Study On LAA/Wi-Fi Coexistence In The Unlicensed Band With LBT Based On Exponential And Polynomial Backoff

At present,an increasing number and variety of services like video,applications,etc.drive the amount of data consumption.Considering the increment of the number of users and devices,which can be fulfilled by the high capacity in the network,one of the challenges is to meet the customer's expectation for high data rates demand,which can be met if the additional spectrum is available.Thus,a promising solution to meet the demand for more bandwidth for expanding the capacity of mobile system can be used by utilizing the unlicensed band as a supplementary band.Unlicensed spectrum is better used as“Licensed Assisted Access" to allow the licensed band through the principle of carrier aggregation.The coexistence can bring performance degradation of Wi-Fi networks.Thus,this thesis provides emphasis on studying the coexistence performance of Wi-Fi and LAA both analytically and through simulation.The purpose of wireless technology is to provide high throughput and fairness in the system.Distributed coordination function(DCF)of 802.11 is followed by exponential backoff mechanism for avoiding the collision.However,the exponential backoff mechanism involves dissimilar medium access delay moment.In a practical view,variance in delay can reach infinite value as medium access delay comes behind power law distribution leading unfairness among users.Moreover,similar throughput as exponential backoff can be achieved by using polynomial backoff mechanism with less latency if the network size is practical and a series of polynomial backoff is set properly.In this thesis,numerical analysis for the coexistence of Wi-Fi and LAA is performed mathematically.Results show that,in the presence of LAA system,Wi-Fi performance is degraded as LAA system are dominant over Wi-Fi system in accessing the channel with higher probability in comparison to Wi-Fi system,whereas collision probability of LAA is low.Firstly,fundamentals for coexistence mechanism were considered,and then system performance for downlink was analyzed for multi-operator deployed with different backoff mechanism through simulation.It can be concluded that Polynomial backoff can be a good option for alleviating exponential backoff in IEEE 802.11,in the case where less delay is required by the network.The demonstration of system performance is presented through the NS-3 simulation tool,and the result for the coexistence mechanism and scenario is presented.