A method of processing a digital broadcast signal is provided. Signaling data for signaling of mobile service data is encoded. Data groups are formed, the data groups including a first data group, a second data group and a third data group. The digital broadcast signal including the data groups is transmitted, the signaling data including first information indicating whether a segmented known data sequence of the second data group is concatenated to a segmented known data sequence of the first data group to form a known data sequence, and/or second information indicating whether a segmented known data sequence of the second data group is concatenated to a segmented known data sequence of the third data group to form a known data sequence.