  We study distributed user association in 5G and beyond millimeter-wave
enabled heterogeneous networks using matching theory. We propose a novel and
efficient distributed matching game, called early acceptance (EA), which allows
users to apply for association with their ranked-preference base station in a
distributed fashion and get accepted as soon as they are in the base station's
preference list with available quota. Several variants of the EA matching game
with preference list updating and reapplying are compared with the original and
stability-optimal deferred acceptance (DA) matching game, which implements a
waiting list at each base station and delays user association until the game
finishes. We show that matching stability needs not lead to optimal performance
in other metrics such as throughput. Analysis and simulations show that
compared to DA, the proposed EA matching games achieve higher network
throughput while exhibiting a significantly faster association process.
Furthermore, the EA games either playing once or multiple times can reach
closely the network utility of a centralized user association while having much
lower complexity.
