How Do Engineers Work Around a Congested RF Spectrum?

July 24, 2020 by Jake Hertz

The usable RF spectrum is a finite resource, and, with enough simultaneous users, congestion can become a serious impediment to reliable communication.

The Internet of Things. 5G. Autonomous vehicles. These emerging technologies share two things in common: 1) they all rely on RF communication and 2) they all promise to introduce millions of devices to the RF spectrum. 


Predicted growth in connected devices worldwide

Predicted growth in connected devices worldwide. Image from IoT Analytics


Congestion in the RF spectrum becomes a serious issue, for example, when it disrupts the communication of military personnel and first responders. As such, this issue has become a point of paramount importance in RF design and development. 


RF Spectrum Congestion and Its Effects

The RF spectrum is a finite resource to be shared by all wireless devices in the world. Oversharing of the spectrum can lead to unintentional interference between signals, making it difficult or impossible for receivers to pick out the correct signal. 

Unintentional interference mostly occurs because generating an RF signal is an imperfect process.

Generating signals of a specific frequency usually results in some unintended power in neighboring frequencies, also known as harmonics. In this case, more powerful signals can drown out a weaker one. In another common case, two signals on the same frequency being broadcast near each other can interfere in similar ways.


Example of harmonics in the frequency domain

Example of harmonics in the frequency domain. Image used courtesy of Nutaq


While engineers have come up with ways to allow users to simultaneously share the spectrum, interference is not entirely unavoidable. Most people have experienced unreliable communication when in highly populated environments like a city—proof of the continuing effects of spectrum congestion. 


Ways of Dealing with Congestion

Engineers have developed many techniques to help avoid interference, both unintentional and, in military applications, intentional (that is, with jammers).

Basic interference mitigation techniques mostly rely on the avoidance approach. The objective is to reduce the probability of user overlap in space, time, and frequency. 

One example of a technique used in CDMA systems is a frequency-hopping spread spectrum. In this technique, the transmitted signal isn’t a single frequency but instead is periodically shifted in frequency. By occupying many different frequencies for short periods of time, there’s a reduced likelihood of signal overlap and interference.


Example of FHSS

Example of FHSS. Screenshot used courtesy of HowTo


The challenge with these techniques is often that there needs to be hardware that can support their range of operation. 


Analog Device's New RF Transceivers

Analog Devices has been looking to address the challenge of RF congestion on the hardware side. Just this week, ADI announced the first product in a new series of RF transceivers meant to combat interference and provide a high dynamic range.

The ADRV900 was designed specifically for mission-critical communication applications such as first responder radios and satellite communications where size, weight, and power are key design considerations. 


Functional block diagram of the ADRV900

Functional block diagram of the ADRV900. Image used courtesy of Analog Devices


The transceiver offers an operating range from 30 MHz to 6 GHz and can support narrowband and wideband applications from 12 KHz to 40 MHz. From the user guide, the ADRV900 incorporates digital signal radio correction algorithms, AGC, DPD, frequency hopping, and channel filtering.

This versatility and embedded functionality gives the transceiver the ability to employ all sorts of anti-interference algorithms and reliably decode a signal in a heavily congested network. 


Accommodating Mission-Critical Communication

While the number of wirelessly connected devices continues to grow, mission-critical applications like first responder radio and satellite communications will be particularly in need of solutions to network congestion. Developments like those from Analog Devices will become increasingly important in ensuring reliable communication.