Phase II Final Report - NASA's Institute for Advanced Concepts

Chapter 4.0 Entomopter Flight Operations
4.3 Entomopter-borne Active Emitters for Navigation and Communication
power compared to conventional systems. Lastly, the subsystem could be reconfigured in real
time to perform the desired function autonomously by the Entomopter itself.
The radiated waveform is assumed to be a modulated
Gaussian waveform (MGW), with its frequency
spectrum shifted to the appropriate
operating frequency. A time-domain plot of a
MGW centered at 18 GHz is shown in Figure 4-14.
f(t)
f()
t
1
Figure 4-14: Time-domain Plot of Modulated
Gaussian Waveform (MGW) Centered at
18 GHz
−0.95
0 t
t (s)
4.24×
10 − 10
4.3.5.1 Communications Analysis
An analysis was performed by Volpe National Transportation System Center [291] in which
peak powers were calculated for MGW pulses for communication and surveillance applications.
For communications, Volpe found that the required peak power is independent of the signal
waveform. Thus, for communications, the conventional range equation can be used or
2 2
(4π
) r k
BTo
BW SNR Lo
P
T
= Equation 4-5
2
G G λ
T
R
where P T is the required peak transmitter power; r is the distance from the receiver to the transmitter;
k B is Boltzman's constant; T o is the effective system noise temperature; SNR is the
received signal to noise ratio; G T and G R are the gains of the transmitting and receiving antennas,
respectively; BW is the signal bandwidth; λ is the wavelength; and L o is additional losses
due to propagation losses, dust, etc. For ultra wideband signals, the time-bandwidth product is
given approximately by [95]
BW ≈ 1
Equation 4-6
T w
where T w is the pulse width in time. Assuming all of the received power is in the informational
signal, Equation 4-5 also can be expressed in terms of the bit energy to noise ratio E b /N o as
2
(4π
) r
P =
T
2
E
k
BTo
BW
N
2
G G λ
T
R
b
o
F L
o
Equation 4-7
where F is the noise figure. Expressed in this manner, we can relate the required power to
achieve bit error rate (BER) performance. Assuming we will use on-off keying (OOK) modulation,
the BER can be expressed as [267]
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