Charters : 5.02 Space Link Coding and Synchronization Working Group

 

In order to establish a common framework within which the Agencies may develop standardized services for Telemetry, Telecommand and Proximity-1 links, the CCSDS advocates adoption of a layered systems architecture. Within this approach, the Coding and Synchronization Layer has the purpose of protecting higher layer data units (i.e. "frames") against errors induced during transmission through the physical path to/from a spacecraft. The Coding layer shall satisfy the System requirement for the delivery of data units to the receiving end upper layer. It shall satisfy this task by encoding the user data from the layer above to protect them against noise-induced errors during transmission through the underlying radio frequency channel and by using suitable synchronization techniques to allow proper identification of the individual data units.. In addition the wide range of environment (space-Earth or space-space, near Earth congested bands and deep space link operations in extreme conditions of SNR, links dependent of atmospheric conditions in the new high frequency bands) requires coding systems with different levels of power efficiency and bandwidth efficiency, or different levels of link reliability or delivered data quality. Additionally, harsh environment impairments such as out-of-synchronization events and adverse weather conditions, demand for the application of higher-layer coding techniques, actually complementing the lower layers channel coding schemes.

The targets mentioned above shall be achieved by defining the methods by which data can be sent from a source to a destination such that distinct messages can be easily distinguishable from one another and their reconstruction can be performed with low error probability, thus improving the performance of the channel. The Coding and Synchronization WG shall provide/maintain standards to be applied to Telemetry, Telecommand and Proximity-1 links to allow Agencies to implement the most appropriate Coding & Synchronization procedures. The characteristics of the codes shall be specified only to the extent necessary to ensure interoperability and cross-support. Correct interaction with the procedures at the Data Link Protocol sublayer and Physical layers shall be ensured too. These goals shall be achieved by updating the existing set of Channel Coding Books by either modifying existing books or creating new books as required and described in the WG Projects. The full list of current goals/projects and completed ones is provided at https://cwe.ccsds.org/fm/Lists/Projects/AllOpenChartersWithAllProjects.aspx (charter 5.02)