Activity Rules for the Combinatorial Clock Auction

In the original proposal for the combinatorial clock auction (Ausubel, Cramton and Milgrom, 2006), a revealed-preference approach was taken to limiting bidders’ activity, based on their earlier activity. However, empirical implementations of the CCA to spectrum auctions have tended to place most or all reliance on a monotonicity condition in eligibility points. This paper proposes activity rules which strike a balance between revealed preference and eligibility-point monotonicity. For the clock auction stage, we propose a hybrid revealed-preference/eligibility-point approach, in which the current round’s bid should satisfy a simplified revealed-preference constraint relative to prior rounds’ bids, but with an eligibility-point safe harbor. For the supplementary round, we propose a tightening of Ofcom’s relative cap, in which supplementary bids must satisfy revealed preference relative to the final clock bid, as well as relative to bids in all eligibility-reducing rounds in which the bidder’s eligibility went below the eligibility points associated with the bid in question.