Proposed Experiments

0185-EX-PL-2001 Text Documents

Wavetronix, LLC

2001-08-01ELS_47644

$The transmitted signals for both FXN and D9D transmissions will have a periodic chirp (FMCW) variation approximately as shown in Figure 2, extending over a time interval of about 3 ms as indicated. The D3D signal will also have an amplitude code component used primarily for telemetry on a particular sensor. f f2 GHz 200 MHz f1 GHz t ~3 ms Fig. 2 . Due to the small fractional deviation of the FM (less than 2%) over a time interval very long compared with the carrier period, the spectral distribution is that shown in Figure 3. Since the power transmitted is less than 10 mW over a 200 MHz band, the power per hertz is correspondingly very small. |signal| X-Band f 200 MHz Fig. 3 The theory of a linear FMCW (chirp) system is based on the relationship between the transmitted chirp and the delayed chirp returned from a reflecting object. The primary use of this relationship is to determine the range of the object. The theoretical relationship used to determine range can be derived using the time-frequency diagram of Figure 4, where the up-chirp component (increasing frequency) is indicated. 2$

The parameters in the figure are:

B=chirp bandwidth, Hz
τ=round trip delay time of return chirp, s
fd=difference frequency between transmitted and received chirps, Hz
R=range to object, m
c=speed of light, m/s
fo=unmodulated carrier frequency, Hz
k=chirp rate of rise, Hz/s = B/T
T=chirp interval

f

τ=2R/c

B
chirp slope=k Hz/s

fd

f t
τ T

Fig. 4

At time τ the frequency of the transmitted chirp is fo+ kτ. Thus, the difference frequency between
the transmitted and received chirps is obtained as:

fd=(fo+kτ)-fo=kτ=(B/T)τ=(B/T)(2R/c)=(2BR)/(cT)

A difference frequency can be obtained by mixing the transmitted chirp with the received chirp
and appropriate filtering. From the equation above the range can then be computed using

R=cTfd/2B

The experimental portion of the program will involve deploying several sensors at typical
highway and intersection configurations where camera and loop detectors are already installed.
This will allow comparison and evaluation of performance characteristics. The effects of chirp
bandwidth on sensor accuracy and precision will be investigated.

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(b) Specific objectives sought from a series of experiments are:
(1). Optimum (minimum) required bandwidth for a desired traffic characterization,
including resolution, precision, and accuracy.
(2). Required transmitted power levels for given range and traffic configurations.
(3). Chirp linearity requirement.
(4). Data storage requirements and possible data transmission to interested parties.

(c) Contributions of the experiments should include:
(1). Determination of a minimum bandwidth for required sensing objectives.
(2). Determination of a minimum power level for given sensor region configuration.

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Document Created: 2001-08-01 15:25:13
Document Modified: 2001-08-01 15:25:13