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Tripti Gupta Priyanka Dwivedi Harpreet Singh
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Uwb Radar Signal Processing for Through the Wall

Jun 04, 2018

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Page 1: Uwb Radar Signal Processing for Through the Wall

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Tripti GuptaPriyanka Dwivedi

Harpreet Singh

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In radar imaging system an electromagnetic wave istransmitted via the antenna system penetrates through thebarrier and is reflected by the investigated object.

It then penetrates again through the barrier and isreceived back via receiving antenna.

Thus, the main objective of the project is to process thereceived data rapidly to generate a 2D image behind thebarrier using Ultra Wideband Radar Signal Processing.

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Ultra wideband is a wireless technology for transmittinglarge amounts of digital data over a wide spectrum offrequency bands with very low power for a short distance.

Ultra wideband radio has the ability to carry signalsthrough doors and other obstacles that tend to reflectsignals at more limited bandwidths and a higher power.

Radar is an object detection system which uses radiowaves to determine the range, altitude, direction, orspeed of objects.

In the applications of UWB involving radar, the signalpenetrates nearby surfaces allowing objects to bedetected behind walls or other coverings.

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Ultra Wideband (UWB) radar systems transmit signalsacross a much wider frequency than conventional radarsystems and are usually very difficult to detect.

UWBs combination of larger spectrum, low power andpulsed data improves speed and reduces interference withother wire-less spectra.

The result is dramatic short range capacity and limitedinterference.

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Currently the world is faced with numerous security issuesthat have put human life in peril.

Detection of objects through the barrier is highly desirablefor police, fire, and rescue, military applications.

The ultimate desire of such a system is to provide detailedinformation in areas that cannot be seen using

conventional measures.

Electromagnetic waves have the ability to penetrate man-made building materials and to image targets behindopaque structures.

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Stepped Frequency Signal is a series of sinusoidal signalshaving different frequencies.

The stepped frequency signal works as the transmittedsignal which hits the target and returns as the receivedsignal (echo) which is detected by the receiving antenna.

The stepped frequency signal is used to determine the

range (position) of the target that is placed behind thewall because this cannot be achieved by using conventionalsinusoidal signals.

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In order to obtain a high range resolution image, a widebandsignal must be used.

We need different frequency steps to extend the range of thetransmitted signal beyond a single cycle (wavelength) which isachieved by using stepped-frequency.

The stepped frequency has the following advantages :wider dynamic rangehigher mean powerlower noise figure

The range of frequencies that is needed for the signal to betransmitted behind the wall should lie between1.99 GHz-10.6 GHz.

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Penetration loss within materialsincrease with frequency as shownin figure thus calling for lowfrequencies of operation.

Size of components and antennasdecreases with frequency, thusmaking higher frequencies moredesirable.

Range resolution increases as

bandwidth increases, which callsfor increasing frequencies.

This range (1.99 Ghz-10.6 Ghz) isselected because of the problemsof skin effect and penetrationdepth.

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Skin effect is the tendency for alternating current ( AC) toflow mostly near the outer surface of a solid electricalconductor, such as metal wire, at higher frequencies. Theeffect becomes more and more apparent as the frequencyincreases.

The range of frequencies set by the FederalCommunications Commission (FCC) for communication is3.1 Ghz-10.6 Ghz.

Skin effect is calculated by:

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A wideband signal is approximated using a finite number Nof monochromatic signals with equally spaced frequenciesf k covering the desired bandwidth f k-1 to f 0.

Range resolutionis given by

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An echo is the reflection of the original signal and isweaker than the original due to the absorption of waveenergy of surface against which the transmitted signal isreflected.

Echo signal also contains noise which gets added becauseof the surroundings.

Echo signal is basically the delayed version of thetransmitted signal because of the noise added to it.

The signal backscattered by the object behind the wall aswell as by the wall itself is attenuated and delayedproportional with the reflectivity properties of the walland with the distance to it.

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The signal that is transmitted by the radar propagatesthrough the air and through the wall.

When the transmitted signal comes across an object that isplaced behind the wall, a portion of the signal is reflected,depends on the reflectivity properties of the object andthe ratio between the size of the object and thewavelength.

As a result, beside the useful signal that come from theobject, reflected signals from air-wall interface as well asfrom the surroundings will be received.

All these returns have no use appear as noise in thereceived signal.

These signals worsen the parameters of the radar andneeds to be removed from the echo signal.

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The received signal is used to find the position of thetarget by calculating the range in which the target lies.

The received data is considered as samples in the spatial

frequency domain.

The main parameters of any radar system are theunambiguous range and the range resolution.

The unambiguous range, L. of an Stepped Frequency radaris given by the formula:

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Matched-filter implementation of time-domaincorrelation.

Data collected at each position is correlated as afunction of round-trip delay time.

This is achieved by time-shifting the signal obtainedto a particular pixel element in the image map.

At the target locations the signal amplitudes will addup coherently and accordingly give the intensityvalue for the pixel.

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Divide the whole region into small pixels (p x q)

Let the transmitter located at the m th position illuminatethe scene with a stepped frequency signal consisting of Kfrequency steps.

The complex amplitudes of the returns are measured andstored by the receiver at n th position.

The process is repeated with the transmitter at the mth

location until all the N receive locations have been usedsequentially.

The above data measurement process is then repeated by

the sequential use of M transmit locations.

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The correlation process is used to turn a long-duration,low-power signal energy into a shorter higher-power pulse,and it suppresses random noise and unwanted signals.

The integrating process in correlation reduces noise levelsbecause of the low coincidence between the referencesignals, random noise and interference.

When the transmitted signal is reflected by randomclutter, the overlapping signals will appear as noise whichwill not be correlated or produce a detectable output.

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