Abstract-This article investigates the mobility management of an ultra dense cellular network (UDN) from an energy-efficiency (EE) point of view. Many dormant base stations (BSs) in a UDN do not transmit signals, and thus a received power based handover (HO) approach as in traditional cellular networks is hardly applicable. In addition, the limited front/backhaul capacity compared to a huge number of BSs makes it difficult to implement a centralized HO and power control. For these reasons, a novel user-centric association rule is proposed, which jointly optimizes HO and power control for maximizing EE. The proposed mobility management is able to cope not only with the spatial randomness of user movement but also with temporally correlated wireless channels. The proposed approach is implemented over a HO time window and tractable power control policy by exploiting mean-field game (MFG) and stochastic geometry (SG). Compared to a baseline with a fixed HO interval and transmit power, the proposed approach achieves the 1.2 times higher long-term average EE at a typical active BS. Index Terms-User-centric handover, ultra-dense cellular networks, spatio-temporal network dynamics, power control, energy-efficiency, mean-field game, stochastic geometry Imagine energy-saving ceiling lights adaptively turn on when walking down a dark corridor. This resembles a cellular network operation where a huge number of base stations (BSs) are deployed [1]- [3] . To maximize energy-efficiency (EE), many user void BSs stand by in dormant mode to be active as soon as a mobile user arrives within their coverage [4] . It is then natural to ask how to make energy-efficient cell coverage in such a ultra-dense cellular network (UDN), by adjusting a handover (HO) rule and power control policy. In addition, implementing energy-efficient HO and power control in a distributed manner is its prime task. A centralized control as in traditional cellular networks is hardly applicable due to the limited front/backhaul capacity compared to the number of BSs in a UDN. To resolve these issues, this article proposes a user-centric association rule (see Fig. 1 ) with a decentralized power control policy for maximizing BS's EE. A notable point is the proposed scheme incorporates user movement and temporal wireless channel dynamics under a large number of BSs. Regardless of this complicated nature, its operation is strikingly simple and tractable (see Fig. 2 ) by the aid of a spatio-temporal network dynamics framework, proposed in our preceding work [5] on the basis of mean-field game (MFG) and stochastic geometry (SG). The contributions of this paper are as follows. • User-centric reverse association in a UDN is proposed. • Closed-form EEs are derived under Brownian motion (BM) mobility with temporally correlated fading (Propositions 2 and Corollary 1). • EE optimal power control policy and HO rule are proposed in tractable forms (Propositions 3 and 4). • Mean-field (MF) interference convergence is proved in a UDN under BM mobility (Proposition 1). User Mobility and Network Deployment. Initial user locations y(t) = {y x (t), y y (t)} at time t = 0 follow a homogeneous Poisson point process (PPP) with density λ b . At t > 0, the users move according to a Brownian motion (BM) represented by a stochastic differential equation (SDE) where the standard Wiener process W(t) = {W x (t), W y (t)} for mutually independent W x (t), W y (t) ∼ N (0, t) and v is the mean displacement distance per unit time, interpreted as average velocity. BS locations follow a homogeneous PPP
In reference REF , Park et al. proposed an energy-efficient user association and power control policy.
User-Centric Mobility Management in Ultra-Dense Cellular Networks under Spatio-Temporal Dynamics
2016 IEEE Global Communications Conference (GLOBECOM)
2016 IEEE Global Communications Conference (GLOBECOM)
Computer Science Mathematics