An approach attaining adjustable designated footprint

In satellite communications, the footprint is characterized by contour lines with specific receiving power. When data is delivered to the area within a specific footprint, called the designated footprint, illegal users outside the boundary of designated footprint (BDF) can still receive the signal with degraded power. In other words, illegal users can obtain the transmitted data with higher error probability. In this paper, we present a special two-stage serially concatenated (2-SC) coding scheme to more precisely define the designated footprint. Hence users outside the BDF are excluded from obtaining the data, i.e. they cannot correctly decode the data. The key technique, 2-SC coding scheme, achieves the brick-wall effect in error performance regarding bit energy-to-noise density ratio ( E_b/N₀). The brick-wall effect has sharp cutoff at a critical E_b/N₀. When the transmitted data is protected by the 2-SC coding scheme, only the users within the designated footprint can successfully decode the data. Otherwise, for users outside the BDF with received E_b/N₀ slightly less than critical E_b/N₀, even if the coding structure is known, they cannot correctly decode the data. Thus the BDF is sharply defined by the critical E_b/N₀. Moreover, by means of purposely-introduced error in the codewords, we can adjust the critical E_b/N₀ and the BDF. We provide comprehensive analysis of the coding performance and further discuss the application of the proposed scheme to enhance secure satellite communications.