Fair and Efficient Spectrum Sharing in Unlicensed Bands: Does Number of Links Matter?

Abstract

The rapid growth of mobile data traffic has become a great challenge to the licensed spectrum in scarcity. Driven by this, deploying networks in unlicensed bands has been drawing significant attention. This work is devoted to study the impact of the number of links on optimal coexistence performance between Licensed-Assisted Access (LAA) and WiFi in unlicensed bands. In particular, we consider three coexistence cases, including 1) single LAA link coexisting with single WiFi link; 2) single LAA link coexisting with multiple WiFi links; 3) multiple LAA links coexisting with multiple WiFi links. The throughput performance in all the three cases is characterized as explicit expressions, based on which the maximum total throughput under the throughput fairness and the corresponding optimal initial backoff window sizes are derived. A systematic comparison among the optimal performance of the three cases is conducted, and it is found that while the maximum total throughput is insensitive to the change of the number of multiple links, the drastic change from single link to multiple links in one network would lead to fierce internal competition in that network, and thus deteriorates both the optimal throughputs of the coexisting network and WiFi. This work sheds important light on the realization of fair and efficient spectrum sharing.