Mobility-Aware User Association for 5G mmWave Networks

In this paper, we design a mobility-aware user association strategy for millimeter-wave (mmW) networks to overcome the limitations of the conventional received power (RSS)-based association strategies in a mobile 5G scenario. More in detail, first the design of a mobility-aware strategy for user association in 5G mmW networks is posed as a constrained optimization problem. Then, it is showed that the proposed strategy exhibits several attractive features: a) it is able to track the dynamic changes in the network topology and in the channel conditions induced by the user mobility; b) it takes into account the distribution of the loads among the small base stations (sBSs), thus overcoming to associate an UE to an already congested sBS. This, in turn, affects positively the overall fairness of the network; c) it overcomes overly frequent handovers between sBSs, and thus the need of frequent re-association; d) it takes into account the peculiar aspects of the mmW communications, such as directionality, sensitivity to blockage, and NLoS propagation effects; and e) it is fully distributed, i.e., each mobile user associates to an sBS independently of each other, stemming from local information only. Furthermore, it is showed that the exhaustive search for the solution of the posed optimization problem is computationally unfeasible. Consequently, within this paper, an efficient algorithm exhibiting a polynomial-time complexity is proposed. Finally, the numerical results validate the benefits of adopting the proposed mobility-aware and fully distributed association rule. In particular, it is quantified the very significant performance enhancement of the proposed association with respect to the conventional RSS-based one.