  In device-to-device (D2D)-enabled caching cellular networks, the user
terminals (UTs) collaboratively store and share a large volume of popular
contents from the base station (BS) for traffic offloading and delivery delay
reduction. In this article, the multi-winner auction based caching placement in
D2D-enabled caching cellular networks is investigated for UT edge caching
incentive and content caching redundancy reduction. Firstly, a multi-winner
once auction for UT edge caching is modeled which auctions multiple contents
for multiple UTs. Then the optimization problem for content caching revenue
maximization is formulated. Specifically, the "cache conflict" restriction
relationship among UTs is used as one of the constraints in the problem to
reduce the content caching redundancy in a UT movement scenario. The problem is
solved by semidefinite programming (SDP) relaxation to obtain an approximate
optimal caching placement. Moreover, the payment strategy of the auction is
developed as a Nash bargaining game for personal profit fairness among the UTs
who win the auction for content caching. Subsequently, a multi-winner once
auction based caching (MOAC) placement algorithm is proposed. In addition, due
to the high complexity of MOAC, we further propose a heuristic multi-winner
repeated auction based caching placement (MRAC) algorithm, which can greatly
reduce the complexity with only tiny performance loss. Simulation results show
that the proposed algorithms can reduce the traffic load and average content
access delay effectively compared with the existing caching placement
algorithms.
