Demonstration of Multi-User Distributed MIMO at mm-Wave Using Sigma-Delta-Over-Fiber and Optical Up-Conversion

Journal article, 2026

Distributed multiple-input-multiple-output (D-MIMO) is a promising technology for future wireless communication systems, but it still has many implementation challenges to overcome. In this paper, we investigate a D-MIMO setup based on sigma-delta-over-fiber (SDoF) and optical up-conversion, which allows low-complexity remote radio heads (RRHs) while simultaneously exploiting the high bandwidth available in the millimeter-wave (mm-wave) spectrum. The optical up-conversion is implemented by mixing two optical frequencies separated by 26.5 GHz with a band-pass sigma-delta modulated signal at a lower intermediate-frequency (IF) at 1.5 GHz in a photodetector, to create a mm-wave carrier at 28 GHz. The same optical frequencies can be used for many RRHs by splitting the power and inserting optical amplification. The fact that the frequency up-conversion is done at the RRH makes it possible to lower the requirement on the central-unit (CU) sample rate, while the phase coherency among the RRHs is preserved as the optical frequencies originate from the same signal source in the CU. We demonstrate through measurements both single- and multi-user MIMO with two phase-synchronized RRHs, showing that SDoF with optical up-conversion is a promising solution for implementing D-MIMO at mm-wave bands.