Demonstration of Virtual MIMO in the Uplink

The authors explains 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.