Aerospace and Electronic Systems - November 2018 - 48
Reconfigurable SDR Architecture for Parallel Satellite Reception
Figure 10.
(A) Setup of case 1: two X DDCs connected to two X Rx ports. (B) Setup of case 2: two X DDCs connected to single Rx port.
Configuration 2: 1 x DDC > 2 x Rx
Figure 10B shows the second configuration, where the output of
the combiner is connected to one of the Rx ports on the AD-FMCOMMS3-EBZ, which in turn is connected to two different DDC
blocks within the firmware.
Figure 11 shows successful operation of the parallel system at
different rates and frequencies. Freq_off clearly indicates two signals; one has an offset of 10 kHz and the second signal has 20 kHz
frequency offset, and both have different messages (Satellite-1 and
Satellite-2).
MEMORY REQUIREMENT
Based on the analysis of number of signals that can be housed in a
spectrum of 1.536 MHz, the memory required to store these signals
is calculated at different stages as listed:
GENERAL RESULTS-DISCUSSION
As discussed in [15], the minimum input sampling rate of the
AD9361 RF front-end is 1.5 MSPS and therefore an integral multiple of 96 KSPS which is 1.536 MSPS (> 1.5 MSPS) was chosen. In
order to analyse the worst-case requirements, the entire spectrum
(1.536 MHz) is assumed to be occupied by available signals. For
the reference waveform chosen, the bandwidth required at different symbol rates is depicted in Table 2.
As satellites in LEO are moving at ∼7.5 km/s, the signals received at the ground station experience the Doppler effect. Therefore, the signal bandwidth needs to account for the Doppler effect-which is +/− 2 kHz from the centre frequency for VHF
48
frequencies at LEO [36] and guard bands. Figure 12A shows the
number of signals that can be accommodated in 1.536 MHz with
and without Doppler.
At 1k2, as many as 850 satellites can fit into 1.536 MHz without taking into account the Doppler effect. However, as the symbol
rate increases, the number of signals that can be accommodated
decreases. The number decreases further when considering the
Doppler effect and guard bands around the valid signal.
1. After the hardware decimation-the hardware/firmware decimation rate varies depending on the symbol rate (for 1k2 signal
the decimation rate is 16 while for 19k2 it is 1).
2. Software decimation-this is done in order to match Alex
Csete's decoder (decimation rate is 10, reducing the sample rate
from 96 ksps to 9.6 ksps for 1k2 signal).
3. Complex down conversion to remove residual 1,200 Hz offset
(decimation rate is 8, from 8.6 ksps to 1.2 ksps for 1k2 signal).
4. The final 5,200 bits for decoding after the demodulation.
IEEE A&E SYSTEMS MAGAZINE
NOVEMBER 2018
Aerospace and Electronic Systems - November 2018
Table of Contents for the Digital Edition of Aerospace and Electronic Systems - November 2018
Contents
Aerospace and Electronic Systems - November 2018 - Cover1
Aerospace and Electronic Systems - November 2018 - Cover2
Aerospace and Electronic Systems - November 2018 - Contents
Aerospace and Electronic Systems - November 2018 - 2
Aerospace and Electronic Systems - November 2018 - 3
Aerospace and Electronic Systems - November 2018 - 4
Aerospace and Electronic Systems - November 2018 - 5
Aerospace and Electronic Systems - November 2018 - 6
Aerospace and Electronic Systems - November 2018 - 7
Aerospace and Electronic Systems - November 2018 - 8
Aerospace and Electronic Systems - November 2018 - 9
Aerospace and Electronic Systems - November 2018 - 10
Aerospace and Electronic Systems - November 2018 - 11
Aerospace and Electronic Systems - November 2018 - 12
Aerospace and Electronic Systems - November 2018 - 13
Aerospace and Electronic Systems - November 2018 - 14
Aerospace and Electronic Systems - November 2018 - 15
Aerospace and Electronic Systems - November 2018 - 16
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Aerospace and Electronic Systems - November 2018 - 18
Aerospace and Electronic Systems - November 2018 - 19
Aerospace and Electronic Systems - November 2018 - 20
Aerospace and Electronic Systems - November 2018 - 21
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Aerospace and Electronic Systems - November 2018 - 23
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Aerospace and Electronic Systems - November 2018 - 25
Aerospace and Electronic Systems - November 2018 - 26
Aerospace and Electronic Systems - November 2018 - 27
Aerospace and Electronic Systems - November 2018 - 28
Aerospace and Electronic Systems - November 2018 - 29
Aerospace and Electronic Systems - November 2018 - 30
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Aerospace and Electronic Systems - November 2018 - 68
Aerospace and Electronic Systems - November 2018 - Cover3
Aerospace and Electronic Systems - November 2018 - Cover4
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