This paper presents the characteristics and functinoalities supported by the next generation of the Integrated Modem and Baseband Unit (IMBU Mk4), developed by Indra in the frame of a contract with ESOC (ESA). The IMBU Mk4 is part of the Portable Satellite Simulator (PSS) that is intended to provide ESA with the tool to validate the Ground Segment TTCP modems of the future missions on ground.
ESA operates the ESTRACK network, which consists of a series of ground stations distributed around the world providing links between spacecraft and its operations centre located at ESOC. The main task of ESTRACK stations is to communicate with ESA missions, up-linking commands (Telecommand) and down-linking data and spacecraft status information (Telemetry).
The Portable Satellite Simulator (PSS) emulates the spacecraft communications subsystem and supports the testing and validation activities of the GS modems (TTCP), validating the compatibility of the future Spacedraft TT&C communications with the Ground modem. The PSS is required in all ESTRACK stations, including the ESOC Ground Station Reference Facility (GSRF). In addition, it has also been used as part of the transportable Network Data Interface Units (NDIUs) for spacecraft validation campaigns for other customer.
The Integrated Modem and Baseband Unit (IMBU) is the PSS HW core. The IMBU implements the TM and TC links physical layer (compliant with ECSS and CCSDS standards) including TM data encoding and modulation and TC synchronisation, demodulation and decoding. The GSTVI SW module, also part of the PSS, is a software emulating the spacecraft TM data generation and TC data processing.
The IMBU implements the physical TC and TM interfaces, e.g. IF, video and baseband data, with the actual GS modems (TTCP). Thus, the IMBU (together with the GSTVI) allows electrical interface testing, IF and baseband validation and spacecraft data validation. The IMBU provides many functionalities to support the test and validation of the GS modems such as fixed TM transfer frame generation, TM Symbol Error Rate Test (by comparing the transmitted TM symbols against the TM symbols recovered by the GS modem), injection of errors on the transmitted TM signal, monitoring of signals at different points of the TM encoder / modulator chain, injection and monitoring of signals at different points of the TC demodulator / decoder chain, use of external reference clocks, etc.
The IMBU Mk4, in addition to the functionalities provided by previous generation, supports many improvements as a wider variety of TM coding and modulation schemes, including LDPC codes and filtered OQPSK, .an extensive range of TM data rates, from 4 sps up to 300 Msps, increasing the maximum data rate in more than one order of magnitude. Furthermore, an improved TM IF interface allows to support higher and wider bands. Thus, in adittion to the traditional 70 MHz TM IF, a transmission band covering the range 420 – 640 MHz is also available simplifying the connection with TTCP modems. Besides, to support the increment in the TM data rate, a new L-band (1550 MHz) interface with extended bandwidth (up to 600 MHz) is also available. Direct digital up-conversion from baseband to the entire IF bands is implemented, avoiding many undesired effects (in-phase and quadrature amplitude unbalance, lack of orthogonality, etc.).
A faster LAN interface (1 GbE) is available to support the increment in the TM data rate and faster input / output signal and baseband data interfaces (LVDS) with the GS modems and local monitoring is supported.
The unit is composed of state-of-the-art HW to reach better performances and it has much more signal processing capabilities, in line with the FPGA devices available today, not only to implement the new features but also to allow potential evolutions in the future. The new unit architecture and the software-defined radio paradigm adopted provide the means to incorporate future functions or waveforms without requiring HW intervention.
Ten units of IMBU Mk4 have been delivered to ESA, that are currently being deployed in the ground stations of the ESTRACK network of ESA, the first unit aleady in operaon in the Cebreros station in Spain. The unit will be used to validate the correct performance of the TTCP modem for the Euclid mission. This mission will deliver about 850 Gbit of compressed data per day, requiring a telemetry link of up to 75 Mbit/s, an exceptional data rate for a space mission, and the new functionalities LDPC-encoding and filtered OQPSK-modulation . Actually, the IMBU Mk4 supports rates up to at least 100 Mbit/s for LDPC-encoded data with coding rates of 1/2, 2/3 and 4/5, producing symbol rates beyond 200 Msps.
This paper will present the specification and performances of the IMBU Mk4 with special emphasis on the advanced capabilities suported like higher IF bands, high TM data rates and LDPC coding among others.

