Luftschnittstelle

Luftschnittstelle is the term used in telecommunications for the radio interface between user equipment (UE) and the access network. It encompasses the wireless link, the radio access technologies, and the signaling exchanged over the air. The Luftschnittstelle integrates the physical layer and the medium access control layers with higher-layer signaling that traverses the wireless medium, enabling user data transfer and control information between devices and the network.

The concept covers the structure and operation of the radio access network (RAN), including base stations, antennas, and radio resources, as well as the protocols responsible for establishing and maintaining connections. Key elements are frequency bands, modulation and coding schemes, resource allocation, and channel management. The Luftschnittstelle also includes mobility management, handover procedures, power control, interference mitigation, and security mechanisms that protect air-interface traffic.

In the context of modern cellular systems, the Luftschnittstelle is defined by standards developed by 3GPP for GSM/UMTS/LTE and 5G. LTE uses OFDMA for the downlink and SC-FDMA for the uplink, while 5G New Radio employs flexible OFDM with selectable numerologies. The air interface supports both user-plane data and control-plane signaling, with mechanisms for QoS, encryption, and authentication. It faces challenges such as spectrum scarcity, regulatory constraints, propagation effects (fading, shadowing), interference, and latency requirements, which drive techniques like adaptive modulation, beamforming, and dynamic spectrum sharing.

Overall, the Luftschnittstelle is the essential wireless link that enables mobile communications by bridging the device and the core network through radio access technologies.