On the Performance of Square, Rectangular, Star, and Hexagonal QAM for Backscatter Systems

Applications on wireless sensing and internet of things (IoT) require communication systems based on low power with high data rates. Thus, backscatter communication plays an important role in the new emerging IoT communications. In the literature, several works have been reported about backscatter modulators with high-order modulation formats. However, only the square quadrature amplitude modulation (S-QAM) scheme is considered, although it is not optimal in the sense of power efficiency. In this letter, the performance of two dimensional (2-D) signal constellations is evaluated, namely rectangular QAM, star QAM, and hexagonal QAM, in terms of the symbol error rate, in backscatter systems context. A power consumption analysis is presented for these modulation schemes. To provide the symbols of the aforementioned constellations, a practical high-order backscatter modulator, corroborated by measurement campaigns, is implemented. Several SER curves are also presented in this work.