Software Defined Radio Use Case for Interoperability

This is the 11th article in a series exploring capabilities and applications of software defined radio (SDR) platforms in today’s industries. This article will focus on applications that demand immense interoperability and explore the capabilities of SDRs that make them suitable for such uses. Click here to see more articles in this series.

The rapid increase in RF protocols and signal processing standards has made it difficult for different radio communication devices to communicate. To ensure that radio communications devices are interoperable, engineers have to test many protocols and standards. Systems for use in mission critical applications such as defense systems, public safety communications systems, and 5G Open Radio Access Network (O-RAN) have strict interoperability requirements.

Interoperability in radio communication systems

Interoperability of radio communication systems refers to the ability of different devices to communicate with one another without restrictions. As new protocols and standards emerge, older systems become incompatible and cannot communicate with newer devices unless they are upgraded. Traditional radio communication systems utilize specific hardware and are designed to serve a specific purpose. It is costly and difficult to upgrade such hardware-defined systems since the process entails changing existing hardware as well as software. In contrast, an SDR platform can be upgraded to communicate with older or newer technologies by simply updating its software. The reconfigurability of SDRs enables decoupling of platform and waveform thereby yielding devices with high interoperability capability. In addition, SDRs utilize flexible software-based signal processing components that are optimized to run on high speed systems.

Due to the high cost of installing new radio communication solutions, a system is usually expected to run for many years. Although it is common for industries to upgrade their systems by replacing some components with new ones, this approach does not help much as far as interoperability of the system is concerned. 

Although it is vital for devices used in mission-critical applications to communicate with other devices, the existence of a broad array of protocols and standards makes it very difficult for rescue teams and military units to communicate. Projects such as Wireless Interoperability for Security (WINTSEC) were started in an attempt to address interoperability problems in today’s radio communication landscape.

Figure 1: A comparison between interoperable and non-interoperable radio systems is shown.

Instances, where the lack of interoperability between radio communication systems has resulted in the loss of lives, are uncountable. For instance, many experts argue that lack of compatibility between radio systems used by different agencies was one of the main reasons why 343 firefighters lost their lives on September 11, 2001. Similarly, as argued by domain experts, lack of effective communication between different agencies is one of the main causes of slow emergency response during natural disasters such as was witnessed in the wake of Hurricane Katrina. 

A broad array of radio communication standards and waveforms are used in today's defense systems. For many years, this diversity has been known to hinder communications between different military forces. For example, in the past, lack of compatibility between the radio systems used by NATO allies and US troops made it difficult for the troops to communicate securely.

Other catalysts for the need for greater interoperability stems from an explosion in the number of connected devices over the last decade, from IoT devices to autonomous vehicles. As the number of wireless radio standards and applications increase, it is necessary to ensure that they are interoperable with the 5G network infrastructure. Figure 1 above compares interoperable and non-interoperable radio systems used by military forces.

Implementing interoperable radio systems with SDR platforms

An SDR system features a radio front end (RFE) that operates on analog signals and a digital back end that processes digitized signals. The RFE performs transmit (Tx) and receive (Rx) functions and is capable of operating over a broad frequency range. Highest performance SDR systems are designed to offer high instantaneous bandwidth, typically 3 GHz or more. In addition, they provide multiple independent channels with dedicated digital-to-analog converters (DACs) and analog-to-digital converters (ADCs).

The digital back end of an SDR platform features a field programmable gate array (FPGA). This reprogrammable component offers a variety of on-board digital signal processing (DSP) capabilities including upconverting, downconverting, modulation, and demodulation. The reconfigurability of FPGAs makes it easy to update radio systems with the latest DSP algorithms and radio protocols. The block diagram in Figure 2 below shows the main components of an SDR system designed for use in applications that demand high interoperability.

Figure 2: This is a simplified block diagram of an SDR system designed for interoperability.

