Why Open Spectrum Matters - The End of the Broadcast Nation

Before Hollywood made Hedy Lamarr "the world's most beautiful woman" she was an Austrian aristocrat married to an arms merchant who was so possessive that she had to drug his maid in order to escape.

In Hollywood, she became friends with George Antheil, an avant garde composer. One day, while playing four-handed piano with him, she realized how to defeat the jamming devices used to keep radio-controlled torpedoes from hitting their target: rather than staying on a single frequency, the transmitter and receiver could be synchronized to switch bands like four hands moving around a piano keyboard.

She and Antheil were awarded a U.S. patent on the invention in 1942, and in 1958 electronics were sophisticated enough to enable the U.S. Navy to begin using frequency hopping as the basis of its communications.

[2]Spectrum-as-pipe does not make sense in a frequency-hopping world. In fact, Lamarr's invention directly contradicts the essence of the pipe metaphor: that there is a single medium, contained by hard walls, from A to B. [3]2. Information Theory.

The next blow to the old metaphors came from Claude Shannon and Warren Weaver in 1949 with their development of Information Theory. The carrying capacity of a water pipe can be known with near certainty.

Likewise, how many beer bottles can be filled per hour can be predicted based on the speed of the conveyor belt. But spectrum is carrying neither water nor bottles.

It's carrying information. And information is not a hard-edged good: It can be compressed, in many circumstances it survives some loss, and it is independent of the medium carrying it.

A system optimized for carrying information, rather than for preserving the integrity of waves, would look much different than what we have today. And it would be much more efficient.

In fact, current research indicates that the amount of information a frequency can carry increases with the number of users. The only question is how much it increases.[4]3. The Internet.

The Internet teaches us three lessons loud and clear.(a) Open standards work. Rather than building a network that connects A to B to C by touching copper to copper, the creators of the Internet built a network by establishing standards for how information is to be moved.

It is because the Internet was not built as a thing that it has been able to bring the world many orders of magnitude more bandwidth than any previous network.  Our current policy, however, treats spectrum as if it were a physical thing to be carved up.

By focusing on open standards rather than on spectrum-as-thing, the medium can become far more efficient and offer far greater capacity.(b) Decentralization works.

Keep the architecture clean and simple. Put the “smarts” in the devices communicating across the network rather than in centralized computers.

 In fact, central control and regulation would have kept the Internet from becoming the force that it has.(c) Lowering the cost of access and connection unleashes innovation beyond any reasonable expectation.Open spectrum will do for wireless communications what the Internet has done for networking computers.Today’s technologyAs a result of decisions based on the science of the early 1900s, we built a system that works around technological limitations that 21st century technology has overcome.

Advances over the past ten years knock into a cocked hat our most important assumptions about wireless communications:“To get good reception, lock onto a signal.” Not any more.

Just as a highway that allows cars to change lanes will have greater capacity than one that locks them into single-lane tunnels, bandwidth increases with adaptive radios that can change their frequencies, modulation, and information routing to compensate for and exploit the current conditions.“A radio is a receiver.” Until recently, a radio was a hard-wired device that could do one thing only: play music, receive voice data, etc.

But software-defined radios are computers, capable of being reprogrammed on the fly. They can be upgraded after they are sold, and that they can dynamically be put to a wide variety of uses, enabling innovation far beyond simply providing more “stations” to listen to.“The more you put into a network, the better it is.” The Internet – an end-to-end network – has proven this idea to be backwards.

It’s precisely because the Internet wasn’t optimized for any particular application that it’s useful to the broadest range of innovations. Spectrum can be architected the same way: as an information transport utilized by “smart devices” such as adaptive and software-defined radios.“The more users, the less bandwidth.” Shannon and Weaver’s Information Theory that guided the development of broadcast and point-to-point networks did not consider the implications of the way our cellular networks currently enable multiple simultaneous users.

In the past decade, a variety of research teams have begun to explore this unknown corner of the theory, and have shown a variety of counterintuitive results that show that our assumptions about capacity and interference are just wrong.

[5]”It’s all about the waves.” No, it’s all about information. Digital communications techniques such as error detection and correction, maximum likelihood estimation, Rake receivers, and other techniques developed based on Shannon's information theory and Digital Signal Processing provide a rich set of techniques that have not been used in radio systems deployed before 1990 (the bulk of commercial systems), i.e. before digital cellular telephones. ”Interference is a law of nature.” Very wideband modulation techniques such as DSSS (802.11b – AKA WiFi), OFDM (802.11a/g), UWB and many others use new technologies to spread information across many frequency bands, creating very high transmission rates at low cost with very little degradation even in noisy environments.

 They do not require "exclusive" use of those frequency bands, especially in a network that uses modern adaptive error-correction techniques, and they do not interfere with older technologies (such as TV) that uses the same frequencies.