HIGH RESOLUTION TIME-OF-ARRIVAL RANGING OF WIRELESS SENSOR NODES IN NON-HOMOGENOUS ENVIRONMENTS

Wireless Sensor Networks (WSN) have emerging applications in homogeneous environments such as free space. In addition, WSNs are finding new applications in non-homogeneous (NH) media. All referred applications entail location information of measured data or observed event. Localization in WSNs is considered as the leading remedy, which refers to the procedure of obtaining the sensor nodes relative location utilizing range measurements. Localization via Time-of-Arrival (ToA) estimation has received considerable attention because of high precision and low complexity implementation, however, the traditional techniques are not feasible in NH media due to frequency dispersion of transmitted ranging waveform. In this work, a novel and effective ToA-based ranging technique for localization in NH media consisting of frequency dispersive sub-media is proposed. First challenges of ToA estimation in NH media regarding frequency dispersion is investigated. Here, a novel technique which improves ToA estimation resolution at fixed bandwidth via maximum rising level detector (MRLD) technique is discussed. The MRLD receiver utilizes oversampling and multiple correlation paths to evaluate with high resolution the path corresponding to the maximum rising level of matched filters output. In order to achieve higher resolution, a novel and effective ToA estimation is introduced that incorporates orthogonal frequency division multiple access (OFDMA) subcarriers. In the proposed technique, pre-allocated orthogonal subcarriers are utilized to construct a ranging waveform which enables high performance ToA estimation in dispersive NH media in frequency domain. Here, we show that each frequency component of propagated waveform is received with different time delay and phase which dramatically increases the number of unknowns in the received signal system model. Then, we propose a novel idea based on frequency domain analysis of the transmitted OFDMA subcarriers to reduce the number of unknowns exploiting feasible approximations. Finally, the proposed ToA technique is applied multiple times at different carrier frequencies to create a system of linear equations which can be solved to compute the available sub-mediums thickness and range. Simulation results prove that the proposed technique offers high resolution range measurements given simulated ToA estimation error at different signal to noise ratio regimes in NH media

ToA Ranging and Layer Thickness Computation in Nonhomogeneous Media

© 1980-2012 IEEE. This paper introduces a novel and effective ranging approach in nonhomogeneous (NH) media consisting of frequency dispersive submedia via time-of-arrival (ToA). Here, the NH environment consists of sublayers with a specific thickness that is estimated throughout the ranging process. First, a novel technique for ToA estimation in the presence of frequency dispersive submedia via orthogonal frequency division multiple access subcarriers is proposed. In the proposed technique, preallocated orthogonal subcarriers are utilized to construct a ranging waveform that enables high-performance ToA estimation in dispersive NH media in the frequency domain. The proposed ToA technique is exploited for multiple ToA measurements at different carrier frequencies, which leads to a system of linear equations that can be solved to compute the thickness of the available submedia and calculate the range. Simulation results for underwater-airborne media and underground channel confirm that the proposed technique offers high-resolution ranging at different signal to noise ratio regimes in the NH media

Weighted OFDMA time-frequency synchronization for space solar power LEO satellites networks: Performance and cost analysis

© 2015 IEEE. This paper introduces a novel time and frequency synchronization technique for space solar power (SSP) satellite networks accomplished by weighted OFDMA sub-carrier training signal scheme. Exploiting OFDMA sub-carriers allows controlling the training signal bandwidth, which reduces the signal dispersion effects imposed by atmospheric layers. Here, we propose the procedure of estimating the weights for each OFDMA subcarrier that optimize an objective function key to the coarse time synchronization. Once time synchronization is complete, the carrier frequency offset that is due to the Doppler effect due to the movement of satellites is estimated exploiting the recursive least square (RLS) algorithm considering unknown channel impulse response (CIR). Analytical and simulation results confirm that the proposed scheme attains fast convergence, high stability, and ideal performances when compared to the relevant Cramer-Rao lower bounds in all ranges of signal-to-noise ratio

Time of arrival estimation in wireless sensor networks via OFDMA

© 2015 IEEE. This paper introduces the coarse time-of-arrival (ToA) estimation in wireless sensor networks (WSN) via orthogonal frequency division multiple access (OFDMA). In the proposed technique, each sensor node exploits a set of orthogonal subcarrier as its allocated signature to respond of the ToA estimation requests transmitted by target nodes. The target node utilizes the orthogonality across sub-carriers to detect the transmitted signatures and their corresponding delays. This technique is energy efficient as it avoids multiple transmissions and receptions inherent in traditional neighbor discovery protocols and ToA estimation techniques in WSN. Moreover, in this technique, network initiation process does not require channel information or time synchronization across sensor nodes. ToA estimation error is calculated theoretically and via simulations. Moreover, the impact of available bandwidth on the performance of ToA estimation is investigated. Simulation results confirm the feasibility of the proposed method even at low signal to noise ratio (SNR) regimes and in multi-path and frequency selective (MPFS) channels

