High resolution indoor localization system using ultra wideband impulse radio

• Main Author: Vashistha, Ankush
• Other Authors: Law Choi Look
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Electrical and electronic engineering
• Online Access: https://hdl.handle.net/10356/143025
• Institution: Nanyang Technological University

Internet of things (IoT) is an emerging technology which enables integration of billions of objects and complex systems over internet with the help of many technologies such as Wi-Fi, ZigBee, Bluetooth, UWB etc. Position estimation has become an essential and crucial factor in various monitoring applications of IoT. Precision localization and positioning has become an attractive area of interest for many new applications and business solutions. Although, the global navigation satellite systems (GNSS) can provide good performance and positioning in outdoor systems, they are not very accurate when it comes to indoor locations or in GNSS-denied environments. With the ease of availability of commercial transceivers, and the demand for accurate positioning systems by various industries, the research interest towards indoor positioning and navigation systems based on ultra-wideband (UWB) technology has been immense. A good localization accuracy can be achieved by using UWB pulses due to their high temporal resolution and multi-path immunity. The UWB systems can be operated in an unlicensed band in the frequency range of 3.1 - 10.6 GHz. The operation in the unlicensed band makes it even more exciting and accessible for di erent commercial applications. However, several GHz of Nyquist sampling rate is required to sample such a large bandwidth signal. A sampling rate of few tens of GHz is suggested for resolving large number of multipaths in UWB based systems. Sampling at such a rate is an expensive solution and thus practically limited by cost and complexity of the required hardware and thus, it is a bottleneck in designing low cost sensor nodes employing UWB for accurate positioning systems. In this thesis, a novel analytical equation is proposed to determine the equivalent time of arrival (E-TOA) for achieving sub-ns resolution, with much reduced analog to digital converter (ADC) sampling frequency (in the order of 2-3 MHz). The timing information is extracted from high resolution channel impulse response (CIR) which is obtained using equivalent time sampling (ETS) technique. The proposed E-TOA equation is different from conventional real-time sampling equation due to the presence of additional transmitter clock drift, and thus sensitive to both the transmitter and the receiver clock drift variations. The validation of the proposed ETOA equation is carried out numerically using simulations along with experimental validation. The effect of timing uncertainties relating to the transmitter clock start time and the receiver clock offset is analyzed with variations in the transmitter and receiver clock drift. It is thus demonstrated, using in house designed sensor nodes, that high ranging accuracy, in the order of few cm, can be achieved by utilizing the proposed analytical E-TOA technique, even with low sampling rate. Reconstructed signal obtained by ETS technique, that require periodic transmission of the same signal repetitively, is severely affected by the variation in transmitter and receiver clock drift as against the real time sampling where the variations are due to receiver node clock drift only. Thus, it requires a protocol to precisely estimate the transmitter and receiver clock parameters at the frame level to accommodate different (multiple) target node at each frame. A scheme, which uses a novel mathematical equivalent time of arrival (E-TOA) model for ETS based system, for clock drift estimation is presented. Based on clock drift estimation parameters, receiver nodes are tuned to the same frequency, while the estimated transmitter frequency is used to estimate the precise equivalent time resolution which is subsequently used to correct the E-TOA measurements. E-TOA measurements are further used to propose an equivalent di erential time di erence of arrival (E-DTDOA) based ranging algorithm, which relaxed the time synchronization requirement between the wireless nodes, and still achieving high time resolution. The E-DTDOA range measurements are subsequently used to obtain precise localization of the target node/s. The feasibility of the algorithm proposed is demonstrated experimentally using in house designed wireless sensor nodes. Utilizing the E-DTDOA mechanism, this thesis further demonstrates experimentally a hybrid sub-1 GHz and UWB-IR based indoor positioning system. The system integrates sub-1 GHz technology for medium access control (MAC) and communication along with UWB-IR technology for the purpose of ranging. The presented positioning system employs energy efficient tags using UWB-IR in transmitter mode and the E-DTDOA as a measurement technique. A static experiment was performed for the system with 10 tags and 4 anchor nodes in an indoor environment. During the experimentation, the accuracy in tags positioning was found to be less than 30 cm in an area of 16m x 5.3m.