06-12-2012, 02:28 PM
COGNITIVE RADIO AND SPECTRUM SENSING TECHNIQUES
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INTRODUCTION
Cognitive radio:
It is a wireless communication system that intelligently utilizes any available side information about the channel conditions of other nodes with which it shares the spectrum.
WHY COGNITIVE RADIO?
Conventional radios are regulated by fixed spectrum allocation policies, which are operated in certain time frames, over certain frequency bands and within certain geographical regions.
These static spectrum assignment policies have resulted in low-efficiency in usage of the precious spectrum resources.
Cognitive radio allows opportunistic access of the licensed frequency bands that are under-utilized.
COGNITIVE RADIOS: MAIN FUNCTIONS
Spectrum sensing - Determining available spectrum holes for CR users and detecting the presence of PR users.
Spectrum management - Making the efficiency of the available spectrum as high as possible.
Spectrum sharing - Coordinating access to the spectrum.
Spectrum mobility - Maintaining seamless transition from one spectrum to another.
Coherent detection sensing
Correlating the known primary signal with the received signal using matched filter to detect the presence of the PU signal and thus maximize the signal-to-noise ratio (SNR).
Coherent detection sensing requires short measurement time.
CYCLOSTATIONARY-BASED SENSING
Cyclostationary based detection is a method for detecting primary user transmissions by exploiting the cyclostationary features of the received signals.
The cyclostationary based detection algorithms can differentiate noise from primary users’ signals.
Comparison of Various Sensing Methods
Coherent detection sensing is more robust than energy detector and cyclostationarity based methods but it requires more information about PRs.
Energy detector based sensing is more practical but cannot work in low SNR envirnment
Cyclostationary-based methods are very complex and perform worse than energy detector based sensing methods when the noise is stationary.
CHALLENGES
Sensing duration and frequency: In order to prevent interference to and from primary license owners, cognitive radio should be able to identify the presence of primary users as quickly as possible.
Detecting spread spectrum primary users: The two major spread spectrum technologies are frequency hoping spread-spectrum (FHSS) and direct-sequence spread spectrum (DSSS) are difficult to sense by present sensing methods.
CONCLUSION
Spectrum is a very valuable resource in wireless communication systems.
Cognitive radio is one of the efforts to utilize the available spectrum more efficiently through opportunistic spectrum usage.
One of the important elements of cognitive radio is sensing the available spectrum opportunities.
[attachment=42788]
INTRODUCTION
Cognitive radio:
It is a wireless communication system that intelligently utilizes any available side information about the channel conditions of other nodes with which it shares the spectrum.
WHY COGNITIVE RADIO?
Conventional radios are regulated by fixed spectrum allocation policies, which are operated in certain time frames, over certain frequency bands and within certain geographical regions.
These static spectrum assignment policies have resulted in low-efficiency in usage of the precious spectrum resources.
Cognitive radio allows opportunistic access of the licensed frequency bands that are under-utilized.
COGNITIVE RADIOS: MAIN FUNCTIONS
Spectrum sensing - Determining available spectrum holes for CR users and detecting the presence of PR users.
Spectrum management - Making the efficiency of the available spectrum as high as possible.
Spectrum sharing - Coordinating access to the spectrum.
Spectrum mobility - Maintaining seamless transition from one spectrum to another.
Coherent detection sensing
Correlating the known primary signal with the received signal using matched filter to detect the presence of the PU signal and thus maximize the signal-to-noise ratio (SNR).
Coherent detection sensing requires short measurement time.
CYCLOSTATIONARY-BASED SENSING
Cyclostationary based detection is a method for detecting primary user transmissions by exploiting the cyclostationary features of the received signals.
The cyclostationary based detection algorithms can differentiate noise from primary users’ signals.
Comparison of Various Sensing Methods
Coherent detection sensing is more robust than energy detector and cyclostationarity based methods but it requires more information about PRs.
Energy detector based sensing is more practical but cannot work in low SNR envirnment
Cyclostationary-based methods are very complex and perform worse than energy detector based sensing methods when the noise is stationary.
CHALLENGES
Sensing duration and frequency: In order to prevent interference to and from primary license owners, cognitive radio should be able to identify the presence of primary users as quickly as possible.
Detecting spread spectrum primary users: The two major spread spectrum technologies are frequency hoping spread-spectrum (FHSS) and direct-sequence spread spectrum (DSSS) are difficult to sense by present sensing methods.
CONCLUSION
Spectrum is a very valuable resource in wireless communication systems.
Cognitive radio is one of the efforts to utilize the available spectrum more efficiently through opportunistic spectrum usage.
One of the important elements of cognitive radio is sensing the available spectrum opportunities.