Development and Investigation of Communication Issues on a CubeSat-onboard Amateur Radio Payload with APRS Digipeater and Store-and-Forward Capabilities

Automatic Packet Reporting System (APRS) is originally a terrestrial packet communication system widely utilized by amateur radio stations to exchange various information. To extend this capability over a geographically broad coverage, a few microsatellites previously carried an APRS digipeater payload for global amateur community use, and then there have been proposals to do this on smaller nanosatellite platforms, such as the CubeSat. Although CubeSat is an attractive platform for this application – due to its substantially simpler design, lower cost, and faster development time – it also presents several technical challenges such as tight space, power, and communication link budgets. In this paper, we discuss the design, development and testing of an amateur radio payload that operates in the 145.825 MHz amateur frequency, consists of mostly commercial-of-the-shelf components and supports both APRS digipeater and store-and-forward (S&F) communication for remote data collection. The payload was carried as a technology demonstration mission of a 1U CubeSat constellation developed at the Kyushu Institute of Technology under the BIRDS-2 Project. Several amateur operators confirmed reception of the payload’s beacon message but full two-way communication failed due to uplink communication problems. This paper also tackles the investigation on the causes of failure through ground-based communication tests, as well as the recommendations from the findings

Nanosatellite Store-and-Forward Communication Systems for Remote Data Collection Applications

