Wideband mm-Wave 6 $\mathrm{ \times }$ 2 Distributed MIMO Transmitter Using Sigma-Delta-Over-Fiber

This article investigates a millimeter-wave sigma-delta-over-fiber distributed multiple-input-multiple-output (D-MIMO) solution, in which a central unit connects two remote radio heads (RRH) with two standardized QSFP28 fiber connections. The four subchannels of the QSFP28 carry three individually controlled intermediate frequency (IF) sigma-delta modulated bitstreams and one local oscillation signal to each RRH. At each RRH, the upconversion to mm-wave frequency is performed while maintaining full phase coherence between all channels and distributed RRHs. This solution offers an effective and scalable way to feed multiple radio heads with coherent signals proper for high performance millimeter-wave D-MIMO systems. Wireless performance of the transmitter is experimentally verified by multiple-input-single-output (MISO) and multiple-user MIMO cases in a 1.4 m × 1.6 m area with 748 MHz wideband signals. The comparison with other publications shows that the proposed system is the first millimeter-wave sigma-delta-over-fiber D-MIMO solution that serves multiple users and reaches the largest bandwidth.