Open Spectrum

"The notion that the airwaves need to be meted out carefully is based on the fact that, in the early 1900s, radio equipment was easily thrown off when signals of the same frequency from more than one source overlapped. We call this phenomenon “interference." In fact, the waves sent out by different transmitters don’t interfere with each other at all. They pass right through each other unchanged. Interference occurs in the receiver, when its antenna picks up multiple signals of the same frequency and has trouble telling them apart. In other words, interference is a function of the intelligence designed into the receiver, not a function of what happens in the airwaves—and receivers can be a lot more intelligent than they were 90 years ago.

Recent advances are enabling radio signals to be coded digitally so they can easily be separated from each other. No longer is there a need to chop the airwaves into distinct regions of frequency and geography." -----Dr. David Reed

For almost a century, governments have imposed detailed limits on the use of radio – who can transmit or receive what frequencies and waveforms, power levels, locations and purposes. Licenses summarize these controls for specific users or “stations”. Most people accept strict rules for radio in the belief that they are necessary to prevent chaos and interference.

However, during the past 20 years, smarter radios have been developed that go a long way toward solving problems which once seemed to require government intervention. Cordless phones can automatically scan a band to select an unoccupied channel. Cellular GSM phone networks dynamically assign frequencies, and set signal levels to the minimum needed for an adequate link. Smart receivers can separate signals that are coded differently even when they occupy the same channel. The combination of these attributes has fueled explosive growth in public demand for wireless devices.

But the wireless boom also drew attention to the fact that regulations designed to protect “dumb” radio equipment from interference create artificial shortages of frequencies. Recent surveys have shown that static frequency assignments can result in band utilisation rates as low as 5 to 10 percent. A few radio experts began making this point in the mid-1990s, laying the groundwork for Open Spectrum to emerge as an alternative model in spectrum management. But it was the US Federal Communication Commission’s 1985 decision to allow new communication technologies in the bands for unlicensed Industrial, Scientific and Medical (ISM) devices that jump-started this evolution.

Communication in the ISM bands must tolerate interference. This is in contrast to traditional spectrum management, where the aim is to prevent interference. Protection against interference is normally achieved by not letting other transmitters use a licensed channel within a geographic “protection zone”. But Wi-fi – a technology that developed in the ISM bands – showed that large numbers of people can share a band, without specifically assigned channels, if everyone uses low power and waveforms designed to soften the effects of interference. With no protection zone, there is no technical justification for licensing Wi-fi. And indeed, most countries now exempt Wi-fi from licensing, as shown by our global survey.

Wi-fi is often cited as Open Spectrum’s “proof of concept”, validating “unlicensed commons” as a practical paradigm in frequency management. However, it is also important to note that Open Spectrum is a much broader concept than Wi-fi. At the same time, Wi-fi works as well as it does because of widespread voluntary acceptance of the IEEE 802.11b standard, and because of mandatory processes of “type approval” (in which equipment is approved by regulators for unrestricted sale if it conforms to certain parameters, particularly as to radiated power and frequency use). Thus, unlicensed is not the same as unregulated. Open Spectrum supporters seem split by this distinction, with some arguing for complete deregulation, and others (like ourselves) embracing type approval as preferable to licensing.

Some people think radio technology is evolving inevitably toward a future where traditional forms of regulation will be impossible. Billions of Radio Frequency Identification (RFID) tags are likely to spread around the world in the coming decade; they will be as hard to control as an epidemic. “Software-defined radio” is another challenge. More and more radio functions that had been performed by hardware are likely to be implemented in software in the future. If this software is open source, or can be modified or replaced after purchase, “type approval” processes are undermined.

Dr. David Reed, father of TCP/IP, brilliantly puts it this way:

“That's why what's happening now is so exciting. New radio transmission and networking technologies can squeeze more and more capacity out of the same spectrum. Some of the improvement comes from the shift from analog to digital transmission. For example, at least five digital TV shows can be broadcast on the same frequencies that a single analog channel now occupies. Similarly, digital cellular systems now carry three times as many phone calls as their analog predecessors. Even greater improvements in spectrum usage will come from a family of technologies that use the computational intelligence of today's wireless devices to allow multiple systems to "share" the same spectrum. The first of these, spread spectrum, replaces ancient high-power, undifferentiated narrowband transmissions with modern low-power, coded wideband. First described during World War II, spread-spectrum technology is already used in many cellular phone networks and in Wi-Fi, but newer systems promise even greater capacity improvements. A newly permitted method of using spectrum, ultrawideband, takes spread spectrum to its logical conclusion, operating at such low power that, subject to appropriate safeguards, it can underlie existing licensed services. That is, preexisting users of the same spectrum bands won't even know the ultrawideband transmissions are there. It will be as if we figured out a way for freight trains to travel on highways, with cars being none the wiser. Standards work is already under way to make ultrawideband the core technology for home entertainment networks, transferring video, audio, and photos among home PCs, stereos, high-definition televisions, and DVD players. And this is only the beginning. Another recent innovation, smart antennas, can focus adaptively to "lock into" a directional signal. Instead of radiating a signal in all directions equally, they figure out where a user is located and direct the radiation accordingly, reducing effective interference with other transmitters. Now, too, novel coding algorithms can take factors that traditionally hampered transmission, such as physical obstacles and motion, and use them to generate information that increases capacity. Perhaps the greatest technological gain in wireless capacity, however, will come from systems that work cooperatively. In a network architecture called a mesh, each RF receiver also acts as a transponder, re-transmitting data sent by other devices in the network. In other words, every new device uses some of the network's capacity but also adds capacity back. Because a device in a mesh no longer needs to send information all the way to its ultimate destination (such as a cell tower), it can use less power. That allows the network to add more devices without any noticeable increase in interference. The approach resembles the distributed architecture of the Internet, in which every router can move traffic along an efficient path".

Software radios are a key enabler for all these advances. A software radio can receive and transmit across a broad range of frequencies; because it processes signals in software, it is far more adaptable than a traditional radio. In principle, a software radio originally used for cellular telephony could, for example, download new software and begin to receive broadcast television signals, or, more likely, access a network that uses a new cellular transmission protocol. Even more sophisticated "cognitive radios" would work cooperatively, analyzing other nearby radios and adapting on the fly to avoid other transmissions."

Just as open standards and open software rocked the networking and computing industry, open spectrum is poised to be a disruptive force in the use of radio spectrum for communications. At the same time, open spectrum will be a major element that helps continue the Internet’s march to integrate and facilitate all electronic communications with open standards and commodity hardware.

Some good places to explore if you want to know more are listed below:

In the context of India, this is a good read.