Recently, cellular Ambient Backscattering has been proposed for 4G/5G/6G networks. An Ambient backscatter tag broadcasts its message by backscattering ambient downlink waves from the closest base station according to a predefined pattern. A tag is detected by smartphones nearby. This paper presents, for the first time, a novel ambient backscatter communication system exploiting uplink ambient waves from smartphones instead of downlink waves. In this novel system, the base station connected to a smartphone monitors the uplink pilot signals and detects tags in proximity. The proposed system is implemented and tested with prototypes of tags, a commercial 4G smartphone and a 4G Software Defined Radio base station. At the base station side, a non-coherent correlator receiver is implemented, and a novel technique based on pre-correlation data processing is proposed to separate useful variations on pilot signals due to tags from variations due to time varying channel effects. To deal with collision between multiple tags, distinct Gold pseudo noise codes with minimum cross correlation are used. Tests are run in different indoor and outdoor environments. A receiver detection probability of 95% has been achieved at 0.5% False-alarm probability when the tag is at 5 meters from the UE. At the refresh rate of 2 seconds, the proposed scheme is suitable for tracking objects at moderate speeds and can therefore be used for many passive IoT-based applications.

翻译：近年来，针对4G/5G/6G网络提出了蜂窝环境反向散射技术。环境反向散射标签依据预设模式反射最近基站的周围下行链路波以广播其信息，由附近智能手机进行检测。本文首次提出一种新型环境反向散射通信系统，该系统利用智能手机发射的上行环境波替代下行波。在该创新系统中，与智能手机连接的基站监测上行导频信号并检测邻近标签。我们通过标签原型、商用4G智能手机及4G软件定义无线电基站实现了所提出的系统并进行测试。在基站侧实现了非相干相关接收机，并提出一种基于预相关数据处理的新技术，以区分标签引起的导频信号有效变化与时变信道效应引起的变化。为处理多标签碰撞问题，采用具有最小互相关性的不同Gold伪噪声码。在多种室内外环境中进行测试，当标签距离用户设备5米时，在0.5%虚警概率下实现了95%的接收机检测概率。在2秒刷新率条件下，该方案适用于中速移动物体的追踪，因此可广泛应用于基于无源物联网的各类应用场景。