Software-defined Radio & Cognitive Radio

SDR and Cognitive Radio to the Rescue

WPI’s Wireless Innovation Laboratory, under the direction of ECE assistant professor Alexander Wyglinski, is a hub of research into an array of wireless communications challenges. Current projects include developing new software-defined radio (SDR) and cognitive radio communication systems and networks. SDR is a wireless platform implementation whose functionality is based almost entirely in executable software, as opposed to conventional wireless devices, where both the digital signal processing and digital communication algorithms are implemented using integrated circuits.

The advantages of SDR are many, including the ability to upgrade devices through software alone, as well as a flexible selection of appropriate software modules supporting different wireless functions. To automate this selection process, artificial intelligence can be employed by the SDR, resulting in a cognitive radio.

Wyglinski is among the many wireless experts internationally who are actively addressing the apparent scarcity of radio frequency spectrum confronting the wireless market.

Traditional RF spectrum allocation is performed by governmental regulatory agencies, such as the Federal Communications Commission, which are responsible for licensing finite frequency bands to various entities, as well as defining transmission constraints that ensure minimal spectral interference between wireless devices.

Licensed entities possess exclusive rights to their allocated RF spectrum, preventing unlicensed transmissions from occurring in these bands, since they may cause unintentional spectral interference. This is analogous to a scenario where one roommate purchases an expensive TV and forbids the other roommate from ever watching it, even when the TV’s owner isn’t around.

With almost all prime RF spectrum (100 MHz to 3 GHz) already licensed and with a growing number of wireless users, applications, and services, the traditional licensing framework is unlikely to keep up with the growing demand for RF spectrum. At the same time, numerous spectrum measurement studies across the nation and around the world show that most RF spectrum is actually underutilized.

As a result, the spectrum scarcity problem is artificially generated by the traditional licensing framework, which does not ensure the efficient usage of spectrum by license holders.

Electrical and computer engineers, along with economists, regulators, lawyers, and other experts, are rethinking the way RF spectrum is utilized. One solution Wyglinski and his team are investigating is a new paradigm called dynamic spectrum access (DSA). It enables an unlicensed device to temporarily borrow unoccupied RF spectrum from the incumbent license holder as long as it can simultaneously respect the rights of the incumbent licensee.

In this model, the roommate who purchased the TV allows the other roommate to use it when he is away, but demands that the roommate hand over control of the set and return everything to its original state (including cleaning the popcorn off the couch) when he returns. As a result, the efficiency of the spectrum utilization is greatly enhanced while maintaining backward compatibility with the traditional spectrum licensing agreements.

Two key technical challenges associated with DSA are accurate sensing of unoccupied frequency bands by the unlicensed wireless devices and the ability to rapidly reconfigure to quickly get out of the way of an Incumbent licensed transmission. Both challenges can be addressed using SDR and cognitive radio technology, where these devices can be designed to be spectrally aware of their transmission environment while simultaneously avoiding interference with incumbent transmissions.

In addition to enabling the DSA paradigm for alleviating the spectrum scarcity problem, SDR and cognitive radio can be used to solve interoperability issues between the communication infrastructures of different government, public safety, and military organizations, especially in disaster-relief situations.