Research On Interference Characteristics And Theoretical Performances In Hierarchical Heterogeneous Wireless Networks

In order to satisfy the unrelenting wireless data demand, low power nodes (LPNs) can be deployed within the seamless coverage of the conventional macro base stations (MBSs), thus high data rate services can be provided by the heterogeneous networking of this two types of nodes. However, the frequency reuse of the MBSs and the LPNs results in severe co-channel interference, which becomes the bottleneck in the improvement of the network performance. In order to improve the performance of the hierarchical heterogeneous network, the co-channel interference should be modeled to capture the interference characteristics, and the theoretical performances in various scenarios and configurations should be evaluated, and the relevant signal processing as well as the resource management should be performed. These are challenging issues in the academic community. This dissertation studies the characteristics of topology, transmit power, node density, transmit antenna number, fading and system load, as well as the techniques of multiple antenna cooperation, interference coordination and user association, to provide insights into the cooperative interference management, resource allocation and the heterogeneous networking technologies. The main contributions of the dissertation are listed as follows:1. Research on the interference distribution in hierarchical heterogeneous wireless networksThe hierarchical heterogeneous network is considered consisting of MBSs and LPNs with full frequency reuse. The locations of the MBSs are exactly known considering the network planning of the operators, whereas the LPNs are often randomly deployed in an unplanned manner considering the traffic demand. A two-tier hierarchical heterogeneous network interference model is proposed in this dissertation, where the locations of the MBSs are deterministic and the locations of the LPNs are distributed following a Poisson point process. The interference is characterized by deriving the analytical results of the probability density functions for both the users associated with the MBSs and that associated with the LPNs, and the impact of the parameters including the transmit power, node density and pathloss exponent are evaluated. It is demonstrated by the simulation results that heavy tail property is observed for the proposed two-tier hierarchical heterogeneous network interference model.2. Differentiated channel modeling and theoretical research of hierarchical heterogeneous wireless networksThe heterogeneous network transmission links have differentiated characteristics of the small scale fading due to the deployment scenario and the heights of antennas. This dissertation focuses on the hierarchical heterogeneous scenario where the cellular network is underlaid with device-to-device (D2D) communications. In particular, the service links of the D2D users are modeled with Rician channels, and other links are modeled with Rayleigh channels to capture the differences of the wireless transmission links in heterogeneous networks. Based on this differentiated channel model, a centralized opportunistic spectrum access control scheme is proposed to reduce the downlink interference from the D2D users to the cellular users. The performances of the D2D communication and the conventional cellular network are evaluated in terms of success probability, average capacity and network capacity, and the mode selection mechanism between the cellular mode and the D2D mode is developed based on the success probability criterion. The impact of the line-of-sight (LOS) component in the Rician channel is revealed based on the analytical results, and the performance gains of the proposed spectrum access control scheme is investigated compared with the conventional random spectrum access control scheme. It is demonstrated by the analytical and simulation results that the transmission reliability of the D2D users is improved with the increase of the LOS component. In addition, given fixed spectrum occupation ratio of D2D communications, more D2D communications can be accommodated in the network by lowering the cellular quality of service (QoS), providing more robust transmission of D2D users or using the proposed spectrum access control scheme.3. Performance optimization of hierarchical heterogeneous wireless networks based on spatial interference coordinationFrom the view of signal processing, multiple antenna based spatial interference coordination is an advanced technology, which can effectively suppress the interference in heterogeneous networks. This dissertation investigates the spatial interference coordination techniques to reduce the cross-tier interference for the uplink transmission and the downlink transmission of hierarchical heterogeneous wireless networks, respectively. The system performances are analyzed in terms of signal to interference plus noise (SINR) as well as average capacity. Moreover, adaptive spatial interference coordination user selection algorithms are proposed to achieve highest network capacity. The impact of the antenna number to the performance of the spatial interference coordination techniques is evaluated in this dissertation, and the trade-offs between enhancing the desired signal and suppressing interference are investigated. According to the simulation results, the transmission reliability and the network capacity can be significantly improved by the proposed spatial interference coordination algorithm which only employs small amount of large scale fading information. In addition, the network capacity is essentially enhanced with the increase of the antenna number under the proposed spatial interference coordination algorithms.4. Performance optimization of hierarchical heterogeneous wireless networks based on user associationFrom the view of resource management, serving node selection for a user has impact on the strengh of interference suffered by the user and the amount of available wireless resources allocated to the user. Suitable user association is an effective way to reduce the interference and also a key technique to optimize the network performance in heterogeneous networks. A bias based user association technique is adopted in this dissertation for a multiple tier heterogeneous network. Moreover, a spatial interference coordination scheme is proposed to suppress the interference from high power nodes to the users in the extended region of lower power cells. The performance is evaluated in terms of success probability in this bias based heterogeneous network. The impacts of transmit antenna number, bias factor and the spatial interference coordination scheme to the load, transmission reliability and network capacity in heterogeneous networks are investigated. It is demonstrated by the simulation results that improved network capacity can be achieved by employing the association bias in dense deployment of LPNs. In addition, the proposed spatial interference coordination scheme leads to both improved transmission reliability and enhanced network capacity in non-fully loaded scenarios.