hendral
2012-03-19, 11:48 PM
The wide proliferation of wireless communications unavoidably leads to the scarcity
of frequency spectra. On one hand, wireless users become increasingly difficult to find
available frequency bands for communications. On the other hand, many preallocated
frequency bands are ironically under-utilized and thus the resources there are simply
wasted. This situation leads to the introduction of cognitive radio, which was
proposed in the last decade to address this dilemma.
Under the cognitive radio model, there are mainly two tiers of users. Primary users
(PU), who typically require stable frequency spectra for communications, are licensed
users and have the rights of priority in using certain frequency spectra. Secondary
users (SU), who typically only need to access frequency spectra momentarily, are
allowed to use frequency spectra only if they do not interfere with the PU. As a
consequence, one can easily see that the ability of sensing an idle spectrum (i.e.,
spectrum sensing) and the ability to momentarily utilize a spectrum without
interfering with PU (i.e., spectrum management) are two essential elements required
for the success of cognitive radios.
http://depositfiles.com/files/yw0q3nfim
http://filepost.com/files/m27c4c51/FoundationCognitiveRadioSystemsITO.pdf/
of frequency spectra. On one hand, wireless users become increasingly difficult to find
available frequency bands for communications. On the other hand, many preallocated
frequency bands are ironically under-utilized and thus the resources there are simply
wasted. This situation leads to the introduction of cognitive radio, which was
proposed in the last decade to address this dilemma.
Under the cognitive radio model, there are mainly two tiers of users. Primary users
(PU), who typically require stable frequency spectra for communications, are licensed
users and have the rights of priority in using certain frequency spectra. Secondary
users (SU), who typically only need to access frequency spectra momentarily, are
allowed to use frequency spectra only if they do not interfere with the PU. As a
consequence, one can easily see that the ability of sensing an idle spectrum (i.e.,
spectrum sensing) and the ability to momentarily utilize a spectrum without
interfering with PU (i.e., spectrum management) are two essential elements required
for the success of cognitive radios.
http://depositfiles.com/files/yw0q3nfim
http://filepost.com/files/m27c4c51/FoundationCognitiveRadioSystemsITO.pdf/