Aerospace and Electronic Systems - May 2019 - 24

Reconﬁgurable Wavelet Based Real Time Imaging System for Low Bit Rate Telemetry Space Missions

Figure 1.
Block diagram of processing electronics.

the processing chain. The output of the color analog camera is digitized by the video ADC. Video ADC converts
analog camera data to CCIR-656 digital format. The compression module accepts the digitized output compatible
with the CCIR-656 format [3].
FPGA configures the video ADC through I2C interface.
It controls the operation of the compression module and
interfaces to all peripheral devices. The compressed data is
written to Dual Port memory, and transmitted through the
telemetry link. Dual Port memory is used because the writing of compressed data as well as transmission through
telemetry should happen simultaneously. The system is
capable of real-time acquisition, compression, and transmission. All programmable parameters are stored in the
reprogrammable memory. The reprogrammable memory is
programmed for each flight to cater to mission requirements.

MODES OF OPERATION OF THE SYSTEM
The system has two modes of operation-low frame rate
mode and high frame rate mode. The default operating
mode is the low frame rate mode in which one frame is
written to memory, transmitted to ground at the available
link rate and only then the subsequent frame is acquired.
In low frame rate mode, we get frames at regular intervals
assuming that the bitrate is constant. During events of
interest, the system receives a capture command, on
receipt of which the system acquires images at a higher
(programmable parameter) frame rate with the selected
camera and stores in onboard memory. The images are
transmitted to ground at the available bit rate. After transmission of all the frames is completed, the system
switches to the low frame rate mode with the camera of
the next event. The system is capable of accepting eight
such capture commands. This feature along with the
programmable features makes it possible for the system to
be used in applications with very low telemetry bit rate.

PROGRAMMABLE PARAMETERS OF THE SYSTEM
For catering to various missions with varied requirements,
various programmable features are built into the system.
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All programmable parameters are stored in
onboard reprogrammable memory. These parameters include the number of frames, frame rate, the
start of transmission of stored images, the
sequence of transmission of images to ground,
compression ratio, and camera selection. These
parameters are fetched from memory on receipt of
capture command. For each capture command,
there is a separate set of programmable parameters
stored in the reprogrammable memory. Thus the
system can work with different frame rate, the
number of frames, transmission sequence, and
transmission start time for each of the eight capture
commands.
Compression ratio is programmable. Optimum value
needs to be set depending on the image quality required
and the telemetry bandwidth available. The compression
ratio will dictate the number of frames obtained in low
frame rate mode as a low compression ratio means an
increase in the time it takes to transmit a frame to the
ground [7]. In capture mode, the frames stored at high
frame rate should be transmitted before the next event
occurs. There is only one compression ratio set for the
system for a particular mission. We have set compression
ratios of 20:1, 32:1, and 50:1 for various missions. It was
seen that beyond 60:1, the image quality significantly
degrades.
Number of frames denotes the total number of frames
that needs to be captured for that particular event. This is
stored in the reprogrammable memory. The maximum
number of frames that can be stored depends on the memory capacity and the compression ratio. The system can
store 250 images onboard at a compression ratio of 32:1.
Frame Rate is the number of frames per second that is
stored in memory in capture mode. As the total number of
frames that can be stored is fixed, varying the frame rate
gives the flexibility to acquire images for varying duration. If the event of interest spans several seconds, then it
can be captured at a lower frame rate to cover the entire
duration.
Start of transmission of stored images is the parameter
that gives the flexibility to transmit the stored images to
the ground at a programmed instant. This is useful if the
telemetry is unavailable during an event, then images will
be transmitted at the preprogrammed time [8].
Sequence of transmission of stored images helps to
obtain a quick summary of the event occurrence. It might
take few hundreds of seconds for the entire images to be
received at the ground, hence the images are transmitted
in the preprogrammed sequence for example: 1,5, 10. . .
followed by the remaining images sequentially. Thus
executives in mission console can quickly assess the
performance of an event in near-real time.
Camera selection parameter selects the camera
with which the processing electronics acquires the

IEEE A&E SYSTEMS MAGAZINE

MAY 2019

Aerospace and Electronic Systems - May 2019

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