D-Band Differential Testbed

To meet the growing demands of next-generation mobility applications with increasing data traffic and stricter latency requirements, every aspect of the communication infrastructure (fiber, backhaul, and cellular) must evolve. Wireless backhaul plays a pivotal role in network mesh interconnectivity, particularly in regions where fiber links are unavailable or prohibitively costly to deploy. Current licensed backhaul links span a broad frequency range, from a few gigahertz to E-band (71–86 GHz), with next-generation deployments targeting the D-Band (135–170 GHz) to achieve higher capacity. However, despite their significantly higher frequencies, next-generation backhaul systems must prioritize spectral efficiency (beyond 256-QAM), adhere to strict channelization, and comply with stringent out-of-band emission requirements to meet performance and regulatory standards.

D-Band is also a key focus for 6G research. 6G aims to be the first generation of wireless technology to improve the quality of human life by bridging the physical, digital, and human worlds. Accomplishing this will mean adding artificial intelligence to networks to make them more efficient and building high-fidelity digital twins. It will also require building upon network architectures like non-terrestrial networks and highly virtualized disaggregated networks that began in 5G and expanding spectrum use. For 6G to meet these goals, the spectrum allotted for wireless communications must be used more efficiently, and new spectrum must be studied. Without expanding into new spectrum bands, it will be impossible to meet the high data throughput and volume needs of applications like immersive telepresence, virtual reality, and extended reality.

This application note discusses a D-Band testbed with differential IQ inputs and outputs being used to perform complete characterization on a Nokia Bell Labs D-Band full-duplex radio system, as demonstrated live at the IMS 2025 event in San Francisco. New VSA IQNC noise correction enhancements provide the added ability to differentiate between sources of noise to remove receive chain and DUT noise from complex EVM measurements.