Multiuser MIMO Achievable Rates With Downlink Training and Channel State Feedback
In this paper, the authors consider a Multiple-Input - Multiple-Output (MIMO) fading broadcast channel and compute achievable ergodic rates when Channel State Information (CSI) is acquired at the receivers via downlink training and it is provided to the transmitter by channel state feedback. Unquantized (analog) and quantized (digital) channel state feedback schemes are analyzed and compared under various assumptions. Digital feedback is shown to be potentially superior when the feedback channel uses per channel state coefficient is larger than 1. Also, they show that by proper design of the digital feedback link, errors in the feedback have a minor effect even if simple uncoded modulation is used on the feedback channel.