  This paper presents a systematic approach to exploit TV white space (TVWS)
for device-to-device (D2D) communications with the aid of the existing cellular
infrastructure. The goal is to build a location-specific TVWS database, which
provides a look-up table service for any D2D link to determine its maximum
permitted emission power (MPEP) in an unlicensed digital TV (DTV) band. To
achieve this goal, the idea of mobile crowd sensing is firstly introduced to
collect active spectrum measurements from massive personal mobile devices.
Considering the incompleteness of crowd measurements, we formulate the problem
of unknown measurements recovery as a matrix completion problem and apply a
powerful fixed point continuation algorithm to reconstruct the unknown elements
from the known elements. By joint exploitation of the big spectrum data in its
vicinity, each cellular base station further implements a nonlinear support
vector machine algorithm to perform irregular coverage boundary detection of a
licensed DTV transmitter. With the knowledge of the detected coverage boundary,
an opportunistic spatial reuse algorithm is developed for each D2D link to
determine its MPEP. Simulation results show that the proposed approach can
successfully enable D2D communications in TVWS while satisfying the
interference constraint from the licensed DTV services. In addition, to our
best knowledge, this is the first try to explore and exploit TVWS inside the
DTV protection region resulted from the shadowing effect. Potential application
scenarios include communications between internet of vehicles in the
underground parking, D2D communications in hotspots such as subway, game
stadiums, and airports, etc.
