Radio Resource Management in Multi-Tier Cellular Wireless Networks

CHAPTER 2

RESOURCE ALLOCATION APPROACHES IN MULTI-TIER NETWORKS

2.1 INTRODUCTION

In a two-tier macrocell–femtocell network, femtocells are deployed over the existing macrocell network and share the same frequency spectrum with macrocells. Due to spectral scarcity, the femtocells and macrocells have to reuse the total allocated frequency band partially or totally which leads to cross-tier or co-channel interference. At the same time, in order to guarantee the required QoS to the macro users, femtocells should occupy as little bandwidth as possible that leads to co-tier interference. As a result, the throughput of the network will decrease substantially due to such co-tier interference and CTI. In addition, severe interference may lead to “deadzones,” that is, areas where the QoS degrades significantly. The deadzones are created due to asymmetric levels of transmission power within the network and the distance between macrocell UE and macrocell base station. For example, a macrocell UE located at a cell edge and transmitting at a high power will create a deadzone to the nearby femtocell UL transmission due to co-channel interference. On the other hand, in the DL transmission, due to high path-loss and shadowing, a cell-edge macrocell UE may experience severe co-channel interference from the nearby femtocells. Thus, it is essential to adopt an effective and robust interference management scheme that would mitigate the co-tier interference and reduce the CTI substantially in order ...