Completely Stale Transmitter Channel State Information is Still Very Useful

Understand

Transmitter channel state information (CSIT) is crucial for the multiplexing gains offered by advanced interference management techniques such as multiuser MIMO and interference alignment.

• Such CSIT is usually obtained by feedback from the receivers, but the feedback is subject to delays.
• The usual approach is to use the fed back information to predict the current channel state and then apply a scheme designed assuming perfect CSIT.
• When the feedback delay is large compared to the channel coherence time, such a prediction approach completely fails to achieve any multiplexing gain.