 Channel Estimation Techniques4.6 New Robust Detection Technique4.7 Systolic Array Implementation4.8 Simulation Results4.9 Complexity AnalysisAppendix 4.A Summary of Inverse QR Algorithm with Inverse UpdatingAppendix 4.B QR Decomposition AlgorithmsAppendix 4.C Subspace Tracking AlgorithmsReferences