Towards improved satellite telecommand link availability

Compliant with the Consultative Committee for Space Data Systems (CCSDS) set of protocols, we explore enhancing the availability service for space links. In particular, we consider specific improved defences against jamming attacks affecting symbol synchronization. More robust adaptive closed-loop symbol synchronizers are designated with a view to the planned update of the CCSDS standard for the telecommand synchronization and channel coding sublayer of the data link layer. It is shown that adaptive schemes exploiting instantaneous jammer state information are recommended to counter destructive attacks that may harm the availability

Frame synchronization for pulsed jammed satellite telecommand links

A new issue of the satellite telecommand synchronization and channel coding sublayer protocol 1 includes LDPC coded communication link transmission units (CLTU) 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, i.e., 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

An efficient NB-LDPC decoder architecture for space telecommand links

In the framework of error correction in space telecommand (TC) links, the Consultative Committee for Space Data Systems (CCSDS) currently recommends short block-length BCH and binary low-density parity-check (LDPC) codes. Other alternatives have been discarded due to their high decoding complexity, such as non-binary LDPC (NB-LDPC) codes. NB-LDPC codes perform better than their binary counterparts over AWGN and jamming channels, being great candidates for space communications. We show the feasibility of NB-LDPC coding for space TC applications by proposing a highly efficient decoding architecture. The proposed decoder is implemented for a (128,64) NB-LDPC code over GF(16) and the design is particularized for a space-certified Virtex-5QV FPGA. The results prove that NB-LDPC coding is an alternative that outperforms the standardized binary LDPC, with a coding gain of 0.7 dB at a reasonable implementation cost. Given that the maximum rate for TC recommended by the CCSDS is 2 Mbps, the proposed architecture achieves a throughput of 2.03 Mbps using only 9615 LUTs and 5637 FFs (no dedicated memories are used). In addition, this architecture is suitable for any regular (2,4) NB-LDPC (128,64) code over GF(16) independently of the H matrix, allowing flexibility in the choice of the code. This brief places NB-LDPC codes as the excellent candidates for future versions of the telecommand uplink standard.This work was supported by Spanish MICINN/AEI under Project TEC2017-86722-C4-3-R

Performance of advanced telecommand frame synchronizer under pulsed jamming conditions

This paper studies frame synchronization for use with the advanced communication link transmission unit format that was recently proposed for updating the telecommand synchronization and channel coding standard for space applications. With a view to improving the robustness against jamming, future satellite telecommand systems are planning to adopt direct-sequence spread spectrum modulation and advanced channel coding. Compared to the frame synchronization algorithm specified in the current Consultative Committee for Space Data Systems (CCSDS) recommendation, we consider a longer start sequence and relax the condition for declaring synchronization. We investigate the performance of this algorithm in the presence of jamming, and show that the frame synchronizer can be designed such that the overall system’s robustness against pulsed jamming is limited by the robustness of the code rather than the synchronizer

State-of-the-art space mission telecommand receivers

Since their dawning, space communications have been among the strongest driving applications for the development of error correcting codes. Indeed, space-to-Earth telemetry (TM) links have extensively exploited advanced coding schemes, from convolutional codes to Reed-Solomon codes (also in concatenated form) and, more recently, from turbo codes to low-density parity-check (LDPC) codes. The efficiency of these schemes has been extensively proved in several papers and reports. The situation is a bit different for Earth-to-space telecommand (TC) links. Space TCs must reliably convey control information as well as software patches from Earth control centers to scientific payload instruments and engineering equipment onboard (O/B) spacecraft. The success of a mission may be compromised because of an error corrupting a TC message: a detected error causing no execution or, even worse, an undetected error causing a wrong execution. This imposes strict constraints on the maximum acceptable detected and undetected error rates

An Efficient NB-LDPC Decoder Architecture for Space Telecommand Links

In the frame of error correction in space telecommand (TC) links, the Consultative Committee for Space Data Systems (CCSDS) currently recommends short block-length BCH and binary LDPC codes. Other alternatives have been discarded due to their high decoding complexity, such as LDPC and eBCH codes with MRB decoding and NB-LDPC codes. NBLDPC codes perform better than their binary counterparts over AWGN and jamming channels, being excellent candidates for space communications. In this brief, we show the feasibility of NB-LDPC coding for space TC applications by proposing a highly efficient decoding architecture. The proposed decoder is implemented for a (128,64) NB-LDPC code over GF(16) and the design is particularized for a space-certified Virtex-5QV FPGA. The results prove that NB-LDPC coding is an alternative outperforming the standardized binary LDPC at a reasonable cost. Given that the maximum rate for TC recommended by the CCSDS is 2 Mbps, the proposed architecture achieves a throughput of 2.4 Mbps using only 8797 LUTs and 5460 FFs (no dedicated memories are used). In addition, this architecture is suitable for any regular (2,4) NB-LDPC (128,64) code over GF(16) independently of the H matrix, allowing great flexibility for the use with the recently proposed short block-length NBLDPC codes in upcoming telecommand uplink standards

Information-theoretic Physical Layer Security for Satellite Channels

Shannon introduced the classic model of a cryptosystem in 1949, where Eve has access to an identical copy of the cyphertext that Alice sends to Bob. Shannon defined perfect secrecy to be the case when the mutual information between the plaintext and the cyphertext is zero. Perfect secrecy is motivated by error-free transmission and requires that Bob and Alice share a secret key. Wyner in 1975 and later I.~Csisz\'ar and J.~K\"orner in 1978 modified the Shannon model assuming that the channels are noisy and proved that secrecy can be achieved without sharing a secret key. This model is called wiretap channel model and secrecy capacity is known when Eve's channel is noisier than Bob's channel. In this paper we review the concept of wiretap coding from the satellite channel viewpoint. We also review subsequently introduced stronger secrecy levels which can be numerically quantified and are keyless unconditionally secure under certain assumptions. We introduce the general construction of wiretap coding and analyse its applicability for a typical satellite channel. From our analysis we discuss the potential of keyless information theoretic physical layer security for satellite channels based on wiretap coding. We also identify system design implications for enabling simultaneous operation with additional information theoretic security protocols

Definizione, studio e progetto preliminare di una tecnica di geo-localizzazione di sorgenti interferenti per satelliti commerciali di telecomunicazioni

L’argomento del dottorato riguarda le telecomunicazioni satellitari commerciali. In particolare tratta della possibilità di poter definire, progettare e valutare mediante analisi e simulazioni, un sistema in grado di geo-localizzare sorgenti interferenti nell’area di copertura dell’antenna a bordo satellite per telecomunicazioni (area di servizio). Tale soluzione tecnologica rappresenta un valido supporto per intervenire a seguito di uno o più eventi interferenti. Tale intervento può essere o di tipo passivo, quanto il satellite non è provvisto di sotto-sistema di contromisura, oppure attivo quando il satellite è provvisto a bordo di sistema di contromisura