The demand for higher data rates for indoor and cell-edge users led to evolution of small cells. LTE femtocells, one of the small cell categories, are low-power low-cost mobile base stations, which are deployed within the coverage area of the traditional macro base station. The cross-tier and co-tier interferences occur only when the macrocell and femtocell share the same frequency channels. Open access (OSG), closed access (CSG), and hybrid access are the three existing access-control methods that decide users' connectivity to the femtocell access point (FAP). We define a network performance function, network productivity, to measure the traffic that is carried successfully. In this dissertation, we evaluate call mobility in LTE integrated network and determine optimized network productivity with variable call arrival rate in given LTE deployment with femtocell access modes (OSG, CSG, HYBRID) for a given call blocking vector. The solution to the optimization is maximum network productivity and call arrival rates for all cells. In the second scenario, we evaluate call mobility in LTE integrated network with increasing femtocells and maximize network productivity with variable femtocells distribution per macrocell with constant call arrival rate in uniform LTE deployment with femtocell access modes (OSG, CSG, HYBRID) for a given call blocking vector. The solution to the optimization is maximum network productivity and call arrival rates for all cells for network deployment where peak productivity is identified. We analyze the effects of call mobility on network productivity by simulating low, high, and no mobility scenarios and study the impact based on offered load, handover traffic and blocking probabilities. Finally, we evaluate and optimize performance of fractional frequency reuse (FFR) mechanism and study the impact of proposed metric weighted user satisfaction with sectorized FFR configuration.

Femtocell is a small cellular base station used by operators to extend indoor service coverage and enhance overall network performance. In Long Term Evolution (LTE), femtocell works under macrocell coverage and combines with the macrocell to constitute the two-tier network. Compared to the traditional single-tier network, the two-tier scenario creates many new challenges, which lead to the 3rd Generation Partnership Project (3GPP) implementing an automation technology called Self-Organising Network (SON) in order to achieve lower cost and enhanced network performance. This thesis focuses on the inbound and outbound handovers (handover between femtocell and macrocell); in detail, it provides suitable solutions for the intensity of femtocell handover prediction, Physical Cell Identity (PCI) allocation and handover triggering parameter optimisation. Moreover, those solutions are implemented in the structure of SON. In order to e ciently manage radio resource allocation, this research investigates the conventional UE-based prediction model and proposes a cell-based prediction model to predict the intensity of a femtocell's handover, which overcomes the drawbacks of the conventional models in the two-tier scenario. Then, the predictor is used in the proposed dynamic group PCI allocation approach in order to solve the problem of PCI allocation for the femtocells. In addition, based on SON, this approach is implemented in the structure of a centralised Automated Con guration of Physical Cell Identity (ACPCI). It overcomes the drawbacks of the conventional method by reducing inbound handover failure of Cell Global Identity (CGI). This thesis also tackles optimisation of the handover triggering parameters to minimise handover failure. A dynamic hysteresis-adjusting approach for each User Equipment (UE) is proposed, using received average Reference Signal-Signal to Interference plus Noise Ratio (RS-SINR) of the UE as a criterion. Furthermore, based on SON, this approach is implemented in the structure of hybrid Mobility Robustness Optimisation (MRO). It is able to off er the unique optimised hysteresis value to the individual UE in the network. In order to evaluate the performance of the proposed approach against existing methods, a System Level Simulation (SLS) tool, provided by the Centre for Wireless Network Design (CWiND) research group, is utilised, which models the structure of two-tier communication of LTE femtocell-based networks.

