A Simple Fragmentation Protocol for Satellite Telemetry Transmission of Large Telemetry from the MIST Satellite
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DEGREE PROJECT IN TECHNOLOGY, FIRST CYCLE, 15 CREDITS STOCKHOLM, SWEDEN 2020 A simple fragmentation protocol for satellite telemetry Transmission of large telemetry from the MIST satellite ERIK FLINK KTH ROYAL INSTITUTE OF TECHNOLOGY SCHOOL OF ELECTRICAL ENGINEERING AND COMPUTER SCIENCE A simple fragmentation protocol for satellite telemetry Transmission of large telemetry from the MIST satellite ERIK FLINK Degree Programme in Information and Communication Technology Date: June 7, 2020 Supervisor: Johan Montelius Examiner: Markus Hidell School of Electrical Engineering and Computer Science Host organization: MIST project Swedish title: Ett enkelt fragmenteringsprotokoll för satellit-telemetri Swedish subtitle: Sändning av stor telemetri från MIST-satelliten A simple fragmentation protocol for satellite telemetry / Ett enkelt fragmenteringsprotokoll för satellit-telemetri c 2020 Erik Flink Abstract | i Abstract MIniature STudent satellite(MIST) is a project at the Royal Institute of Technology (KTH) in Stockholm where students build a satellite. The satellite will be placed into orbit around the earth carrying six experiments. One of the experiments on-board the MIST satellite will need to send larger units of data than the radio on-board can send at a time. Therefore, the data will need to be fragmented before it is sent and then defragmented when it is received. The fragmentation protocol to be used, and its implementation, will need to meet the MIST satellite’s requirements and limitations. It should add as little overhead and complexity as possible. This thesis proposes a fragmentation protocol and presents an implementa- tion that enables experiments on-board the MIST satellite to send larger units of data than on-board radio allows. The design of the protocol is based on existing network protocols, but tailored for use on the MIST satellite. The proposed protocol may be possible to use in other satellites or embedded systems applications. This may however require some modifications. Keywords fragmentation, network, protocol, satellite, communication ii | Abstract Sammanfattning | iii Sammanfattning MIniature STudent satellite(MIST) är ett projekt på Kungliga Tekniska Högskolan(KTH) i Stockholm där studenter bygger en satellit. Satelliten kommer att placeras i omloppsbana runt jorden med sex experiment ombord. Ett av experimenten ombord på MIST-satelliten behöver skicka större data än vad radiomodulen ombord kan sända åt gången. Därför behöver datan fragmenteras innan den skickas och sedan defragmenteras då den tas emot. Fragmenteringsprotokollet som ska användas, och dess implementation, behöver uppfylla MIST-satellitens krav och begränsningar. Protokollet bör tillföra så lite overhead och komplexitet som möjligt. Detta examensarbete föreslår ett fragmenteringsprotokoll och presenterar en implementation som möjliggör för experimenten ombord MIST-satelliten att sända större data än vad radiomodulen tillåter. Protokollets design är baserat på existerande nätverksprotokoll, men skräddarsytt för att användas av MIST- satelliten. Det föreslagna protokollet kan användas av andra satelliter eller inbyggda system. Detta kan dock kräva vissa anpassningar. Nyckelord fragmentering, nätverk, protokoll, satellit, kommunikation iv | Sammanfattning Acknowledgments | v Acknowledgments I would like to thank MIST project manager Sven Grahn, MIST OBC team supervisor John Wikman and all other members of MIST team 11 who helped me during the thesis project. I would also like to thank MIST OBC team supervisor David Broman for introducing me to the MIST project and this topic. Due to the ongoing COVID-19 pandemic, work on this thesis was done from home without access to OBC hardware and ground station equipment. John Wikman made the equipment remotely available from his home, for which I am very grateful. Lastly I want to thank Johan Montelius for being my supervisor, supporting me during my thesis work, and those who have helped me to proofread this report. Stockholm, June 2020 Erik Flink vi | Acknowledgments CONTENTS | vii Contents 1 Introduction1 1.1 Background...........................1 1.2 Problem.............................2 1.3 Purpose.............................2 1.4 Goal...............................2 1.5 Methodology..........................3 1.6 Delimitations..........................3 1.7 Sustainability and ethics....................3 1.8 Structure of the thesis......................4 2 Background5 2.1 Network communication protocols...............5 2.2 Cube satellites..........................7 2.3 The MIST project........................7 2.4 Technologies used during the project.............. 12 3 Methodology 13 3.1 Identification of requirements and limitations......... 