What is Beyond RF?

The IR handset would have a simple waveguide; a small, clear, plastic rod would work to carry the energy, just as a fiber-optic cable does.

Spectrum has become a semi-precious commodity. Telecom applications gobble bandwidth like popcorn, and the world’s governments parsimoniously distribute access. When we exhaust technical fixes, like refarming and narrowbanding, what will we do to keep loading users?

New spread-spectrum technologies continue to emerge, such as ultra-wide-bandwidth impulse radio, which may be able to overlay communications on existing frequencies. But what will telecom life be like — someday — after radio? Will the world’s telecommunications requirements force or drive us to move beyond RF?

“Beyond RF” … There is a strange ring to that pair of words. I will skip the impractical references to pulp science-fiction and TV starship heroes and focus on the possibilities for a communications medium that is somehow “beyond RF.”

(Editor’s Note: If it wasn’t for radio magazines, we might not have contemporary science fiction. In the 1940s, Radio-Electronics magazine Editor Hugo Gernsbach started filling in the back of his radio publication with speculative-fiction essays. This gave rise to the birth of serious American science-fiction magazines and writing, the most prestigious award for which now bears his name: the “Hugo.”)

In the 1950s, the famous author Robert Heinlein wrote a novel wherein he speculated on what he called “additional spectra”: magical energies that, once controlled, could cure or kill. The energies we use to communicate with today could meet his definition. Let us take a stab at this subject and, as a bonus, spend some time speculating on what it would take to make any of this commercially viable.

Let us begin with the notion that communication takes place when two individuals exchange information across a communications channel. The medium or channel we use today might be wireline, TDMA/CDMA/DAMPS or AMPS handsets, laser beams (safely contained within fiber-optic cables, to be sure) or beams of microwave energy. All of the former fall into the RF spectrum. Moving “up” the electromagnetic spectrum and “down” in wavelength, the submillimeter signals become infrared energy. Go shorter still, and we are into X-rays, gamma-rays, cosmic-rays and — who knows?

Current technology can be “stretched,” and the operating frequencies can be increased with “RF lenses.” If you have worked on microwave systems, the notion of focusing the energy with a Huygens, Fresnel or Kirchoff diffraction element is probably familiar to you. A handset with extremely low energy levels and a suitable lens might give us additional spectrum to use within a portable product. It would require an extensive set of receiving elements — a cloud of them — to capture and translate the intelligence onto a broadband waveguide. I see this as a maybe — if the modulation schemes can be sorted out. Impulse modulation might offer additional use of existing electromagnetic spectrum for more communications channels.

Getting past microwave, infrared may hold some promise. IR has the potential for more bandwidth — and hence more channels. Work with this technology is quite promising.

Japan Telecom and Nakayo Telecommunications are jointly developing a new hybrid communications system that combines infrared and wireless. So far, the system can transmit data at 6Mbps as far as 200m.

Nippon Telegraph and Telephone is working with IR technology for handsets. Building-interior applications, such as high-rises and subways, readily come to mind. The IR handset would have a simple waveguide; a small, clear, plastic rod would work to carry the energy, just as a fiber-optic cable does. Health and radiation concerns should be inconsequential. Watch for this technology in the near term. When last I was in Japan, there were a lot of tall buildings and subways, so a considerable market is available to drive development.

Not all IR research is in the Orient. Current efforts by Pouyan Djahani and Joseph M. Kahn at the University of California-Berkeley deal with replacing traditional single-element receivers with imaging receivers and replacing diffuse transmitters with multibeam (quasi-diffuse) transmitters. Link-performance targets are to find the minimum transmitter power that will achieve bit-error rates of less than 10^-9 with 95% probability.

Djahani and Kahn’s results indicate that in line-of-sight links, imaging receivers can reduce the required transmitter power by as much as 13dB compared to single-element receivers. In non-LOS links, imaging receivers and multibeam transmitters may reduce the required transmitter power by as much as 20dB.

X-out the X-files

We can safely rule out X-ray and gamma-ray communications channels for portable applications. I, for one, would not stick my head into an operating microwave oven, and this spectrum offers that same environment for the mobile user. For extremely wide bandwidth channels that might be used in space-to-ground and space-to-space applications, it might make a lot more sense.

X-ray lasers and “grasers” (gamma-ray lasers) are operational already, and they offer tremendous potential for point-to-point channels. Issues such as radiation properties, directionality (Gaussian beams), and spatial and temporal coherence will have to be sorted out with appropriate modulation schemes before you will see these systems in use, however.

Can you channel-split an atom?

Next, we enter the realm of subatomic speculation. What about “atomic” transmissions? Can subatomic particles be coded, manipulated or transmitted as a means of communications?

There are a total of 24 fundamental particles (see the glossary at the left): six “flavors” of quarks (defined in three generations of two), six leptons (also in three generations) and an equal number of antiparticles. We can combine quarks of different flavors, and all of the mesons and baryons that are known, to date, can be explained. I won’t touch on bosonic particles (any of the 13 types) or neutrinos. (Do they really exist?)

