A radio is any kind of device that wirelessly transmits or receives signals in the radio frequency (RF) part of the electromagnetic spectrum to facilitate the communication or transfer of information. In today’s world, radios exist in a multitude of items such as cell phones, computers, car door openers, vehicles, and televisions.
Traditional hardware-based radio devices limit cross-functionality and can only be modified through physical intervention. This results in higher production costs and minimal flexibility in supporting multiple waveform standards. Many smartphones and similar devices currently have up to about 8 different radios optimized to receive various signals of different frequency bands and standards.
Software-defined radio (SDR) is a radio communication system where components that have been traditionally implemented in hardware (e.g. mixers, filters, amplifiers, modulators/demodulators, detectors, etc.) are instead implemented by means of software or firmware operating on programmable processing technologies.
SDR is “a radio in which some or all of the physical-layer functions are software-defined,” per the Wireless Innovation Forum (formerly the SDR Forum). SDR is a radio communication system, which gives the possibility of software control of modulation method, coding scheme, filtering, wideband or narrowband operations, spread spectrum techniques, bandwidth, channel access techniques and waveform requirements. Almost all of the functionality associated with the physical layer (PHY) is implemented in software using digital signal processing (DSP) algorithms.
This process must be dynamic and requires the receiver to be flexible that is, adaptable and reconfigurable, more or less in real time without the need to physically modify the hardware. Software reconfigurability involves digitizing signals as close as possible to the antenna, because high speeds require large bandwidth.
Software-defined radio technology provides an efficient and comparatively inexpensive solution to this problem, allowing multimode, multi-band, and/or multi-functional wireless devices that can be enhanced using software upgrades.
SDR concept-based designs are used in existing and next-generation wireless technologies or standards such as WLAN, Mobile-WiMAX, 4G LTE, LTE-Advanced, 5G NR (New Radio) etc. Terminals must then adapt their hardware to suit wireless networks such as GSM, EDGE,
UMTS, IEEE 802.11a / b / g, LTE and the booming 5G.
These devices include field-programmable gate arrays (FPGA), digital signal processors (DSP), general-purpose processors (GPP), programmable System on Chip (SoC), or other application-specific programmable processors. The use of these technologies allows new wireless features and capabilities to be added to existing radio systems without requiring new hardware.
For these reasons, most of the existing SDR hardware platforms are built around FPGAs like the USRP2 from Ettus Reseach LLC, the Rice Wireless Open-Access (WARP) research platform, the Berkeley 3 emulation engine. (BEE3), the University of Kansas Agile Radio (KUAR). , Small Form
Factor Software Defined Radio (SSF-SDR) and Intelligent Transportation System (ITS) from NICT.
For software platforms, next to Desktop PC software such as Gqrx, SDR #, HDSDR, PowerSDR, QtRadio, GNU Radio, Matlab-Simulink, OSSIE and WARPnet etc, there are also Android mobile versions like SDR Touch and glSDR as well as a few that provide a web interface like WebSDR and
ShinySDR, which can be used for simple remote access to the receiver.
An SDR consists of a radio front end and digital back end. The SDR’s radio front-end contains the receive (Rx) and transmit (Tx) functions to receive and transmit signals over a wide bandwidth; this is also what the antenna is connected to. State-of-the-art modern SDR systems cover an ultra-wide frequency spectrum from 0 to 18 GHz (and upgradeable to even higher upper bounds).
When designing an SDR terminal, it is necessary to choose a computing platform for the digital part, a radio front end, and to make a compromise between the sampling frequency, the complexity of the terminal and the energy consumption. The cost functions of the computing platform are programmability, flexibility, power consumption and computing power.
There are various approaches to design and implement SDR modules on hardware platforms viz. GPP (General Purpose Processor), DSP (Digital Signal Processor) and FPGA (Field Programmable Gate Array)
ASICs offer the best possible performance at the lowest cost of silicon, but they suffer from a lack of flexibility and a high one-time engineering cost. DSP processors are based on the Harvard architecture, an extension of the Von-Neumann architecture, and are unable to meet SDR speed requirements despite a set of arithmetic and control instructions optimized for signal processing algorithms. Systems on a Chip (SOC) have limited flexibility. FPGAs are dynamically reconfigurable, and this high-performance, programmable hardware can efficiently perform highly parallel, compute intensive signal processing functions.
