A Study On Sleep Scheduling And Resource Allocation Based Energy Efficiency In Small Cell Networks

With the rapid development of mobile Internet and rapid popularity of smart mobile devices, users'demand for mobile communication service is changing. In future mobile communication networks, users'demand for data service will be much more than that for void service. Increasing the data throughput of a mobile communication network has become an important research topic for future mobile communication networks. To achieve this objective, the concept of small cell networks has been introduced in mobile communication networks. As an important component of a future mobile communication network, a small cell network will be able to improving the capacity and coverage of a cellular network, and provide faster data communication service. However, the massive deployment of small cells will increase the energy consumption of a cellular system. Therefore, how to reduce the energy consumption of a cellular system while not affecting the performance of a small cell network has become an important research topic in small cell networks.This thesis studies the energy efficiency problem in small cell networks. Based on sleep scheduling and resource allocation, it proposes a distributed base station on/off mechanism, a sleep mode based resource allocation algorithm and a resource adjustment strategy with fairness for small cell networks.First, the thesis proposes a distributed base station on/off mechanism (D-OCM). D-OCM considers a macro-cell system with multiple small cells, where each small cell base station (SBS) has two states:sleep and working. A working SBS can actively go into a sleep state, while a sleep SBS can be activated by a neighbor SBS. To support D-OCM, each base station needs to maintain three tables to store relevant network status information on its neighbor base stations. Both the MBS and an SBS build the tables using the network status information collected from the users within their coverage. Each base station, either the MBS or an SBS, makes a decision to activate an SBS in a sleep state or to deactivate an SBS in a working state based on the traffic load within its coverage. Simulation results show that the proposed D-OCM mechanism can significantly reduce the energy consumption of the system as compared a traditional control mechanism.Based on D-OCM, the thesis further studies the resource allocation problem under the change of the network topology and proposes a resource allocation algorithm based on a sleep mode (RASM). The network topology changes when an SBS is deactivated or activated. A newly activated SBS will receive multiple requests from users and thus need to allocate resources for the users. RASM consists of two phases:spectrum allocation and power optimization. The spectrum allocation can be described as an MxN assignment problem, which can be solved by using a Hungarian algorithm. The power optimization of small cell can be performed through communication with neighbor small cells. Simulation results show that RASM can achieve higher energy efficiency than the random allocation algorithm.Given that D-OCM and RASM have not considered the user fairness problem, the thesis proposes a resource allocation algorithm considering user fairness (RACF). RACF consists of a resource block allocation algorithm and a resource block adjustment algorithm. The resource block allocation algorithm allocates multiple resource blocks for users based on the different interferences each resource block receives at different users under the condition that each user transmits at fixed power. Meanwhile, the resource block adjustment algorithm allocates a resource block with lower interference for a lower data rate user by adjusting the resource blocks in the current small cell and the resource blocks of neighbor small cells, and further optimize the resource block allocation by adjusting the resource blocks of neighbor small cells. The objective is to ensure the user fairness in the current small cell while not affecting the performance of neighbor small cells. Simulation results show that RACF can effectively improve the system throughput while effectively ensuring the user fairness.