IEEE - Aerospace and Electronic Systems - November 2019 - 16

Deep-Space Optical Communication Link Engineering: Sensitivity Analysis

Figure 8.
Data rate versus range, Hb ¼ 85 W=m2=mm=sr, different
receivers, no array.

Figure 7.
Data rate versus range, Hb ¼ 15 W=m2=mm=sr, different
receivers, no array.

detected power, uncoded BER, uncoded SER, hard capacity, soft capacity, etc., are derived according to the formulas presented in previous sections. It must be noted that
since the available signaling parameters, i.e., the coding
rates RECC, the PPM order M, and the slot duration Tslot
define a fix number of data rates, the achieved data rate
will be smaller than the capacity. However, if RECC was
free to take any value then the capacity and the achieved
data rate will be closer. The flow chart of the methodology
is illustrated in Figure 6.

NUMERICAL RESULTS
In this section, numerical results using the proposed methodology are presented. For the simulations, MATLAB is used.
To begin with, assuming a single photon counting
detector (no Array) the maximum achieved data rate is
investigated for different link ranges in Astronomical Units
(AU)2, different receiver aperture diameters 4/6/8/10 m and
different background radiance 15/85 W/m2/mm/sr. The values for background radiance may be interpreted as low and
high that could represent day/nighttime conditions or large/
small Sun-Earth-Probe angles. The inputs to the link budget
tool are listed in Table 2. In Table 3, intermediate and final
outputs for the case of the 4-m receiver for 0.3/07/1.3 AU
range assuming 15 W/m2/mm/sr radiance of planets and sky
are listed, thus allowing for cross-validation with other
tools. For the rest of the cases in this paper, the resulting
data rates are reported in the following figures. For all the
numerical results a power link margin of 4 dBs is assumed.
In Figure 7, the data rates for the low noise conditions,
i.e., Hb ¼ 15ðW=m2 =mm=srÞ versus the distance are
reported for each aperture assuming only one single detector (no detector array).
In Figure 8, the data rates for the high noise conditions, i.e., Hb ¼ 85ðW=m2 =mm=srÞ versus the distance
2

Distances include Venus and Mars orbits.

are reported for each aperture assuming only one single
detector (no detector array).
Now, assuming a single photon counting detector
array with size 32, the maximum achieved data rate is
investigated for different ranges, different receiver aperture diameters 4/6/8/10 m and different background radiance 15/85 W/m2/mm/sr. The same inputs as before are
assumed, except for the detector array size which is 32. In
Table 4, detailed outputs for the case of the 4-m receiver
in 0.3/07/1.3 AU range assuming 15-W/m2/mm/sr radiance of planets and sky are presented.
In Figure 9, the data rates for the low noise conditions,
i.e., Hb ¼ 15ðW=m2 =mm=srÞ versus the distance are
reported for each aperture assuming a detector array with
size 32.
In Figure 10, the data rates for the high noise conditions,
i.e., Hb ¼ 85ðW=m2 =mm=srÞ versus the distance for each
aperture are presented assuming a detector array with size 32.
From these first numerical results, it can be observed
that for the given system considerations the achieved data
rates with the detector array are higher for distances up to
1 AU. For longer distances, since the received power is
extremely low and, in case of the detector array, the noise
photon rate is higher than the signal photon rate, it can be
shown that equal or even higher data rate can be achieved
with only one detector. When multiple detectors are used,
on the one hand, the blocking loss is minimized but on the
other hand the noise increases.
In Figure 11, we highlight the change in the slope of
the achieved data rate versus the distance assuming a
detector array with size 32 and a 10-m aperture receiver.
This slope change is due to the relative strength between
signal and noise flux and has been discussed in [28] and
[29]. The transition from 1\R2 to 1\R 4 is happening around
the 2 AU and 10 Mbps point.
Finally, in Figures 12 and 13, the achieved data rate
for three different transmitter diameters, i.e., 0.135, 0.22,
and 0.4 m versus distance for two receiver aperture diameters (6 m and 10 m) is reported. It is assumed a detector
array with size 32 and high noise conditions Hb ¼ 85
ðW=m2 =mm=srÞ.

IEEE A&E SYSTEMS MAGAZINE

NOVEMBER 2019

IEEE - Aerospace and Electronic Systems - November 2019

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