Communications Subsystem
CubeEyes RF and Communications Technical Report
| rfcommunication_reportdocx.docx.docx |
Telemetry and Control
Satellite health and controls will be relayed via the UTRX Half Duplex UHF transceiver from Clyde-Space. Utilizing a GMSK modulation scheme coupled with the AX.25 protocol, this radio will be compatible with many off-the-shelf groundstation receivers, making the creation of a world-wide network relatively cheap.
UTRX by Clyde-Space
http://www.clyde-space.com/cubesat_shop/communication_systems/350_utrx-half-duplex-uhf-transceiver
Image Data Download
While the UTRX is a versatile transceiver, it does not have a high enough bit rate to download imaging data in a timely fashion. WIth a typical JPEG-compressed 6576 x 4384 image weighing in at 3.8 MB, the UTRX, transmitting at its highest baud rate of 9600 over GMSK, would take over 6 minutes to transmit just one image down to Earth.
As a supplementary system, we have also opted to include Clyde-Space's S-Band QPSK-modulated transmitter. This device is capable of transmitting at a rate of 2 Mbps, taking only 2 seconds to transmit that exact same image file. As discussed in the page detailing the imaging system, each satellite can be expected to collect roughly 869 MB of JPEG image files. At 2 Mbps, it will take 58 minutes to transmit the data collected from a single orbit. Since an entire orbit is only ~90 minutes, receiver stations will be needed all over the planet in order to enable a near-constant window of transmission for the satellites.
Furthermore, since there will be multiple satellites attempting to transmit image data to any single ground station at any given time, we have modified the S-Band transmitter to include a CDMA encoder, (and ground stations with complementary decoders and multiplexers), to enable each satellite to transmit without risk of interference from other CubeEyes satellites.
S-Band Downlink
http://www.clyde-space.com/cubesat_shop/communication_systems/301_cubesat-s-band-transmitter
Ground Station Transceivers
Our CubeSat antennas have a beamwidth of 60 degrees. In order to guarantee near perfect coverage to enable constant S-Band image download connection, we will
All of our Earth stations will be based upon the STAC system from Clyde-Space, modified to support S-Band communication.
STAC System
http://www.clyde-space.com/cubesat_shop/ground_stations/343_satellite-tracking-and-control-station-stac
S-Band to L-Band Downconverter:
http://www.clyde-space.com/cubesat_shop/communication_systems/351_s-band-to-l-band-down-converter
Satellite health and controls will be relayed via the UTRX Half Duplex UHF transceiver from Clyde-Space. Utilizing a GMSK modulation scheme coupled with the AX.25 protocol, this radio will be compatible with many off-the-shelf groundstation receivers, making the creation of a world-wide network relatively cheap.
UTRX by Clyde-Space
http://www.clyde-space.com/cubesat_shop/communication_systems/350_utrx-half-duplex-uhf-transceiver
Image Data Download
While the UTRX is a versatile transceiver, it does not have a high enough bit rate to download imaging data in a timely fashion. WIth a typical JPEG-compressed 6576 x 4384 image weighing in at 3.8 MB, the UTRX, transmitting at its highest baud rate of 9600 over GMSK, would take over 6 minutes to transmit just one image down to Earth.
As a supplementary system, we have also opted to include Clyde-Space's S-Band QPSK-modulated transmitter. This device is capable of transmitting at a rate of 2 Mbps, taking only 2 seconds to transmit that exact same image file. As discussed in the page detailing the imaging system, each satellite can be expected to collect roughly 869 MB of JPEG image files. At 2 Mbps, it will take 58 minutes to transmit the data collected from a single orbit. Since an entire orbit is only ~90 minutes, receiver stations will be needed all over the planet in order to enable a near-constant window of transmission for the satellites.
Furthermore, since there will be multiple satellites attempting to transmit image data to any single ground station at any given time, we have modified the S-Band transmitter to include a CDMA encoder, (and ground stations with complementary decoders and multiplexers), to enable each satellite to transmit without risk of interference from other CubeEyes satellites.
S-Band Downlink
http://www.clyde-space.com/cubesat_shop/communication_systems/301_cubesat-s-band-transmitter
Ground Station Transceivers
Our CubeSat antennas have a beamwidth of 60 degrees. In order to guarantee near perfect coverage to enable constant S-Band image download connection, we will
All of our Earth stations will be based upon the STAC system from Clyde-Space, modified to support S-Band communication.
STAC System
http://www.clyde-space.com/cubesat_shop/ground_stations/343_satellite-tracking-and-control-station-stac
S-Band to L-Band Downconverter:
http://www.clyde-space.com/cubesat_shop/communication_systems/351_s-band-to-l-band-down-converter