Performance Analysis of LAA and WiFi Coexistence in Unlicensed Spectrum Based on Markov Chain

License-assisted access (LAA) is a candidate feature in 3GPP Rel-13 to meet the explosive growth of traffic demand. The main idea of LAA is to deploy LTE in the unlicensed band (mainly the 5GHz band), which is abundant with available spectrum. However, the major concern is the coexistence between WiFi and LAA in the same band. This paper presents a new framework to evaluate the downlink performance of coexisting LAA and WiFi networks. By using Markov chain, analytical models are established based on WiFi distributed coordination function (DCF) and two listen-before-talk (LBT) schemes. These two LBT schemes are Cat 3 and Cat 4 LBT, which mainly differ in medium access schemes in terms of backoff procedure. Unlike most existing works, which focus on the impact on WiFi performance posed by LAA, the performance of LAA is also evaluated. Our analysis shows that throughput of a WiFi network can be enhanced by adding or replacing WiFi access points (APs) with LAA E-UTRAN Node Bs (eNBs), at the expense of different levels of WiFi performance degradation. A trade-off between WiFi protection and LAA-WiFi system performance enhancement is observed. WiFi throughput and delay are less affected by Cat 4 LBT scheme, while Cat 3 LBT scheme provides higher LAA-WiFi system throughput. The choice of LBT schemes relies on the network planning priority, WiFi performance protection and LAA system performance requirements.