s them into a user data stream. Because of this, the traffic on the BS approach links is multiplied, as compared with the original user information. If the same configuration is adopted in the 4G RAN, in which the handover may occur more frequently, the load on both the approach links and the RNC signal processing equipment will be heavier, thereby causing a serious cost increase in the RAN. The RAN structure proposed for the 4G RAN is a cluster cellular RAN, as shown in Figure 5.7. In this configuration, BSs are grouped into a 'cluster' and there is a 'cluster head' BS connected to the CN. BSs in a cluster are linked to each other by a kind of local area network (LAN). RNC functions are distributed to each BS. Distributed Base Station Control In order to reduce the load on both the approach links and signal processing on specific equipment, most of the layer 1 signal processing control is distributed among the BSs. The uplink signal is received by Fourth Generation Mobile Networks multiple BSs (slave BSs) and then the received signal is forwarded to one of the BSs that process the uplink signal as a temporal agent (master BS). As the MT moves, the role of the master BS (the temporal agent) is passed to an adjacent BS, and as a result some BSs are newly incorporated into the group and some are removed from the group. Thus, the BS communicating with an MT forms a kind of 'virtual BS' represented by the master BS. If the received layer 1 signals are transferred only within the cluster, diversity handover control is closed within the cluster, but if they are transferred by IP packets and the BSs work as a router, then the diversity handover can be carried out independently of the cluster. Downlink packet signals are multicasted from the cluster head BS to the other BSs in the cluster. Multihopping Wireless Connections The approach links in the present RANs are constructed both of optical fibre and radio links, and radio media are preferred as link transmission media from the viewpoint of system cost. The 4G RAN is e