Tuesday, July 28, 2020

Cognitive Radio

Via Slashdot.org: Neural Network-Enhanced 'Cognitive Radio' Communicates With ISS

To understand Cognitive Radios, you have to understand that the term Cognitive Radio came directly from Joseph Mitola's research in the mid to late 90's.

He was well known for being a software guy who got into RF. His early research was in software radios and the term "Cognitive Radio" was coined in 1999.

To understand why "cognitive radio" became a thing, one has to understand why "software radios" became a thing.

First, virtually all radio systems (even those developed now) are done by deciding the spectrum, modulation, and propagation methods up front. You do this so you can decide what the link budget (bandwidth) of your connection is, determine whether the signal is analog or digital, pulsed or CW, the modulation, demodulation, filters, mixers, noise floor, sampling, amplification, antennas, etc. This is why you typically see new wifi and cellular systems determined "by spec". The spec informs the hardware design and vice versa. This is also why you often hear about bandwidth allocation as a hot topic - not only is bandwidth fundamentally "squatters rights", so that organization and adherence to rules is important, the bandwidth allocation also fundamentally informs which physics are important and therefore the hardware of the radio system itself.

Second, the digital theory of information fundamentally transformed radio, and was in the process of transforming radio for several decades. There was a lot known about the digital equivalence of physical devices like filters, and phenomenon like noise, and ideas like channel capacity, but due to the nyquist theorem, it was actually very difficult to take advantage of any of the knowledge gained because computers were simply not fast enough to perform the necessary mathematical operations quickly to convert voltages to bits, compute, modify the bits, then convert back to voltage - especially at higher and higher frequencies. (Notice how your communications devices get faster and faster data rates over time? You can thank the fact that computing hardware is getting faster and faster.)

With the advent of fast computational devices (DSPs, mostly) it became possible to implement a lot of the theoretical advantages of digitized waveforms.

Third, RF designers started to look at the fundamental hardware building blocks of a radio, especially the filtering, modulation/demodulation. and mixing stages - which were often analog components that were "off the shelf" and fixed quantities, and created theories around how to create generalized digital representations of these devices. Once the fundamental building blocks became well understood in terms of how to build software representations of these devices, and hardware became fast enough to implement some of these software representations of once fixed hardware devices (in practice, this is still extremely primitive - even in 2020 terms), researchers began to earnestly look at how one might be able to create dynamically reconfigurable RF systems.

And the representation of these dynamically reconfigurable RF systems? Of course, it is done as a language, and therefore, programmed in software. Hence the field of "Software Radio."

Now that you realize how radio got into the software domain, you have to understand that the term "cognitive radio" is just any software radio that implements Mitola's Congitive Cycle, which is basically just a feedback loop, where a radio listens to its environment and then adapts its RF operation to best reach the receiver.

There was a program in 2012 called COMMEX (Communication through Extreme Interference) by DARPA that was ultimately won using a Cognitive Radio approach.

This is just a vastly simplified explanation. To really understand the concept of how AI can be used to steer the software radio system to receive receivers through difficult links / signal paths, you have to understand that AI is just a combination of linear algebra and statistical mathematics being used to solve objective functions. But now, maybe you have more to explore in terms of why AI and Cognitive Radio became a thing, and why it might be useful for this kind of situation.

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