An Adaptive Negative Feedback Controller for Indoor Wireless Communications

An adaptive negative feedback controller structure in the transmitter is presented for indoor wireless communications, where the channel may vary due to rotation and small movement of the mobile terminal. The preliminary version of such negative feedback controller is popularly known as Tomlinson Harashima (TH) precoder in wireless communications. The proposed scheme presents a fast adaptive version of the same with the help of an adaptive algorithm. The existence of a feedback channel is assumed that sends the received input at mobile terminal to the transmitter, i.e., to the base station for adapting the coefficients at the transmitter in the downlink. In the downlink, for fast and adaptively tracking the TH precoder we use a version of Variable Step-size Least Means Square (VSLMS) adaptive algorithm. In the uplink the channel is estimated and the values are used in downlink along with the algorithm. Indexing terms: Negative feedback control, Tomlinson-Harashima precoder, Adaptive channel estimation, Indoor wireless communications.