• A femtocell is a small cellular base station designed for use in
residential or small business environment.
• It connects to the service provider’s network via broadband
(such as DSL or cable) and typically supports 2 to 5 mobile
phones in a residential setting.
• A femtocell allows service providers to extend service
coverage inside of your home - especially where access would
otherwise be limited or unavailable - without the need for
expensive cellular towers.
• It also decreases backhaul costs since it routes your mobile
phone traffic through the IP network.
• As given in the Femto forum “ Femtocells are low-power wireless
access points that operate in licensed spectrum to connect
standard mobile devices to a mobile operator’s network using
residential DSL or cable broadband connections ”
• They are (similar to Wi-Fi) hotspots which will connect the
subscriber to the cellular network using Broadband connection at
• A femtocell is sometimes referred to as a “home base station”,
“access point base station”, “3G access point”, “small cellular base
station” and “personal 2G-3G base station”.
enables secondary users to sense which portion
of the spectrum are available (spectrum hole),
select the best available channel,
coordinate spectrum access
vacate the channel when a primary user reclaims
the spectrum usage.
Need for cognitive femtocell
• Co-channel deployments of closed subscriber group
femtocells cause coverage holes in macrocells due to co-
• Femtocells need licensed spectrum but the available radio
resources are limited .The solution is to utilize the available
• Cognitive radio (CR) and Femtocell (FC) are both attractive
technologies due to their marvelous potential to solve
problems in current wireless communication systems.
• The creative combination of CR and FC, resulting in cognitive
femtocell (CFC), will be an essential part of the future wireless
• In order to meet stringent requirements of the LTE Advanced
standard, cognitive radio is integrated with femtocells to
• CR-enabled femtocells can actively sense their environment
and exploit the network side information obtained from
sensing to adaptively mitigate interference.
• Main characteristics of cognitive femtocell
Cognitive radio technology in
Self Configuration Module
• Enables femtocells to smoothly perform
• Minimizes the performance degradation
• Avoids co channel collisions of multiple
• Ensures that femtocell work in the best
Steps in cognitive femtocell
The cognitive module first senses the
environment and collects specific
information of all layers
Then the cognitive engine analyzes
spectrum characteristics and estimates
The self-configuration module exploits
cognitive information in a spectrum state
database to optimize parameters of all
layers in dynamic surroundings.
spectrum holes to
interference in half
of the received
signal space, and
leave the other half
for the desired
The GSOIA solution
• The goal is to opportunistically exploit spectrum holes to
improve network spectral utilization
The GSOIA solution
• With the opportunistic interference avoidance
approach, CFAPs exploit spectrum holes obtained from
sensing to avoid inter-tier interference
• Gale Shapley Algorithm: A one-to-one policy to avoid
multiuser collisions is utilized to mitigate intra-tier
Steps in OIA
• CFAP listens to scheduled information from MBS
• CFAP periodically senses spectrum to identify
• CFAP compares sensing outcomes with scheduled
information to identify spectrum opportunities
Steps in GS Algorithm
• Each CFAP first calculates the utility of every channel in a spectrum
resource pool. Then the CFAP sets a backoff timer for every channel
that is inversely proportional to channel utility.
• When a backoff timer expires, the CFAP checks the busy tone of the
corresponding channel. If there is no busy tone over this channel,
CFAP immediately selects it for communications. Otherwise, CFAP
abandons this channel and waits for next backoff timer expiration.
• The process continues until each CFAP captures one channel or all
channels are allocated.
• Mitigate both inter tier and intra tier interferences
• With the opportunistic interference avoidance approach, CFAP
interweave their signals with those of macrocells without
significantly impacting their communications.
• Gale-Shapley spectrum sharing provides a one-to-one
matching policy to avoid collisions among multiple femtocells
Summary and conclusion
• Since both cognitive radio and femtocell are promising
technologies to enable energy efficiency in wireless networks,
the interplay between them improves energy efficiency.
• CR enabled femtocells have good potential to break the
spatial reuse barrier of cellular systems.
• GSOIA provides one to one matching policy and avoid
collisions among multiple femtocells.
•  Li Huang, Guangxizhu and Xiaojiang ,” Cognitive Femtocell
Networks:An Opportunistic Spectrum Access for Future Indoor
Wireless Coverage” IEEE Wireless Commun., vol. 20, no. 2, 2013, pp.
•  K. Zheng, Y. Wang, W. Wang, “Energy-Efficient Wireless In-Home:
the Need for Interference-Controlled Femtocells,” IEEE Wireless
Commun., vol. 18, no. 6, 2011, pp. 36–44.
•  A. Damnjanovic et al., “A Survey on 3GPP Heterogeous
Networks,” IEEE Wireless Commun., vol. 18, no. 3, 2011, pp. 10–21.
•  I. F. Akyildiz et al., “Next Generation/Dynamic Spectrum
Access/Cognitive Radio Wireless Networks: A Survey,” Computer
Network J., vol. 50, no. 13, 2006, pp. 2127–59.
•  T. Yucek and H. Arslan, “A Survey of Spectrum Sensing Algorithms
for Cognitive Radio Applications,” IEEE Commun.Surveys & Tutorials,
vol. 11, no. 1, 2009, pp. 116–30.
• D. Lopez-Perez et al., “Interference Avoidance and Dynamic
Frequency Planning for WiMAX Femtocells Networks,” Proc. IEEE
Int’l. Conf. Commun. Sys., Nov. 2008,