4.7 Mobility Management and Power Optimization
After the major LTE procedures have been introduced in the previous sections, the following sections now take a look at the general mobility management and power consumption optimization functionality. LTE knows two general activity states for mobile devices. These are the RRC Connected state and the RRC Idle state. This state model is much simpler than the one used in UMTS, which has many more states such as Cell-DCH, Cell-FACH, Cell-PCH, URA-PCH and Idle.
4.7.1 Mobility Management in Connected State
While the mobile device is in RRC Connected state, it is usually fully synchronized with the network in the uplink and the downlink directions and can hence transmit and receive data at any time. While the mobile device is in this state, a user data tunnel is established on the S1 interface between the eNode-B and the serving-GW and another tunnel is established between the serving-GW and the PDN-GW. Data arriving for the mobile device can be immediately forwarded to the device. Data waiting to be transmitted in the uplink direction can also be sent immediately, either over continuously allocated resource blocks on the uplink shared channel or, during times of lower activities, after a quick scheduling request via the uplink control channel. Furthermore, the mobile device actively monitors the signal quality of the serving cell and the signal quality of neighboring cells and reports the measurements to the network. The network can then ...