Performance Evaluation of Heterogeneous Networks Schemes in LTE Networks Husam Eldin Elfadil, Mohammed Adil Ibrahim Ali, Mohammed Abas Department of Electrical and Electronic Engineering University of Khartoum Khartoum, Sudan Abstract— 3GPP Long Term Evolution (LTE) is a standard for wireless communications to achieve high spectral efficiency, high peak data rates, as well as flexibility in frequency and bandwidth. By using frequency reuse of one in LTE networks, high spectral efficiency is achieved. However, the Inter-Cell Interference (ICI) resulted from the frequency reuse of one is a main limitation in these networks. Heterogeneous Networks (HetNets) has been proposed as an Inter-Cell Interference Coordination (ICIC) technique in Orthogonal Frequency Division Multiple Access (OFDMA) based LTE networks. HetNets use different size of eNodeBs in each cell in such a way cell-edge throughput is increased. This paper focuses on evaluating a number of HetNet schemes. A broad comparison among different schemes is performed by using a proposed mechanism which depends on Monte Carlo simulations. Simulation results show that that cell-edge throughput can be increased but only at certain bandwidth division schemes between Macro and Pico nodes. However, the throughput can further increase by using Almost Blank Sub-frames (ABS), in which only the Pico nodes transmit data. Keywords—heterogeneous networks (HetNets); inter-cell interference coordination (ICIC); orthogonal frequency-division multiple access (OFDMA); long term evolutin (LTE) I. INTRODUCTION Initial deployments of LTE networks are based on so-called homogeneous networks consisting of base stations providing basic coverage (called macro base stations). The concept of heterogeneous networks has recently attracted considerable attention to optimize performance particularly for unequal user or traffic distribution. Here, the layer of planned high-power macro eNBs is overlaid with layers of lower-power eNBs that are deployed in a less well planned or even entirely uncoordinated manner. Such deployments can achieve significantly improved overall capacity and cell-edge performance and are often seen as the second phase in LTE network deployment [1]. Heterogeneous network planning was already used in GSM. The large and small cells in GSM are separated through the use of different frequencies. This solution is still possible in LTE. However, LTE networks mainly use a frequency reuse of one to maximize utilization of the licensed bandwidth. In heterogeneous networks the cells of different sizes are referred to as macro-, micro-, pico- and femto-cells; listed in order of decreasing base station power as shown in Table I. The actual cell size depends not only on the eNB power but also on antenna position, as well as the location environment; e.g. rural or city, indoor or outdoor. The HeNB (Home eNB) was introduced in LTE Release 9 (R9). TABLE I. TRANSMIT POWER AND COVERAGE FOR DIFFERENT TYPES OF NODES Type of nodes Transmit Power Coverage Macro cell 46 dBm Few km Pico cell 23 – 30 dBm < 300 m Femto cell < 23 dBm < 50 m Relay 30 dBm 300m RRH 46 dBm Few km A Pico base station has a comparably low transmit power, e.g. 1 W compared to 40 W of a macro base station. Additionally, Pico antennas have a lower gain compared to macro antennas and they are mounted lower than macro antennas which results in a higher path loss. Due to these reasons the footprint of a Pico cell is much smaller compared to the footprint of a macro cell. However, in most cases the same amount of bandwidth is used for Pico and Macro cells yielding an inhomogeneous distribution of network capacity: A low number of Pico users share the same amount of resources as the high number of macro users leading to unfairness with respect to the resources available for Macro and Pico users. Also, Macro UEs at the edge of Pico cell will cause serious uplink interference to Pico due to its high transmit power according to long distance from Macro cell. In order to offload more traffic from overloaded Macro and reduce uplink interference, Cell Range Expansion (CRE) scheme has been introduced in LTE-A [2]. In homogeneous networks the User Equipment (UE) normally access to the cell with the strongest received Down Link signal (SSDL), hence the border between two cells is located at the point where (SSDL) is the same in both cells, this also typically coincides with the point of equal Path Loss for the Up Link (PLUL) in both cells. But in a heterogeneous network as shown in Fig. 1, with high-power nodes in the large cells and low-power nodes in the