SDR technology trends
In markets such as signals intelligence (SIGINT), electronic warfare, test and measurement, public-safety communications, spectrum monitoring, and military communications (MILCOM), Software Defined Radios have become the de facto industry standard. Some of these markets were using hardwired application-specific integrated circuits (ASICs), while others were already using programmable digital signal processors (DSPs)
The technology that drove the move to SDR in these markets was the advent of RF integrated circuits (RFICs) from companies like Analog Devices and cost-effective DSP-intensive FPGAs from companies like Xilinx. These two technologies came together to meet a multibillion dollar need in the military tactical radio market, creating something of a “market ripple,” where the market had a huge impact on the evolution of SDR technology far beyond just the MILCOM market.
The Joint Tactical Radio System (JTRS) program funded the development and productization of SDR for military radios, which created a strong ecosystem of vendors including semiconductors, tools, and software companies. On the tools front, SDR required waveforms to be as portable as possible between different hardware platforms, which resulted in tools like the Software Communications Architecture (SCA) Core Framework, as well as better programming tools from electronic design automation (EDA) and semiconductor companies.
The next market ripple, the third generation, occurred when 4G LTE handsets moved consistently to SDR architectures. This shift was enabled by low-power, high-performance DSP cores optimized for handsets offered by companies such as Ceva, Tensilica, and Qualcomm. Like baseband ASICs for infrastructure, these cores would be integrated into application-specific standard products (ASSPs) or ASICs for much of the PHY processing, coupled with hardware accelerators. Once this changeover occurred, SDRs increased orders of magnitude in volume and reach to become the de facto industry standard for radios.
As the ubiquity of 4G handsets has propelled SDRs, the prospects of emerging technologies such as 5G, the Internet of Things (IoT), and sensor networks promise to again increase the volume of SDRs by another order of magnitude. What will be the technology driver lifting SDR to these lofty heights? As with previous leaps in SDR adoption, it will likely be a combination of both hardware and software technologies.
One of the next technology drivers in hardware looks to be the combination of analog and digital technology onto a single monolithic chip to reduce cost and size, weight, and power (SWaP). For infrastructure, this driver could be FPGAs with integrated analog-to-digital converters (ADCs) and digital-to-analog converters (DACs). For handsets and sensors, this could be application processors, also with integrated ADCs and DACs.
While general-purpose processors (GPPs) have served the SDR community well in the past, they are struggling to meet the performance required for areas like 5G and MILCOM. Software tools such as the LabVIEW FPGA Module and RF Network on Chip (RFNoC) offer a streamlined user experience that makes FPGA programming vastly more efficient.
Ultimately, integration will drive the next generation of SDRs. The integration of analog and digital technology into mixed-signal chips will be key, but SDRs have fundamentally reached a point where the primary limitation on growth is in software, not hardware. Without software development environments that can seamlessly program both GPPs and FPGAs, the additional hardware features of next-generation SDRs will be underused and development will stall. The ability of tools like LabVIEW FPGA to enable wireless engineers who are not HDL experts to develop and rapidly iterate on sophisticated designs offer the best opportunity moving forward to unlock the next generation of SDRs.
This military requirement of the delivery of data such as mapping, images, and video to a soldier in the battlefield requires wider bandwidths that create challenges for the radio platforms, primarily around size, weight, and power (SWaP).
The traditional radio frequency (RF) signal chains used by MILCOM platforms will not scale to wider bandwidths and digital modulation schemes without consuming much more power, and they will also increase in size and weight. This growth in SWaP is unacceptable to the soldier, who needs a smaller, more capable radio that can be powered for long mission durations on minimal battery power. Thus, next-generation MILCOM platforms will require new RF signal chain architectures.
One revolution in small-form-factor radio design has been integrated RF transceivers. Integrated transceivers reduce size and power by repartitioning the radio in several ways. First, RF and analog devices can be transferred to the digital domain – RF filters becoming digital filters, for instance. The digital implementations of these blocks are more efficient and more programmable than their RF counterparts.
Second, discrete RF signal chains are often heterodyne architectures, which require several layers of frequency conversion, filtering, amplification, and digital sampling. Integrated transceivers can use a zero-intermediate frequency (ZIF) architecture that drastically reduces the required components in the signal chain, specifically the required filtering and amplification stages. Removing these stages reduces both size and power draw.
