Application-Aware Opportunistic D2D Link Schedulers: Traffic Offloading and User Perceived QoS

Device-to-Device (D2D) communications hold the promise of enabling substantial traffic offloads from wireless infrastructure while increasing area spectral efficiency. Doing so requires exploiting available spatio-temporal traffic locality. This paper considers the design of scheduling algorithms for dynamic D2D networks where links are set up to mediate file transfers among close by users, but with limited ‘contact’ times or deadlines. Our focus is on improving three performance metrics: (1) overall offload data; (2) number of transfers which complete within their deadlines; and (3) file transfer delays. The design and evaluation of existing D2D scheduling algorithms has mostly focused on optimizing the network’s sum rate subject to fairness concerns for a fixed set of links. Starting from a dynamic scenario where links share a single collision domain, this paper investigates optimal scheduling algorithms which exploit application layer context. These results drive our proposal for application-aware versions of state-of-the-art schedulers such as FlashLinQ and CSMA/CA. Our simulations show that these schedulers could achieve substantial performance improvements depending on the operational scenario, i.e., density of users, file and contact time distributions, etc. We also show that performance can be further enhanced by incorporating both application-aware scheduling and admission control. Finally we investigate scenarios where D2D links have no deadlines. We show that application-aware schedulers result in smaller average file transfer delays and can increase the stability region of the system. This is in part due to their ability to reduce spatial clustering of links due to interference coupling in the dynamic setting.