On the Fundamentally Asynchronous Nature of Interference in Cooperative Base Station Systems

Cooperative transmission by base stations can significantly improve the spectral efficiency of multiuser, multi-cell multiple input multiple output systems. The authors show that in such systems the multiuser interference is asynchronous by nature, even when perfect timing-advance mechanisms ensure that the desired signal components arrive synchronously. They establish an accurate mathematical model for the asynchronism, and use it to show that the asynchronism leads to a significant performance degradation of existing linear precoding designs that assumed synchronous interference. They consider three different previously proposed precoding designs, and show how to modify them to effectively mitigate asynchronous interference.