Radio Resource Management in Multi-Tier Cellular Wireless Networks

CHAPTER 6

CALL ADMISSION CONTROL IN FRACTIONAL FREQUENCY REUSE-BASED TWO-TIER NETWORKS

In a cellular network, CAC is responsible for admission or rejection of an incoming request from a UE into the network based on some predefined criteria while taking the network load conditions and QoS requirements of both incoming and existing users into account. To enable spectrum sharing between macrocells and small cells in OFDMA-based two-tier networks, one of the three access modes, namely, open, closed and hybrid access, can be employed. In the open access mode, the MUEs are allowed to connect to either their own macrocell base stations (MBSs) or SBSs. In contrast, in the closed access mode, in a two-tier macrocell–femtocell network, for example, only certain users (subscribers) belonging to the so-called Closed Subscriber Group (CSG) are allowed to connect to each FBS. For a typical hybrid access scheme, limited spectrum access at each small cell is granted for MUEs, which wish to establish connections. An efficient CAC policy is required in this case to coordinate spectrum sharing and admission control for both types of users, which should strike a balance between achieving high spectrum utilization and protecting QoS requirements for small cell users. Note that in this case both the connection-level QoS measures at the network layer (e.g., connection blocking and connection dropping probabilities) and the packet-level QoS measures (e.g., packet error rate and packet throughput) at ...