A cellular device that maintains its own network connection while using sidelink communications to relay traffic bidirectionally between the network and a nearby remote device that itself has no direct network coverage.

Key Points

Maintains its own normal cellular connection to the network while simultaneously establishing a sidelink connection to one or more out-of-coverage remote devices
Relays traffic bidirectionally between the remote device and the network, functioning as a bridge rather than a destination for the traffic itself
Extends effective network coverage into areas with no direct cellular signal, as long as a relay-capable device with network connectivity is within sidelink range
Particularly relevant for public safety scenarios, where a first responder device with network coverage can relay connectivity to colleagues who have moved into a coverage-denied area — a building interior, an underground space, a disaster-affected zone
Distinct from a UAV relay, which achieves coverage extension through an airborne platform rather than another ground-based cellular device acting as an intermediary

Concept

A relay UE effectively extends the edge of network coverage by one additional hop — a remote device with no direct signal to any base station can still reach the network as long as a relay-capable device that does have coverage is within sidelink range, with the relay device forwarding traffic in both directions without needing to be the traffic's actual origin or destination.

Explainer

The practical value relay UE delivers is coverage extension without requiring new network infrastructure — rather than deploying an additional base station to cover a small pocket of otherwise-uncovered area, a single relay-capable device already present and connected can extend usable coverage to nearby out-of-coverage devices dynamically, exactly where and when it's needed rather than through fixed infrastructure investment. This makes relay UE particularly valuable in scenarios where the coverage gap is temporary, unpredictable, or too small to justify dedicated infrastructure — a first responder moving into a building's interior, a worker temporarily out of range in a large industrial site — rather than a permanent coverage solution. For CE verticals, relay UE capability is most relevant to field operations in complex physical environments where personnel or equipment may temporarily move beyond fixed network coverage — underground or enclosed spaces in mining and energy operations, or tactical field scenarios in government and defense contexts — providing a dynamic, infrastructure-light coverage extension mechanism that complements rather than replaces fixed network planning.

Cite this entry

Relay UE. ConnectedEarth Knowledge Base. https://connectedearth.space/knowledge-base/relay-ue/ (updated 13 September 2026).