This paper provides a comprehensive study of the harmonics generated by a frequency shifted backscatter communication system. The suppression and the manipulability of different harmonics are of importance to avoid detrimental inter-user interference when a number of backscattering nodes (and perhaps also other active wireless users) operate simultaneously in a network. In this paper the harmonics generated by a widely adopted open-short backscatter tag architecture is firstly presented. Then the ideal backscatter system which generates no unwanted harmonics is discussed, which inspires various harmonic suppression strategies. In particular, practical constraints of the backscatter tag hardware capabilities are applied, e.g., the number of discrete reflection coefficients that can be synthesized, and the dimension of the reflection coefficients (real-valued or complex-valued). Furthermore, the dual-transistor based IQ backscatter modulator is found useful to suppress all mirror harmonics and any specified higher order harmonics. The applicability of these proposed harmonic suppression approaches are demonstrated by an exemplar backscatter network consisting of multiple nodes performing binary frequency shifted keying (2FSK) modulated backscatter communications simultaneously.

中文翻译：

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频移反向散射通信中的谐波抑制

本文对移频后向散射通信系统产生的谐波进行了全面的研究。当多个反向散射节点（可能还有其他活动的无线用户）在网络中同时运行时，不同谐波的抑制和可操作性对于避免有害的用户间干扰非常重要。本文首先介绍了由广泛采用的开-短反向散射标签架构产生的谐波。然后讨论了不会产生有害谐波的理想反向散射系统，这激发了各种谐波抑制策略。尤其是，施加了反向散射标签硬件功能的实际限制，例如可以合成的离散反射系数的数量，以及反射系数的尺寸（实数值或复数值）。此外，发现基于双晶体管的IQ背向散射调制器对于抑制所有镜像谐波和任何指定的高阶谐波非常有用。这些示例性的谐波抑制方法的适用性由示例性的反向散射网络证明，该网络由多个节点同时执行二进制频移键控（2FSK）调制的反向散射通信组成。