Cognitive radio Project
Introduction:
In the near future and with rapid growth of wireless communications many
exciting new technologies that will require ever more spectrum.
Figure shows the use of frequency spectrum :
Figure analyses the use of spectrum:
And also nowadays a large portion of the radio spectrum is not in use for
significant periods of time in certain areas. Thus, there are a lot of spectrum holes,
in frequency bands that are assigned (licensed) to a user (we call this user as a
primary user) specifically when the license owner not utilized this frequencies in
all times and geographic locations. On the other hand, most of the unlicensed
spectrum are heavily accessed by users and have high spectrum utilization
according to the possibility of open access. These observations lead us to a key
idea: the spectrum utilization can be drastically increased by allowing secondary
users to access the spectrum holes that are unutilized by the primary user at certain
time and space. Cognitive radio has been proposed as a means to achieve such
dynamics. A cognitive radio senses the spectral environment over a wide
frequency band and exploits this information to opportunistically provide wireless
links that can best meet the demand of the user, but also of its radio environments.
The cognitive-radio devices have two important functionalities: spectrum sensing
and adaptation. A secondary terminal first senses the spectrum environment in
order to learn the frequency spectrum unoccupied by primary users. Once such a
spectrum hole is found, the secondary terminal adapts its transmission power,
frequency band, modulation, etc., so that it minimizes the interference to the
primary users. Even after starting the transmission, the secondary terminal should
be able to detect or predict the appearance of a primary user so that it makes the
spectrum available for the primary user. Basically, the primary users should not
change their communication infrastructure due to these operations. Thus, these
sensing (including the detection) and adaptation of the secondary users must be
done independently of the primary users. Thus, cognitive radio allows users to
utilize a frequency band more densely in time and space, thereby leading to a
drastic increase of the total spectrum efficiency. So Cognitive radio requires
innovative and unprecedented techniques (hardware/digital signal
processing/spectrum management techniques) in order to sense and adapt to the
spectrum.
Problem Statement:
Cognitive radio operation requires accurate information about the environment by
scanning or sensing the spectrum in order to identify the occupied and unoccupied
channels (spectrum shaping). But in some cases when some of the primary user are
behind an obstacle or shadow or fade of the signal; a problem of hidden node
occur which is considered as the most major problem in the cognitive radio
technology. The figures below depict this problem.
