  In [1], we proposed a two-tier model for creating and maintaining a
distributed hash table (DHT) overlay of smartphones. The purpose was to reduce
Internet usage and increase D2D content sharing over LTE-A/5G network. However,
the real challenge is not in creating a two-tier model, but to evolve an
efficient overlay that offers enhanced opportunities for device-to-device (D2D)
content sharing over the existing model. In this paper, we formulated the
selection of tier-1 devices as finding P-medians in a distribution network and
solved it using Lagrangian relaxation method. Tier-2 devices become clients
seeking content sharing services from tier-1 devices. A strong motivation in
this work is to raise a user's perception of the grade of service known as
Quality of Experience (QoE). We analyzed the QoE assessment challenge for
resource-constrained smartphones under the proposed model of enhanced D2D
communication. Our focus is to establish a framework to assess QoE for apps and
services over LTE-A/5G networks with an improved level of D2D communication.
The simulation and the experimental results validate the claim that substantial
improvements in QoE are indeed possible with the proposed mathematical model
for selection and placement of tier-1 mobile devices and maintaining a DHT for
D2D communication.
