This paper addresses two fundamental and interrelated issues in
device-to-device (D2D) enhanced cellular networks. The first issue is how D2D
users should access spectrum, and we consider two choices: overlay (orthogonal
spectrum between D2D and cellular UEs) and underlay (non-orthogonal). The
second issue is how D2D users should choose between communicating directly or
via the base station, a choice that depends on distance between the potential
D2D transmitter and receiver. We propose a tractable hybrid network model where
the positions of mobiles are modeled by random spatial Poisson point process,
with which we present a general analytical approach that allows a unified
performance evaluation for these questions. Then, we derive analytical rate
expressions and apply them to optimize the two D2D spectrum sharing scenarios
under a weighted proportional fair utility function. We find that as the
proportion of potential D2D mobiles increases, the optimal spectrum partition
in the overlay is almost invariant (when D2D mode selection threshold is large)
while the optimal spectrum access factor in the underlay decreases. Further,
from a coverage perspective, we reveal a tradeoff between the spectrum access
factor and the D2D mode selection threshold in the underlay: as more D2D links
are allowed (due to a more relaxed mode selection threshold), the network
should actually make less spectrum available to them to limit their
interference.

本文提出了一种分析和优化设备对设备 (D2D) 增强移动通信网络中频谱分配和通信模式选择的通用方法，利用随机空间泊松点过程建立了可行的混合网络模型，采用两个 D2D 频谱分享方案的加权比例公平效用函数来优化两个选择，最终提出一个权衡频谱访问因子和 D2D 模式选择阈值的性能 - 覆盖度折衷。