What Are Cognitive Radio Networks?
Cognitive (or smart) radio networks are an
innovative approach to wireless engineering in which radios are designed
with an unprecedented level of intelligence and agility. This advanced
technology enables radio devices to use spectrum (i.e., radio
frequencies) in entirely new and sophisticated ways. Cognitive radios
have the ability to monitor, sense, and detect the conditions of their
operating environment, and dynamically reconfigure their own
characteristics to best match those conditions.
Using complex calculations, xMax cognitive radios can identify
potential impairments to communications quality, like interference, path
loss, shadowing and multipath fading. They can then adjust their
transmitting parameters, such as power output, frequency, and modulation
to ensure an optimized communications experience for users.
Fig:Cognitive Radio Network
Cognitive vs. Conventional:
Conventional, or “dumb” radios, have been designed with the
assumption that they were operating in a spectrum band that was free of
interference. As a result, there was no requirement to endow these
radios with the ability to dynamically change parameters, channels or
spectrum bands in response to interference. Not surprisingly, these
radios required pristine, dedicated (i.e., licensed) spectrum to
operate.
By contrast, xMax cognitive radios have been engineered from the
ground up to function in challenging conditions. Unlike their
traditional counterparts, they can view their environment in great
detail to identify spectrum that is not being used, and quickly tune to
that frequency to transmit and/or receive signals. They also have the
ability to instantly find other spectrum if interference is detected on
the frequencies being used. In the case of xMax, it samples, detects and
determines if interference has reached unacceptable levels up to 33
times a second.
The following image illustrates how xMax cognitive radios operate
differently from conventional radios. It shows screen captures of
spectrum analyzer readings taken from an xMax network tower in Ft
Lauderdale, FL. The frequencies being measured are in the unlicensed 900
MHz ISM band. Because this spectrum is unlicensed (i.e., free of charge
for anyone to use) it is used by hundreds, if not thousands of radios
in the local area for applications like cordless phones, baby monitors,
commercial video security systems, etc.
The figure at the left shows how a conventional radio would view
this—as an environment having an unacceptable level of interference for
communicating. The figure at the right shows what this same interference
looks like to xMax. xMax is able to divide these frequencies into very
small time segments (33 milliseconds) and find usable gaps where it can
transmit its short and highly efficient signals—at moments when the
spectrum is quiet.
xMax divides the 900 MHz spectrum block shown into 18 channels—giving
it 18 opportunities (windows) every 33 milliseconds to find available
spectrum.
In short, the xMax cognitive radio network sees windows of opportunity where other radios see walls of interference.
To reduce “thrashing” and unnecessary channel switching due to
temporary and very short-lived interference phenomenon, or degraded
network conditions (that do not cause a noticeable impact to performance
or quality), actual channel and handovers decisions are made by
trending multiple samples and measurements. The system only switches
from its current channel when extreme levels of interference exceed its
built-in interference mitigation capabilities. This enables xMax to use
frequencies and find available bandwidth where other radios can only see
static, yet its real-world tuned algorithms reduce signaling overhead
and optimize throughput and quality.
Cognitive Radios Improve Spectrum Efficiency:
The ability of xMax cognitive radios to make real-time autonomous
decisions and dynamically change frequencies (referred to as dynamic
spectrum access, or DSA) allows them to intelligently share spectrum and
extract more bandwidth—which improves overall spectrum efficiency. It
achieves this by “opportunistic use” of shared frequencies like
unlicensed spectrum.
xMax cognitive radio technology was designed to be “frequency
agnostic.” That is, its cognitive “Identify and Utilize” spectrum
sensing technology can be used to power radios in any frequency band.
This is beneficial since the FCC and wireless regulatory bodies around
the world are in the process of opening up new spectrum, as well as
reclassifying existing spectrum, to be made available for opportunistic
use by cognitive radios.
This would allow new market entrants, utilities, public safety,
enterprise and even existing wireless operators to offer new services,
additional bandwidth and higher capacity without requiring these
entities to purchase expensive and scarce wireless spectrum.
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