The spectrum up for bids is the PCS H Block, which is a paired 10MHz block in the 1915-1920MHz and 1995-2000MHz bands for uplinks and downlinks respectively. The H Block is a 65MHz block of spectrum that has been called ideal for mobile broadband use by Congress. The problem for bidders is that the spectrum touches the border of a swath of spectrum owned by Dish Networks.
The FCC will take comments from the public through August 5th with responses due on August 16th. After all of the responses and replies are in, the FCC will issue final rules for the auction. You can read the draft by clicking on the sourcelink.
source: FCC via Phonescoop