Software radio is the art and science of building radios using software. Given the constraints of today's technology, there is still some RF hardware involved, but the idea is to get the software as close to the antenna as is feasible. Ultimately, we're turning hardware problems into software problems.
By radio, I mean any kind of device that intentionally transmits or receives signals in the radio frequency (RF) part of the electromagnetic spectrum. This of course includes our every day AM and FM radios such as those in our homes and cars. TV's are radios that happen to turn the signals they receive into moving pictures and sound. Cell phones and cordless phones are radios. Garage door openers are radios. Car door openers are radios. Wireless internet cards (WiFi / 802.11) are radios. Shortwave, satellite, pagers, GPS, radar, NMR / MRI, the list goes on and on.
Well, you might not. However, there are at least a few things that software radios can do that haven't been possible before:
First off, let's make sure we're on the same page with regard to free software. Free software means the user has the freedom to run, copy, distribute, study, change and improve the software. Access to the source code of the program is a precondition for this freedom. Without the source code there is no straight forward path to study or improve a piece of code.
What's so good about that?
Taking things apart and seeing how they work is one of the time tested ways to get a real education. Free software encourages this, and makes available complete, working systems, some of breathtaking complexity, for study by anyone who chooses. The only cost is your time.
An organization's first job is to ensure its survival. This puts a mighty constraint on what research or development a company will undertake. A company will not "innovate itself out of business". Free software developers, operating for the most part under a different set of constraints, are free to design new systems that challenge pre-exising assumptions and business plans. Discontinuos innovation is possible.
Traditional radio design is a hardware intensive process that typically results in a closed proprietary system. These system are closed to examination, study or improvement by outsiders, that is, people who weren't on the design team. By moving more of the radio design into software, bigger portions of the system are made available for study, tinkering and improvement.
In addition, projects are underway to design "free hardware" where the complete design is documented and available to all. These boards and systems, which we expect will be built and sold by existing hardware vendors, will serve as a flexible open platform for free software radio development.
GNU Radio is a free software toolkit for learning about, building and deploying software radios. Being free software, it comes with complete source code so anyone can look and see how the system is built. In addition to support for broadcast and narrow band FM radios, GNU Radio has a complete implementation of an ATSC digital HDTV transmitter and receiver.
Please see the GNU Radio home page for information, links to the source code, or to sign up for the mailing list.