Research On Femtocell Technologies Of Two-Tier Networks

With the rapid development of wireless communication technology and mobile internet, wireless data traffic is growing sharply at an alarming rate. Recent investigation shows that more than60percent of voice services and more than90percent of data traffic take place in indoor environment, and these percentages are continuously increasing. Hence, providing high-speed and high-quality coverage for voice and data services of indoor users is becoming increasingly important. As a more effective wireless access technology, Femtocell base station (Femtocell BS) has been attracted much attention for enhancing indoor coverage and improving network capacity in the communication industry, and has been a research hotspot at different standard mobile communication networks.After the deployment of femtocells in the topology of conventional macrocellular networks, the new network architecture is composed of two clearly separated layers, the macrocell layer and the femtocell layer. Such a network architecture is usually called a two-layer or two-tier femtocell networks by academics. Under the support of the National Natural Science Foundation of China:"key technology research of green Femtocell SON in IMT-A system"(Grant No.61271179), the National S&T Major Project of China:"Cross-layer optimization technology for IMT-Advanced systems"(Grant No.2010ZX03003-001), and the National S&T Major Project of China:"key research and development on SON technology of IMT-Advanced systems"(Grant No.2010ZX03003-001), the key technologies of two-tier femtocell networks are researched in this paper, including interference management technologies, energy-efficient self-organization technologies, and BS operating model control technologies. The main research work and innovative achievements are as follows:(1)The related theories and key technologies of two-tier femtocell networks are analyzed.1) The introduction of the femtocell is elaborated from three aspects, including the reasons of the indoor coverage weakness, the reasons of the indoor coverage improvement and the existing indoor coverage enhancement technologies.2) The architecture of the femtocell and two-tier femtocell networks, femtocell access methods and standardization process of the femtocell are generalized.3) The challenges of key technologies in two-tier femtocell networks are comprehensive overviewed and analyzed, concluding interference management technologies, energy-efficient self-organization technologies, and BS operating model control technologies. The research statuses of those technologies are detailed summarized and analyzed, and the main problems of those technologies to be solved are pointed out.(2)The interference problems in two-tier femtocell networks are addressed.1) According to related3GPP technical specifications and technical reports, a downlink system level simulation platform for two-tier femtocell networks are set up, and the six classic interference scenarios of two-tier femtocell networks are evaluated.2) According to conclusions obtained by1), the interference management scheme based on dynamic clusters and spectrum allocation is presented in single macrocell based two-tier femtocell networks. Simulation results show that the proposed scheme can solve the interference between femtocells effectively, and significantly improve the throughput of the femtocell network and spectrum efficiency while ensuring the SINR of femtocell users.3) According to conclusions obtained by1), the femtocell interference management scheme based on soft frequency reuse and spectrum allocation is proposed for two-tier femtocell networks with multi-macrocells. Simulation results show that the proposed scheme can effectively solve the cross-tier interference, and maximize energy efficient of the whole network under the premise of guaranteeing a given data rate of the macrocell users and femtocell users.(3)In order to improve the energy efficiency and implement the self-organization function for two-tier femtocell networks, a green self-organized scheme based on a non-cooperative game with dual-utility and pricing is proposed.1) A power self-optimization model based on a non-cooperative game with pricing is established. According to this model, a macrocell-femtocell dual-utility framework and the problem formulation are given.2) The existence, uniqueness and characteristic of the Nash Equilibrium for the proposed game are discussed.3) Utilizing marginal utility theory, variable price coefficients of the Nash Equilibrium are analyzed, and a distributed power self-optimization algorithm based on Firefly Optimization Theory is proposed for two-tier femtocell networks.4) The optimal combinations of the key parameters for macrocell utility function and femtocell utility function are obtained through numerical simulations, respectively. Meanwhile, through the system level simulation, the performances of the proposed scheme and the classic power allocation scheme on the transmit power of the base stations, the SINR of the users and the system energy efficiency are comparative analyzed, and the influence of the variable price coefficients of the femtocell utility function on the proposed scheme is also evaluated.(4)In order to address the energy consumption and the pilot pollution caused by continuous pilot transmit in femtocell networks, a hybrid BS-cooperative pilot control scheme in virtual cell-based femtocell networks is proposed.1) According to the femtocell network topology, a leader-member virtual cell framework is established. Moreover, because of the time variation characteristic of the femtocell network topology, the role assignment algorithm for the newly installed Femtocell BS is presented.2) The femtocell leader acts as an autonomous entity and is responsible for detecting active calls in the virtual cell coverage, while the femtocell members without active connections can entirely shut down pilot transmissions and the related processing all the time.3) To analyze the performance of the proposed scheme, a state transition model is established.4) Utilizing the semi-Markov process, the proposed scheme is theoretically analyzed, and then the analytic formulas of energy consumption and average cumulative delay and interference time are derived as well as three prominent related schemes.5) Simulation results verify that the theoretical analysis is reasonable in terms of interference time, average accumulative delay and energy consumption, and the timer range of the proposed scheme has a significant influence on the energy consumption and average accumulative delay.6) Simulation results also show that the proposed scheme outperforms three existing schemes in terms of interference time and energy consumption.