10,979 research outputs found
Multi Detector Fusion of Dynamic TOA Estimation using Kalman Filter
In this paper, we propose fusion of dynamic TOA (time of arrival) from
multiple non-coherent detectors like energy detectors operating at sub-Nyquist
rate through Kalman filtering. We also show that by using multiple of these
energy detectors, we can achieve the performance of a digital matched filter
implementation in the AWGN (additive white Gaussian noise) setting. We derive
analytical expression for number of energy detectors needed to achieve the
matched filter performance. We demonstrate in simulation the validity of our
analytical approach. Results indicate that number of energy detectors needed
will be high at low SNRs and converge to a constant number as the SNR
increases. We also study the performance of the strategy proposed using IEEE
802.15.4a CM1 channel model and show in simulation that two sub-Nyquist
detectors are sufficient to match the performance of digital matched filter
Statistics of the MLE and Approximate Upper and Lower Bounds - Part 1: Application to TOA Estimation
In nonlinear deterministic parameter estimation, the maximum likelihood
estimator (MLE) is unable to attain the Cramer-Rao lower bound at low and
medium signal-to-noise ratios (SNR) due the threshold and ambiguity phenomena.
In order to evaluate the achieved mean-squared-error (MSE) at those SNR levels,
we propose new MSE approximations (MSEA) and an approximate upper bound by
using the method of interval estimation (MIE). The mean and the distribution of
the MLE are approximated as well. The MIE consists in splitting the a priori
domain of the unknown parameter into intervals and computing the statistics of
the estimator in each interval. Also, we derive an approximate lower bound
(ALB) based on the Taylor series expansion of noise and an ALB family by
employing the binary detection principle. The accurateness of the proposed
MSEAs and the tightness of the derived approximate bounds are validated by
considering the example of time-of-arrival estimation
Statistical Studies of Giant Pulse Emission from the Crab Pulsar
We have observed the Crab pulsar with the Deep Space Network (DSN) Goldstone
70 m antenna at 1664 MHz during three observing epochs for a total of 4 hours.
Our data analysis has detected more than 2500 giant pulses, with flux densities
ranging from 0.1 kJy to 150 kJy and pulse widths from 125 ns (limited by our
bandwidth) to as long as 100 microseconds, with median power amplitudes and
widths of 1 kJy and 2 microseconds respectively. The most energetic pulses in
our sample have energy fluxes of approximately 100 kJy-microsecond. We have
used this large sample to investigate a number of giant-pulse emission
properties in the Crab pulsar, including correlations among pulse flux density,
width, energy flux, phase and time of arrival. We present a consistent
accounting of the probability distributions and threshold cuts in order to
reduce pulse-width biases. The excellent sensitivity obtained has allowed us to
probe further into the population of giant pulses. We find that a significant
portion, no less than 50%, of the overall pulsed energy flux at our observing
frequency is emitted in the form of giant pulses.Comment: 19 pages, 17 figures; to be published in Astrophysical Journa
Experimental Characterization of System Parameters for Ranging in IEEE 802.15.4a using Energy Detectors
The IEEE 802.15.4a standard for impulse radio ultrawide band (IR-UWB) communication systems defines a ranging scheme which relies on the measurement of the round-trip propagation time of electromagnetic pulses. Accuracy is strongly dependent on the estimation of the timeof-arrival (TOA) of the pulse that is spread in time due to multipath propagation. The major concern therefore is the proper detection of the leading edge. In this work, the ranging capabilities of the standard are analyzed for an energy detector receiver. Emphasis is put on the influence of transmitter and receiver parameters, which are evaluated for a set of measured scenarios. It is shown that sub-meter ranging accuracy can be achieved with fixed parameter settings
A New RSSI-based Centroid Localization Algorithm by Use of Virtual Reference Tags
A good design of node location is critical for efficient
and effective wireless communications. This paper presents an
improved algorithm, in order to solve the low localization
accuracy caused by traditional centroid algorithm. The
improved algorithm combined with VIRE system and
traditional centroid algorithm. The VIRE algorithm is
introduced and the signal propagation model is utilized to
construct virtual reference tags in the location area. Simulation shows that this further developed algorithm has further improved the accuracy of positioning up to 35.12% compared
to the traditional centroid algorithm. It is concluded that this algorithm can further improve the locating accuracy in comparison with the original centroid algorithm
Secret Key Generation Based on AoA Estimation for Low SNR Conditions
In the context of physical layer security, a physical layer characteristic is
used as a common source of randomness to generate the secret key. Therefore an
accurate estimation of this characteristic is the core for reliable secret key
generation. Estimation of almost all the existing physical layer characteristic
suffer dramatically at low signal to noise (SNR) levels. In this paper, we
propose a novel secret key generation algorithm that is based on the estimated
angle of arrival (AoA) between the two legitimate nodes. Our algorithm has an
outstanding performance at very low SNR levels. Our algorithm can exploit
either the Azimuth AoA to generate the secret key or both the Azimuth and
Elevation angles to generate the secret key. Exploiting a second common source
of randomness adds an extra degree of freedom to the performance of our
algorithm. We compare the performance of our algorithm to the algorithm that
uses the most commonly used characteristics of the physical layer which are
channel amplitude and phase. We show that our algorithm has a very low bit
mismatch rate (BMR) at very low SNR when both channel amplitude and phase based
algorithm fail to achieve an acceptable BMR
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
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