  We consider a D2D-enabled cellular network where user equipments (UEs) owned
by rational users are incentivized to form D2D pairs using tokens. They
exchange tokens electronically to "buy" and "sell" D2D services. Meanwhile the
devices have the ability to choose the transmission mode, i.e. receiving data
via cellular links or D2D links. Thus taking the different benefits brought by
diverse traffic types as a prior, the UEs can utilize their tokens more
efficiently via transmission mode selection. In this paper, the optimal
transmission mode selection strategy as well as token collection policy are
investigated to maximize the long-term utility in the dynamic network
environment. The optimal policy is proved to be a threshold strategy, and the
thresholds have a monotonicity property. Numerical simulations verify our
observations and the gain from transmission mode selection is observed.
