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Communication Technologies for Commanding and Control of Aerospace Systems

Communication Technologies for Commanding and Control of Aerospace Systems. Mauro De Sanctis Università di Roma Tor Vergata.

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Communication Technologies for Commanding and Control of Aerospace Systems

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  1. Communication Technologies for Commanding and Control of Aerospace Systems Mauro De Sanctis Università di Roma Tor Vergata

  2. The Telemetry, Tracking & Command (TT&C) subsystem is used to interface the control segment on ground with the spacecraft both in uplink (telecommand link) and in downlink (telemetry link). Telemetry includes data on the status of the platform (e.g. temperature) and the status of the payload (e.g. data on power output of transponders, pointing direction of antennas, antenna and transponder switch configurations). WhatisTT&C?

  3. The TT&C subsystem is managed by operators on a 24/7 basis through specialized software for Human Computer Interaction (HCI). The requirements of the TT&C subsystem and the HMI software is: fast anomaly detection and mitigation; large number of spacecrafts controlled by a single operator; high level of reliability. Human Computer Interaction in TT&C

  4. TT&Cfor the Alphasat TDP#5 Experiment

  5. Current TT&C systems adopt a standard encapsulation procedure to generate the telecommand packet that is defined by the European Cooperation for Space Standards (ECSS). ECSS-E-ST-50-04C, “Space Data Links – Telecommand Protocols, Synchronization and Channel Coding”, July 2008: The segmentation sublayer breaks long data units into smaller portions (TC segments) so that they are consistent with the limited length of the frames in the transfer sublayer. The transfer sublayer contains procedures for generating and processing TC Transfer Frames, i.e. variable length data structures designed for the efficient transfer of variable length data units. The synchronization and channel coding sublayer establishes an error controlled data channel through which data can be transferred. Synchronization for the codeblock and delimiting of the beginning of user data are provided by the communications link transmission unit (CLTU) data structure. The physical layer accepts CLTU from the upper sublayer and performs data transmission through the physical channel. TT&CStandard

  6. The synchronization and channel coding sublayer splits the TC Transfer Frame into information blocks each of 56 bit. The information blocks are BCH encoded using a BCH(63,56) channel code and a filler bit equal to zero is included at the end of each codeblock. N BCH codeblocks (each 64 bits long) are encapsulated into a Communication Link Transmission Unit (CLTU). The constraint on the length of a TC Transfer Frame, 1024 octets, imposes a limit on the CLTU, which is composed by a maximum of 1186 octets, with N equal to 147 BCH blocks. ECSS Standard

  7. To further increase the robustness to jammers, additional channel coding could play a fundamental role. Latency and complexity should be taken into account. Direct Sequence Spread Spectrum transmission is considered with a limitation on the length of the spreading sequence (low synchronization time and low processing gain). No need to change the TT&C standard. Robustness of Satellite Telecommand Links to Jamming Attacks

  8. Different types of jammers are considered: The Broadband Noise (BBN) jammer spreads Gaussian Noise over the total frequency range of the spread spectrum band. The Partial Band Noise (PBN) jammer adds noise only over some frequency range of spread spectrum band. The Tone Jammer consists of one Continuous Wave (CW) tone. The Pulsed Jammer interferes on a block of contiguous symbols of the useful signal Robustness of Satellite Telecommand Links to Jamming Attacks

  9. Simulation Results Robustness of Satellite Telecommand Links to Jamming Attacks

  10. Simulation Results Robustness of Satellite Telecommand Links to Jamming Attacks

  11. The TT&C of a satellite system requires highly robust telemetry and telecommand links. Current standards for TT&C can be enhanced by introducing an extra level of channel coding. For some kind of jammers (BBN, PBN), the concatenation BCH+Convolutional Code could provide a good compromise between performance and latency. In the case of pulsed jammers, the only scheme able to work effectively is the concatenation of RS+BCH. Conclusions

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