Cognitive-Empowered Femtocells: An Intelligent Paradigm for Femtocell Networks

Table 1

Comparison between cooperative and stand-alone sensing.

	Cooperative Sensing	Stand-alone Sensing
Density	Highly dependent on the density of sensing nodes.	N/A
	Highly dependent on independency of observation.
Heterogeneity Signals	May result in the situation where secondary users	N/A
	submit different sensing results and conclusions due to
	different perceptions of heterogeneity signals.
Communication Overhead	Heavier communication overhead.	N/A
Time Sensitivity	Introduce additional delay from collecting sensing results	Able to promptly use available sub-bands once
	from sensing nodes to making the decision,	identifying the availabilities.
	resulting staled sensing results.
Spatial Diversity Gain	Achieve spatial diversity gain with certain densities and	Not able to achieve.
	uncorrelated observations.
Fading Signals	Higher detection sensitivity under proper density.	Able to achieve detection sensitivity by using feature
		detection techniques, such as cyclostationary detection,
		and covariance-based detection.
Coordination	Sensing and access are fully controlled by the	May result in disorderly accesses to the same available
	central controller.	sub-bands like a swarm of bees.
Reliability	Highly depends on the data fusion scheme as well as	Highly depends on sensing techniques.
	the credibility of sensing nodes.