SCA Software Communications Architecture
- Software Communications Architecture, SCA used for defining the software structure and interfaces for the software defined radios and their designs.
The Software Communications Architecture, SCA is a software standard that is used in conjunction with the Software Defined Radio, SDR. The Software Communications Architecture, SCA provides a common standard that aims to provide portability of some elements, and a common interface so that different modules written by different groups can be brought together easily.
The concept for the Software Communications Architecture came out of the Joint Tactical Radio System, JTRS. During the project it was necessary to assemble software for the Software Defined Radio from a number of different suppliers. It was also necessary to be able to re-use software wherever possible. Accordingly the Software Communications Architecture was defined and implemented.
SCA Software Communications Architecture is aimed at governing the structure and operation of the software within a Software Defined radio enabling them to load waveforms, run applications, and be networked into an integrated system. The use of SCA also provides improved levels of interoperability among radio sets. This results from the fact that the one piece of software used to generate a particular waveform software can be imported into the software of several radio sets. In this way small differences that may have existed if the software for different sets came from different sources would not exist.
The SCA Software Communications Architecture basically describes the software components within a Software Defined Radio and in particular it defines the interfaces. The use of SCA provides two main advantages:
- It enables software elements or modules to be written by different organisations and to be brought together.
- It enables the re-use of some modules, thereby improving interoperability and providing significant cost savings.
SCA Software Communications Architecture software falls into one of three categories. It is useful to categorise them because they need to be handled in slightly different ways, and some can be re-used across several platforms while others may not. The three SCA categories may be defined as follows:
- Management: Software which falls into this SCA category is used for managing the radio system. Various applications may include plug and play; deployment and configuration software.
- Node: This software may comprise such applications as bootstrapping and access to hardware.
- Application: This type of software is used particularly for the signal processing. Examples of this may include waveform generation, demodulation, frequency translation, etc.
Of these three different SCA software categories only the application software can be re-used between different platforms. The other two need to directly interface with the platform hardware and are therefore platform specific.
Despite the fact that only the application SCA software can be transported this nevertheless produces very significant cost savings. Generating the software for a specific waveform is a very costly exercise requiring very many man-years of software effort in development and then in rigorous testing. Additionally, the ability of being able to port it across several platforms means that any inconsistencies should not be noticeable and cause any problems because all radios will work in the same manner.
Middleware known as CORBA, Common Object Request Broker Architecture is used to facilitate inter-module communications. Its use is an integral part of the SCA Software Communications Architecture standard and it is a key element in enabling modules and elements of software written by different organisations to be brought together
CORBA is a standard software defined by the Object Management Group (OMG). Its aim is to enable software modules written in a variety of different computer languages and running on different platforms to be brought together and operate.
SCA compliance and testing
In order that any software can be declared as SCA software it needs to be tested for SCA compliance. In this way the API (Applications Programming Interface) can be determined as compliant and it will operate with other SCA complaint software. Also its performance is tested for correct operation.
SCA Software Communications Architecture is an ideal standard to use for large Software Defined radio SDR projects where different software elements may be brought in from different software houses. It provides a robust interface between the different software modules that allows components to communicate together reliably in a known standard format. However the use of SCA Software Communications Architecture does place an overhead on the complexity of the system. This may mean that SCA may not be the right choice for many smaller projects. Whether to use SCA or not is a design choice that needs to be made at the beginning of the project.
By Ian Poole
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