The power of radio is not that it speaks to millions, but
that it speaks intimately and
privately to each one of those million. The Italian
inventor, Guglielmo Marconi,
successfully transmitted wireless signals in his radio
telegraphy experiments, which
began in 1895 and continued through 1899. Radio is
transmission of audio by using
radio waves to reach a large audience. The radio waves were
first studied and identified
by German physicist Heinrich Hertz in 1886. Radio is
converted by a transducer to
electrical signal, which transmitted and modulates a radio
waves. Radio waves are used
to carry information to all the world from the transmitter
to the radio receiver by
modulating g the radio signal in the transmitter. The first
commercial radio were begin
around 1900 and continue till date. The use of radio waves
is regulated by law which is
coordinated by an international body to prevent interference
between the users. Joe
Mitole phrased tat as communications technology continues
its rapid transmission from
analog to digital, more functions of contemporary radio
systems are implemented in
software radio. The software radio is widely applicable to
track radios, peer network, air
and traffic management. The radio receivers has increased
118% worldwide in 1966.
The software radio is a powerful architecture frame- work
that helps us deliver such
advanced radio services in a way that leverages the
economics of contemporary
microelectronics and software technologies.
The different radio systems use different modulation
methods. They are amplitude
modulation, frequency modulation, frequency shift keying and
orthogonal frequency
division multiplexing such as wife networks, cell phones,
digital television broadcasting
and digital audio broadcasting to transmit digital data. In
some modulation the radio
wave is not transmitted but just one or both modulation
sidebands. The Radio waves
includes tiny oscillating voltage in the receiving antenna
which is a weaker replica at the
receiver. The air waves are a resource shored by many users.
The two radio
transmitters in the same area to transmit on the same
frequency will interfere with each
other. The radio consist of a power supply, an antenna, a
multi- band RF converter, and
a single chip containing AIDIA converters with an on-chip
general purpose processor
and memory that perform the, radio functions and required
interfaces. The canonical
mobile software radio terminal interfaces directly to the
user. The canonical base station
interfaces to the public switched telephone network (PSTN).
The Fully instrumented
base stations support operations and maintenance, developers
and researchers via
services development workstations. The placement of the
A/D/A con- averters as close
to the antenna as possible and the definition of radio
functions in software are the hall-
marks of the software radio. Thus, although software radios
use digital techniques,
software-controlled digital radios are generally not
software radios. The key difference is
the total programmability of software radios, including
programmable RF bands.
channel access modes, and channel modulation.
The near-real-time environment management stream
continuously characterizes radio
environment usage in frequency, time and space. This
characterization includes
channel identification and the estimation of other
parameters such as channel
interference levels (depending on the specific signaling and
multiple access scheme)
and subscriber locations. The environment management stream
employs block
operations such as fast Fourier transforms (FFTs), wavelet
transforms, and matrix
multiplies for beam forming. Channel identification results
are needed in times on the
order of hundreds of microseconds to hundreds of
milliseconds, while power levels may
be updated in milliseconds and subscriber locations may be
updated less frequently.
The block structure of such operations is readily
accommodated by a MIMD parallel
processor. The interface between this highly parallel
environment management stream
and the pipelined channel processing streams must
synchronize the environment
management parameters to the channel processing streams.
On-line and off-line
systems analysis, signal processing, and re hosting tools
allow one to define
incremental service enhancements.
In conventional wireless communications built around base
stations, transmit-
power levels are controlled by the base stations so as to
provide the required
coverage area and thereby provide the desired receiver
performance. On the
other hand, it may be necessary for a cognitive radio to
operate in adecentral-
izedmanner, thereby broadening the scope of its
applications. In such a case,
some alternative means must be found to exercise control
over the transmit
power. The key question is: how can transmit-power control
be achieved at the
transmitter? A partial answer to this fundamental question
lies in building
cooperative mechanisms into the way in which multiple access
by users to the
cognitive radio channel is accomplished. The cooperative
mechanisms may
include the following. 1)Etiquetteandprotocol. Such
provisions may be likened to
the use of traffic lights, stop signs, and speed limits,
which are intended for
motorists (using a highly dense transportation system of
roads and highways) for
their in-dividable safety and benefits. 2)Cooperative ad hoc
networks. In such
networks, the users communicate with each other without any
fixed
infrastructure. To mitigate interference, it is proposed
that each node create a
transmit-receive schedule. The schedule is communicated to a
nearest neighbor
only when a source node’s schedule and that of the
neighboring node permit the
source node to transmit it and the neighboring node to
receive it.
The driving force behind competition in a multiuser
environment lies in having to
operate under the umbrella oflim-itations imposed on
available network resources.
Given such an environment, a particular user may try to
exploit the cognitive radio
channel for self-enrichment in one form or another, which, in
turn, may prompt
other users to do likewise. However, exploitation via
competition should not be
confused with the self- orientation of cognitive radio which
involves the assignment
of priority to certain stimuli (e.g., urgent requirements or
needs).In any event, the
control of transmit power in a multiuser cog-native radio
environment would have
to operate under two string-gent limitations on network
resources: the interference-
temperature limit imposed by regulatory agencies, and the
availability of a limited
number of spectrum holes depending on usage. What we are
describing here is a
multiuser communication-theoretic problem. Unfortunately, a
complete
understanding of multiuser communication theory is yet to be
developed. Never-the
less, we know enough about two diverse disciplines, namely,
information theory and
game theory, for us to tackle this difficult problem in a
meaningful way. However,
before proceeding further, we digress briefly to introduce
some basic concepts in
game theory.
The automated radio links which transmit digital data
between computer and other
wireless devices using radio waves, linking the devices
together transparently in a
computer network. Computer networks can transmit any form of
data: in addition to
email and web pages, they also carry cell phone, audio, and
video content (called
streaming media). Security is more of an issue for wireless
networks than for wired
networks since anyone nearby with a wireless modem can
access the signal and
attempt to log in. The radio signals of wireless networks
are encrypted using WPA.
Radio astronomers use Radio telescopes, large radio antennas
and receivers, to
receive and study the radio waves. Since astronomical radio
sources are so far away,
the radio waves from them are extremely weak, requiring
extremely sensitive receivers,
and radio telescopes are the most sensitive radio receivers
in existence. In applications
where access to multiple bands with multiple radio access
modes is a necessity, the
software radio can reduce hardware size, weight and power
through fewer radio units.
The need for such improvement appeared as chronic
"interoperability" problems in
military applications over a decade ago. Software radios
address military issues as
discussed in the companion article in this issue on
Speakeasy. the military soft- ware
radio. Software radios are also useful in introducing new
channel access modes into
bands where established modes must be accommodated for a
number of years. As
PCS and satellite mobile applications proliferate, the
commercial sector is encountering
continuing pressure for the increased flexibility and
seamlessness of software radios