Finally, the ZIF architecture is a more efficient use of the digital converters, which in a wideband system can drive overall power consumption. While commercial platforms have been able to take advantage of ZIF transceivers for the last decade, the first products with MILCOM-applicable features have only come to market in the last few years.
What’s needed for the backbone of the MILCOM radio circuitry is integrated transceivers, which are making great strides toward providing single-chip solutions that will integrate the bulk of the receiver and transmitter signal chains while maintaining features such as frequency-hopping, AGC, and the ability to upgrade to future waveforms. Building on these transceivers as a core block of the radio will enable the next generation of MILCOM radio systems.
Multiple technological advancements have improved the capabilities of software defined radios, ensuring connectivity in numerous terrains and contributing to increased situational awareness. The utilization of multiple technologies, including time-division multiplexing (TDM), voice over internet protocol (VoIP), satellite communications, cryptographic devices, tactical radios, cellular, SCIP, Wi-Fi, and WiMAX, has resulted in several compatibility issues. The installations of various types of modems in a communication network have also resulted in interoperability-related issues, owing to the variance in protocols as vendors add their specific value-added protocols as per the mission requirements.
Several Army Warfighters Information Network-Tactical (WIN-T) units, along with combat support divisions, procure such modems and related products to suit their platforms or architectures. Variance in the network infrastructure can also turn into an impediment owing to the inability of dissimilar protocols to interconnect with each other.
The Joint Tactical Radio System (JTRS) Program
The Joint Tactical Radio System (JTRS) program funded the development and productization of SDR for military radios, which created a strong ecosystem of vendors including semiconductors, tools, and software companies. The Joint Tactical Radio System (JTRS) was a program of the US military to produce radios that provide flexible and interoperable communications.
The vision and mission was: Provide optimal communications support for joint
operations, by enabling coordination and integration of military communications through a cohesive joint tactical radio infrastructure, that provides the means of digital information exchanges, among joint war fighting elements, while enabling connectivity to civil and
Acquire a family of affordable, high-capacity, tactical radio systems to provide interoperable and upgradeable line of-sight, beyond-line-of-sight, and wireless mobile network Control, Communications, Computers, and Intelligence (C4I) capabilities to the warfighters in the field.
Examples of radio terminals that require support include hand-held, vehicular, airborne and dismounted radios, as well as base-stations (fixed and maritime). As new product families of unmanned aerial vehicles, aircraft, spacecraft, drones, satellites, communications and navigation systems are presented to the market every year, the SDR solutions continue to evolve along with the customers’ needs.
To realize the JTRS Program Mission, the JTRS must be
• Modular, enabling additional capabilities and features to be added to JTR sets,
• Scaleable, enabling additional capacity (bandwidth and channels) to be added to JTR sets, and
• Backwards-compatible, allowing JTRS to communicate with the legacy radios it will eventually replace, allowing dynamic intra-network and inter-network routing for data transport that is transparent to the radio operator.
SDR applications enable size, weight and power (SWaP) reductions, jamming or interception resistance, TRANSEC and COMSEC features, multi-channel Tx or Rx radio functionality and improvements of other capabilities important for the most demanding communications networks. After more than 30 years of technological deployment and myriad applications, it can be quite reliably said that SDR is no longer exclusively related to tactical radios, but has expanded to aerospace, radar, medical imaging, GNSS, and other diverse communications systems.
Software Communications Architecture (SCA)
To realize the JTRS Goals and Mission, the family of JTRS software-defined radios will be
designed around a Software Communications Architecture (SCA) that can support the needed functionality and expandability of the JTRS.
- SCA is an open architecture framework that tells communications systems designers how elements of hardware and software are to operate in harmony within an SCA-compliant system.
- Enables communication platforms (e.g. software-defined radios) to load applications (e.g. waveforms), run these applications, and be networked into an integrated system.
- Is used by communication platforms (e.g. radios, etc.) hardware and software design engineers just as a building architect or planner uses a local building code to design and build homes.
Is not a system specification.
• It is a set of rules that constrain the design of systems, to achieve SCA objectives.
• SCA objectives, originally conceived to meet JTRS objectives, are applicable to any communications system with the goals of component portability, interchangeability, and
• Comprised of interface and behavioral specifications, general rules, waveform APIs, and security requirements.
