Demonstration of Virtual Mimo in the Uplink

We demonstrate how virtual MIMO techniques can be implemented in a next-generation mobile communication system. In order to test basic principles, joint spatiotemporal processing of two users has been implemented in an uplink scenario. A prerequisite of virtual MIMO is accurate synchronization. It is shown that the carrier frequency offset can be reduced to a few Hz only at small signal-to-noise ratios. Based on remote synchronization via the downlink, a technique called frequency advance is applied in the uplink, i.e. the terminals correct their frequency offsets in the digital baseband prior to data transmission. The principle has been implemented and tested in real-time using system parameters of the long term evolution (LTE) of the 3 generation (3G) of cellular systems. Two user’s signals have been successfully detected on the same radio resource.