Normalized amplitude of channel state information: The robust parameter for indoor localization in wireless sensor networks

Location information plays a remarkable role in wireless sensor networks in collecting information to support distributed spectrum sensing and directional wireless charging. To decide the optimal operating frequency band of wireless sensor network, the location information of the wireless sensor network nodes should be known to fulfill the geographical map of the spectrum using the technique of distributed spectrum sensing. In addition, wireless charging also needs the location information of the wireless sensor network node for the directional wireless charging is much more efficient than the omnidirectional wireless charging. The location of the wireless sensor network node is estimated by Wi-Fi signal because the Wi-Fi infrastructures are widely deployed not only for Internet wireless access but also for the communication between wireless sensor network nodes. The most of our daily life is spent in the indoor environment, and the channel state information is one of the most important parameters of fingerprint in indoor localization. The channel state information is not a constant parameter for various timing synchronization and frequency offset even in the same location; therefore, a new parameter—normalized amplitude of channel state information—is proposed to be a robust parameter, which is insensitive to timing synchronization and frequency offset. In this article, we first formulate the received signal in a multipath channel by taking timing synchronization and frequency offset into consideration, then we derive the closed-form expression of channel state information, and propose the new parameter—normalized amplitude of channel state information. Finally, the robustness of the new parameter is verified by numerical simulations.