In this thesis, our objective is to improve the energy efficiency and load balance for wireless networks. We first study the relationships between the base station (BS) on/off operation and traffic distribution. A cooperative power saving method called clustering BS-off (CBSO) scheme is proposed. Instead of adopting a unified and consistent BS-off scheme in the whole network, the proposed centralized and distributed CBSO schemes can adaptively group BSs in several clusters based on the traffic fluctuations with space and time. Second, to further improve the network load balance and energy efficiency in distributed manner, we propose a power efficient self-organized virtual small networking (VSN) protocol. A heuristic firefly algorithm is applied to arrange the BSs' operation in small groups based on the traffic level. By jointly considering the load balance, the effectiveness of the proposed algorithm is demonstrated based on the average and min-max traffic levels of BSs' groups. Finally, the importance of detailed BS operation between active and sleep modes is considered. The operating procedure of femtocell base station, i.e., HeNB, is modeled as an MAP/PH/1/k queueing system. Such queueing analysis particularly focuses on the HeNB vacation process with user priorities. The HeNB's power on/off scheme is modeled as alternative service and vacation periods. The hybrid access is regarded as high and low priority users in the queuing system. We further propose the adaptive service rate and vacation length (ASV) method, so that the HeNB can work in a more energy-efficient way while satisfying QoS requirements such as blocking probability and users waiting time. Simulation results show the effectiveness of the proposed strategies and the overall network energy efficiency can be improved significantly. / October 2016

<p>The new mobile standard Long Term Evolution delivers high data rates, small delay and a more efficiently utilized RF spectrum. A solution to maintain this performance in user dense areas or areas with bad reception is the deployment of so-called femtocells. Femtocells are small base stations that are deployed indoors and share the RF spectrum with the whole mobile network. The idea is that femtocells will increase mobile operators network coverage and capacity while it at the same time increase users data throughput. There are several challenges with femtocells, both technical and economical ones. The most debated issues is how femtocells should schedule users while operating in an environment where other femtocells and base stations are interfering. In this work we developed a simulation tool to simulate the scheduling interaction between femtocells and base stationsin order to show the performance of radio resource schedulers. This rapport also aims to evaluate an approach to a femtocell scheduler to solve this issue in a satisfying way. The report gives a description of the structure of the implemented simulation tool together with some reflections on how future designs of similar or more complex simulation environments could be done.</p>

This thesis studies cooperative techniques that rely on femtocell user diversity to improve the downlink communication quality of macrocell users. We analytically analyze and evaluate the achievable performance of these techniques in the downlink of Rayleigh fading channels. We provide an approximation of both the bit-error rate (BER) and the data throughput that macrocell users receive with femtocell user cooperation. Using simulations, we show that under reasonable SNR values, cooperative schemes enhance the performances of macrocells by improving the BER, outage probability, and data throughput of macrocell users significantly when compared with the traditional, non-cooperative schemes. / Graduation date: 2012

The new mobile standard Long Term Evolution delivers high data rates, small delay and a more efficiently utilized RF spectrum. A solution to maintain this performance in user dense areas or areas with bad reception is the deployment of so-called femtocells. Femtocells are small base stations that are deployed indoors and share the RF spectrum with the whole mobile network. The idea is that femtocells will increase mobile operators network coverage and capacity while it at the same time increase users data throughput. There are several challenges with femtocells, both technical and economical ones. The most debated issues is how femtocells should schedule users while operating in an environment where other femtocells and base stations are interfering. In this work we developed a simulation tool to simulate the scheduling interaction between femtocells and base stationsin order to show the performance of radio resource schedulers. This rapport also aims to evaluate an approach to a femtocell scheduler to solve this issue in a satisfying way. The report gives a description of the structure of the implemented simulation tool together with some reflections on how future designs of similar or more complex simulation environments could be done.

H υποστήριξη της τεχνολογίας των femtocells, σε περιβάλλον Long Term Evolution Advanced (LTE-A), δίνει ώθηση στο δυναμικό ερευνητικά πεδίο των ετερογενών δικτύων. Αν και προσφέρουν πολλαπλά πλεονεκτήματα, η συνύπαρξη ετερογενών σταθμών βάσεων δημιουργεί και μια σειρά τεχνικών προκλήσεων, με κυριότερη τη δημιουργία παρεμβολών που έχουν ως αποτέλεσμα την υποβάθμιση των παρεχόμενων υπηρεσιών. Στα πλαίσια της εργασίας αυτής παρουσιάζονται και αναλύονται μέθοδοι διαχείρισης ισχύος και κατανομής συχνοτήτων για την ακύρωση παρεμβολών, και αναπτύσσεται και προτείνεται ένα περιβάλλον προσομοίωσης ετερογενών LTE-A δικτύων. Ο προσομοιωτής επιτρέπει τη δημιουργία δισδιάστατης τοπολογίας με παράταξη femtocells πάνω από macrocell δίκτυο σε γραφικό περιβάλλον, την εξομοίωση των συνακόλουθων φαινομένων παρεμβολών και την πρόβλεψη και σύγκριση της απόδοσης του δικτύου μετά από την εφαρμογή διαφορετικών μοντέλων διαχείρισης ισχύος και σχημάτων κατανομής συχνοτήτων για την εξάλειψη των παρεμβολών. / Femtocells technology support, in Long Term Evolution Advanced (LTE-A) environments, promotes the dynamic research on the field of heterogeneous networks. While offering many advantages, the coexistence of heterogeneous base stations creates a number of technical challenges, the main of which is interference phenomena that lead to the degradation of service. In this work, we present and analyze methods of power management and frequency allocation for interference cancellation, and develop and propose a simulation environment for heterogeneous LTE-A networks. The simulator allows the creation of 2-D topologies with femtocells deployments over macrocell networks, the simulation of the resulting interference phenomena and the prediction and comparison of the network's performance after the application of different models of power management and frequency allocation schemes for interference cancellation.

