Mr. Saurav K. Subedi Profile

Saurav K. Subedi

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Proceedings Article | 28 May 2013 Paper

Precise RFID localization in impaired environment through sparse signal recovery

Saurav Subedi, Yimin Zhang, Moeness Amin

Proceedings Volume 8753, 87530H (2013) https://doi.org/10.1117/12.2018144

KEYWORDS: Antennas, Reflection, Wave propagation, Radiation effects, Error analysis, Received signal strength, Wireless communications, Phase measurement, Radio propagation, Signal attenuation

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Radio frequency identification (RFID) is a rapidly developing wireless communication technology for electronically identifying, locating, and tracking products, assets, and personnel. RFID has become one of the most important means to construct real-time locating systems (RTLS) that track and identify the location of objects in real time using simple, inexpensive tags and readers. The applicability and usefulness of RTLS techniques depend on their achievable accuracy. In particular, when multilateration-based localization techniques are exploited, the achievable accuracy primarily relies on the precision of the range estimates between a reader and the tags. Such range information can be obtained by using the received signal strength indicator (RSSI) and/or the phase difference of arrival (PDOA). In both cases, however, the accuracy is significantly compromised when the operation environment is impaired. In particular, multipath propagation significantly affects the measurement accuracy of both RSSI and phase information. In addition, because RFID systems are typically operated in short distances, RSSI and phase measurements are also coupled with the reader and tag antenna patterns, making accurate RFID localization very complicated and challenging. In this paper, we develop new methods to localize RFID tags or readers by exploiting sparse signal recovery techniques. The proposed method allows the channel environment and antenna patterns to be taken into account and be properly compensated at a low computational cost. As such, the proposed technique yields superior performance in challenging operation environments with the above-mentioned impairments.

Proceedings Article | 11 May 2012 Paper

Improving detection range via correlation of long PN codes

Saurav Subedi, Zhonghai Wang, Y. Rosa Zheng

Proceedings Volume 8357, 835729 (2012) https://doi.org/10.1117/12.930919

KEYWORDS: Receivers, Modulation, Signal detection, Electronic circuits, Environmental sensing, Signal generators, Sensors, Positive feedback, Computer simulations, Signal processing

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This paper proposes a correlation method for detecting super-regenerative RF receivers via stimulation. Long PN sequences are used as to stimulate the unintended emissions from the RF receivers. High correlation between known PN sequence and stimulated unintended emissions from RF receivers helps improving the detection range compared to passive detection and power detection methods. Although RF receivers generate unintended emissions from their nonlinear devices, without stimulation, the power of these unintended emission is usually lower than --70dBm, as per the FCC regulations. Direct detection (passive detection) of these emissions is a challenging task specially in noisy conditions. When a stimulation signal is transmitted from distance, superregenerative receivers generate unintended emissions that contain the stimulation signal and its harmonics. Excellent correlation property of PN sequence enables us to improve the range and accuracy of detecting the super-regenerative receivers through stimulation method even in noisy conditions. The experiment involves detection of wireless doorbell, a commercially available super-regenerative receiver. USRP is used for transmitting the stimulant signal and receiving unintended stimulated emissions from the doorbell. Experiments show that the detection range of the proposed method with long PN sequences is much larger than passive detection and power detection methods.

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