Date Added: Nov 2012
In multi-user wireless communications, the knowledge of Channel State Information at Transmitters (CSIT) is important for the multiplexing gain (or degrees of freedom). For example, consider a K-user (K x K X networks) X network with K single-antenna transmitters and K single-antenna receivers, where each transmitter intends to send an independent message to each receiver. Without CSIT, the achievable sum Degree of freedom (DoF) is only one. Thus, orthogonal transmission schemes such as Time-Division-Multiple-Access (TDMA) attains the optimal performance in terms of DoF.