Efficient representation and feedback signaling of channel state information in frequency division duplexing MIMO systems

In order to fully benefit from the potential offered by the application of multiple-input-multiple-output (MIMO) configurations in mobile radio systems, the knowledge of the radio channels should be available and considered in the signal processing algorithms both at the transmitter and the receiver. At the receiver this knowledge can be gained by state of the art training sequence based, semi-blind or blind channel estimation. However, at the transmitter the channel knowledge is not readily available and has to be imparted from the receiver by signaling the relevant information back to the transmitter, which ties up transmission resources. Therefore, a cost efficient signaling concept for this purpose is proposed, which relies on subspace methods. A quantitative example is discussed to show how this concept can be applied and how it performs in different scenarios.