Node-B

The Node-B is physical unit of radio transmission/reception with cells. It can support both TDD and FDD modes and can be colocated with GSM BTS to reduce implementation costs. It connects to UE via Uu W-CDMA radio interface and RNC via Iub ATM interface. The figure 3.3 below shows the Node B connected to UE and RNC.

The main task of Node B is the conversion to and from the Uu radio interface, including forward error correction (FEC), rate adaptation, W-CDMA spreading/despreading, and quadrature phase shift keying (QPSK) modulation on the air interface. It measures quality and strength of the connection and determines the frame error rate (FER), transmitting these data to the RNC as a measurement report for Handover and macro diversity combining. The Node B is also responsible for the FDD softer Handover. This micro diversity combining is carried out independently, eliminating the need for additional transmission capacity in the Iub.
The Node B also participates in power control, as it enables the UE to adjust its power using down-link (DL) transmission power control (TPC) commands via the inner-loop power control on the basis of up link (UL) TPC information. The predefined values for inner-loop power control are derived from the RNC via outer-loop power control.