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

FemtoCell

Uday Sankar.VResearch 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…