Analysis of Generalized CCA Errors and Mitigation in LTE-LAA Spectrum Sharing System

Abstract

Carrier sense multiple access with collision avoidance (CSMA/CA) procedures have been specified for medium access control (MAC) in several incumbent and emerging wireless systems, such as wireless local area network (WLAN) and long-term evolution (LTE) with license assisted access (LAA). Clear channel assessment (CCA) errors in carrier sensing can cause significantly degraded network performance. Analyzing the impact of CCA errors in the MAC backoff and transmission process is a challenging task, and very few works have explicitly addressed this. Existing analytical work is only valid for special cases such as independent CCA errors, and the result lacks generality for extension to coexistence systems. In this paper, we try to fill this technical gap by modelling generalized CCA sensing errors which can be either fully correlated or independent due to the fading channel. We develop a new Markov model using matrix-vector representation which captures generalized CCA error events, and analyze the impact of CCA errors on the key performance indicators (KPIs), such as the throughput of both LTE-LAA and WLAN systems. To mitigate the effects of mis-detection and collisions which can cause the network throughput to drop to nearly zero, we propose a soft-collision method to reduce the performance loss. Finally, we program the LTE-LAA and WLAN CCA algorithms and implement extensive computer simulations. Comparisons between analytical and simulation results show consistent matching, and illustrate loss caused by sensing errors and improvement brought by the soft-collision method. This result provides a powerful analytical tool on CSMA/CA MAC-layer performance evaluation with imperfect sensing, applicable to both single and coexistence systems, and has practical value for countermeasure designs against sensing errors.