NewSpace Testing Considerations and Techniques
2021-03-15 | 9 min read
The space industry is in the midst of dramatic change. Hundreds of companies are getting into space with an incredibly wide variety of business models and mission types – from communications to earth imaging, weather forecasting, mining asteroids, and even to interplanetary human existence.
Many NewSpace companies are planning to deploy large constellations of satellites, especially in the low Earth orbit (LEO). NewSpace drives the changing of the business models in the space with shorter lifetimes, high performance, and a substantially lower investment comparing with traditional satellites. These changes have been disruptive, affecting design processes, design and verification test requirements, and cost of test. Space racing is changing and the pressure to produce is ramping up.
Development in NewSpace
Reduced launch costs and the advancement of reusable rockets drive today’s satellite industry revolution. The lower barrier to entry allows the rapid development of LEO constellations comprising hundreds or thousands of satellites. Also, millions of ground and user terminals, as a transparent relay to a preferred commercial user device, require to deliver robust forward and reverse communication links and high quality of service. Satellite and terminal engineers need to accurately characterize RF components and sub-systems to ensure their devices’ performance meets the design requirements.
The telecommunication industry has been developing standardization studies on the benefits of satellite coverage as part of the mix of access technologies for 5G since 2018. In Release 15 and Release 16, 3GPP studied the feasibility and standard adaptations needed to enable New Radio (NR) over satellite systems referred to as Non-terrestrial Networks (NTN). In Release 17, the NTN will be carried out along the lines of the preceding studies in 2022 and deliver continuous innovation in the space industry.
Time-to-market pressure is ever-present in the commercial market. For NewSpace, schedule pressure driven by the market is higher for meeting a specific launch window or replacing the existing satellites. Engineers need to shorten their product development lifecycle and reduce test time and cost in production.
NewSpace drives different challenges in volume, performance, cost, and schedule comparing with the traditional space industry.
NewSpace Testing Considerations – bandwidths, modulation techniques, and millimeter-wave
With strong demand for faster data throughput, satellite communications increase signal bandwidths and use higher-order modulation schemes to improve their spectral efficiency. However, wider bandwidths also gather more noise, and higher-order modulation schemes are sensitive to system noise. Both of these bring test challenges in signal generation and signal analysis.
In addition, the complex modulation schemes do not only improve spectral efficiency but also need to minimize nonlinear amplification in the RF power amplifier. In my earlier post, I discussed that amplitude and phase-shift keying (APSK) improves nonlinear distortion for satellite communications; orthogonal frequency-division multiplexing (OFDM) increases spectral efficiency for high-throughput satellite communications. Figure 1 shows evaluating the performance of a channelized satellite transponder with multiple independently modulated signals. However, both modulation techniques bring in test challenges — generating and analyzing custom, proprietary modulation schemes. Engineers spend a lot of time to simulate and analyze the custom modulated signals.
Another change that we are seeing is the move towards the use of higher frequencies. As the C and Ku bandwidths grow increasingly congested, global interest in the Ka-band for commercial satellite communications has risen sharply. Increasing channel bandwidth not only enables higher data rates per client, but also extends the number of channels for higher system capacity. High-throughput satellites now use transponders with bandwidths up to 2.1 GHz to achieve required data rates at Ka-band. Most HTS typically file for 3.5 GHz bandwidth in Ka-band: 27.5 – 31 GHz for uplink and 17.7 – 21.2 GHz for downlink.
Build a Wideband Stimulus-Response RF Test System
The utilization of higher frequencies and wider bandwidths in satellites requires more complex testing and characterization to ensure that components and systems meet demanding space requirements. For a variety of test scenarios essential to the design, verification, and manufacturing of satellite components and systems, signal analysis and signal generation are the fundamentals of a robust test system.
The integration of such a test system requires a combination of software and hardware tools. You can use off-the-shelf instruments to build the system, but need to calibrate the frequency responses across the entire bandwidths of both the signal generation and analysis. Figure 2 illustrates both calibrated transmit and receiver hardware ready for making measurement of your wideband component DUT’s true performance.
For signal generation, you need:
- a calibrated vector signal generator (VSG) to upconvert the baseband signals to the desired frequency,
- and a power meter or a vector signal analyzer (VSA) to calibrate the frequency responses.
For signal analysis, you need:
- a signal analyzer downconverting the input signal to a wideband IF signal,
- a high-speed digitizer or an oscilloscope to acquire the IF signal or the direct RF signal for analysis,
- and a comb generator or vector signal generator to calibrate the frequency responses.
Integrate the test system above with optimum performance is challenging. You need to build a tool to calibrate the whole test system. Also, you need to remove the effects of test fixtures, adapters, switches, or cables that degrade measurement accuracy. Establish calibration planes at the exact DUT input and output connection by calibrating all signal paths. This solution is limited by the maximum 2-GHz bandwidth for signal generation and the oscilloscope's dynamic range for wideband vector signal analysis.
Test Requirements for Modern Satellite Communications
For satellite communications systems, uncovering errors before deployment is critical. Once the systems are deployed, fixing the errors is difficult and costly. So, to simulate all the various scenarios that may impact the communications links is important to characterize the individual wideband component. Once changing test setups, such as the signal generator’s output levels, the signal bandwidths, and the frequencies, the test system needs to be recalibrated or load the correction data before the specific measurements. This increases test time dramatically and cannot meet the requirements – lower cost, tight schedule, and high-volume production.
Keysight new signal analyzer N9042B UXA and M9384B VXG signal generator, which lets you unravel the complexities, revealing what’s really happening in your wideband system. It helps you build a 4-GHz wideband test system easier and quicker, and that lets you explore a wider range of various test scenarios and make accurate repeatable measurements. Solving these problems during design, simulation and test enable you to meet the challenges of test complexity and cost of test.