Software Defined Radios in Space Applications

Software-Defined Radios (SDRs) are a revolutionary piece of technology that have brought about significant changes in terrestrial communication systems. However, their impact goes beyond earth. The space industry has started to harness the power of SDRs for a variety of applications, from satellite communications to deep space exploration.

What is an SDR?

SDR is a type of radio communication system where components that were traditionally implemented in hardware (e.g. mixers, filters, modulators, demodulators) are implemented using software at the application level or firmware level. This allows user to change and configure the functionality of radio without changing the hardware for intended use and brings in tremendous flexibility in operations.

Why use SDR in Space?

1. Flexibility: Space missions often last many years, and during that time, communication protocols, data rates, and modulation schemes can evolve. There is a risk of the conventional space radio hardware becoming gradually outdated. With SDR, these parameters including advanced error correction and interference mitigation techniques can be implemented / updated in space thus making the mission meeting the emerging requirements.
2. Cost Effective: Instead of designing custom radios for each mission, a generic SDR can be developed and then customized via software for specific mission needs thus saving mission costs.
3. Adaptability: SDRs can adapt to dynamic space environments. For instance, if a spacecraft encounters interference, the SDR can be reprogrammed to use a bet fit modulation scheme and frequency to counter such scenarios.
4. Multi-Mission Capability: A single SDR platform can support multiple mission objectives for example Space to Ground Communications, Inter Satellite links and onboard communication purposes.
5. Agility: SDRs can handle different satellite constellations and communication standards.

Applications in Space Technologies

1. Satellite Communications: Commercial, Scientific, and military satellites are using SDRs to facilitate communications with ground stations, enhancing efficiency of satellite constellations.
2. Deep Space Exploration: Probes exploring distant planets, asteroids, or the outer solar system benefit from adaptability of SDRs. They can adjust their communication methods as they move further from Earth and encounter various space phenomena.
3. Space Science: Instruments abord satellite or space stations can use SDRs to process signals, study space weather, or even search for extraterrestrial signals.
4. Inter-Satellite Links: SDRs enable dynamic formation flying missions where multiple small satellite collaboratively perform tasks. They can establish and-hoc networks in space, adjust to the relative motion of the satellites, and share data seamlessly.

Technical Aspects of Space Qualified SDRs

  RF Frontend:

While a lot of flexibility is available in the digital domain, SDRs require a carefully designed RF front-end to:

• Convert the high frequency satellite signals to baseband or intermediate frequency.
• Amplification of weak signals received from distant satellites.
• Filter out unwanted signals and noise.
• Power Amplifiers to boost the transmission power.

2. Analog – to Digital Converters (ADCs): ADCs play a crucial role in translating the analog world of RF to the digital domain where the software can progress the signals. Space qualified SDRs requires high-resolution ADCs to ensure the subtle nuances of the signal are captured, allowing for precise demodulation and error correction. DAC does the reverse, converting digital samples into analog signals for transmission.

3. Digital Down / Up Converter: Often used in SDRs to further down-convert (or Up-convert) the digital signal to a lower (or higher) intermeditate frequency or baseband. This is done in the digital domain using algorithms.

4. Digital Signal Processing (DSP): Once the signal is in the digital domain, DSP techniques are employed for:

- Channelization: Dividing the bandwidth into individual channels.

- Demodulation: Extracting the original data from the modulated signal.

- Modulation: Prepare signals for transmission i.e. modulate a signal.

- Error Correction: Implementing algorithms to correct for error induced during transmission.

5. Software Layers: Several layers of software are involved, including:

- Firmware: Closest to the hardware, it manages the operation of the SDR platform.

- Middleware: Provides common software services and libraries for SDR applications.

- Application Layer: This is where specific communication protocols and user applications reside.

6. SDR Waveforms: Waveforms in the context of SDR refer to the specific modulation, encoding, and protocol characteristics of a signal. Below are some of the many waveforms or standards that can be implemented on an SDR and many of them are applicable for Space qualified SDRs as well.

• AM/FM: The basic modulation schemes used for commercial broadcast radio.
• LTE (Long Term Evolution): A standard for high-speed wireless broadband.
• GSM/UMTS: Mobile communication Standards.
• Wi-Fi: includes various IEEE 802.11 standards such as 802.11a/b/g/n/ac/ax.
• Bluetooth: A short-range communication standard.
• ZigBee: A low-power, short range communication protocol often used in IoT devices.
• LoRa: Long Range communication protocol, typically for low power, long range IoT devices.
• DAB/DAB+ (Digital Video Broadcasting – Terrestrial): Digital Radio Standard.
• GPS (Global Positioning System): Signals from GPS Satellites can be decoded using SDR to obtain positioning information.
• ADS-B (Automatic Dependent Surveillance – Broadcast): A surveillance technology for aircraft.
• NFC (Near Field Communication): Short-range frequency wirless communication technology.
• P25, DMR, TETRA: Digital radio standards used in public safety, security, ad similar professional communication.
• ISM Band applications: Applications such as wireless sensors, industrial control, etc. which operate in the Industrial, scientific, and medical frequency bands.
• Satellite Communications: Satellite communications including satellite interner, weather satellite image, reception etc.

7. Security: With the flexibility of SDRs comes potential vulnerabilities. Its’ vital to implement robust security measures, such as encryption and authentication, to prevent unauthorised access and ensure the integrity of the communicated data.

Challenges and the Road Ahead:

While SDRs offer numerous advantages, there are few challenges:

1. Power Consumption: SDRs especially when performing complex tasks, can be power-hungry. Given the constraints of Satellite Power, optimising SDRs for poser efficiency is crucial.
2. Reliability: Space environments are harsh, with radiation posing a significant threat to electronics. Ensuring that SDRs remain reliable under such conditions is a design challenge.
3. Latency: Real-time operations, especially in inter-satellite communication, require low-latency responses. As software layers can introduce delays, optimising SDR for swift execution is vital.

Avantel Experience in Development of SDRs

Avantel has a legacy of three decades and has been offering various indigenous solutions in the areas of Wireless, SATCOM, Radar and embedded & application software to meet specific requirements of strategic customers. In the Space technologies front, Avantel has an established SATCOM vertical offering solutions to space technology downstream applications, and the product portfolio extends from various flavours of SDRs as platform equipment to the earth station electronics. Avantel solutions have been operating in various platforms viz. Aircraft, Ships, Submarines, Strategic vehicles and portables. Presently, the solutions are offered in MSS & UHF Satcom band and Ku band radios are on the anvil. In the SDR domain, Avantel has developed SCA 4.1 compliant SDR for HF communications and is in the process of converting its UHF Satcom SDR waveforms in compliance to SCA 4.1 standard. Avantel has the necessary wherewithal to replicate the above success to offer space qualified SDR solutions to the Upstream of space technologies as well.

Conclusion

The future of SDR in space technologies seems promising. As computing power increases and software frameworks become more advanced, the capabilities of spaceborne SDRs will expand. Cognitive radio technology shall further enable the SDR to intelligently adapt to changes in the radio environment, making it possible to operate in dynamic and unpredictable communication environments.  The adoption of AI and machine learning could allow SDRs to automatically adapt to space environments and optimize communication in real-time. In view of their adaptability, versatility, and the cost effectiveness, SDRs are poised to shape the future of space exploration and satellite communications. As research and development continue, their role in orbit and beyond is going to be significant in future space technologies.