In order to improve the downlink datarate of Deep Space missions, the maximisation of the G/T is envisaged. As the gain G cannot be modified without heavy modifications to the antenna structure, including the shape of the antenna, the system noise temperature T can be minimised more easily by using cryogenic technologies.
The ESA’s Deep Space antenna network currently operates satellites at X-band. The LNAs receivers are using cryogenic LNAs (cooling down to below 15 K) and the feeds (X -band up- and downlink) are at room temperature. Cooling down partially, or fully, the feed components reduces significantly the system noise temperature and according to the noise temperature measurements on the early-developed prototype, it is expected to improve the G/T by 1.5dB at X-band.
Following the design and development of a prototype cryogenic cooled-feed (receiver) at X-Band and its transmission feed at room temperature, the system is now undergoing a major upgrade to make it ready for operations in an ESA’s Deep Space Antenna.
This upgrade includes the following major steps:
1. Test and measure the performance of the transmission feed at high power, up to 20kW. This has been done with the support of NASA-JPL. Then analyse results and identify improvements on the feed design and manufacture process,
2. Improve the operation of the new cryocooler redundancy and maintenance system, called double-sleeve which includes two cryocoolers running in parallel and the possibility to remove one cooler while the other is still running the RF critical components at cryogenic temperature.
3. Further reduce the cryogenic temperature of the critical RF components from the early prototype performance,
4. Design a new monitoring and control system with critical function such as LNA biasing circuits directly embedded on the receiver.
The paper will present and discuss the results of the cryogenic and RF tests done on Rx and Tx chains as well as the improvement of the new cryocooler redundancy and maintenance system.

European Space Operation Centre ESOC commissioned to Rheinmetall Italia (RhI) a contract for a Pre-Development phase for an X-Band 80 kWcw Power Amplifier.

Following a tradeoff phase between a single or multiple power amplifier, to reach the required output RF power level, the chosen architecture is conceptually the same of the existing 20 kW HPA, already developed by Rheinmetall and installed in Malargue and Cebreros Deep Space Station (DSS), and is based on an existing single 100 kWcw klystron.

Nevertheless, even if such Klystron was already adopted by JPL, in the Goldstone Deep Space Communication Complex, its use leads to some criticalities relevant to the high power handled to the output waveguide components, the required thermal and electrical stabilities to fulfil the Spectrum purity and ADEV and the cathode high voltage level.

The limited space available in the DSS required a configuration of the HPA divided in three main subsystems managed by a centralized M&C.

The availability increase of the HPA, to enable Operative Mission Success, has led to use of reliable and proven hardware solution and/or some redundancy to reduce the single point failure and increase the fault tolerance and /or graceful degradation characteristics.

Optimized operating modes have been introduced, to increase the overall efficiency and system flexibility, for the RF transmitted power levels less than the maximum permitted.

The technical objectives of this TRP study is to simplify the Ground Station (GS) architecture currently used by ESA in Deep Space Antenna (DSA) by implementing the concept of Software Defined Radio (SDR). The main advantages of using SDR architecture are to:
. Minimize number of Radio Frequency (RF) hardware components like mixers, oscillators or filters because replaced by digital functions,
. Minimize maintenance and procurement costs compared to a traditional architecture,
. Counteract analogue RF chain imperfections (interference, distortion, aging) with easily-reprogrammable digital functions,
. Increase flexibility to support multiple signals from multiple spacecrafts,
. Increase configurability/re-configurability and ease new software function installation.

More particularly, S- and X-bands breadboards have been designed and contain a sampler architecture to down convert the incoming RF signal to Intermediate Frequency (IF) and digitise it with a suitable Analogue to Digital Converter (ADC). Doing this will prove the concept of sampling RF signal directly at X-band without the traditional down conversion scheme. The breadboard functions are to:
. Output the IF signal within the actual Telemetry, Tracking and Control Processor (TTCP) bandwidth at S- and X-bands (for Deep Space and Near-Earth services) and by design at K- and Ka-bands,
. Digitise directly the incoming S- and X-bands signals with a high-speed ADC and process digitally the signals to retrieve I and Q data,
. Compare both quality of signals to demonstrate the RF direct sampling concept.

The Critical Design Review will be held in the coming weeks. The preliminary breadboard architecture has been successfully designed and is currently detailed to provide:
. The main RF front-end functions (low-noise amplification and attenuation to ensure adequate dynamic range),
. The RF sampling is ensured with a Track and Hold Amplifier (THA) which is an innovative technology able to enlarge significantly the analogue bandwidth of RF ADC. A theoretical nonlinear model has been simulated and successfully compared to the measurement of a commercial state-of-the-art device able to operate up to 30GHz,
. The digitiser is a high-performance ADC able to sample at 10 or 5GSps depending on the single- or dual-channel input configuration. The selected commercial ADC is also equipped with a high-speed Field Programmable Gate Arrays (FPGA) that can provide SDR basic Digital Signal Processing (DSP) functions like Digital Down Conversion (DDC) in quadrature, digital filtering, decimation and other custom functions, if adequately programmed.

This contract has been also extended to the study of high-speed RF Digital to Analogue Converter (DAC). The aim was to survey the actual commercial state-of-the-art technologies, select and test the most relevant circuit to generate the RF signals used by ESA in DSA ground stations. Using an RF DAC that samples at 6GSps, it was possible to generate S- and X-band signals within the performance required by ESA and very promising results have been obtained at Ka-band.

The paper will present and discuss all the results available for the RF sampling, ADC and DAC activities.