Wideband mm-wave Spectrum-Efficient Transmitter Using Low-Pass Sigma–Delta-Over-Fiber Architecture

The millimeter-wave (mm-wave) band offers large bandwidth and promises high data rates for wireless communication systems. This work proposes an mm-wave radio-over-fiber (RoF) architecture suitable for wideband mm-wave communication, using a low-pass sigma–delta modulation approach. The central unit (CU) generates baseband sigma–delta bitstreams, in-phase/quadrature (
$I/Q$
) components, which are transported to a remote radio head (RRH) using a standard QSFP28 optical interconnect link connection. In the RRH, the baseband
$I/Q$
signals are upconverted to the mm-wave band, amplified, and transmitted through an antenna. The performance of the resulting sigma–delta-over-fiber (SDoF) transmitter architecture is experimentally verified at 28 GHz, demonstrating a state-of-the-art symbol rate up to 1.5 Gsym/s. Furthermore, in over-the-air (OTA) measurements, the architecture is shown to support 1 Gsym/s with 5.9% error vector magnitude (EVM) for 64/256/1024 quadrature amplitude modulation (QAM) cases over a 5-m wireless distance. The results demonstrate the feasibility of the proposed architecture for the realization of wideband mm-wave distributed antenna systems.