A team of researchers from the Instituto de Telecomunicações (IT) and the University of Aveiro (UA), led by IT researcher Arnaldo Oliveira, has experimentally validated a fully digital transmitter implemented on a single FPGA, demonstrating its potential for simpler and more flexible radio units in future 6G networks.
The All-Digital Transmitter (ADTx) generates radio-frequency signals directly in the digital domain, eliminating the need for conventional analogue components such as digital-to-analogue converters, mixers and local oscillators. The system uses a high-speed FPGA transceiver to generate the RF signal, which can then be transmitted over optical fibre without intermediate decoding or analogue processing.
The team tested the technology in a real Radio-over-Fiber (RoF) communication system, using a Delta-Sigma-over-Fiber (ΔΣoF) approach. The demonstrator incorporates a delta-sigma modulator operating at 25.6 Gbps, with carrier frequencies ranging from 100 MHz to 12.5 GHz and signal bandwidths of up to 1 GHz.
Experimental validation included eye-diagram, spectral, and vector signal analysis. For a 16-QAM signal at 3.2 GHz, the measured Error Vector Magnitude (EVM) was 0.85% at the fibre input and 2.32% at the output, remaining well within the 3GPP 5G NR specification limit of 3.5%.
The results demonstrate the feasibility of significantly simplifying remote radio units by concentrating processing and reconfigurability in a central FPGA-based unit. This architecture could support future C-RAN, O-RAN and distributed MIMO (D-MIMO) scenarios, while reducing the complexity of equipment at the radio site.
The work was developed within the Microelectronics Agenda, one of the Innovation Agendas funded through Portugal’s Recovery and Resilience Plan (PRR). The team is now exploring further developments, including ASIC implementations, AI-assisted coding and electronic-photonic co-design.