Energy efficient ranging in wireless sensor networks via a new time slot-based round-trip algorithm

This paper introduces a ranging algorithm for wireless sensor networks. Here, a novel time slot based technique is applied for ranging of sensor nodes within the clustered sensor network. The proposed technique avoids clock synchronization of sensor nodes by exploiting the round-trip time-of-flight measurements. Moreover, it is energy efficient as it avoids the complexity inherent in multi-user detection or point-to-point ranging incorporated in traditional round-trip techniques. The performance and feasibility of the proposed method are studied by evaluating the required number of transmissions and receptions and the duration of ranging process. © 2014 IEEE

Joint Neighbor Discovery and Time of Arrival Estimation in Wireless Sensor Networks via OFDMA

© 2015 IEEE. This paper introduces joint neighbor discovery (ND) and coarse time-of-arrival (ToA) estimation in wireless sensor networks (WSNs) via orthogonal frequency-division multiple access. In the proposed technique, each sensor node exploits at least one orthogonal sub-carrier as its allocated signature, to respond the ND and ToA estimation requests transmitted by target nodes. The target node utilizes the orthogonality across sub-carriers to detect the transmitted signatures and their corresponding delays. This technique is energy efficient as it avoids multiple transmissions and receptions inherent in traditional ND protocols and ToA estimation techniques in WSN. Moreover, in this technique, network initiation process does not require channel information or time synchronization across sensor nodes. The performance of the proposed method is studied by evaluating the probabilities of false alarm and miss detection of the ND. In addition, ToA estimation error is calculated theoretically and via simulations. Moreover, the impact of available bandwidth on the performance and energy efficiency of ND and ToA estimation are investigated. Simulation results confirm the energy efficiency and the feasibility of the proposed method even at low signal-to-noise ratio regimes and in multi-path and frequency selective channels

High resolution ToA estimation via optimal waveform design

This paper introduces a novel method to improve the Time of Arrival (ToA) estimation resolution for a fixed available bandwidth in the presence of unknown multipath frequency selective (MPFS) channels. Here, the maximum rising level detector technique is proposed which utilizes oversampling and multiple correlation paths to evaluate with high resolution the path corresponding to the maximum rising level of matched filters output. However, employing such technique demands for transmission of waveform that creates a very high rising level at autocorrelation center. This paper proposes an efficient technique to design proper waveforms (very high rising level at autocorrelation center) via minimization of weighted integrated sidelobe level, exploiting the trust-region algorithm. The performance of the proposed technique is evaluated via simulations of the ToA mean square error, and compared with the state-of-the-art approaches considering the same bandwidth, and Cramer-Rao lower bound as benchmark. Simulations confirm that the ToA resolution is improved as the number of correlation paths increases and verify the feasibility of the proposed technique compared with the available approaches for the MPFS channels

OFDMA-based high resolution sensor node ToA estimation in non-homogenous medium of human body

© 2016 IEEE. This paper introduces a novel and effective time-of-arrival (ToA) based range measurement of sensor nodes deployed within Non-homogenous (NH) medium consisting of time and frequency dispersive sub-medias via orthogonal frequency division multiple access (OFDMA) subcarriers. In the proposed technique, each sensor node exploits pre-allocated orthogonal subcarriers to construct a ranging waveform which enables ToA estimation in dispersive NH media. Here, a set of measurements applying different carrier frequencies are employed to construct a system of linearly independent equations for the available NH channel. The system of equations is used to calculate the thickness of each sub-media. The results are incorporated to refine the estimated ToA and calculate the actual distance between each transmitter and receiver within NH media. Simulation results confirm that the proposed technique is feasible for ranging within NH medium such as human body considering time and frequency dispersion impacts on wide-band waveform

High-resolution OFDM-based sensor node ranging within in-homogeneous media of human body

This paper introduces an effective ranging technique for sensor nodes implanted within human body leveraging a novel merger of high-resolution time-of-arrival (ToA) and direction-of-arrival (DoA) estimations. Human body is an in-homogeneous media (IHM) consisting of frequency dispersive sub-media (body organs) with unknown thicknesses that entail addressing two open problems: 1) high-resolution ToA estimation of a wideband ranging waveform propagated within IHM consisting of multipath and dispersive channels and 2) calculation of straight line range between implanted sensor node and receiver sensor array on human body. In the proposed technique, pre-allocated orthogonal frequency division multiplexing is utilized to construct a ranging waveform leveraging equally spaced and orthogonality properties of its sub-carriers which enable high-performance ToA estimation in frequency domain. The estimated ToA, however, cannot be utilized to calculate the straight line range due to refraction of propagated waveform at sub-media boundaries. Therefore, a merger of ToA and DoA is proposed that exploits multiple measurements at different carrier frequencies to develop a system of linear equations. The straight line range, then, is estimated by solving this system of equations with respect to thicknesses of available sub-media. The exploited approximations are discussed and verified via theoretical evaluations and simulations for human body to prove the feasibility of the proposed technique