Listening to everything, everywhere: Software-defined radio
We use radio units every day in a variety of different forms. They enable us to communicate without cumbersome cables, on a mobile basis and independent of location. But what else will the radio units of the future be able to do for us? Because digitalisation has long since found its way into the world of radio signals. This opens up completely new opportunities in the electromagnetic field.
Dr. Christof Schüpbach, specialist area Communication and Electromagnetic Protection, competence sector Science and Technology
We use the advantages of wireless communication today constantly and extensively. With a smartphone, a computer or a smartwatch – we can surf the Internet, watch the latest videos and look at photos on social media or call up the data from the meteorological station in the garden. A wide variety of radio signal types, radio technologies and standards, such as WiFi, 4G, 5G and Bluetooth are used for this purpose. In our everyday life, we hardly need to think about how all these things are compatible with each other. But what if we now want to master a new standard, so to speak, talk a new radio language?
New signal type thanks to software update
The common wireless technologies such as WiFi or mobile communications usually work on electronic chips, which are permanently installed in our electronic devices. These chips thus only understand their own language, or their own radio standard. In order to be able to use a new or different radio standard, the entire hardware needs to be renewed. In a nutshell – we need to buy a new device. But what if just a software update were sufficient for this purpose? This is exactly what is possible with what are known as software-defined radios, SDR for short. As the name states, the radio protocol is integrated in a software programme here. This means that the transmitted and received signals are processed using software. A radio protocol can therefore be adjusted and exchanged as desired, without the hardware having to be replaced.
This of course has many advantages. Above all, it extends the service life of the device. The same device can also be used for various different applications. It is thus possible to communicate with various different radio systems, for example, detect objects using radar methods or reconnoiter other radio systems. This is particularly attractive for the military, as often little space, weight and energy are available for many different systems.
Cooperative communication
In conventional radio networks, only one transmitter can ever send a message to one receiver at the same time and on the same frequency, otherwise the signals from different sources would interfere with each other. By contrast, these mutual interference signals, or simply interference, are deliberately permitted and profitably exploited in modern cooperative communication networks. Here, several stations transmit messages to several receivers in parallel – simultaneously and on the same frequencies. The undesired, interfering signal components are eliminated by skilful coding and simultaneously the desired signal components are overlaid by several sources such that they are reinforced. Thus if a transmitting station fails during a transmission or if the radio signal is deflected or attenuated, the signals from the other sources still reach the receivers and the transmissions continue without interruption. The receivers thus do not even notice that a transmitting station has failed or is no longer reachable. As a result of what is known as this diversity gain, the range, the data transmission rate and the number of users who can be served will drastically increase compared with conventional wireless networks. The networks will thus become much more efficient. The new radio units which the Swiss military would like to use going forward are also SDRs and might in future also be able to use algorithms which are currently still being examined in the research programme.
Passive radar
A passive radar uses broadcasting signals to detect echoes of aircraft. This will be possible thanks to SDR receivers and a high level of computer power. We are examining the technology in our research using our in-house developed demonstrator, shown here, with which we have also already participated in international campaigns as part of NATO/PfP research activities.
Millionfold measurement of the signal
SDR will be made possible by increasingly powerful electronic components. These will be able to digitalise radio signals shortly after their arrival on an antenna. These analogue-to-digital converters measure the signal several million to billion times per second and convert it into a sequence of numbers. The number sequence is then processed as required by a digital processor, such as a conventional computer. Only then is it possible to transmit photos or videos, for example. As the computing capacity in such processors is likewise increasing, very complex algorithms can also be implemented. This will enable completely new communication procedures which are not possible in a purely analogue form as is found in older, conventional radio systems.
Anyone can intercept a radio unit
In the meantime, several different SDR devices are available in all price and performance classes on the market. As an amateur, it is possible to buy a small receiver for just CHF 20 and to use it to receive and decode a wide range of radio signals. Thus it would be possible for any person, with little effort, to listen in to air radio messages or to decode pager messages.
More professional devices are of course considerably more expensive, but are able to achieve much more in return. They often have an enormous scanning speed and can capture signals in various ways, if necessary from several antennas simultaneously. The latter makes it possible, for example, to determine the direction of incidence of a signal, which offers great potential for reconnaissance and radar applications.
Challenges
Although a wide variety of these SDR devices are available, it is still not always very easy to use them. This is because so far, there are no standards in the interfaces between a radio unit and the processor unit. This means that the software has to be changed often if a different SDR device is used. The high data rates also lead to the fact that the signals frequently cannot be processed by conventional computer processors, but that very specialised processors come into play. These are, in turn, much more difficult and complex to programme.
Several research activities in conjunction with SDR
Today, the latest radio systems are already software-defined and in future, there will be fewer and fewer conventional radio systems with a predetermined radio language. Not only for this reason, but also because SDR devices enable multiple new measurements, employees in armasuisse’s research programme “Communication” are involved in many projects with SDR technology. For example, they are examining new radio signal types for future radio standards, looking at complex techniques for processing signals which enable cooperative communication, and using communication signals to detect aircraft. The very possibility of doing several things at the same time using the same device is particularly attractive for the military. In total, the results from the individual research findings could help to implement the following future scenario.
Radio unit of the future: Ears for everything
Imagine a radio unit of the future. From the outside, it will probably not appear very different from those in use today. But things look different on the inside. If the device is not actually having to communicate, it will constantly scan the electromagnetic spectrum and, for instance, continuously measure the dispersion conditions for the radio signals, recognise and classify foreign signals, detect which frequencies are occupied according to which patterns, intercept foreign radio transmissions and search for certain words using vocal recognition. Finally, it will also detect echoes of aircraft and vehicles in broadcasting signals.
On the one hand, this can considerably improve the quality of radio communication. This is because the device adjusts automatically to the environment at all times and selects the correct signal type and the correct frequency. On the other hand, such a device supplies the soldier and the entire integrated network with important additional information which can powerfully consolidate the overall operational picture. For example, it can warn the soldier if signals from drones are detected or foreign radio units are in the vicinity. Or the device sounds an alarm if certain words are spoken via radio. And in addition, it continuously forwards all the information to various positions in order to create an overall operational picture. The troops of the future will thus incidentally also become sensors who keep their ears open, always, everywhere and for everything.