Received: 23 August 2018 Revised: 21 December 2018 Accepted: 25 February 2019 DOI: 10.1002/sat.1305 RESEARCH ARTICLE Frame synchronization for pulsed jammed satellite telecommand links Nele Noels Marc Moeneclaey Telecommunications and Information Processing Department, UGent, Ghent, Belgium Correspondence Nele Noels, UGent, Sint-Pietersnieuwstraat 41, B-9000 Ghent, Belgium. Email: nele.noels@ugent.be Funding information European Space Agency, Grant/Award Number: SATNEX IV COO1/P1 "Physical Layer Security" Summary A new issue of the satellite telecommand synchronization and channel coding sublayer protocol includes LDPC-coded communication link transmission units (CLTUs) that contain a 64-bit start sequence. The novel data structures allow operation at lower signal-to-noise ratios than before and offer improved protection against jamming attacks. This paper considers the corresponding CLTU frame synchronization process. We derive practical algorithms to locate the start sequence in the presence of high noise levels and pulsed jamming. The different algorithms are compared in terms of implementation complexity and performance under various jamming conditions. It is shown that among the considered frame synchronizers, those involving a full search over the entire observation window provide the desired accuracy, ie, they guarantee a frame synchronization error probability that is significantly smaller than the codeword error rate, for codeword error rates near a target value of 10 -4 . Among these synchronizers, the full-search hard-decision–directed correlation-based algorithm has the lowest complexity. KEYWORDS frame synchronization, pulsed jamming, satellite telecommand system 1 INTRODUCTION With a view of increasing the robustness of satellite telecommand (TC) links against jamming, the planned next-generation TC systems adopt direct-sequence spread-spectrum (DSSS) modulation with a very long pseudo-noise (PN) spreading code repetition period and a high spreading factor, along with advanced channel coding. 1 In previous studies, 2-4 the codeword error rate (CER) performances of the recommended coding schemes have been investigated under DSSS modulation in the presence of jamming, assuming perfect chip, carrier, symbol, and frame synchronization. The present study focuses on frame synchronization. Frame synchronization in additive white Gaussian noise (AWGN) channels is a well-investigated problem. 5-8 In contrast, frame synchronization in the presence of jamming has received only limited attention in the literature. Algorithms, specifically designed to operate under jamming conditions, are described and evaluated in previous studies. 9-11 The usual space TC packet transmission scenario, where a known start sequence (SS) is prefixed to each block of coded data, is considered only in Driessen 10 ; however, the corresponding analysis is limited to continuous jamming and so does not include the important case of pulsed jamming. More recently, the performance of a simple frame synchronization procedure based on sequential hypothesis testing and hard symbol-decisions has been studied under pulsed jamming conditions in Noels and Moeneclaey. 12 The considered frame synchronizer was designed with the objective to minimize the modifications to the legacy SS search algorithm described in the CCSDS standard 1,13 for missions using a (63,56) modified BCH code with a hard-limiting detector followed by a triple-error-detection or a single-error-correction decoder. A possible way to further reduce the synchronization error probability (SEP) under jamming is to adopt more involved frame synchronization algorithms, similar to the ones proposed in Pfletschinger et al 8 and Liang et al 14 for AWGN and fading channels but generalized to include pulsed jamming. The outline of this paper is as follows. Section 2 describes the pulsed jammed TC communication system under investigation. Section 3 formulates the corresponding maximum-likelihood (ML) frame synchronization rule. The latter is theoretically optimal in the sense of minimum SEP but difficult to implement in practice. Several practical ML-based frame synchronization algorithms are considered in Section 4. As opposed Int J Satell Commun Network. 2019;1–15. wileyonlinelibrary.com/journal/sat © 2019 John Wiley & Sons, Ltd. 1