Due to compact design, cost-effectiveness and shorter development time, a nanosatellite constellation is seen as a viable space-based data-relay asset to collect data from remote places that are rather impractical to be linked by terrestrial means. While nanosatellites have these advantages, they have more inherent technical limitations because of limited space for subsystems and payloads. Nanosatellite S&F communication systems are notably challenging in this respect due to requirements on antennas, transceivers, and signal processing. Although nanosatellites can be scaled up for better resources and capabilities, smaller platforms (i.e., ≤6U CubeSat) tend to be used for cost-effectiveness and lower risk. This thesis dealt with the problem of designing a nanosatellite S&F communication system for delay-tolerant remote data collection applications considering: (a) technical constraints in hardware, processing capabilities, energy budget and space in both the nanosatellite and ground sensor terminal (GST) sides; (b) physical communication layer characteristics and constraints such as limited available bandwidth, LEO channel Doppler, attenuation and fading/shadowing effects, low transmit power and data rate, and multi-user interference among asynchronously transmitting terminals. We designed, developed, and operated an amateur radio payload with S&F communication and APRS-DP capabilities, and performed a post-launch communication failure investigation. We also investigated suitability of E-SSA protocol for IoT/M2M terminals to nanosatellite communication by analyzing performance and energy efficiency metrics. The thesis comprises nine chapters. Chapter 1 describes the research background, problem, objectives, state of research, potential contributions of this thesis, and a gist of methodology detailed in later chapters. Chapter 2 and 3 provide an extensive literature review. Chapter 2 reviews the previous research works on using nanosatellites for S&F communication for remote data collection, and the previous nanosatellite S&F missions. Such research works and nanosatellite missions were undertaken primarily in the context of non-commercial/civil applications. Then, Chapter 2 surveys the recent commercial nanosatellite IoT/M2M players and examines their proposed systems in terms of satellite platform, constellation design, communication technology, targeted applications, requirements, and performance. Chapter 3 presents a literature review on communication system architecture, physical layer and random-access schemes, protocols, and technologies relevant to satellite IoT/M2M systems. In the context of IoT/M2M applications, the constraints in energy budget, transmit power and available bandwidth limit the system’s capacity in terms of amount of data that can be received and number of GSTs that can be supported. In both nanosatellite and GST sides, there are stringent limitations in hardware complexity, processing capabilities and energy budget. Addressing these challenges requires a simple, spectrally and energy efficient asynchronous random-access communication protocol. This research investigated using the enhanced spread spectrum Aloha (E-SSA) protocol for satellite IoT/M2M uplink (terminal to satellite) communication and analyzed its performance and suitability for the said application. Chapter 4 discusses the BIRDS-2 CubeSat S&F remote data collection system, payload design, development, tests, and integration with the BIRDS-2 CubeSats. Chapter 5 discusses the investigation on communication design issues of BIRDS-2 CubeSat S&F payload, tackling both the methodology and findings of investigation. It is noted that there are only a few satellites that have carried an APRS-DP payload but even some of these failed due to communication, power, or software issues. In BIRDS-2 Project, considering tight constraints in a 1U CubeSat equipped with other subsystems and payloads, we developed a S&F/APRS-DP payload and integrated it with each of the three 1U CubeSats of participating countries. After launching the CubeSats from the ISS, several amateur operators confirmed reception downlink beacon messages, but full two-way communication failed due to uplink communication failure. Thus, this research not only studied the design and development of a S&F/APRS-DP payload suitable for a CubeSat platform, but also systematically investigated the causes of communication failure by on-orbit observation results and ground-based tests. We found that uplink failure was caused by two design problems that were overlooked during development, namely, the poor antenna performance and increased payload receiver noise floor due to satellite-radiated EMI coupled to the antenna. Chapter 6 first describes the enhanced spread spectrum Aloha (E-SSA) based nanosatellite IoT/M2M communication model implemented in Matlab and derives the mathematical definitions of packet loss rate (PLR), throughput (THR) and energy efficiency (EE) metrics. Then, it tackles the formulated baseband signal processing algorithm for E-SSA, including packet detection, channel estimation, demodulation and decoding. Chapter 7 presents the simulation results and discussion for Chapter 6. Chapter 8 tackles the S&F nanosatellite constellation design for global coverage and presents the results and findings. Chapter 9 describes the laboratory setups for validating the E-SSA protocol and then presents the findings. Finally, Chapter 9 also gives the summary, conclusions, and recommendations. Simulation results showed that for E-SSA protocol with the formulated algorithm, THR, PLR and EE metrics are more sensitive to MAC load G, received power variation σLN and Eb/N0, due to imperfect detection and channel estimation. With loose power control (σLN=3dB), at Eb/N0=14 dB, the system can be operated up to a maximum load of 1.3 bps/Hz, achieving a maximum THR of 1.25 bps/Hz with PLR<0.03. Without power control (σLN=6dB,9dB), at Eb/N0=14 dB, maximum load is also 1.3 bps/Hz, but achievable THR is lower than ~1 bps/Hz and PLR values can be as high as ~0.23. Worse PLR results are attributed to misdetection of lower power packets and demodulation/decoding errors. Both are caused by the combined effects of MUI, channel estimation errors, imperfect interference cancellation residue power, and noise. The PLR and THR can be improved by operating with higher Eb/N0 at the expense of lower energy efficiency. Then, laboratory validation experiments using a SDR-based platform confirmed that with G=0.1, Eb/N0=14dB, σLN=6dB, the formulated algorithm for E-SSA protocol can still work even with inaccurate oscillator (±2 ppm) at GSTs, obtaining experimental PLR result of 0.0650 compared to simulation result of 0.0352. However, this requires lowering the detection thresholds and takes significantly longer processing time. For the S&F nanosatellite constellation design, it was found that to achieve the target percent coverage time (PCT) of more than 95% across all latitudes, a 9x10 Hybrid constellation or a 10x10 Walker Delta constellation would be required.九州工業大学博士学位論文 学位記番号：工博甲第506号 学位授与年月日：令和2年9月25日1: Introduction|2: Nanosatellite S&F Research, Missions and Applications|3: Satellite S&F Communication Systems and Protocols|4: BIRDS-2 CubeSat S&F Data Collection System, Payload Design and Development|5: Investigation on Communication Design Issues of BIRDS-2 CubeSat APRS-DP/S&F Payload, Results and Discussion|6: E-SSA-based Nanosatellite IoT/M2M Communication System Model and Signal Processing Algorithm|7: Simulation Results and Discussion for E-SSA-based Nanosatellite IoT/M2M Communication System|8: Nanosatellite Constellation for Global Coverage|9: Experimental Laboratory Validation for E-SSA Protocol, Research Summary, Conclusions and Recommendations九州工業大学令和2年