The award of 800 MHz (digital dividend) spectrum in Denmark included onerous coverage obligations, designed to improve availability of 10Mbps services in areas where coverage was poor.
The national coverage target was split into three regional obligations that were by default attached to the lots on offer. However, the auction included the novel approach of allowing bidders to bid for exemptions from the coverage obligation in some or all regions, with the restriction that the supply of exemptions for each region could be at most one less than the number of winning bidders. This maximised the chances of assigning every coverage obligation, whilst giving some flexibility for bidders to share the burden between them.
This approach to including coverage obligations in auction design was presented by DotEcon at the 2014 Latin America Spectrum Management Conference in Rio de Janeiro. The presentation is available here.