Radio Interoperability in 5G and 6G Multiradio Base Station
The 5G system enables flexible and high data rate communication between nearby vehicles, infrastructure nodes, or pedestrians to enable smart traffic use-cases. However, fully autonomous driving vehicles supporting real-time, high-quality, and high data rate sensor data sharing will require data rates beyond 5G, which a future 6G system will support. Mobile devices (UE) and base stations (BTS) supporting the 5G and the future 6G are implemented as multi-mode devices, where multiple radios supporting different systems are integrated into one. The highest 5G data rates are enabled with 5G millimeter wave (mmW) radios, but those face interoperability challenges of harmonic transmissions (TXs) of Long Term Evolution (LTE) and Wi-Fi radios. The 6G radios will suffer co-channel interference from the fundamental TXs of legacy cellular systems. An analog baseband signal of 6G radio will be wider than the frequency allocations of current wireless systems. Similarly, the fundamental TXs of LTE and Wi-Fi may introduce co-channel interference to the analog intermediate frequency (IF) interface of 5G mmW.A minimum 111 dB isolation requirement is calculated for the co-channel interference from the LTE antenna to the 5G mmW analog IF interface. The measured isolation in the 5G mmW proof-of-concept radio was 67 dB, significantly lower than the requirement. The 5G mmW OTA link measurements show that a narrow interference can block the 5G mmW operation if the IF signal has co-channel interference distorting the 5G synchronization signals. The 5G mmW analog interface measurement verifies that the future 6G multi-mode UEs and BTSs will face severe radio interoperability challenges with 5G, LTE, and Wi-Fi transmissions.