Pulsed, modulated or “wobbulated,” can these particles be the media of our telecommunications future? It’s hard to say, but history does remind us that, at one time, we thought communications above 14 megacycles was impossible. The “state of the art” changed, and now we have 800MHz handsets to stay in touch. (As an aside, mu mesons have already been generated and used for laboratory-test communications … in April, 1972!)

The process remains the same

No matter what we use as a communications channel medium, several other support functions must exist. I will explain by using the current analog, then extrapolate for the future.

The National Institute of Standards and Technology establishes (what else?) standard measurements so that we can build, maintain and promote communications systems, among other things. More importantly, accurate measurements allow us to stay out of each others’ hair. Interference will kill a commercial communications system faster than a tax increase.

How you might “calibrate” a lepton stream or define the “bandwidth” for bosonic-based system elements is way beyond me, but someone (or some agency) will have to establish acceptable measurement standards for manufacturers and system operators before anything can work, commercially. International (or interplanetary — who knows?) standards that use a common engineering language will be the foundation of any system.

Some kind of “Federal Communications Commission” or rather, its future analog, will be needed to define and to maintain communications channel boundaries, sort out safety issues, resolve interference and protect consumers. Industry working groups may fill this need, in addition to providing a way to establish standards for interoperability of both equipment and any accessories (such as terminals and data readers) that may be offered.

There will be a need for either venture capital for development or government-supported R&D that will then be shared with the industry. Some type of government support may be necessary until the technology matures. Free enterprisers may howl, but historically, from the early railroad system to the Internet of today, the hand of the government was necessary to midwife the complete birth of a technology.

Once the technology matures, the subsidy can be eliminated and the resulting new businesses can be taxed to recover the initial outlay. In some cases, constraint of competition may be necessary in the early days of an industry. Until they are established, markets may be limited, and expensive products have a way of going under. (Does “Iridium” ring a bell?)

Get too many players in an infant market, and competition from other technology segments will be keys to that system’s downfall. (And the government can be credited for its salvation.)

“Some things never change.” This is as true in the communications business as anywhere else. No matter what futuristic communications media we put into use, some functions of regulation and cooperation must be in place for new technologies to be successful.

Contributing Editor Koehler is a network operations manager at a major Alaskan communications corporation. His email address is [email protected].

Will packet data become particle data?

For a lot of us, nuclear physics in school never got past the proton, the neutron and the electron. Here’s a refresher glossary on subdividing the invisible:

Antiparticle

For most particle types (and every fermion type) there is another particle type that has exactly the same mass, but the opposite value of all other charges (quantum numbers). This is called the antiparticle. For example, the antiparticle of an electron is a particle of positive electric charge called the positron. Most boson types also have antiparticles, except for those that have zero value for all charges, such as a photon or a composite boson made from a quark and its corresponding antiquark. In these cases, there is no distinction between the particle and the antiparticle; they are the same object.

Antiquark

The antiparticle of a quark.

Baryon

A hadron made from three quarks. The proton (up-up-down) and the neutron (up-down-down) are both baryons. They may also contain additional quark-antiquark pairs.

Boson

A particle that has integer intrinsic angular momentum (spin) measured in units of h-bar (spin = 0, 1, 2 …). All particles are either fermions or bosons. The particles associated with all the fundamental interactions (forces) and composite particles with even numbers of fermion constituents (quarks) are bosons.

Fermion

Any particle that has odd-half-integer (½, ⅔ …) intrinsic angular momentum (spin), measured in units of h-bar. All particles are either fermions or bosons. Fermions obey a rule called the Pauli Exclusion Principle, which states that no two fermions can exist in the same state at the same time. Many of the properties of ordinary matter arise because of this rule. Electrons, protons and neutrons are all fermions, as are all the fundamental matter particles, both quarks and leptons.

Flavor

The name used for the different quark types (up, down, strange, charm, bottom, top) and for the different lepton types (electron, muon, tau). For each charged lepton flavor, there is a corresponding neutrino flavor. In other words, flavor is the quantum number that distinguishes the different quark/lepton types. Each flavor of quark and lepton has a different mass.

Gluon

The carrier particle of the strong interactions.

Hadron

A particle made of strongly interacting constituents (quarks and/or gluons). These include the meson and baryons. Such particles participate in residual strong interactions.

Lepton

A fundamental fermion that does not participate in strong interactions. The electrically-charged leptons are the electron, the muon, the tau and their antiparticles. Electrically-neutral leptons are called neutrinos.

Meson

A hadron made from an even number of quark-antiquark constituents. The basic structure of most meson is one quark and one antiquark.

Muon

The second flavor of charged leptons (in order of increasing mass), with electric charge — 1.

Neutrino

A lepton with no electric charge. Neutrinos participate only in weak and gravitational interactions and are therefore difficult to detect. There are three known types of neutrinos, all of which have extremely small mass.

Particle

A subatomic object with a definite mass and charge.

Quark

A fundamental fermion that has strong interactions. Quarks have electric charge of either +⅔ (up, charm, top) or -⅓ (down, strange, bottom) in units where the proton charge is 1.

Tau

The third flavor of charged lepton, with electric charge — 1.

Source: Lawrence Berkeley National Laboratory