Increasingly defence organisations around the world have invested in a variety of custom radio systems, using many different air interfaces, to perform specific tasks. However, a key challenge for operations today is ensuring that all of these different air interfaces can be interoperable in the field, and that seamless communications can be conducted on any of the legacy systems. SDR can provide exactly this capability, delivering support for multiple air interfaces within a single, flexible implementation.
SDR architectures have been used for military and defence applications, such as the Joint Tactical Radio System (JTRS). This makes use of the platform”s ability to be reprogrammed from a high level description of the new radio waveform to use new communications protocols. However, the SDR challenge is to find a practical implementation that meets a demanding range of requirements that often leads to complex power amplifier, filtering and antenna switching arrangements. For troops on the ground this can mean bulky, heavy radio equipment that can only be moved in a vehicle.
The ModStar architecture has been designed to enable implementation of SDR modules that can link multiple communication platforms in a lightweight device that would be far more portable for troops. Portability is further enhanced by Nujira’s highly efficient Coolteq envelope tracking technology for power amplifiers, that can extract double the power output from a given power transistor. Equipment and battery size are minimised by reducing filtering and power consumption requirements, allowing new smaller form factors or wider bandwidths to be achieved.
The ModStar architecture uses an open loop polar modulator with non-continuous time feedback and software pre-distortion. The advantage of this architecture is that the radio design is simplified, with the most significant design challenges being moved into the digital domain where they can be resolved with an integrated and scalable solution.
Tim Phipps, Wireless Homeland Security Business Development Manager, Cambridge Consultants stated: “As well as being more useable for troops, ModStar also delivers higher RF performance compared to alternative solutions – enabling military organisations to maximise their use of existing communications. The polar loop modulator we have incorporated into the ModStar architecture is an extremely robust technique, that has been used in millions of mobile phones, that can deliver exceptional performance with extremely high reliability for military applications.”