CDMA — Code Division Multiple Access, developed by Qualcomm and used in many cellular networks — uses a different spread-spectrum variant called direct-sequence spread spectrum, in which the signal is spread by XORing it with a pseudorandom code sequence rather than by hopping between frequencies. Again, the conceptual relationship to spread-spectrum is real, and the engineering is different.
GPS satellites transmit navigation signals using CDMA-like spread-spectrum techniques that allow multiple satellites to broadcast on the same frequency simultaneously, with each satellite’s signal distinguishable by its unique pseudorandom code.
The honest summary is that the concept of spread-spectrum communication — defeating interference by distributing a signal across frequencies rather than concentrating it on one — is real, was articulated in the Lamarr-Antheil patent in a specific form, and was later developed independently by engineers into the practical wireless systems that now underlie Bluetooth, cellular telephony, and GPS navigation. The specific mechanism of the patent was never implemented. The concept it exemplified was.
## Recognition Deferred
Why did it take so long? This is the question that hangs over the entire story, and it does not have a single answer.
Part of the answer is institutional. The National Inventors Council received thousands of proposals during the war, and the Navy declined many of them for reasons that were partly practical and partly bureaucratic. The Lamarr-Antheil proposal faced genuine technical obstacles, and an institution under wartime pressure could not develop every promising idea. This is not an excuse; it is a partial explanation.
Part of the answer is the gap between the patent’s expiration and the commercial deployment of frequency-hopping technology. The patent expired in 1959. Commercial spread-spectrum technology did not reach consumers until the 1990s. During those three decades — in which frequency hopping moved from classified military application to commercial product — there was no active patent holder to claim credit, no financial incentive for the companies deploying the technology to trace it to a 1941 document, and no cultural mechanism for connecting a Hollywood actress with a communications engineering history.