1. Campus Hotspot 6G High-Order MIMO System

We established a world-leading 6G upper-mid-band High-Order MIMO system and conducted a series of innovative 6G experiments at NSYSU Campus. The experiment scenarios and results are shown in Figure 1 and Figure 2, 16×8 MIMO in campus outdoor hotspots (central plaza) achieved the terminal spectral efficiency of 45 bps/Hz. 16×12 MIMO in the public open space of the College of Electrical Engineering and Computer Science building achieved the terminal spectral efficiency of 60 bps/Hz. The spectral efficiencies in the above two experiments are better than the current 5G mid-band 3.5 GHz 4×4 MIMO terminal spectral efficiency in the same scenario, at least quadrupling the performance, making our team a global leader in upper-mid-band 6G High Order MIMO technology.

These research findings include the below key technologies: (a) the number of receive antennas exceeding the number of MIMO spatial signal streams; (b) high-density Rx MIMO antennas with high gain and wide radiation beamwidth; (c) High-Order MIMO baseband technology; and (d) upper-mid-band High-Order MIMO test platform technology. These Technologies are all ahead of domestic and international research teams. In the future, 6G upper-mid-band is expected to achieve at least 400 MHz carrier bandwidth, enabling transmission speeds of up to 18 Gbps in outdoor hotspots and 24 Gbps in indoor open spaces, which is 16 times the speed of the current 5G mid-band 100 MHz bandwidth 4×4 MIMO. This will fully meet the requirements of future 6G mobile devices.

Figure 1: 16×8 MIMO at Campus Outdoor Hotspot (Central Plaza) Achieving a Terminal Spectral Efficiency of 45 bps/Hz

Figure 2: 16×12 MIMO at Indoor Public Open Space of the College of Electrical Engineering and Computer Science Building (Including Line-of-Sight, Non-Line-of-Sight, and Crowd-Gathering Scenarios) Achieving a Terminal Spectral Efficiency of 60 bps/Hz

Considering the higher path loss at the upper-mid-band, which is disadvantageous for MIMO systems supporting multipath environments, our team successfully developed the world's first active reconfigurable intelligent surface (RIS)-assisted MIMO-OFDM system. We verified that this technology can significantly improve the performance of current 5G commercial base stations. Figure 3(a) shows that using active RIS technology in a campus environment increased the 5G signal-to-noise ratio (SNR) from 7.5 dB to 15 dB, achieving a 100% improvement. This proves the practical application of active RIS in commercial fields. Additionally, Figure 3(b) shows that by combining the Industrial Technology Research Institute's (ITRI) O-RAN and active RIS technology, we successfully increased the SNR by over 100% in areas with weak communication signals by deploying RIS. This result shows the potential of RIS in assisting the integration of O-RAN systems.

Figure 3: Active RIS Assisting Campus 5G Commercial Signal and ITRI O-RAN, Achieving Over 100% SNR Improvement

2. 6G upper-mid-band MIMO Radar Sensing System Testing

Significant achievements of this research include developing a super-resolution algorithm using the Frequency Estimation Algorithm (FEA) with a distributed MIMO continuous-wave radar operating in the unlicensed 5.8 GHz band for simultaneous positioning and non-contact vital sign sensing of multiple subjects in the environment. The received signals contain phase components caused by the antennas and the human body. By using FEA technology to eliminate the Doppler phase caused by human vital signs, the positioning information of the human body can be obtained from multiple sets of baseband signals. As shown in Figure 4, the MIMO radar uses a 4T4R architecture, achieving a positioning accuracy of 0.1 meters and a vital sign sensing error of 0.02 Hz without occupying bandwidth, with the closest adjacent human body being only 0.23 meters away.

Furthermore, for the first time, we combined high spatial resolution MIMO radar with high sensitivity original self-injection locking (SIL) radar to form a 4D imaging radar, capable of tracking multiple individuals and identifying specific body parts for non-contact vital sign sensing. As shown in Figure 5, the radar uses an 8T8R MIMO FMCW architecture, operating in the unlicensed 6 GHz band, detecting multiple moving targets to obtain imaging, positioning, and speed information for each target. It achieved an angular resolution of less than 7 degrees, a positioning error of less than 3%, and a speed sensitivity of less than 0.3 mm/s. The self-injection locking technology improved speed sensitivity by over 70%, successfully sensing human vital signs, including breathing and heartbeat.

Figure 4: Distributed MIMO Continuous-Wave Radar for Positioning and Vital Sign Sensing of Multiple Subjects

     About key components, the designed reflective liquid crystal phase shifter uses a differential line structure, with periodically loaded variable capacitors formed by metal patterns on the upper and lower glass substrates and liquid crystal sandwiched in between, achieving controllable phase shifting. This design can be compatible with existing LCD production lines, significantly reducing production difficulty. Additionally, reducing the liquid crystal layer thickness results in a response time in milliseconds, comparable to existing LCD displays, achieving rapid switching. As shown in Figure 6, the 3.5 GHz phase shifter produced has a loss of about 4 dB, a maximum phase shift of 280°, and a bandwidth of about 300 MHz, meeting the bandwidth requirements of upper-mid-band.

Figure 5: 4D Imaging MIMO Radar for Tracking Multiple Subjects and Identifying Specific Body Parts for Vital Sign Sensing

Figure 6: Reflective Liquid Crystal Phase Shifter Operating at 3.5 GHz