DR. Carmine Clemente - University of Strathclyde
Domenico Gaglione - University of Strathclyde
Radar traditionally operates by generating a radio signal for a few thousandths of a second or less, followed by a listening period for reflections. These reflections are then filtered to extrapolate the position, size, and speed of objects. The concept of a Communicating Radar (Co-Radar) system exploits the fact that the radar does not need to focus solely on these operations. We can use the radar system to additionally transmit and receive application-specific information, such as aircraft altitude or other forms of sensed data, with no need for additional hardware. This drives additional functionality with no extra weight. As an added benefit, no additional power is required to transmit the communications data, thereby extending aircraft flight time.
Co-Radar offers significant advantages for the aeronautical industry, as it powers the design of low-powered aircraft by maintaining a low weight, which is proportional to engine and fuel requirements. Taking all opportunities to minimise weight ensures a more efficient aircraft. Additionally, incorporating the two technologies into a single system makes it possible to reuse existing radar and reduce the overall cost of production.
Co-Radar on USRP Devices
We implemented the entire software framework for the Co-Radar system with LabVIEW software and USRP (Universal Software Radio Peripheral) devices for both the radar/communication transmission and for the communication receiver. Figure 2 shows the high-level block diagram of the implemented system.
In addition to target range detection, we also computed the spectrogram of the target to show the real-time Doppler and micro-Doppler target signature.
The signal received by the communication receiver in LabVIEW is then shared with The MathWorks®, Inc. software through the Ethernet interface. This allowed us to reuse the demodulation code that we had previously developed in the MathWorks development environment. That is a great benefit of LabVIEW; it enables users to port data into other software environments and back again, which really expedited the prototyping process. With time, we plan to develop this demodulation functionality in LabVIEW, to bring the entire system code into a single environment for simplicity. However, we appreciated the ability to reuse our existing code implementation.
Concept Validation in Controlled Environment
By choosing the NI platform for our research, we could validate the application code prior to purchasing the USRP device through simulations available in LabVIEW. We found the USRP radio very easy to use. I started using it with minimal knowledge of LabVIEW software, and in a few weeks I could develop a full working prototype of a complex system like the Co-Radar. In addition to the benefit of rapid prototyping, we had support from NI with getting started in developing our application.
We have validated the concept across the airways in a laboratory environment, using one USRP device to provide the collocated transmit and receive channels required for a monostatic radar, while using a second USRP device as a communication receiver, as shown in Figure 3.
We have tested the radar system itself and transmission up to a distance of 20 m. For the specific design that we developed for low-powered aircraft, an average power consumption of 50 W per day would deliver over 30 km of unambiguous range and communication. The next stage of validation would be to test the Co-Radar system in the field using a low-powered air vehicle. The target, in this case a human participant, moved towards and away from the radar within the designated walking area shown in Figure 3. The movement of the target introduces a Doppler and micro-Doppler modulation to the radar return signal, which can then be visualized using a spectrogram. The spectrogram shown in Figure 4 clearly shows the participant approaching and receding from the USRP radar system.
At the same time, we validated the traditional radar functionality, we used a second USRP device to discern the communication data embedded in the radar signal. We assessed and compared the performance of the communication link with those obtained from simulations. Figure 4 shows the results.
The NI software defined radio platform represents the ideal solution for rapid prototyping of RF systems thanks to its flexibility, performance, and seamless LabVIEW software support. When selecting the best system for our experimental activities, the USRP platform proved the most flexible and easy-to-use system for both teaching and proofs of concept. Handling RF signals has never been so easy. We used the USRP system to validate complex, novel concepts in just a few weeks.
Our unique Co-Radar system represents the first step in a challenging new research area. Our group successfully validated the concept of Co-Radar across the airways and will continue using the NI platform to further our research. The Co-Radar testbed will be an invaluable platform for algorithm development and further design improvements.
Many aerospace engineers and academic researchers have already seen the Co-Radar demonstrator, which increases the impact of our work. This would not have been possible without NI products.