tem, respectively. As it can be seen in the figure, the SINR deteriorates more rapidly in the reuse-1 system, leaving a shorter time for the execution of the handover (~300 ms in the reuse-1 case and several seconds in the reuse-3 case). A fast handover execution is not only needed to combat the rapid change of link quality but also is important from the user-perceived performance point of view. This means that, in order to achieve good handover performance from a radio efficiency and also from a user-perceived quality point of view, it is required to have low interruption time and no user data packet losses during the handover. In order to meet these requirements, the following handover procedure is used in LTE, as illustrated in Figure 4.8. Without discussing all details of the procedure, we would like to point out a few important aspects to observe. After the decision for a handover has been made in the © 2009 by Taylor & Francis Group, LLC Architecture and Protocol Support for RRM Source Target eNode B eNode B UL/DL data Measurement reports Handover decision Handover request Admission decision Handover request ack Handover command Detach from source cell Start data forwarding access to target cell Forwarding of data SN status transfer Random access UL grant Handover complete Path switch request Start of UL/DL data Update bearer request UL/DL data Update bearer response Path switch request ack Release resources Release resources finish forwarding Last packet on forwarding path Figure 4.8 Handover message sequence. source eNode B, it signals to the selected target eNode B and requests the reserva- tion of resources. If the admission decision has passed successfully in the target, the target eNode B prepares a transparent container (which is for interpretation only for the UE, including necessary information for the UE to access the target cell) and sends it back to the source eNode B in the handover request acknowledge mes- sage. Next, the source eNode B can command the UE to execute the handover and at the sam