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.
