Feedback of Downlink Channel State Information Based on Superimposed Coding

Abstract

In closed-loop FDD MIMO system, downlink channel state information (DL-CSI) is usually feedback to base station in forms of codebook or CQI, both of which aim at lowering the feedback quantity at the cost of limited feedback precision and heavy processing complexity at mobile side. Meanwhile, the recently proposed direct channel feedback method incurs great system overhead due to its exclusive occupation of uplink bandwidth resources. We propose a low-cost feedback method for DL-CSI, which spreads unquantized and uncoded DL-CSI and superimposes it onto uplink user data sequences (UL-US). Exclusive occupation of system resources by DL-CSI can thus be avoided. Due to spreading, DL-CSI can be estimated accurately with little power allocation at the cost of some UL-US's SER performance