FemtoCell
Uday Sankar.V
Research Scholar,
Performance Analysis Lab,
IISc,Bangalore
Contents
•
•
•
•
•
•
Introduction
FemtoCells
Issues and Challenges
Interference
Mitigation
Conclusion
•
Information
• Voice : 10kbps data rate
– Can tolerate Low signal quality
– continuous
– ARPU is low in saturated market
• Data : Multi Mbps data rate
– Require much higher signal quality
– Bursty in nature
– ARPU is high in saturated market
Data rate
α
Signal quality
• How to get improved signal quality?
– Getting Transmit and Receiving antennas close to
each other.
– Provides the benefits of high quality links and
more spatial reuse.
– New approach: For wireless access, we can look
for packet data and IP based systems.
Some small Analysis
• Data Traffic is Bursty
– It increases the LAN speed
i.e: requires more bandwidth
• User requirement: Need same QOS as like in
wireline IP connection
• More Bandwidth requirement is nothing but
improving spectral efficiency.
• How can we improve spectral efficiency?
• Enhance the signal processing capability to a
point where the channel efficiency is close to
the Shannon bound
• Use of smart antennas/MIMO and higher
order modulation
• Increasing the sectorisation of a cell or
reducing the cell size.
• Shall we consider it as shrinking existing macro cell?
• Macro cell has hierarchical architecture and manual
cell planning.
– This process do not scale to support the millions of smaller
cells
– Does not provide ubiquitous (Any where , anytime high
speed network access)
• Ubiquitous requires three components/characteristics:
– Scalability
– Ability to provide a cost effective architecture that could
sustain cellular mobility
– The mechanism that would lace such an architecture into
an autonomic paradigm
• The above concepts are embedded in BSR
(base station router) concepts
– Combines all functions of a Radio Access Network
and core network in a single network element.
i.e: Node B,RNC,serving GPRS support node
(SGSN), gate way GPRS support node (GGSN)
• This architecture is called as flat cellular
architecture.
Ref: 3GPP standard
• Current cellular system is designed and planned
based on concept of shared resources.
– wireless cell shares radio resources with those users
that cohabit in cell
i.e: individual BW that user can expect is limited.
– This is called Public bandwidth concept
– Acceptable for voice service.
– Data service need same availability of larger
bandwidth and low delay as those of wired
connection to the internet.
– This is called private bandwidth concept
• Incorporating all above concepts into a cell called
as FEMTO CELL.
• Focusing areas includes hot zones,
inbuilding,home and enterprise e areas
• Femtocell deployment
– In secondary frequency band
• Lower spectral efficiency/area
• Cochannel deployment
– Macrocell and femto cell have deployed in same
frequency band
• Results in interference issue
Issues and Challenges
•
•
•
•
•
•
•
•
Interference mitigation and access control
System selection and access control
Handoffs
Security aspects
Location detection
Network architecture and scalability
Network and frequency planning
Integration with operators core network
• Deployment of co channel femtocells will impact
existing macro cell networks affecting their capacity
and performance.
• To mitigate this effects the following issues to be
investigated
–
–
–
–
Access methods : open, close and hybrid access
Frequency band allocation
Timing and synchronization
Self organization
• Since number and position of FAP’s will be unknown, interference
management cannot be further handled by the operator using
traditional network planning and optimization techniques
Interference analysis
• Since femto cells are deployed by users in an
unplanned manner and also has restricted access (to
protect the use of limited access), it creates
interference with existing users.
• Assumed that femto cells are synchronized with that of
the umbrella macro cells.
• Two types of interferences
– Cross layer interference
• Situations in which the aggressor (FAP) and the victim (macro cell
user) of interference belong the different network layers
– Co layer interference
• Here the aggressor(FAP) and the victim(neighbour femto cell user)
belong to same network layer
Proposed methods for overcome
interference
• Interference cancellation technique
– Disregarded due to errors in the concellation process
• Use of sectoral antennas at FAP
– Reducing interference by decreasing the number of
interferers
• Dynamic selection of predefined antenna
patterns
• All above are hardware based apporach (costly)
• Interference avoidance (power and subchannel
management)
– Good alternative
• Power control algorithms and radio resource
management are tools often used in cellular
systems to mitigate interference
– If not users located far from a basestation will be
jammed by users in much closer positions
• This method can be applied in FAP also
• Eg: in closed access femto cells, users located far from
the FAP and being asked to raise their power level
might produce high level of interference to neighboring
femtocells or even to the macro cell
Interference management technique
as per 3GPP (release 7 standard)
• Since, RF coverage of femto cells are not manually
optimized by the cellular operator and deployment is
generally adhoc, RF interference issues may arise
unless appropriate mitigation methods are utilised.
• Proposed interference management technique
• Downlink
– Femto cell carrier selection
– DL Transmit power self calibration
• Uplink
– Adaptive attenuation at the femto cell
– Limiting the transmit power of femto cell users
Simple femto-macro interference
model
Example of Femto-Macro interference
scenerio
Conclusion
• Femtocell basic concepts
• Issues and challenges
• Interference mitigation techniques.
Thank you…