3.5 The UMTS Terrestrial Radio Access Network (UTRAN)
3.5.1 Node-B, Iub Interface, NBAP and FP
The base station, called Node-B in the 3GPP standards, is responsible for all functions required for sending and receiving data over the air interface. This includes, as shown in Section 3.3, channel coding, spreading and despreading of outgoing and incoming frames as well as modulation. Furthermore, the Node-B is also responsible for the power control of all connections. The Node-B just receives a transmission quality target from the RNC for each connection and then decides on its own if it is necessary to increase or decrease the transmission power in both uplink and downlink directions to meet the target.
Size and capacity of a Node-B are variable. For locations with a high number of data and voice calls, the Node-B is used in a sectorized configuration. This means that the 360 degrees coverage area of a Node-B is divided into several independent cells, each covering a certain area. Each cell has its own Cell-ID, scrambling code and OVSF tree. Each cell also uses its own directional antennas, which cover either 180 degrees (2 sector configuration) or 120 degrees (3 sector configuration). The capacity of the Iub interface, which connects the Node-B to an RNC, depends mainly on the number of sectors of the Node-B.
While GSM only uses some of the 64 kbit/s timeslots on an E-1 link to the base station, UMTS base stations require a much higher bandwidth. To deliver high datarates, Node-Bs ...