Blind Iterative Decision Feedback Equalizers for Block Qam Transmission Systems

A novel blind initialization procedure for iterative decision feedback equalizers in block-based transmission systems is proposed and investigated. It relies on an initial stage using Regalia’s blockbased Constant Modulus iterative algorithm for the blind computation of a linear equalizer; then a switch to decision feedback mode is performed. It is shown how the building blocks of the decision feedback equalizer (feedforward and feedback filters, automatic gain control and phase rotation) can be blindly estimated. Due to the unknown lag introduced by the blind linear equalizer, delay synchronization of the feedforward and feedback filters is also required. These filters are then refined over successive decision feedback iterations. This approach can also be used as a blind channel identifier for other block receiver designs, such as soft ISI cancelers and decoder-aided (i.e. turbo) equalizers.