Study On The Fair Coexistence Of LTE-U And WiFi

With the advent of the mobile Internet era, mobile data traffic is growing exponentially, and human beings’ increasingly high requirement of mobile communication is in conflict with the growing shortage of spectrum resources. In such a context, LTE-U(LTE-Advanced in Unlicensed Spectrum), a technology which applies LTE-Advanced into unlicensed spectrum comes into being. Compared with the main user of existing unlicensed bands—Wi Fi technology, resorting to the centralized resource management strategies, LTE-U technology can not only effectively improve the spectrum efficiency of unlicensed bands, but also significantly enhance the capacity of the cellular network. However, in LTE-U technology, due to adopt the exclusive channel occupancy mode, a daunting challenge is how to reasonably share the spectrum resource of unlicensed bands with Wi Fi in the deployment of LTE-U. Nevertheless, since the study of LTE-U has just started, some existing strategies only explore the method of coexistence, without considering the fairness of resource utilization. We know a win-win situation can occur only in the condition of fair distribution of resource, so this paper makes a further research on the coexistence of Wi Fi and LTE-U on the basis of a summary description of the current LTE-U technology researches, as well as emphatically discusses the fairness of their time domain coexistence. In this paper, the research contents and results are organized as follows:1. This paper first analyzes the differences between LTE-U and Wi Fi, and their impact on both of two technologies deployed in the unlicensed bands. Then after summarization of the existing LTE-U and Wi Fi coexistence strategies and comparison the advantages and disadvantages between them, we conclude that the existing coexistence strategies do not fully consider the users’ fairness between different networks.2. The dissertation establishes the mathematical model of time domain coexistence of LTEU and Wi Fi, then on this basis, we introduce the α-fairness theory and build a optimization problem to maximize the throughput of coexistence system consisting of LTE-U and Wi Fi with the constraints of the α-fairness. Then we solve the convex optimization problem through Lagrangian multiplier method and KKT(Karush-Kuhn-Tucker) condition, obtain the channel access probability of LTE-U e NB and the scheduling probabilities of LTE-U Users when realizing the α-fairness. Then a new α-fairness time domain coexistence algorithm is proposed base on the solving results which applies to the coexistence of LTE-U and Wi Fi. Besides, this paper also proves that under the premise of equal Wi Fi per node throughput, the throughput of coexistence system monotonically decreases with the increase of α, at the same time the Jain index is monotonical increasing. So the tradeoff between system throughput and users’ fairness can be easily realized by adjusting the value of α.3. We set up the LTE-U and Wi Fi coexistence simulation platform. On that platform, we first verify the effectiveness of the α-fairness time domain coexistence algorithm. Then we analyze the influence of LTE-U silent period length to the algorithm and how to acquire the value of α on the premise of guarantee the throughput performance of existing Wi Fi nodes. Finally, compared with the traditional fixed airtime allocation algorithm through simulation, two advantages of our α-fairness time domain coexistence algorithm are affirmed. On the one hand, it can carry on the tradeoff between the system efficiency and fairness through adjusting the α value. On the other hand, it is sensitive to the variation of coexistence networks, so under the condition of a given value of α, it can adjust the channel access probability of LTE-U e NB self-adaptively to achieve the goal of fair coexistence of LTE-U and Wi Fi in the unlicensed bands.