Interference management and system optimisation for Femtocells technology in LTE and future 4G/5G networks

Femtocells are seen to be the future of Long Term Evaluation (LTE) networks to improve the performance of indoor, outdoor and cell edge User Equipments (UEs). These small cells work efficiently in areas that suffer from high penetration loss and path-loss to improve the coverage area. It is said that 30% of total served UEs in LTE networks are vehicular, which poses challenges in LTE networks due to their high mobility, high vehicular penetration loss (VPL), high path loss and high interference. Therefore, self-optimising and dynamic solutions are required to incorporate more intelligence into the current standard of LTE system. This makes the network more adaptive, able to handle peak data demands and cope with the increasing capacity for vehicular UEs. This research has drawn a performance comparison between vehicular UEs who are served by Mobile-Femto, Fixed-Femto and eNB under different VPL scales that range between highs and lows e.g. 0dB, 25dB and 40dB. Deploying Mobile-Femto under high VPLs has improved the vehicular UE Ergodic capacity by 1% and 5% under 25dB and 40dB VPL respectively as compared to other eNB technologies. A noticeable improvement is also seen in signal strength, throughput and spectral efficiency. Furthermore, this research discusses the co-channel interference between the eNB and the Mobile-Femto as both share the same resources and bandwidth. This has created an interference issue from the downlink signals of each other to their UEs. There were no previous solutions that worked efficiently in cases where UEs and base stations are mobile. Therefore, this research has adapted an efficient frequency reuse scheme that worked dynamically over distance and achieved improved results in the signal strength and throughput of Macro and Mobile-Femto UE as compared to previous interference management schemes e.g. Fractional Frequency Reuse factor1 (NoFFR-3) and Fractional Frequency Reuse factor3 (FFR-3). Also, the achieved results show that implementing the proposed handover scheme together with the Mobile-Femto deployment has reduced the dropped calls probability by 7% and the blocked calls probability by 14% compared to the direct transmission from the eNB. Furthermore, the outage signal probabilities under different VPLs have been reduced by 1.8% and 2% when the VPLs are 25dB and 40dB respectively compared to other eNB technologies

Data Traffic Analysis and Small Cell Deployment in Cellular Networks

In this thesis, the study of small cell deployment in heterogeneous networks is presented. The research work can be divided into three aspects. The first part is user data traffic analysis for an existing 3G network in London. The second part is the deployment of additional small cells on top of existing heterogeneous networks. The third part is small cell deployment based on stochastic geometry analysis of heterogeneous networks. In the first part, an analysis of 3G network user downlink data traffic is presented. With the increasing demands for high data rate and energy-efficient cellular service, it is important to understand how cellular user data traffic changes over time and in space. A statistical model of time-varying throughput per cell and the distribution of instantaneous throughput per cell over different cells based on throughput measurements from a real-world large-scale urban cellular network are provided. The model can generate network traffic data that are very close to the measured traffic and can be used in simulations of large-scale urban-area mobile networks. In the second part of the work, three different small-cell deployment strategies are proposed. As the mobile data demand keeps growing, an existing heterogeneous network composed of macrocells and small cells may still face the problem of not being able to provide sufficient capacity for unexpected but reoccurring hot spots. The proposed strategies avoid replanning the overall network while fulfilling the hot spot demand by optimizing the deployment of additional mobile small cells on top of the existing HetNet. By simplified the optimization problem, we first proposed a fixed number deployment algorithm and then extend it into deployment over existing network algorithm to solve the joint optimization problem. The simulation results show that these two proposed algorithms require less small cells to be deployed while providing higher minimum user throughput. Moreover, a reduced-complexity iterative algorithm is proposed. The simulation results show that it significantly outperforms the random deployment of new small cells and achieves performance very close to numerically solving the joint optimization in terms of minimum user throughput and required number of new small cells, especially for a large number of unexpected hot-spot users. In the third part, a stochastic geometry analysis is provided for a heterogeneous network affected by a large hot spot. Based on the analysis, the optimal numbers of additional small cells required in the HS and non-HS areas are obtained by minimizing the difference between the numbers of macrocell users after and before the HS occurs. Then an algorithm is proposed to maximize the average user throughput by jointly optimizing the locations of additional small cells and user associations of all cells. Simulation results show that the proposed algorithm can maintain the average user throughput above a threshold with excellent fairness among all users even for a very high density of HS users

Localization and mobility management in heterogeneous wireless networks with network-assistance

The nowadays heterogeneous wireless network (HWN) is a collection of ubiquitous wireless networking elements (WNEs) that support diverse functional capabilities and networking purposes. In such a heterogeneous networking environment, localization and mobility management will play a key role for the seamless support of emerging applications, such as social networking, massive multiplayer online gaming, device-todevice (D2D) communications, smart metering, first-responder communications, and unsupervised navigation of communication-aware robotic nodes. Since most of the existing wireless networking technologies enable the WNEs to assess their current radio status and directly (or indirectly) estimate their relative distance and angle with respect to other WNEs of the same Radio Access Technology (RAT), the integration of such information from the ubiquitous WNEs arises as a natural solution for robustly handling localization between (not necessarily homogeneous) WNEs and mobility management of moving WNEs governed by resource-constrained operation. Under the viewpoint of investigating how the utilization of such spatial information can be used to enhance the performance of localization and mobility management in the nowadays HWN, in this work we focus and contribute in the following four research areas: i) localization and peer-discovery between non-homogeneous WNEs, ii) network-assisted D2D discovery in cellular networks, iii) energy-efficient handover (HO) decision in the macrocell – femtocell network, and iv) network-assisted vertical handover decision (VHO) for the integrated cellular and WLAN heterogeneous wireless network

D13.1 Fundamental issues on energy- and bandwidth-efficient communications and networking

Deliverable D13.1 del projecte europeu NEWCOM#The report presents the current status in the research area of energy- and bandwidth-efficient communications and networking and highlights the fundamental issues still open for further investigation. Furthermore, the report presents the Joint Research Activities (JRAs) which will be performed within WP1.3. For each activity there is the description, the identification of the adherence with the identified fundamental open issues, a presentation of the initial results, and a roadmap for the planned joint research work in each topic.Preprin

Femtocell exclusion regions in hierarchical 3-sector macrocells for co-channel deployments

In co-channel deployments of macro and femto cells, the much higher transmit power of a macrocell base station (MBS) than that of a femtocell access point (FAP) may create a femtocell exclusion region (FER) around an MBS, where reliable femto downlink (DL) services cannot be guaranteed. In this paper, we analyze the DL outage probability (OP) of orthogonal frequency division multiple access (OFDMA) based femtocells in terms of their locations with respect to nearby 3-sector MBSs, and derive the expression of FER radius as a function of the azimuth angle relative to the MBS, which can be directly used to divide the macrocell coverage area into inner and outer regions for hybrid frequency assignments. Simulation results show that the obtained closed-form expressions can be used to accurately predict the location-dependent femto DL OP and the non-circular FER in hierarchical 3-sector macrocells. Our results also show that the FER shrinks at edges between macro sectors, giving more space for co-channel deployment of femtocells to improve spatial reuse. © 2012 IEEE