What is RAT?
RAT (Radio Access Technology) refers to the underlying physical connection method used by a radio-based communication network. Each generation of mobile technology constitutes a distinct RAT — GSM (2G), UMTS/WCDMA (3G), LTE (4G), and NR (5G). Modern devices typically support multiple RATs simultaneously (multi-RAT), and networks implement inter-RAT mobility to hand users seamlessly between technologies based on coverage, capacity, and service requirements.
How Does RAT Work?
A UE supporting multiple RATs contains separate radio protocol stacks and RF chains (or shared chains with reconfigurable RF front-ends) for each technology. The device and network collaborate on RAT selection: the UE reports measurements from multiple RATs, and the network decides when to redirect or hand over the user to a different RAT. In 5G, inter-RAT procedures include: LTE-to-NR redirection (for initial 5G access), EN-DC (simultaneous LTE+NR), NR-to-LTE fallback (for voice via EPS fallback), and inter-RAT cell reselection in idle mode. The UE’s RAT capabilities are reported to the network during registration (UE Capability Information message).
Use Cases
Multi-RAT device design and certification, inter-RAT mobility and handover management, network RAT selection and load balancing, spectrum refarming from legacy RATs to 5G NR, and 2G/3G sunset planning with RAT migration strategies.
3GPP / Standards Reference
3GPP TS 38.300 (NR overall — inter-RAT mobility), 3GPP TS 36.300 (E-UTRAN — inter-RAT procedures), 3GPP TS 23.501 (5GS — interworking with EPS)
Related Terms
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This glossary entry is part of the 5GWorldPro Complete 5G Glossary. To go deeper into 5G architecture and technology, explore our 5G Training courses.
