ion as those collected during the drive tests with the advantage that UEs can further retrieve and report parameters from indoor environments. The home eNB (HeNB) concept was introduced in LTE Rel-9, which defines a low-power node primarily used to enhance indoor coverage. Home eNBs and particularly femtocells are privately owned and deployed without coordination with the macro-network; as such, if their operating frequency is the same as the frequency used in the macro-cells and access to them is limited, then there is a risk of interference between the femtocell and the surrounding network. The use of different cell sizes with overlapping coverage and creation of a heterogeneous network adds to the complexity of network planning. In a net- work with a frequency reuse of one, the UE normally camps on the cell with the strongest received signal power, hence the cell edge is located at a point where the received signal strengths are the same in both cells. In homogeneous network deployments, this also typi- cally coincides with the point of equal path loss of the uplink in both cells, whereas in a heterogeneous network, with high-power nodes in the large cells and low-power nodes in the small cells, the point of equal received signal strengths is not necessarily the same as that of equal uplink path loss. Therefore, a challenge in heterogeneous network planning is to ensure that the small cells actually serve certain number of users. This can be done by increasing the area served by the small cell through the use of a positive cell selection offset which is referred to as cell range extension (Fig. 1.21). A drawback of this scheme is the increased interference in the downlink experienced by the UE located in the extended cell region and served by the base station in the small cell. This effect may impact the quality of reception of the downlink control channels. It is important to high- light that indoor small cells (femtocells) operate in three different access modes: open, closed, and hybrid. In open access mode