Harmonics-Controlled Frequency Division Multiple Access without Harmonics and Sidebands Interference in Backscatter Communications

Yohei Konishi, Shinsuke Ibi, Kazuhiro Kizaki, Takuya Fujihashi, Takashi Watanabe, Shunsuke Saruwatari

Abstract: In backscatter communications, data is transmitted with up to 1/1000 of the power consumption, instead of the typical several tens of milliwatts. However, if there are multiple nodes for backscatter communication in the same space, harmonics and sidebands limit the number of multiplexing nodes. Both are suppressed by switching the impedance in multiple steps or generating the signal with opposite phases; however, these methods increase the hardware cost of the backscatter tag. This paper proposes harmonics-controlled frequency division multiple access (HC-FDMA), which allows multiple access interference in backscatter communications without hardware modification. HC-FDMA consists of two modules: a modulation scheme and a channel selection algorithm. The modulation scheme controls the harmonics to an arbitrary channel using ∆Σ modulation. The channel selection algorithm optimizes the frequencies of the signal component, harmonics, and sidebands. Targeting IEEE 802.15.4-compatible backscatter, backscatter communication using HC-FDMA achieves 1.45 times multiplexing compared to the case without HC-FDMA. In addition, the analysis results characterize the capability of HC-FDMA.