Prompt mechanism for online auctions with multi-unit demands

We study the following TV ad placement problem: identical time-slots are on sale within a period of days and only one time-slot is available each day. Advertisers arrive and depart online to bid for some time-slots to publish their ads. Typically, advertiser arrives at the 'th day and wishes that her ad would be published for at most days before she departs. The goal is to maximize the social welfare which is the sum of values of the published ads. In this paper, we design a competitive online mechanism in which each advertiser is motivated to report her private value truthfully and can learn her payment at the very moment that she wins some time-slots. When all demands 's are uniform, we prove that our mechanism achieves a non-trivial competitive ratio of . We also study general cases and derive upper and lower bounds.