SDRs have many unique capabilities that make them an ideal choice for implementing interoperable radio systems. To start with, these devices offer multiple independent channels for MIMO operations. This feature makes it possible for a single radio system to communicate with different radio protocols. The design of SDR systems also enables them to tune to multiple frequencies and radio protocols. This capability makes these devices ideal for a wide range of applications that involve frequency hopping such as the technologies used for secure communications. In addition, channels of an SDR system can be configured to be used for transmit or receive functions. This flexibility allows you to adjust the capacity of your radio systems depending on your needs.

The FPGAs used in SDR systems support a broad array of digital signal processing (DSP) functionalities including digital upconversion and downconversion, waveform generation, Ethernet packetization and so on. This capability allows implementation of a wide range of protocols and radio communication algorithms. In addition, the architecture of an SDR system makes it possible to achieve the latency and reliability demanded by mission critical applications.

High-end SDR systems are generally compatible with various interfaces and UHD. This capability enables SDR-based radio systems to support a wide range of control functions such as changing waveform type, center frequency, gain and even complicated functions such as those involving cryptographic algorithms. Furthermore, SDR systems offer filtering, adjacent channel rejection and other capabilities that enable users to tune into signals of interest with high fidelity. In addition, using the FPGA IP cores allows implementation of complex techniques used in 5G MIMO applications such as beamforming and beam steering.

The interoperability capabilities of SDR platforms make them an ideal choice for use in mission critical applications. To start with, their multiple independent channels mean that they can be used for multiple transmit and receive functions simultaneously over different bands and paths. Secondly, the ability of SDR systems to operate over a wide frequency ensures better interference mitigation, more access to data, extended signal analysis and more capacity to accommodate additional applications.

The reconfigurability of SDR systems means that new protocols and DSP algorithms can be implemented without modifying the existing hardware. This makes them a cheaper alternative as compared to traditional radio systems that require hardware modifications to support new and emerging technologies. In addition, the reconfigurability of SDR platforms enables industries to develop application-agnostic systems that use the same hardware to support different applications.

Enhancing waveform portability in radio communication systems with SDRs

Waveforms are a critical part of every communication system since they provide the means through which information is transmitted and received. The security of files is greatly determined by the characteristics of the waveform used in their transmission. For instance, tactical waveforms that are widely used for sending pictures offer high tolerance to interception and detection by third parties.

The waveforms used in today's civilian and military applications are expensive to develop yet they are rarely re-used. Using one waveform for multiple applications can help industries to cut their expenses. However, this can only be achieved with platforms that are optimized to allow waveform portability.

To mitigate obsolescence of waveforms as platforms are upgraded, it is critical to ensure that new platforms can support old waveforms. As a way of enhancing this portability, it is increasingly becoming common for customers to request for hardware equipment that supports their existing waveforms. This approach ensures that the same waveform is used across devices from different manufacturers, thereby mitigating waveform obsolescence.

The Joint Tactical Radio System (JTRS) Information Repository allows industry to access a broad array of waveforms used by the US military. One of the main benefits of this move is that it makes it possible for industries to port waveforms from one platform to another. The plan by ENC to develop three new waveforms is likely to enhance interoperability of the radio communication systems used by European Armed Forces. The three waveforms are ESSOR 3DWF, ESSOR NBWF, and ESSOR SATCOM WF.

Complete SDR waveform portability is a difficult process that demands careful planning. To achieve an optimal level of portability, it is critical to incorporate key measures right from the beginning of the process. Using elements such as Software Communications Architecture (SCA) and Common Object Request Broker Architecture (CORBA) can greatly accelerate this process. Another aspect that can be of great benefit to the process is use of good structured programming techniques. Interoperability Device Testing (IoDT) helps to ensure that codes can be transferred from one platform to another without altering their functionality. To achieve full waveform portability, it is also necessary to certify and accredit waveforms.

