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Sunday, November 6, 2011

TRENDS AND FORCES RESHAPING THE WIRELESS WORLD: Advances in Radio Technology


The development of technologies and the associated policy and regulatory regimes that govern their use are often closely coupled. For example, from the late 19th century until recently, the roadways for communication and transmission of information (e.g., the telephone system, broadcast television, and radio) were, like those for transporting people and physical goods, owned, managed, and regulated by a relatively small number of institutions. 

The concerns and assumptions underlying policies were grounded in the technical realities and economic and political imperatives of the time. The interplay between technology and policy was apparent as early as the 1910s. The growth of radio communications and the spectrum policy that emerged reflected a compromise on a framework for spectrum management. When spectrum regulation began, the primary obstacle to signal reception was noise. Because of the quality of components available at that time and the nature of the most popular frequency bands of the day (which were selected for their longer propagation distances), noise was a significant problem, and interference (i.e., human-generated noise from other transmissions) from other sources was regarded as intolerable and something to be avoided. Accordingly, a regulatory structure was set up that allocated frequencies with specific power levels and bandwidth masks uniquely to single broadcasters or services in a given geographic area. For the most part, the environment consisted of a small number of high-power transmitters separated by frequency and geography, and a very large number of mute receivers. Licenses granted the right to broadcast using a few kilohertz of spectrum and also provided an “address” (in the form of, for example, AM radio channel numbers) in addition to a means to avoid interference.

Today, radios routinely operate in frequency ranges where background noise is limited and dealt with rather easily. The very large number of active transceivers means that the primary challenge is separating the desired signal from the signals of all the other potentially interfering transmitters, not avoiding noise. The huge number of devices associated with many modern services means that frequencies must be shared (and that the particular frequencies in use at any given time are not apparent to the user). For example, many cell phones share a particular block of spectrum at any given time, with the sharing enabled by separation by code (code division multiple access) or time slice (time division multiple access) as well as location (which cell the phone is currently in). These challenges were not fully anticipated by traditional spectrum allocation and licensing schemes. Moreover, in the past 50 years, a number of changes—including a fundamental new understanding of physics and information theory; vast increases in the computation that can be performed by a compact, cheap, low-power device; and improvements in analog components—have allowed for very inexpensive processing of signals in ways not contemplated when many spectrum polices were established and allocations were made. In short, radio-frequency communication today is being profoundly changed by a related set of technological advances—both in the capabilities and performance of individual radios and in the design of networks and systems of radios. These advances include;

·         A shift in favor of digital signal processing and use of low-cost complementary metal-oxide-semiconductors integrated circuit technology for both digital and analog radio components;

·         The advent of new radio systems architectures that rely on distributed (and often Internet-Protocol-based) control and on more localized transmission using microcells and mesh networks, rather than traditional architectures that rely on centralized switching or wide area transmission;

·         The development of a variety of techniques, including more robust receivers, antenna arrays, frequency agility, and new modulation techniques and coding algorithms, to permit dynamic, fine-grained, and automated exploitation of all available degrees of freedom—that is, not just static separation in frequency and space but also dynamic use of frequency, time, space, and polarization—along with “code” —to distinguish radio signals; and

·         The development of technologies that permit flexible and adaptable radios that can sense and respond to their operating environment and can coordinate their operation in an increasingly dynamic, distributed, and autonomous fashion.

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