Tradeoff between Co-channel Interference and Collision Probability in LAA Systems

Small cell base stations (SBSs) have been deployed in heterogeneous networks to improve the spectrum efficiency on licensed channels by reusing the spectrum resource of the macro base station (MBS). To relief the shortage on the licensed spectrum resources, licensed-assisted access (LAA) has been introduced to LTE small cell systems to share the unlicensed channel with the Wi-Fi users. In this paper, we investigate the fundamental tradeoff between the collision probability (CP) to the Wi-Fi users and the co-channel interference (CI) power to the MBS in such a heterogeneous LAA system. A multi-objective resource allocation problem is first formulated while guaranteeing the quality-of-service (QoS) of small cell users (SUEs). Then, the double waterfilling-line power allocation on the licensed and unlicensed channels is developed to analyze the CI-CP tradeoff and the weighted Tchebycheff method is applied to convert the multi-objective optimization problem into a single objective optimization problem. To find the complete set of Pareto optimal solutions to the tradeoff problem, a novel feasibility method is proposed. Based on the simulation results, the proposed joint resource allocation algorithm can achieve a flexible CI-CP tradeoff according to the QoS of SUEs in LAA systems.