Until the 4th Generation (4G) cellular 3GPP systems, a user equipment's (UE)
cell association has been based on the downlink received power from the
strongest base station. Recent work has shown that - with an increasing degree
of heterogeneity in emerging 5G systems - such an approach is dramatically
suboptimal, advocating for an independent association of the downlink and
uplink where the downlink is served by the macro cell and the uplink by the
nearest small cell. In this paper, we advance prior art by explicitly
considering the cell-load as well as the available backhaul capacity during the
association process. We introduce a novel association algorithm and prove its
superiority w.r.t. prior art by means of simulations that are based on
Vodafone's small cell trial network and employing a high resolution pathloss
prediction and realistic user distributions. We also study the effect that
different power control settings have on the performance of our algorithm.

本文研究了基于信号强度进行的移动设备与基站的关联在 5G 系统中的不足，提出了一种根据基站实际负载以及可用回程容量进行关联的算法，并通过基于 Vodafone 小型基站试验网络的模拟优越性得到了验证。

5G 系统中的载荷和回程感知的解耦式下行 / 上行接入

Load & Backhaul Aware Decoupled Downlink/Uplink Access in 5G Systems

This paper addresses the cell association problem in the downlink of a
multi-tier heterogeneous network (HetNet), where base stations (BSs) have
finite number of resource blocks (RBs) available to distribute among their
associated users. Two problems are defined and treated in this paper: sum
utility of long term rate maximization with long term rate quality of service
(QoS) constraints, and global outage probability minimization with outage QoS
constraints. The first problem is well-suited for low mobility environments,
while the second problem provides a framework to deal with environments with
fast fading. The defined optimization problems in this paper are solved in two
phases: cell association phase followed by the optional RB distribution phase.
We show that the cell association phase of both problems have the same
structure. Based on this similarity, we propose a unified distributed algorithm
with low levels of message passing to for the cell association phase. This
distributed algorithm is derived by relaxing the association constraints and
using Lagrange dual decomposition method. In the RB distribution phase, the
remaining RBs after the cell association phase are distributed among the users.
Simulation results show the superiority of our distributed cell association
scheme compared to schemes that are based on maximum signal to interference
plus noise ratio (SINR).

本文提出了一种针对多层异构网络中基站有限资源分配的小区关联问题的解决方案，通过分别考虑长期速率最大化和全局中断概率最小化两个问题，设计了一个统一的分布式算法来进行小区关联，与使用最大信干噪比（Signal to Interference plus Noise Ratio）方案相比表现更卓越。