SDR-based interoperable systems for mission critical applications

Today’s warfighters require advanced multi-mission and agile waveform systems. These waveforms are required to take minimum development time and be capable of supporting a broad range of applications including command, communications, control, surveillance, intelligence, and reconnaissance. As highlighted in the 2018  National Defense Strategy, deepening interoperability is required to achieve capable security alliances and partnerships. 

SDR systems are capable of delivering radio systems that are interoperable with a broad array of tactical systems including HF, HaveQuick, DAMA, SINGARS and a variety of data links such as Link-4A and Link 11. Furthermore, the architecture of these platforms allows them to be integrated with a wide range of military radio systems from handheld units used in battlefields to multichannel radio systems used in command and control centers.

Another important aspect of interoperability is in public safety applications. For instance, the Disaster Incident Response Emergency Communications Terminal (DIRECT) is a tool suite that helps to address lack of interoperability between the radio systems used by different emergency response agencies. This tool suite utilizes National Guard organic Warfighter Information Network-Tactical (WIN-T) infrastructure and provides inter-agency teams with commercial phone, commercial wireless, internet access and 4G LTE capability to ensure effective communication when responding to emergencies. Plans are underway to boost this tool suite further by making it compatible with the FirstNET broadband network. Interoperable solutions such as DIRECT enable synchronized emergency response in the wake of natural disasters.

Reliance on proprietary radio access networks (RAN) has left mobile phone operators entirely dependent on network equipment manufacturers thereby limiting innovation and flexibility. The Open RAN paradigm disaggregates the RAN functionality by utilizing a reconfigurable software-defined mobile network solutions and open interfaces to build networks that can be realized using off-the-shelf-hardware components. The O-RAN paradigm enables interoperability of a wide range of technologies including Internet of Things (IoT), machine learning (ML), artificial intelligence (AI) and C-V2X.

As compared to the architecture of traditional telecommunication infrastructure, the O-RAN paradigm enables operators to make significant savings. In addition, with O-RAN, it is easier to optimize the design of base stations, small cells and access points. Figure 3 below shows some of the main differences between the components of traditional RAN and O-RAN.

Figure 3: Differences between traditional RAN and O-RAN are shown.

As networking technologies evolve and advanced networks such as 5G emerge, the need for flexibility and reconfigurability is increasingly becoming a key consideration factor. The desire to optimize interoperability has catalyzed the emergence of development tools such as the Open Air Interfaces (OAI) platform. This open source and publicly available software suite allows implementation and customization of various network components including base stations, user equipment and core networks. In addition, OAI is designed to support commercial off-the-shelf SDR platforms. 

Using virtualization and containerization allows development of flexible RAN network infrastructure capable of supporting slicing and interoperability of different services. OAI testbeds are used to study the performance and interoperability of virtualized network infrastructure. SDR platforms support a wide range of open source software tools and virtualization techniques making them suitable for realizing a variety of mobile network functionalities. Figure 4 shows a simplified architecture of a 5G network slicing framework.

The network slicing paradigm enables operators of mobile networks to create virtual networks that cater for a specific segment of clients and applications. As advanced networks such as 5G emerge, different applications will benefit by leveraging different strengths of these advanced networks. For instance, machine-to-machine (M2M) communications and mobile broadband have slightly different needs when it comes to latency, speed, and edge computing resources. Network slicing can therefore enable mobile operators to prioritize specific resources and offer solutions that are tailored to the specific needs of an application.

Figure 4: This is the architecture of a generic network slicing framework.

The flexibility and reconfigurability of SDRs make them an unmatched solution for implementing radio systems for use in industries that demand immense interoperability. Per Vices offers a wide range of SDR platforms that are optimized to deliver high performance and flexibility. These platforms are suitable for a wide range of uses including mission critical applications such as defense and public safety communication systems.

Conclusion

The reconfigurability and performance capabilities of SDR platforms enable realization of interoperable radio systems. These capabilities make them suitable for use in mission critical applications such as military, public safety, and O-RAN. The next article will focus on the capabilities of SDR platforms that make them ideal for satellite applications.

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