Multi-User Networks with Outdated Channel State Information

Multi-User Networks with Outdated Channel State Information

In a communications system consisting of multiple transmitters and multiple receivers, channel state information (CSI) is necessary at the receivers for decoding of the transmitted data, and at the transmitters for managing the interference in the network. At the receivers the CSI is obtained by transmission of pilot symbols and the transmitters obtain the CSI through feedback links from the receivers. In time-varying channel, due to delays the CSI obtained by the transmitters (CSIT) can be different to the actual channel state. In the extreme case the available CSIT and the true channel state are not correlated, which means traditional interference management techniques are not applicable.
For the aforementioned delayed CSIT setting, a new interference management technique achieving good number of degrees of freedom (DoF) was recently proposed. The proposed approach is a multi-phase transmission, where in each consecutive phase the delayed CSIT from the previous phases is used to reduce the amount of the produced interference. The reduction is possible if the terms transmitted in the next phase depend on the interference terms overheard at the unintended receivers in the previous phases, which can be reconstructed at the transmitters using the delayed CSIT.

The purpose of the project is to study different types of networks under delayed CSIT setting. New transmission schemes are to be proposed, which will provide greater number of achievable DoF and/or greater sum-rate of the communication system.