backhauling, which consumes valuable radio resources and may cause additional interference and latency. Recall that a UDN is a densified HetNet. The user association in HetNets follows a load-based association rule, where the users are biased to connect to the nearest small cell to offload their traffic. The small cells are usually lightly loaded due to the limited coverage area; hence, the association of a given user to the nearest small cell gives the user a higher data rate privilege. The biasing of users to small cells is performed via virtual extension of their coverage area. Interference management is a challenging task in densified networks. Various types of small cells are deployed with large densities to provide the users with very high throughput con- nections. The use of inter-cell coordination to mitigate the interference requires increasing sig- naling overhead due to the large number of deployed small cells. Thus, distributed control is preferred to mitigate the interference in a UDN. A UDN can be defined as a network where there are more cells than active users. In mathe- matical terms, PBS Puser' where PBS denotes the area density of access nodes and Puser denotes the area density of users. Another definition of UDN can be solely given in terms of the access node density irrespective of the user density. The access nodes in UDN envir- onments are typically low-power small cells with a small footprint, resulting in a small COV- erage area. Accordingly, the inter-site distance would be in the range of meters or tens of meters. Strong interference between neighboring cells is a limiting factor in UDN. The 56 Chapter 1 proximity of the small cells to each other in a UDN environment causes strong interference, thus the use of effective interference management schemes is inevitable to mitigate the interference of neighboring cells. Densification of wireless networks can be realized either by deploying an increasing number of access nodes or by increasing the number of links per unit area. In the first a