Multi-Carrier and Spread Spectrum Systems: From OFDM and MC ...

220 ApplicationsLTECore networkWCDMA/HSPACore networkRNCRNCeNodeBNodeBeNodeBeNodeBNodeBNodeBFigure 5-3Comparison of RAN architecture between LTE and WCDMA/HSPA5.2.3 Radio Access Network (RAN) ArchitectureThe architecture of the radio access network (RAN) of LTE is shown in Figure 5-3. Forcomparison, the RAN architecture of WCDMA/HSPA is also shown in order to highlightthe differences. A significant difference between WCDMA and LTE is that LTE doesnot support macro diversity, which is the case for WCDMA/HSPA. A radio networkcontroller (RNC) is omitted with LTE, which reduces the latency in the RAN. This leadsLTE to shift more complexity into the eNodeB, which in LTE terminology refers to thebase station.Besides the physical layer processing, the LTE eNodeB has the tasks of mobility managementand radio resource management, which both belong in the WCDMA/HSPA RANto the tasks of the RNC. The eNodeBs in the LTE RAN are directly connected to eachother and the handover decisions are taken by the eNodeB. In WCDMA/HSPA this taskbelongs to the RNC.5.2.4 Radio Protocol ArchitectureThe LTE protocol stack is split into the user plane and the control plane. The user planetransports all user information from voice to data while the control plane is used only forcontrol signalling. Figure 5-4 illustrates the LTE protocol stack.All protocols shown here are located in the base station (eNodeB) and mobile terminalstation (UE) respectively. The functions of the different protocol layers are summarizedin the following.Radio Resource Control (RRC)The RRC is part of the control plane and is responsible for configuring the layer 1 andlayer 2 protocols PDCP, RLC, MAC, and PHY. The main services and functions of the