The SCA Achieves its Objectives by…
Defining an open, distributed, component-based, object-oriented architecture
Separating applications from the operating environment
Segmenting application functionality
Defining common interfaces for Managing & Deploying Software Components
Defining common services & APIs to support device and application portability
Open-Architecture Specification for Space and Ground Software-Defined Radios
In March 2021, International technology standards organization Object Management Group® (OMG®) released a beta version of the Space Telecommunications Interface (STI) specification. Based on OMG’s Systems Modeling Language® (SysML®), the new specification establishes an open architecture for space and ground software-defined radios (SDRs) for space and navigation communications systems.
“Many space projects either use hardware radios that cannot be modified once deployed, or SDRs that depend on the radio provider and involve significant effort to add new applications,” said Steve MacLaird, SVP, Government & Industry Strategy, Object Management Group. “Software-based SDRs enable advanced operations that reduce mission life-cycle costs for space or ground platforms. OMG’s systems modeling language SysML was chosen as the foundation of the STI specification because it allows engineers and program managers to use an open, modular approach as they develop SDRs.”
The STI specification identifies the data types, application programming interface, and associated operational patterns that compliant SDR platforms are required to implement. A common programming interface enables portability of SDR applications between radio-platform providers, and a metamodel for a hardware/software architecture (rather than a specific SDR implementation), ensures adaptability to a wide variety of platforms and applications.
Parallel and independent software and platform development allows software to be modified late in the development process or after deployment, enabling new requirement updates or bug fixes. Dependence on a single SDR provider is reduced by separating application development from hardware platform development.
The architecture enables the reuse of applications across heterogeneous SDR platforms, reducing dependence on a single vendor or platform type and assists in the development of software-defined, reconfigurable technology to meet future space communications and navigation system needs.
“For space missions, Software Defined Radio (SDR) systems are deployed in environmental conditions that require unique provisions in order to accommodate such communication services as new frequencies, latencies, data rates and dynamic reconfiguration of components,” said Jeff Smith, Co-chair of the OMG Analysis and Design Platform Task Force and Chief Systems Engineer at Sierra Nevada Corporation supporting the Multi-Agency Collaboration Environment (MACE). “The expanded space communication specification will support the ability to collect and provide voice, video, data and networking signals to process and share communications throughout the spectrum agnostically. It will also support a networking layer and standardized interfaces for interacting with networks that support cross-platform security measures.”
Responses to this RFP are intended to address the following issues associated with space communications:
- Radiation Suitable Processing: The use of radiation capable processors limits both the footprint and complexity of the infrastructure.
- Spacecraft Resource Constraints: Each mission has specific allowances for the resources a radio can consume such as, real-time performance, mission classes (high-capacity), network, reconfigurability and reprogrammability. Overhead for supporting an open architecture must be balanced against these spacecraft constraints.
- Reliability (fault tolerance, guaranteed delivery) and Availability: Reliability is of paramount importance to space radios in both manned and unmanned missions. For example, if communication to a satellite is lost, the ability to command and control the satellite is also lost.
- Specialized Signal Processing Abstraction: The architecture should support the abstraction of the platforms that waveforms are deployed on so they are able to execute on a variety of different specialized signal processor elements including Digital Signal Processors (DSPs), FPGAs, and Application-Specific Integrated Circuits (ASICs).
- Static Deployment: The hardware resources assigned to the radio platform onboard the spacecraft are fixed and verifiable, and rarely will be changed. Waveforms may change operating parameters, due to commands from the flight computer, or autonomously, due to waveform input signal levels or other predetermined conditions.
- Long Mission Development Times: The development time of the radios is often much longer compared to their commercial equivalents. This often leads to requirements creep. The ability to make software changes aids in the ability to make any late enhancements before the radio has been launched. The SDR enables more efficient change management.
- Space Waveforms: The waveforms that are used for these applications often are unique to the space environment. For example, NASA utilizes a selected set of waveforms that correspond to frequency allocations and existing space assets.
- Small Space Market: The number of radios built for space use is much lower than most terrestrial markets. The cost to develop and maintain the open architecture must be in proportion to the overall market. It is anticipated that this specification will be size agnostic and capable of being utilized on CubeSats
References and Resources also include: