Performance Modeling of LAA LBT with Random Backoff and a Variable Contention Window

This paper studies the performance modeling of an LTE LAA category-4 listen before talk (LBT) procedure for data transmission in an unlicensed spectrum band. A 3-D Markov model is developed to describe the category-4 LBT procedure of an LAA eNode B. This 3-D Markovmodel takes into account the frame synchronization problem ($\mathrm{i}.\mathrm{e}.$, the GAP period) and transmission priority in the category-4 LBT procedure, which are not consideredin all existing modeling of LTE LAA LBT procedures. Based on the 3-D Markov model, a performance model is further derived for investigating the steady-state transmission probability of an LAA eNodeB. The derived performance model is justified through simulation results. It is demonstrated that the existence of the GAP period has an impact on the performance of an LTE LAA system and an LAA category-4 LBT procedure with a reservation signal filling in the GAP period outperforms one without using a reservation signal.