Analysis of Channel Access Priority Classes in LTE-LAA Spectrum Sharing System

To provide differentiated quality of service in long-term evolution (LTE) license assisted access (LAA) procedure, the 3GPP has defined several channel access priority classes (CAPCs). They use distinct arbitration inter-frame space (AIFS), contention window (CW) size, and payload duration. While evaluating the effects of CW size and payload duration is relatively straightforward, accurately modelling and analyzing the effect of AIFS has not been satisfactorily addressed. Available methods on analyzing different AIFSs are accurate for only limited parameter setups, or involve systematic approximations. Different from existing results, we develop a non-homogeneous per-slot Markov chain model to represent the state of each priority class during and after the AIFS, and analyze the channel access probability (CAP), successful transmission probability (STP), and average throughput of each class. Some novel features of our method include: 1) we model and solve the per-slot class-dependent link statistics (such as CAP and STP), which vary based on the slot location; and 2) we provide an in-depth analysis on the average throughput, and design a multi-class combinatorial procedure to evaluate average time spent per successful transmission on each delay cell. We program the LAA CAPC algorithms and implement extensive Monte Carlo simulations, which validate the accuracy of our analytical results even in very low throughput region for lower priority classes, and demonstrate the effects of AIFS and other parameters in an LAA system. These results provide solid progress for evaluating priority classes in the LTE-LAA system and other spectrum sharing systems, and can be extended to support system and parameter optimization.