Air interface

The air interface, or access mode, is the communication link between the two stations in mobile or wireless communication. The air interface involves both the physical and data link layers (layer 1 and 2) of the OSI model for a connection.

Physical Layer

The physical connection of an air interface is generally radio-based. This is usually a point to point link between an active base station and a mobile station. Technologies like Opportunity Driven Multiple Access (ODMA) may have flexibility regarding which devices serve in which roles. Some types of wireless connections possess the ability to broadcast or multicast.

Multiple links can be created in limited spectrum through FDMA, TDMA, or SDMA. Some advanced forms of transmission multiplexing combine frequency and time division approaches like OFDM or CDMA.

Data Link Layer

The data link layer in a air interface is often divided farther than the simple Media access control (MAC) and Logical link control (LLC) sublayers found in other OSI terminology. While the MAC sublayer is generally unmodified, the LLC sublayer is subdivided into two or more additional sublayers depending on the standard. Common sublayers include;

• Radio Link Control (RLC)
• Packet Data Convergence Protocol (PDCP)
• Radio Resource Control (RRC)

Standards

• GSM/UMTS
• various UTRA