There is no way with 10+ years of the SDR "family" being in production that this chap "invented SDR."
Not sure if the SDR radio company(s) have actual patents (one would hope so) but any company or individual that would go to market with a non-patented 'invention' or discovery is probably just asking for legal issues and mucho lawyers fees. Sure the patent filer in the OP didn't invent SDR (since we all know it's been around for a while) but if he was the first to patent it, he will have some leverage in court. Look at the early discoveries in radio and technology and see examples of patents being filed on things that existed or was known to have existed, such as the regenerative receiver first done by Edwin Armstrong and then claimed (and won) by Lee DeForest 2 years later ....
Many of Armstrong's inventions were ultimately claimed by others in patent lawsuits. In particular, the regenerative circuit, which Armstrong patented in 1914 as a "wireless receiving system," was subsequently patented by Lee De Forest in 1916; De Forest then sold the rights to his patent to AT&T. Between 1922 and 1934, Armstrong found himself embroiled in a patent war, between himself, RCA, and Westinghouse on one side, and De Forest and AT&T on the other. At the time, this action was the longest patent lawsuit ever litigated, at 12 years. Armstrong won the first round of the lawsuit, lost the second, and stalemated in a third. Before the Supreme Court of the United States, De Forest was granted the regeneration patent in what is today widely regarded as a misunderstanding of the technical facts by the Supreme Court justices.
So it might appear that having a patent first on some item or idea doesn't always mean that you're protected from 'poachers'.