Generation and analysis of LTE TM9 MU-MIMO signal with instrument-based software defined radio demonstration

This paper presents the software/hardware integration for verifying the LTE multiuser beamforming transmission in terms of a cost-effective computer-based software defined radio (SDR) platform. According to LTE transmission mode 9 (TM9) spec, we have developed the corresponding MIMO vector signal generator and analyzer (VSG/VSA) software, which can be run on a personal computer with interface with some general-purpose SDR platform. Then a realistic 4-layer multiuser beamforming experiment is performed on this platform. In so doing, we adopt the signal-to-leakage-noise-ratio (SLNR) based precoding scheme to find the beamforming weights at the basestation, assuming that the four users (UEs) have line-of-sight channels with known directions-of-arrivals. The testing results are compared with Keysight's 89600 LTE VSA in terms of beampattern and error vector magnitude (EVM). It is shown that generated TM9 signal can be successfully demodulated, and the SLNR precoding can successfully form a beam toward the desired UE while nulling the other UEs. Moreover, our VSG/VSA software along with the MIMO SDR platform can achieve an EVM comparable to that of the leading commercial instrument.