PROTOCOL ARCHITECTURE WCDMA

 shows the air interface protocol architecture. The protocol architecture is similar to the current ITU-R protocol architecture, ITU-R M.1035. The air interface is layered into three protocol layers:

·          The physical layer (layer 1, L1);

·          The data link layer (layer 2, L2);

·          Network layer (layer 3, L3).

The physical layer interfaces the medium access control (MAC) sublayer of layer 2 and the radio resource control (RRC) layer of layer 3. The physical layer offers different transport channels to MAC. A transport channel is characterized by how the information is transferred over the radio interface. Transport channels are channel coded and then mapped to the physical channels specified in the physical layer. MAC offers

different logical channels to the radio link control (RLC) sublayer of layer 2. A logical channel is characterized by the type of information transferred. Layer 2 is split into following sublayers: MAC, RLC, packet data convergence protocol (PDCP) and broadcast/multicast control (BMC). Layer 3 and RLC are divided into control and user planes. PDCP and BMC exist in the user plane only. In the control plane, layer 3 is partitioned into sublayers where the lowest sublayer, denoted as RRC, interfaces with layer 2. The RLC sublayer provides ARQ functionality closely coupled with the radio transmission technique used.