| With the rapid development of mobile communication,the demand from people for communication ser-vices is growing,the future 5G network mobile data traffic business demand will increase by 1000 times.Faced with such explosive traffic growth,how to improve the performance of wireless communication net-works will become the focus of attention.Nowadays,studies have shown that the spectrum utilization has been very close to the theoretical limits,adding available frequency to the limited spectrum resources is im-practical,while millimeter-wave communication with rich spectrum of resources is a very good way to solve this problem and it will become one of the key technologies in 5G communication network.The charac-teristics between millimeter wave and traditional microwave are different,the system model and processing methods also have a huge difference,moreover,heterogeneous network is an important deployment of future cellular network and it also brings the complexity of the network topology.This thesis will investigate the performance of millimeter wave heterogeneous networks.This paper first studies the scenario of a two-tier heterogeneous network.Macro base station are de-ployed according to a homogeneous Poisson Point Process(PPP)distribution,pico base stations are deployed according to a Poisson Hole Process(PHP)distribution and the deployment of mobile users follows a ho-mogeneous PPP.This deployment allows the number of pico base stations near the macro base station to be decreased,thereby reducing the interference from pico base stations for mobiles users who are served by macro base stations,what's more,this is more in line with the practical situation.In this paper,we use the mathematical tool of stochastic geometric to derive the closed expression of the downlink SINR coverage probability Pc and the rate coverage probability.Then Monte Carlo simulation and numerical simulation are used to verify the correctness of the closed expressions.The effects by system parameters such as the density of pico base station and the radius of exclusion region on Pc are discussed,the relationship between the rate coverage probability and the density of pico base station is also studied and we compare the performance between traditional microwave system and millimeter system in the end.The results show that increasing the density of pico base stations is not always beneficial to Pc,there is an optimum value.Moreover,we also find that there exists an approximate value of the radius of exclusion regions to get the best Pc.Finally,we have observed that the achievable rate in mmWave for this non-uniform cellular network can be significantly higher than that of the traditional microwave system due to the unique features of mmWave.Next,we consider a mixed heterogeneous networks of millimeter-wave and microwave(sub-6GHz),the microwave network can cover the areas where mobile users can not be served well by millimeter-wave,thus it could overcome the disadvantage of millimeter-wave with poor tolerance of penetration.The carrier frequency of macro base stations is less than 6GHz and they are located as a homogeneous PPP.Helpers operate at the millimeter-wave frequency and also follows the homogeneous PPP distribution and they have storage function with hard disk(cache).Mobile users are also deployed according to the homogeneous PPP distribution.We derive the analytical expressions of SINR coverage Pc and energy efficiency EE for this system model and then verify it by Monte Carlo simulation and numerical simulation.The effects by system parameters such as the density of helpers,the limited storage capacity etc.on the system performance are discussed.The results show that increasing the density of the helpers could improve Pc,however,it is not always beneficial to EE,there is an optimum value.Moreover,we find that Pc and EE will perform better when the size of cache increases.Finally,we have observed that increasing the cache size could offset the loss when helpers become sparser. |
PDF Full Text Request