Indoor Localization System Using Commensal Radar Principle

Indoor localization has a wide range of applicability in personal health applications. There is a need for specialized indoor localization methods [1] like Time of Arrival (TOA), Time Difference of Arrival (TDOA), Angle of Arrival (AOA) and Received Signal Strength Indicator (RSSI) due to limited usability of global positioning system (GPS). The proposed work uses a novel commensal radar system (inspired by biological inter-species coexistence where one system exploits other without detrimental effect) which uses communication radiation as the illuminator, called CommSense[2]. It uses LTE communication infrastructure due to its wide availability in indoor environments. Therefore, we call this system LTE-CommSense [3]. We believe, utilization of orthogonal frequency division multiplexing (OFDM) and multiple input and multiple output (MIMO) may provide better resolution for this scenario. LTE signal provides high range resolution due to its wide bandwidth ranging from 1.4 to 20 MHz. Following this principle, the proposed system uses only passive receiver nodes that uses existing LTE communication signal. Communication receiver modules extracts information which is affected by the channel condition. It uses the same spectrum of the communication system without any detrimental influence on it. The communication signal strength between LTE (user equipment (UE)) and (eNodeB) gets affected by the span of the channel. Following the CommSense principle, we use three passive nodes (PN) for two dimensional (2D) indoor localization. These PNs determine respective distances of the (UE) by measuring incident signal power at the PNs with which it communicates with the (eNodeB). After the respective distances are calculated, we use these distances for trilateration to determine the co-ordinate of the UE. Depending on the PN placements, the trilateration algorithm is modified to have less calculation complexity. The calibration of the system to calculate the distance of the UE from a PN is performed. We setup a testbed to calculate the accuracy of our proposed method in a indoor laboratory environment. Without any loss of generality, we place the PNs at right angle to each other to reduce the computational complexity for trilateration. Use of LTE for RSSI based indoor localization and demonstration on SDR platform is a novel effort. First we evaluated the accuracy of distance calculation of individual PNs. The evaluated distance values using our proposed approach along with the actual distance values are compared with the ground truth measurements.