In paper 'Fundamental Limits of Coded Caching: Improved Delivery Rate-Cache Capacity Trade-off',   in placement phase, the authors first generate K non-overlapping subfiles, each of size F/K bits, and then used similar coded placement with another related paper, where contents are
cached in XOR-ed form in the placement phase. However, unlike that paper, instead of XORing subfiles of all the files in the database, they XOR subfiles in pairs. You've also read that paper. Provide the full name of that paper.