An Introduction to SOSA

These days, anyone implementing a Department of Defense (DoD) system is likely aware of the directive to use a Modular Open Systems Approach (MOSA). The Sensor Open Systems Architecture (SOSA) has emerged as the prevalent MOSA standard. This includes the Army's SOSA instantiation known as C5ISR/EW Modular Open Suite of Standards
(CMOSS). Many factors fuel the drive to an open standard, including cost containment, sustainability, accelerated acquisition, rapid technology insertion, and faster capability transition.

The SOSA Technical Standard defines a reference architecture that aligns with many of the industry's existing standards, such as VITA's OpenVPX. By using these existing standards, prior work can be leveraged and SOSA then picks applicable parts to use. An example of this is the use of OpenVPX to define plug-in-card (PIC) hardware, including its interface profile definition (IO specification). By my last count, the VITA standard defines over sixty distinct 3U VPX profiles, whereas SOSA uses only about 15% of those and, in some cases, may add additional requirements.

SOSA defines modules, services, and the runtime environment. The fundamental building blocks of the SOSA architecture are the SOSA modules, hardware and software, and the SOSA interfaces. Modules perform physical and/or logical functions and exhibit behavior. Hardware, either individual PICs or a complete chassis, may leverage a variety of form factors that meet specific system requirements. SOSA PICs are generally 3U or 6U VPX, and if a smaller form factor is needed, there is an emerging VITA 90.X standard called VNX+, which SOSA already specifies in the current technical standard.

A SOSA chassis may consist of any number of slots and a mix of PICs needed for the required system function. It is also possible for a chassis to include non-SOSA elements — for example, a custom RF conditioning circuit. The backplane is designed to support the mix of functions needed for that system, which may include a power supply, processor, timing, switch, and RF payload PIC. External interface to and from the chassis is described in the SOSA technical standard in addition to the environmental and mechanical requirements.

Photo credit: United States Department of Defense

If we look at a particular PIC, such as a Software Defined Radio (SDR) RF payload, it needs to be built with a matching profile to the chassis slot it would operate in. The profile definition may also include an aperture block that defines the RF coax connections and/or fiber optic connections. This would also need to match between the PIC and the slot it's used in. Once the SDR is in a chassis MORA, the Modular Open RF Architecture is used to control it. MORA defines the software and hardware interfaces for RF modules in detail and is used to configure and control the modules as well as set up the data transport between hardware Components.

A major piece to building SOSA modules is verification to the standard. The conformance methodology is a complex task. Developing the process, requirements, and rules to enforce this process has been an ongoing effort for some time. The SOSA technical standard is also a living standard, currently at version 2 with more to follow.

MORA (Modular Open Radio Frequency Architecture) is an open standard that is focused on RF SDR, tuner and RadioHead payloads in a VPX chassis. Before standards like MORA, every piece of RF hardware might have had a unique process for identifying the hardware in the VPX chassis, or for controlling aspects of the hardware in the chassis during operating - parameters like frequency, bandwidth, and gain. MORA standardizes both the identification and control of these VPX RF payloads. For the user, this allows for rapid adoption of new technology. A MORA compliant device can be inserted into the VPX chassis and be immediately recognized by the other devices already in the chassis, as well as expose the new RF hardware's capability to the rest of the chassis. Finally, the new RF hardware can be easily controlled through a standard set of instructions that is common across all MORA compatible RF payloads. This standardization allows for more rapid RF payload integration and system upgrades as new technology becomes available. 

SOSA aligned products are just beginning to make it to market. One such product is the Sidekiq VPX400: a new wideband RF transceiver in a 3U VPX form factor. It is a modular solution that enables rapid deployment in SIGINT and EW platforms, while reducing power consumption, total slot count, and integration time.

In 2022, Epiq demonstrated MORA 2.4 compliance with the Sidekiq VPX400 at the Open Innovation Lab (OIL) located at Aberdeen Proving Grounds (APG). At the OIL demonstration, Epiq Solutions integrated a Sidekiq VPX400 card with a SOSA-aligned processor card in a 3U VPX chassis.

With the tremendous benefits of flexibility for users, we believe that these standards will continue to gain momentum and attract rapid innovation in the coming years.