Smartphones are affordable devices nowadays, capable of embedding a large variety of sensors such as magnetometers or orientation sensors, but also the hardware needed to connect them to most wireless communication technologies such as Wi-Fi, Bluetooth, or cellular networks. Therefore, they are handy devices able to perform received signal strength indicator (RSSI) measurements for a wide variety of applications such as cellular coverage maps, indoor localization, or proximity tracking. However, to the best of our knowledge, the accuracy of such measurements has never been rigorously assessed. The goals of this article are to assess the accuracy of the RSSI measurements made with a commercial off-the-shelf (COTS) smartphone in a variety of conditions and how possible inaccuracies can be corrected. We primarily focus on the long-term evolution (LTE) RSSI, but we also extend our results to the Bluetooth RSSI. In this article, we build a controlled experimental setup based on commodity hardware and on open-source software. We evaluate the granularity and limitations of the Android application programming interface (API) that returns the RSSI. We explore how reliable the measurements in a controlled environment with a mono-polarized antenna are. We show that the orientation of the smartphone, the position or orientation of the source, and the transmission power have a significant impact on the accuracy of the measurements. We introduce several correction techniques based on radiation matrix manipulations and on machine learning in order to improve measurement accuracy to less than 5-dBm RMSE, when compared to a professional equipment. We also explore the reliability of measurements made in an outdoor realistic environment. We show that although transmission diversity available in LTE base stations significantly improves the measured RSSI regardless of the smartphone orientation, the Bluetooth RSSI remains largely sensitive to the smartphone orientation.

中文翻译：

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评估智能手机 RSSI 测量的准确性


如今，智能手机是经济实惠的设备，能够嵌入各种传感器（例如磁力计或方向传感器），而且还可以嵌入将其连接到大多数无线通信技术（例如 Wi-Fi、蓝牙或蜂窝网络）所需的硬件。因此，它们是方便的设备，能够为各种应用执行接收信号强度指示器 (RSSI) 测量，例如蜂窝覆盖地图、室内定位或接近跟踪。然而，据我们所知，此类测量的准确性从未经过严格评估。本文的目标是评估在各种条件下使用商用现成 (COTS) 智能手机进行的 RSSI 测量的准确性，以及如何纠正可能的不准确性。我们主要关注长期演进 (LTE) RSSI，但我们也将结果扩展到蓝牙 RSSI。在本文中，我们基于商用硬件和开源软件构建了一个受控实验装置。我们评估返回 RSSI 的 Android 应用程序编程接口 (API) 的粒度和限制。我们探讨了在受控环境中使用单极化天线进行测量的可靠性。我们表明，智能手机的方向、源的位置或方向以及传输功率对测量的准确性有重大影响。我们引入了几种基于辐射矩阵操作和机器学习的校正技术，以便与专业设备相比，将测量精度提高到低于 5 dBm RMSE。我们还探讨了在室外现实环境中进行的测量的可靠性。 我们表明，尽管 LTE 基站中可用的传输分集显着改善了测得的 RSSI（无论智能手机方向如何），但蓝牙 RSSI 仍然对智能手机方向非常敏感。