Femto access points (FAP) are low-power cellular base stations that are designed to be autonomously deployed by customers indoors. Due to spectral scarcity, FAPs are expected to share spectrum with underlying macrocells. Closed access refers to the strategy where only Owners of the FAP are allowed access; whereas the FAP is open to everyone under Open access. Challenges such as dead zones or excessive signaling arise when implementing these two access strategies. Cognitive ac¬¬cess control is a hybrid approach that would have the FAP first senses the environment, prioritizes different classes of users, and then reserves a portion of femtocell radio resource for Owners while distributing the remaining to Visitors. Simulation results have shown that by utilizing the proposed Cognitive access control and reserve resource dynamically with the surrounding environment, both Macro-user and Owner throughputs will improve over the macrocell-only baseline, as well as both Closed and Open access strategies.

Femto access points (FAP) are low-power cellular base stations that are designed to be autonomously deployed by customers indoors. Due to spectral scarcity, FAPs are expected to share spectrum with underlying macrocells. Closed access refers to the strategy where only Owners of the FAP are allowed access; whereas the FAP is open to everyone under Open access. Challenges such as dead zones or excessive signaling arise when implementing these two access strategies. Cognitive ac¬¬cess control is a hybrid approach that would have the FAP first senses the environment, prioritizes different classes of users, and then reserves a portion of femtocell radio resource for Owners while distributing the remaining to Visitors. Simulation results have shown that by utilizing the proposed Cognitive access control and reserve resource dynamically with the surrounding environment, both Macro-user and Owner throughputs will improve over the macrocell-only baseline, as well as both Closed and Open access strategies.

One of the major driving elements behind the explosive boom in wireless revolution is the advances in the field of modulation which plays a fundamental role in any communication system, and especially in cellular radio systems. Hence, the elaborate choice of an efficient modulation scheme is of paramount importance in the design and employment of any communications system. Work presented in this thesis is an investigation (study) of the feasibility of whether multilevel FSK modulation scheme would provide a viable alternative modem that can be employed in TDMA cordless communications systems. In the thesis the design and performance analysis of a non-coherent multi-level modem that offers a great deal of bandwidth efficiency and hardware simplicity is studied in detail. Simulation results demonstrate that 2RC pre-modulation filter pulse shaping with a modulation index of 0.3, and pre-detection filter normalized equivalent noise bandwidth of 1.5 are optimum system parameter values. Results reported in chapter 5 signify that an adjacent channel rejection factor of around 40 dB has been achieved at channel spacing of 1.5 times the symbol rate while the DECT system standards stipulated a much lower rejection limit criterion (25-30dB), implying that CP-QFSK modulation out-performs the conventional GMSK as it causes significantly less ACI, thus it is more spectrally efficient in a multi-channel system. However, measured system performance in terms of BER indicates that this system does not coexist well with other interferers as at delay spreads between 100ns to 200ns, which are commonly encountered in such indoor environment, a severe degradation in system performance apparently caused by multi-path fading has been noticed, and there exists a noise floor of about 40 dB, i.e. high irreducible error rate of less than 5.10-3. Implementing MRC diversity combiner and BCH codec has brought in a good gain.