Earth Observation (EO) and Intelligence, Surveillance and Reconnaissance (ISR) Systems equipped with Synthetic Aperture Radar (SAR) and/or High Resolution Optical instruments are designed for high-performance operations in terms of fast revisit time, for very short system response time and for providing actionable intelligence with low data latency. The increased reliance on this data for increasingly more urgent applications has created demand for decreasing latency, for all datasets, including optical Earth Observation, radar and weather satellites.
To achieve this goal, higher transmission rates for data download are needed with the growing numbers of satellites featuring increasing instrument resolutions. At the same time, the limited available bandwidth especially in the X-band used for Earth Observation Downlinks (8.025 GHz to 8.4 GHz) calls for more bandwidth efficient modulation schemes.
For usage on large EO satellites, new data transmission solutions have been developed to efficiently use the available radio frequency (RF) bandwidth by using Adaptive Coding & Modulation (ACM) as a key technology, allowing the data rate to adapt to link characteristics. At the same time, high performance forward error correction coding with SCCC and high order modulation schemes (up to 64-APSK) are used, yielding both high power efficiency and high spectral efficiency. The implemented solutions follow the CCSDS 131.2-B-1 standard for Flexible and Advanced Coding & Modulation Schemes for High Rate Telemetry Applications.
Such systems are currently being implemented in multiple high-end missions, so that the technology is already proven today in terms of End-to-End performance and data integrity. However, these systems follow the traditional approach of subsystems relying on bulky Travelling Wave Tube Amplifiers (TWTA) not suitable for small Earth Observation satellites. Due to the rapid evolution that takes place in instrument designs for small Earth Observation satellites reaching high resolutions, the need for compact solutions, employing the transmission technology described above, is strongly increasing also for these kind of missions.
Therefore, a very compact digital design employing plastic packaged components is a key enabler for a compact solution. In the same sense, the usage of Solid State Power Amplifiers (SSPA) allows to reduce size and weight compared to TWTA based solutions. Furthermore, newly available GaN MMICs in X Band allow for designs with higher RF output power of up to 20 W (in saturation) due to improved efficiency and with that reduced dissipation and DC power consumption.
A further important element in a downlink transmission system is the RF output filter, which is needed to limit out-of-band emissions. Especially in the adjacent Deep Space Network band (8.4 to 8.45 GHz) high filter rejection is required. In legacy systems, filter designs with very low insertion loss have been used, leading to bulky and heavy designs. A new approach is part of the presented system that allows for a compact filter design still maintaining high filter rejection performance.
The paper will share details on a highly integrated one-box transmitter design specifically suited for small Earth Observation satellites. This will include a description of the concepts for the digital section, the power amplification stage as well as the RF output filter.
A discussion of advantages compared to legacy systems, including cost, will be included. On the other hand, also limitations of the solution (symbol rate, class 2/3 design) will be discussed.
In terms of End-to-End performance, such sophisticated systems need to account for the ground station receiver characteristics. The proposed solution has therefore been verified using ground station demodulators available on the market, yielding very high bit-error rate performance at very low implementation loss.
In this context, the End-to-End approach also includes accounting for adapting to varying link conditions due to weather changes and elevation angle in the flyover. Therefore, an evaluation of the link budget will be included focusing on the usage of Adaptive or Variable Coding & Modulation (ACM/VCM) techniques. ACM requires an uplink feedback channel with low latency which may be challenging for Earth Observation missions employing small low-cost satellites. VCM however only needs a pre-scheduling of the downlink passes which can be based on short-term weather predictions. This can become a key enabler for maximizing data throughput. When employing multiple ground station sites, techniques like the CCSDS File Delivery Protocol and further protocols to implement Delay/Disruption Tolerant Networking become an additional aspect that will be discussed.

For Earth observation missions, the amount of data collected for science applications is always increasing while the available bandwidth remains the same. For LEO satellites applications, this could be achieved by acquiring signal at lower elevation, in order to increase the contact duration. Another solution would be increment the modulation order to maximize the bitrate. Some years ago, these two solutions would have been antagonists, until CCSDS introduced Variable Coding and Modulation techniques into its standards. Two standards have been adopted by CCSDS as blue book:
- CCSDS Space Link Protocols over ETSI DVB-S2 Standard, CCSDS 131.3-B-1 (March 2013), defines recommended options and interfaces with CCSDS standards for the European TV standard ETSI EN 302 307 (first publication in March 2005).
- Flexible Advanced Coding and Modulation Scheme for High Rate Telemetry Applications, CCSDS 131.2-B-1 (March 2012) is a new standard based on Serially Concatenated Convolutional Turbo Coding scheme.

These two standards aim in getting closer to channel Shannon’s limit by offering the ability to dynamically changing the modulation order and the coding rate. Therefore, it is possible to use robust transmission scheme at low elevation while using higher order of modulation and lower coding rate at higher elevation. The most advanced usage of these standards foreseen is to automatically perform these coding and ratio changes using a feedback from the receiving side; this is called Adaptive Coding and Modulation (ACM).

Zodiac Data Systems has been involved since 2009 with ESA and CNES to implement both SCCC & DVB-S2 standards on its COTS Cortex HDR High Data Rate (HDR) demodulator. Today the Cortex HDR supports these two standards and is ready for ACM operations.

The aim of this paper is to introduce a new concept of transmission using CCSDS File Delivery Protocol (CFDP), a reliable file transfer protocol defined in CCSDS 727.0-B-4 (January 2007), over an ACM transmission. A first section will introduce the concepts of ACM transmission and the necessary impact on the system architecture. A second section will introduce CFDP standard and how this protocol can take advantage of an ACM architecture. Last section will presents simulation results of CFDP over ACM transmission.

Future HTS (High throughput satellite) is expected to increase functional requirement for its payload. And the demand for high-speed telecommand and telemetry link to meet various payload requirement will also increase. Realtime payload monitoring and control, resource management system and on-board calibration function will be one requirement for the system. Current data rate of several Mbps will not be enough for user requirement and a few tens of Mbps data rate is required for next generation payload system. Since it is a link for payload control, tolerance to interference, high availability and reliability are also important factor.

We have studied high data rate telecommunication link for next generation high throughput payload to meet user requirement. In terms of resource reduction, it is assumed that the mission telecommand and telemetry link is allocated in band of the existing payload link and ACM (Adaptive Coding and Modulation) scheme is adopted to realize high availability.

In this study, we designed payload configuration and frequency assignment plan for realizing 10-20Mbps telecommand and telemetry link. We introduce design result of the entire communication architecture and telecommand and telemetry link with its link budget.