NTT and JAXA Demonstrate Satellite MIMO Capacity Gain in LEO Tests
Japan’s NTT and space agency JAXA have reported successful in-orbit demonstrations of multiple-input multiple-output (MIMO) communications and satellite IoT technologies, achieving significant improvements in transmission capacity and the ability to support simultaneous low-power device connections.
The experiments were conducted using the LEOMI satellite MIMO/IoT payload onboard JAXA’s Small Demonstration Satellite No. 4, launched in December 2025. Testing began in March 2026 as part of a programme to validate technologies for higher-capacity satellite communications and wide-area IoT services.
The most significant result came from the MIMO trials, which demonstrated how multiple antennas can transmit separate data streams using the same frequency resources to increase overall communications capacity.
NTT and JAXA achieved an average capacity improvement of approximately 1.94 times using a 2x2 MIMO configuration, increasing to 2.67 times with a 3x3 configuration, compared with conventional single-input single-output (SISO) communications.
MIMO is already widely used in terrestrial 4G and 5G networks, but applying it to LEO satellites introduces additional challenges. Rapid satellite movement creates changing signal propagation conditions, including Doppler shifts and timing differences, making it more difficult to separate multiple signals received at geographically distributed ground stations.
The researchers used interference compensation, channel modelling and signal-processing techniques to address these challenges. They also found that measured capacity variations closely matched their analytical models, suggesting that future satellite MIMO systems could be optimised using predicted orbital conditions and ground antenna configurations.
Alongside the capacity tests, NTT and JAXA demonstrated satellite reception of simultaneous low-power wide-area (LPWA) IoT transmissions in the 920MHz band.
Signals sent from two different ground locations using the same frequency were successfully received by the satellite, separated and demodulated through signal processing. The result demonstrates the potential to accommodate multiple low-power IoT devices using shared spectrum resources without requiring terrestrial base station coverage.
NTT and JAXA plan to continue testing under different orbital and radio conditions, including varying antenna configurations and IoT transmission scenarios, to establish the performance and operational limits of the technologies.