Next generation earth-to-space telecommand coding and synchronization: ground system design, optimization and software implementation

Abstract

The Consultative Committee for Space Data Systems, followed by all national and international space agencies, has updated the Telecommand Coding and Synchronization sublayer to introduce new powerful low-density parity-check (LDPC) codes. Their large coding gains significantly improve the system performance and allow new Telecommand services and profiles with higher bit rates and volumes. In this paper, we focus on the Telecommand transmitter implementation in the Ground Station baseband segment. First, we discuss the most important blocks and we focus on the most critical one, i.e., the LDPC encoder. We present and analyze two techniques, one based on a Shift Register Adder Accumulator and the other on Winograd convolution both exploiting the block circulant nature of the LDPC matrix. We show that these techniques provide a significant complexity reduction with respect to the usual encoder mapping, thus allowing to obtain high uplink bit rates. We then discuss the choice of a proper hardware or software platform, and we show that a Central Processing Unit-based software solution is able to achieve the high bit rates requested by the new Telecommand applications. Finally, we present the results of a set of tests on the real-time software implementation of the new system, comparing the performance achievable with the different encoding options.

Performance Improvement of Space Missions Using Convolutional Codes by CRC-Aided List Viterbi Algorithms

“…The LDPC encoders are based on their generator matrices. The LDPC parity check matrices are sparse, but this is not the case for the generator matrices which are dense, then the number of elementary operations for the large CCSDS TM LDPC codes is not negligible, even when some simplifications obtained by exploiting their block-circulant structure are applied [34]. Moreover, the CCSDS LDPC codes require a different generator matrix for each code-rate, making the onboard complexity not negligible.…”