13 3.2 Examination of existing protocols............... 13 3.3 Design.............................. 14 3.4 Implementation......................... 14 3.5 Evaluation............................ 14 4 Existing Protocols 17 4.1 User Datagram Protocol (UDP) and Internet Protocol (IP)... 17 4.2 Transmission Control Protocol (TCP)............. 18 4.3 Reliable Data Protocol (RDP).................. 19 4.4 Cubesat Space Protocol (CSP)................. 19 4.5 Summary and Applicability................... 20 viii | Contents 5 Design 21 5.1 Design considerations...................... 21 5.2 Header fields.......................... 22 5.3 Fragmentation.......................... 24 5.4 Defragmentation........................ 25 6 Implementation 33 6.1 On-board software implementation............... 33 6.2 Ground station implementation................. 34 7 Analysis 37 7.1 Time complexity analysis.................... 37 7.2 Protocol overhead........................ 39 7.3 Theoretical net data rate..................... 39 8 Discussion 41 8.1 Time complexity........................ 41 8.2 Overhead............................ 41 8.3 Data rate............................. 42 8.4 Reliability............................ 42 8.5 Other use cases......................... 42 8.6 Conclusions........................... 43 8.7 Future work........................... 43 References 45 LIST OF FIGURES | ix List of Figures 2.1 Total Nanosatellites & CubeSats Launched [1].........7 5.1 Fragmentation protocol fields.................. 22 5.2 Pseudocode for generating fragments from a data block.... 25 5.3 Pseudocode for processing received fragments......... 28 5.4 Pseudocode for creating a new block buffer.......... 29 5.5 Pseudocode for inserting a fragment in an existing block buffer 30 5.6 Pseudocode for creating a block object from a block buffer.. 31 x | LIST OF FIGURES LIST OF TABLES | xi List of Tables 2.1 Experiments on-board the MIST satellite [2]..........8 2.2 BER over a typical ground station pass............. 11 7.1 Fragmentation protocol overhead for different block sizes with a fragment size of 214 bytes.................. 39 7.2 Theoretical net data rate for different block sizes with a fragment size of 214 bytes................... 40 xii | LIST OF TABLES LISTINGS | xiii Listings 6.1 The fragmenter struct...................... 33 6.2 Fragmentation API....................... 34 6.3 Defragmenter fields....................... 35 6.4 BlockBuffer fields........................ 35 6.5 Block fields........................... 35 6.6 Defragmentation API...................... 36 xiv | LISTINGS List of acronyms and abbreviations | xv List of acronyms and abbreviations Eb=N0 energy per bit to noise power spectral density ratio AAUSat3 Aalborg University CubeSat-3 API Application Programming Interface APID Application Process ID AX.25 Amateur X.25 BER Bit Error Ratio BPSK Binary Phase Shift Keying CCSDS Consultative Committee for Space Data Systems CSP Cubesat Space Protocol CUBES CubeSat x-ray Explorer using Scintillators ECSS European Cooperation for Space Standardization IETF Internet Engineering Task Force IP Internet Protocol ISIS Innovative Solutions In Space KTH Kungliga Tekniska Högskolan MIST MIniature STudent satellite MTU Maximum Transmission Unit OBC On-Board Computer PUS Packet Utilization Standard RDP Reliable Data Protocol RFC Request for Comments xvi | List of acronyms and abbreviations SFP Small Fragmentation Protocol SST Service Subtype ST Service Type TCP Transmission Control Protocol TRXVU ISIS Transceiver, UHF Transmitter and VHF Receiver TT&C Telemetry, Tracking and Command TTL Time To Live UDP User Datagram Protocol UHF Ultra High Frequency VHF Very High Frequency Introduction | 1 Chapter 1 Introduction In this thesis, a protocol for fragmenting data sent over a limited connection is proposed, examined and implemented for usage in the MIniature STudent satellite(MIST) satellite. This chapter first gives some background to and describes the problem that is addressed. The purpose and goals are then presented. The methodology and the delimitations are also described. 1.1 Background Cube satellites, or CubeSats, are a standardized type of small satellites that consists of one or more 10 ∗ 10 ∗ 10 centimeter cube units weighing 1.33 kg each [3]. The MIST project is a project at KTH where student teams build a three-unit (3U) CubeSat. The satellite will be launched into orbit around the earth carrying six experiments owned by different entities. The MIST satellite will be controlled by a On-Board Computer(OBC) that is purchased from Innovative Solutions In Space(ISIS), but the software is developed by a MIST sub-team at KTH. The OBC will collect data from the satellite’s experiments and sub-systems and send it down to a ground station located at KTH Campus in Stockholm. Data will be sent