Clearing the Way for Ambulances Using FM Radio and the NI SDR Platform

Carlos Bosquez, Universidad Politécnica Salesiana

"NI tools helped us apply the theoretical concepts of RF communications exposed in an academic context to the resolution of a major social problem in a practical manner."

- Carlos Bosquez, Universidad Politécnica Salesiana

The Challenge:

Reducing response time for outpatient medical equipment by increasing the attention level of civilian drivers in the path of an emergency vehicle.

The Solution:

Alerting drivers about an approaching ambulance by interfering with the FM radio signal of their vehicles using NI LabVIEW system design software, the NI LabVIEW Modulation Toolkit, and the NI USRP™ (Universal Software Radio Peripheral) platform.


Carlos Bosquez - Universidad Politécnica Salesiana
Santiago Orellana - Datalights Cia. Ltda.


Cities with heavy traffic are common around the world. For a patient traveling in an ambulance with an emergency situation, the arrival time at the medical center is a key factor in health and chance of survival. Therefore, seeking solutions to reduce travel time is necessary.


The Ecuadorian advertising agency, Maruri, proposed ​​using LabVIEW and RF signal generator equipment to produce alerts on the radios of cars driving in front of ambulances. The idea, called the Radio Ambulance Project, was developed as an undergraduate thesis project at the Universidad Politécnica Salesiana (UPS) of Guayaquil. Maruri funded the final prototype and currently works with the Ecuadorian Association of Radio and the Association of Private Clinics and Hospitals of Ecuador to make the project feasible as a turnkey solution. 


The UPS uses PXI systems equipped with a generator and a vector signal analyzer of up to 6.6 GHz in its RF laboratories. The flexibility, bandwidth, and power of LabVIEW programming make PXI a perfect platform for researching and developing wireless communication systems.


NI Alliance Partner Datalights worked with Universidad Politécnia Salesiana to provide training on NI equipment. Part of this training included several experiments, one of which was observing the frequency spectrum of radio stations on the FM band using NI-RFSA Soft Front Panels and LabVIEW, then demodulating the signal of a station using the NI LabVIEW Modulation Toolkit to listen the audio. The second step was generating an empty carrier in the frequency of the FM radio station to cancel the original emission in the receptors located in the area where the power of the generated signal is greater than the power of the station. The third step was to modulate, in FM, an audio message recorded on the computer hard drive on the generated carrier to interfere with the emission of the radio station. This resulted in the audio message generated by the PXI bypassing the original transmission of the radio station.


The PXI platform is excellent for laboratory use, but is not the best solution for an application like the Radio Ambulance Project because of its size, weight, capacity (which would be underutilized), and power consumption. We chose to migrate to the NI USRP platform, which included an appropriate form factor, cost, and performance to meet our requirements.



For the migration, we only needed to modify 15 percent of the source code to replace the drivers from the PXI to the NI USRP, which saved a lot of application development time. In addition, we added code so the carrier could change its frequency carrier automatically to interfere with several selected radio stations. Figure 1 shows a schematic diagram of the system.


For the proof of concept, we used an NI USRP-2920 transceiver. DataLights provided advice and developed the code source in LabVIEW. UPS students conducted system design, integration, and installation in an ambulance. We conducted the test in June 2013 in Guayaquil by driving in the city in the early morning hours to avoid inconveniencing other drivers. We used an ambulance equipped with the system, and a second vehicle drove in front of the ambulance and tuned to different frequencies to evaluate the performance. We performed the test with a low-power signal, which covered approximately 30 meters and avoided massive interference. The proof of concept was a total success and included no cost.



Figure 2 shows the front panel of the LabVIEW VI used in the proof of concept. Because of the low transmission power of the NI USRP-2920 (50 mW to 100 mW), the distance in which it is possible to interfere with the signal from the FM station is only a few meters, so we selected an RF amplifier to extend the range of interference. 


In the proof of concept, we used an omnidirectional antenna, which caused interference to the radio receivers of the vehicles on the sides and the back of the ambulance. This could cause confusion and discomfort for listeners. The system only requires radiating the signal to the vehicles in front of the ambulance, so we needed to use a directional antenna and adequate gain, which is part of the design of the final system.


We used a laptop as a controller, but we plan to use a human-machine interface screen or an embedded computer with the software application on the final system. We used a voltage inverter to convert the 12 V DC from the electrical system of the ambulance to 120 V AC to power the NI USRP, the power amplifier, and the computer. We estimate that the final project can work with a DC.



Maruri Grey estimated a 40 percent reduction in the travel time of an ambulance, which significantly increases the chances of patient survival. By the proof of concept and prototype, we demonstrated that it is technically feasible to implement the project. However, legal factors and regulations for using the radio spectrum in each country impede operating the system in an open and massive manner. The next step is to work on these regulations with the appropriate entities to implement the project.


NI tools helped us apply the theoretical concepts of RF communications exposed in an academic context to the resolution of a major social problem in a practical manner. Video demonstrations on YouTube are available under the titles “Radio Ambulance Maruri Grey” and “Radio Ambulance Technical Approach.”


Author Information:

Carlos Bosquez
Universidad Politécnica Salesiana

Figure 1. Schematic Diagram of the Radio Ambulance
Figure 2. Front Panel of the Proof of Concept That Emits the Audio Signal on Different FM Stations