DigiScatter: efficiently prototyping large-scale OFDMA backscatter networks

Recently proposed OFDMA backscatter could improve both concurrency and spectrum allocation flexibility for backscatter systems based on OFDM. However, we find that it is remarkably inefficient for the existing design to scale up in prototyping: it requires one-by-one offline computation to obtain tags' operating parameters, in order to ensure orthogonality among subcarriers in the system; moreover, the tag hardware has to be dedicatedly modified offline before being assigned multiple subcarriers. The inefficiency is caused by the current analog frequency synthesis design for the tag. This paper proposes DigiScatter, an OFDMA backscatter system realizing digital frequency synthesis, which provides an efficient prototyping approach for large-scale OFDMA backscatter networks. In DigiScatter, we for the first time integrate IDFT into the tag design; such a simple but effective improvement enables the system to support high concurrency and flexible spectrum resource allocation through pure software configurations in an online manner. We build a prototype and conduct comprehensive experiments to validate our design. DigiScatter physically realizes 100 and 300 concurrent OFDMA backscatter transmissions in 2.4GHz and 900MHz respectively, and provides frequency synthesis capability for supporting 1019 concurrent transmissions.