nts, uses the knowledge for scheduling, and tells its UL decision (PhyMode and power) to the UT (see Figure 8.14 for the MSC). The CQI handler in the BS keeps all information of DL and UL channel qual- ity (CQ). In regular intervals, the UT sends DL-CQI measurements and uplink resource requests (UL-RREQs). Resources are granted in the DL-MAP and UL-MAP, together with commands concerning which power and PhyMode to use on the uplink. 8.4.11 Routing Because fixed relay infrastructures do not have an ad hoc or mesh component, the interconnection graph is a tree, SO routing is not an issue and is easily performed in the BS. Tables in the BS know the location of a destination MAC address and the RN that is responsible for it. © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology Measurement control Packet data Packet data packet data UL resource grants Measurement report Handover request HO decision Handover announce Handover request ACK Handover command Packet data Deliver buffered Detach from RN1 packets to target Buffer packets DL data forward Buffer packets from source Association request (UL resource request) Association request Association ACK Association ACK (UL resource grant) Release resources Packet data Packet data Figure 8.13 Message sequence chart for a network-initiated handover between relays RN1 and RN2. © 2009 by Taylor & Francis Group, LLC Multihop Extensions to Cellular Networks DL-Traffic DL-MAP DL-DATA DL-CQI DL-MAP DL-DATA UL-Traffic UL_RREQ Handler UL_RREQ UL-MAP UL-MAP UL-DATA UL-DATA Figure 8.14 Message sequence chart for the CQI over a multihop link. 8.4.12 Intercell Interference Mitigation Radio cells have a frequency repetition factor (also called cluster order) that speci- fies the density of cells operating on the same frequency band. For LTE, it is often assumed that there is no frequency reuse distance, SO all cells have the same fre- quency band. In any case, all cells using the same frequency band interfere with each other. This is especially