Energy Efficient Research On User Association And Resource Allocation In Heterogeneous Networks

With the foreseeable exponential upsurge in Millimeter wave communication,joint investigation of millimeter wave and microwave networks will be significant in the design of future wireless networks.Multi-tier Het Net architecture for simultaneous wireless transmission in small cells using millimeter wave and macro cells using microwave is essential to provide sustainable service expected in the near future.Meanwhile,with the growing application of the future communication,the cost of high energy consumption will restrict its development.The Het Net communication aiming at developing eco-friendly and cost-efficient systems has drawn significant attention.As a result,an important question that arises is how to energy-efficiently operate Het Net communication appropriatelyUnder Het Net circumstance containing millimeter wave cells,the energy efficiency and the quality of users are simultaneously considered.Based on the focus,two especially effective ways,dynamic user association and resource allocation have been proposed.Because of the availability of largely unused bandwidth in the millimeter wave frequencies and commercial equipment based on highly directional antennas for transmission and reception,reduced interference between links enables co-frequency transmissions by exploiting spatial reuse,the network performance can be improved significantly.Based on the above considerations,the main work and achievements of the thesis are as follows.1.According to the special characteristics of millimeter wave,we set up a reasonable system and give a deduction of the system energy efficiency formula.Then,through the analysis ideas,this paper starts a detailed design on the system energy efficiency optimization algorithm.2.In part of the user association algorithm based on energy efficiency,considering short distance transmission of millimeter wave,the paper first gives the classification scheme of users by reference receiving signal,and analyses the characteristics of various types of users.Based on this,we mainly focus on user association of type C and propose its association algorithm by considering the four factors: let the average receiving signal power,available bandwidth,communication cost and the possible interference as the judgment target.Especially for defining available bandwidth,we define it by co-frequency transmission users and interfering users in millimeter wave system.Using proposed algorithm,we can initialize each user's association.3.Based on user association model,we propose a resource allocation algorithm which can be divided into two parts.First,we consider resource allocation for millimeter wave.With the enabled co-frequency transmission,there will be more resource blocks that can be allocated to users,and the transmission power of users can be reduced while most users can still achieve their throughput needs.Since the transmission power can be reduced,the algorithm will improve energy efficiency.Meanwhile,after the algorithm allocates more resource blocks to each user,it readjusts some user's association according to the value of signal to interference ratio.Then,we also consider resource allocation for microwave system.By using matching theory,we try to improve the number of users which can achieve their quality of service.Simulation results show that the proposed algorithm can always optimize energy efficiency under lower transmission power and guarantee the qualities of users.