Evaluating Downlink MU-MIMO: Laboratory Experimentation and Results

The Third Generation Partnership Project (3GPP) finalized the radio interface specifications for the next generation mobile communication system, Long Term Evolution (LTE), as Release 8 [1], [2]. LTE provides full IP packet-based radio access with low latency and adopts orthogonal frequency division multiple access (OFDMA) and single-carrier frequency division multiple access (SC-FDMA) as multiple access schemes in the downlink and uplink, respectively. In Japan, the NTT DOCOMO launched a commercial LTE service in December 2010 under the new service brand Xi (crossy) [3]. Meanwhile, in 3GPP standardization, there have been efforts toward establishing an enhanced LTE radio interface, LTEAdvanced (LTE Release 10 and beyond), and specifications for LTE Release 10 were finalized [4], [5]. In LTE-Advanced, it is necessary to support a wider bandwidth than that in LTE Release 8, i.e., 20 MHz, to satisfy the high level requirements corresponding to the target peak data rate of greater than 1 Gb/s. To this end, LTEAdvanced supports carrier aggregation (CA) up to 100 MHz by aggregating multiple component carriers (CCs) with backward compatibility to LTE Release 8. In addition, to satisfy the requirements for further improvement in terms of spectrum efficiency, enhanced multiple-input multiple-output (MIMO) techniques such as higher-order MIMO multiplexing and multiuser (MU)-MIMO are supported.