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Article analysis:

The article "Exploiting Cyclic Features of Walking for Pedestrian Dead Reckoning with Unconstrained Smartphones" presents a unified framework to address the three sub-problems involved in pedestrian dead reckoning (PDR) using smartphones. The authors propose a solution that sequentially rotates the device frame to the Earth frame through sensor fusion, which allows for robust step detection and counting, heading estimation, and step length estimation.

The article provides a thorough experimental analysis that confirms the effectiveness and advantages of the proposed PDR framework and algorithms. However, there are some potential biases and missing points of consideration in this article.

Firstly, the authors only focus on using inertial sensors in smartphones for PDR without considering other technologies such as WiFi or Bluetooth beacons. While inertial sensors are widely available in COTS smartphones, they have limitations such as drift errors over time. Therefore, it would be beneficial to explore how combining different technologies can improve PDR accuracy.

Secondly, the authors claim that their proposed algorithm is tolerant of various smartphone placements. However, they do not provide evidence or experiments to support this claim. It would be helpful to see how their algorithm performs under different smartphone placements and orientations.

Thirdly, while the authors mention that PDR is a complementary technique to balance accuracy and costs in outdoor and indoor positioning systems, they do not discuss any potential risks associated with relying solely on PDR for indoor positioning. For example, if a user walks through an area with no features or landmarks to detect steps accurately, PDR may not provide reliable localization information.

Finally, the article does not present any counterarguments or alternative solutions to PDR using smartphones. It would be useful to see how other techniques such as WiFi fingerprinting or Bluetooth beacons compare with PDR in terms of accuracy and cost-effectiveness.

In conclusion, while the proposed PDR framework presented in this article shows promise for improving localization accuracy using smartphones' inertial sensors, there are potential biases and missing points of consideration that should be addressed in future research.