565 research outputs found
An energy efficient sub-threshold baseband processor architecture for pulsed ultra-wideband communications
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (p. 79-83).Ultra-wideband (UWB) communications is currently being explored as a medium for high-data-rate last-meter wireless links. Accordingly, there has been much interest in integrating UWB radios onto battery-operated devices, creating a strong demand for energy efficient UWB systems. The objective of this work is to describe how operating the digital baseband processor in the sub-threshold region and increasing the degree of parallelism can translate into energy savings across the entire UWB receiver. While sub-threshold operation is traditionally used for low energy, low performance applications such as wrist-watches, this work examines how sub-threshold operation can be applied to low energy, high performance applications. Simulation results for a 100-Mbps UWB baseband processor using the digital logic cell library of a 90-nm process are presented.by Vivienne Sze.S.M
A high speed image transmission system for ultra-wideband wireless links
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Includes bibliographical references (p. 97-98).Ultra-wideband (UWB) communication is an emerging technology that offers short range, high data rate wireless transmission, with low power consumption and low consumer cost. Operating in the 3.1 GHz - 10.6 GHz frequency band with bandwidth above 500 MHz, it is an overlay technology that can co-exist with other narrowband services in the same frequency range, thus alleviating the problem of over-crowded spectrum. In particular, pulse-based UWB technologies allows for building of ultra-low power, medium- to long-range transceivers, at the expense of data transmission rate. This thesis presents a pulse-based, non-coherent UWB wireless image transmission platform. The system features a one-way wireless link. On the transmitter side, a host PC processes the images into transmittable packets in MATLAB, and sends them to the UWB radio through an interfacing FPGA module. On the receiver side, the UWB receiver radio receivers the packets, decodes the bits, and passes them back to the receiver host PC through another interfacing FPGA module. The receiver host PC collects the decoded bits and reconstructs the original image in MATLAB. The unidirectional wireless channel is complemented by a feedback path, provided through internet connection between the two host PCs. To improve usability, graphical user interfaces are setup on both host PCs. The overall system transmits 120 x 160 uncompressed bitmap images. It achieves a maximum payload data rate of 8 Mb/s.(cont.) It is able to transmit data reliably, with above 95% packet reception rate and below 2 x 10-5 bit error rate, for distances up to 16 meters. At 16 meters, the system has a maximum transmission data rate of 2.67 Mbps.by Helen He Liang.M.Eng
Localization and Fingerprint of Radio Signals Employing a Multichannel Photonic Analog-to-Digital Converter
[EN] The fingerprint and localization of radio signals employing a multichannel photonic analog-to-digital converter (ADC) is proposed, analyzed, and demonstrated in a laboratory experiment. The photonic ADC detects the radio signals with high sensitivity in a large bandwidth without down-conversion stages. This is of special interest when processing emerging low-power wireless standards like ultra-wideband (UWB) radio. The optical processing in the multichannel photonic ADC is tailored for the localization and fingerprint of generic radio transmitters when orthogonal-frequency division multiplexing (OFDM) modulation is employed in the transmission. The photonic ADC includes engineered optical and electrical amplification. The experimental work demonstrates that detection of radio signals with -65 dBm power with signal-to-noise ratio better than 20 dB is feasible, which is in good accordance with the theoretical analysis. The multichannel photonic ADC comprises five optical channels which are precisely time-aligned in optical domain achieving 0.23-m spatial resolution (median) in the localization of radio transmitters. The experimental work also demonstrates that photonic-ADC processing is adequate for OFDM-based UWB radio-signal fingerprint including estimation of the average power, frequency band of operation, and time-frequency hopping pattern if applicable. UWB transmitter localization has been experimentally demonstrated with 0.4-m error.This work was supported in part by the European 7th Framework Program Project UCELLS FP7-IST-216785. The work of M. Morant was supported by Spain FPU MEC under Grant AP2007-01413.Llorente, R.; Morant, M.; Puche, JF.; Romme, J.; Amiot, N.; Uguen, B.; Duplicy, J. (2010). Localization and Fingerprint of Radio Signals Employing a Multichannel Photonic Analog-to-Digital Converter. IEEE Transactions on Microwave Theory and Techniques. 58(11):3304-3311. https://doi.org/10.1109/TMTT.2010.2076730S33043311581
Processing of ultra-wideband low-frequency signals, for application in Foliage Penetration (FOPEN) Synthetic Aperture Radar (SAR) systems
Foliage Penetration (FOPEN) radar systems were introduced in 1960, and have been constantly
improved by several organizations since that time. The use of Synthetic Aperture Radar (SAR)
approaches for this application has important advantages, due to the need for high resolution in two
dimensions. The design of this type of systems, however, includes some complications that are not
present in standard SAR systems.
FOPEN SAR systems need to operate with a low central frequency (VHF or UHF bands) in order
to be able to penetrate the foliage. High bandwidth is also required to obtain high resolution. Due to the
low central frequency, large integration angles are required during SAR image formation, and therefore
the Range Migration Algorithm (RMA) is used. This project thesis identifies the three main complications
that arise due to these requirements. First, a high fractional bandwidth makes narrowband propagation
models no longer valid. Second, the VHF and UHF bands are used by many communications systems.
The transmitted signal spectrum needs to be notched to avoid interfering them. Third, those
communications systems cause Radio Frequency Interference (RFI) on the received signal.
The thesis carries out a thorough analysis of the three problems, their degrading effects and
possible solutions to compensate them. The UWB model is applied to the SAR signal, and the
degradation induced by it is derived. The result is tested through simulation of both a single pulse stretch
processor and the complete RMA image formation. Both methods show that the degradation is negligible,
and therefore the UWB propagation effect does not need compensation.
A technique is derived to design a notched transmitted signal. Then, its effect on the SAR image
formation is evaluated analytically. It is shown that the stretch processor introduces a processing gain that
reduces the degrading effects of the notches. The remaining degrading effect after processing gain is
assessed through simulation, and an experimental graph of degradation as a function of percentage of
nulled frequencies is obtained.
The RFI is characterized and its effect on the SAR processor is derived. Once again, a processing
gain is found to be introduced by the receiver. As the RFI power can be much higher than that of the
desired signal, an algorithm is proposed to remove the RFI from the received signal before RMA
processing. This algorithm is a modification of the Chirp Least Squares Algorithm (CLSA) explained in
[4], which adapts it to deramped signals. The algorithm is derived analytically and then its performance is
evaluated through simulation, showing that it is effective in removing the RFI and reducing the
degradation caused by both RFI and notching. Finally, conclusions are drawn as to the importance of each
one of the problems in SAR system design
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