1. Performance Analysis Lab,
FemtoCell
Uday Sankar.V
Research Scholar,
Performance Analysis Lab,
IISc,Bangalore

2. Contents Introduction FemtoCells Issues and Challenges Interference
Mitigation
Conclusion

3. Data rate α Signal quality
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

4. 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.

5. 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?

6. Use of smart antennas/MIMO and higher order modulation
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?

7. 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

8. 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.

9. Ref: 3GPP standard

10. i.e: individual BW that user can expect is limited.
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

11. 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

12. 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

13. To mitigate this effects the following issues to be investigated
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

14. 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

15. 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

16. This method can be applied in FAP also
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

19. 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

20. Simple femto-macro interference model

21. Example of Femto-Macro interference scenerio

22. Conclusion Femtocell basic concepts Issues and challenges
Interference mitigation techniques.

23. Thank you…