Research On Delay Performance Of LTE And WiFi Coexistence Network

With the rapid increase in the number of mobile communication users,the increasing variety of service types,and the popularity of Internet applications,the demand for data traffic has risen sharply.This puts a great strain on cellular networks.Some technologies are introduced into Long Term Evolution systems such as massive multiple-input multiple-output(MIMO),device-to-device(D2D)and heterogeneous networks with small cells.Despite these cutting-edge technologies,limited licensed spectrum remains the bottleneck in network capacity increases.In order to solve this problem,some technologies have been proposed to use unlicensed bands transmitting LTE data traffic.The most concerned scheme is LTE in unlicensed spectrum(LTE-U).In the context of LTE-U/WiFi coexistence network,this paper studied the transmission delay performance of WiFi system based on the listen-before-talk protocol(LBT)and traffic offloading technology.Specific work and results are as follows:1.For the WiFi system delay problem in LTE-U/WiFi coexistence network.First of all,this paper presented a model applied to pure WiFi network.The probability of successful transmission of WiFi users,the probability of collision of transmission and the probability of channel idleness are obtained by finding the attempted transmission probabilities and collision probabilities of WiFi users at any time slot.Based on this,the user's back-off time,data packet collision time,and the time elapsed for the data packet to successfully transmit on the channel are obtained,respectively,thereby obtaining the WiFi transmission delay mean value.Then,based on the LBT coexistence protocol,the model is extended to the LTE-U/WiFi coexistence network.By analyzing the impact of LTE-U users on WiFi users in coexisting networks,we obtained the WiFi transmission delay average.The simulation results show that a small transmission delay average of WiFi can be obtained by using a small number of LTE-U users and offloading users from the LTE-U system to the WiFi system.In addition,WiFi systems can achieve smaller average transmission delay with larger LTE-U contention windows(CWs).For the WiFi system itself,better delay performance can be obtained with a small CW and a higher transmission rate.2.This paper studied the WiFi transmission delay performance of LTE-U/WiFi coexistence network from the perspective of WiFi access probability.Firstly,based on the LBT coexistence protocol and the total probability formula,we proposed a model to calculate the WiFi access probability in LTE-U/WiFi coexistence network and derive WiFi access probability expression as a function of the numbers of LTE-U and WiFi users.Simulation results show that offloading users from the LTE-U system to WiFi systems and large-size LTE-U CWs can help to achieve better WiFi access probabilistic performance.Next,we optimized the WiFi access probability in two different types of coexistence networks.The first type of coexistence network consists of one WiFi access point(AP)and one LTE base station(BS).Under the condition of ensuring the average throughput of the coexisting network users,the target is optimized by offloading LTE-U users to the WiFi system.In this coexistence network,we obtained the maximized WiFi access probability expression and obtained the number of offloaded users.Then,based on the analysis of one AP and one BS coexistence network,we investigated the optimization of WiFi access probabilities in the coexistence network consists of one BS and multiple APs.With our proposed algorithm,the minimum WiFi access probabilities are optimized and the number of users offloaded from the LTE-U system to each AP is obtained.