NetDoFs of the MISO broadcast channel with delayed CSIT feedback for Finite Rate of innovation channel models

Abstract

Channel State Information at the Transmitter (CSIT) is of utmost importance in multi-user wireless networks, in which transmission rates at high SNR are characterized by Degrees of Freedom (DoF, the rate prelog). In recent years, a number of ingenious techniques have been proposed to deal with delayed and imperfect CSIT. However, we show that the precise impact of these techniques in these scenarios depends heavily on the channel model. We introduce the use of linear Finite Rate of Information (FRoI) signals to model time-selective channel coefficients, a model which turns out to be well matched to DoF analysis. Both the block fading model and the stationary bandlimited channel model are special cases of the FRoI channel model (CM). However, the fact that FRoI CMs model stationary channel evolutions allows to exploit one more dimension: arbitrary time shifts. In this way, the FroI CM allows to maintain the DoF unaffected in the presence of CSIT feedback (FB) delay, by increasing the FB rate. We call this Foresighted Channel Feedback (FCFB). We then consider netDoF, by accounting also for the DoF consumed in training overhead and feedback. We work out the details for the MISO broadcast channel (BC), including optimization of the number of users, and exhibit unmatched netDoF performance compared to existing approaches.