Femtocells have been introduced as a solution to poor indoor coverage in cellular communication which has hugely attracted network operators and stakeholders. However, femtocells are designed to co-exist alongside macrocells providing improved spatial frequency reuse and higher spectrum efficiency to name a few. Therefore, when deployed in the two-tier architecture with macrocells, it is necessary to mitigate the inherent co-tier and cross-tier interference. The integration of cognitive radio (CR) in femtocells introduces the ability of femtocells to dynamically adapt to varying network conditions through learning and reasoning. This research work focuses on the exploitation of cognitive radio in femtocells to mitigate the mutual interference caused in the two-tier architecture. The research work presents original contributions in mitigating interference in femtocells by introducing practical approaches which comprises a power control scheme where femtocells adaptively controls its transmit power levels to reduce the interference it causes in a network. This is especially useful since femtocells are user deployed as this seeks to mitigate interference based on their blind placement in an indoor environment. Hybrid interference mitigation schemes which combine power control and resource/scheduling are also implemented. In a joint threshold power based admittance and contention free resource allocation scheme, the mutual interference between a Femtocell Access Point (FAP) and close-by User Equipments (UE) is mitigated based on admittance. Also, a hybrid scheme where FAPs opportunistically use Resource Blocks (RB) of Macrocell User Equipments (MUE) based on its traffic load use is also employed. Simulation analysis present improvements when these schemes are applied with emphasis in Long Term Evolution (LTE) networks especially in terms of Signal to Interference plus Noise Ratio (SINR).

The wireless networks of the future are likely to be tiered, i.e., a heterogeneous mixture of overlaid networks that have different power, spectrum, hardware, coverage, mobility, complexity, and technology requirements. The focus of this dissertation is to improve the performance and increase the throughput of tiered networks with resource/interference management methods, node densification schemes, and transceiver designs; with their applications to advanced tiered network structures such as heterogeneous networks (i.e., picocells, femtocells, relay nodes, and distributed antenna systems), device-to-device (D2D) networks, and aeronautical communication networks (ACN). Over the last few decades, there has been an incredible increase in the demand for wireless services in various applications in the entire world. This increase leads to the emergence of a number of advanced wireless systems and networks whose common goal is to provide a very high data rate to countless users and applications. With the traditional macrocellular network architectures, it will be extremely challenging to meet such demand for high data rates in the upcoming years. Therefore, a mixture of different capability networks has started being built in a tiered manner. While the number and capabilities of networks are increasing to satisfy higher requirements; Modeling, managing, and maintaining the entire structure has become more challenging. The capacity of wireless networks has increased with various different advanced technologies/methodologies between 1950-2000 which can be summarized under three main titles: spectrum increase (x25), spectrum efficiency increase (x25), and network density (spectrum reuse) increase (x1600). It is vital to note that among different schemes, the most important gain is explored with increasing the reuse and adding more nodes/cells into the system, which will be the focus of this dissertation. Increasing the reuse by adding nodes into the network in an uncoordinated (irregular in terms of power, spectrum, hardware, coverage, mobility, complexity, and technology) manner brought up heterogeneity to the traditional wireless networks: multi-tier resource management problems in uncoordinated interference environments. In this study, we present novel resource/interference management methods, node densification schemes, and transceiver designs to improve the performance of tiered networks; and apply our methodologies to heterogeneous networks, D2D networks, and ACN. The focus and the contributions of this research involve the following perspectives: 1. Resource Management in Tiered Networks: Providing a fairness metric for tiered networks and developing spectrum allocation models for heterogeneous network structures. 2. Network Densification in Tiered Networks: Providing the signal to interference plus noise ratio (SINR) and transmit power distributions of D2D networks for network density selection criteria, and developing gateway scheduling algorithms for dense tiered networks. 3. Mobility in Tiered Networks: Investigation of mobility in a two-tier ACN, and providing novel transceiver structures for high data rate, high mobility ACN to mitigate the effect of Doppler.