2Contents Introduction FemtoCells Issues and Challenges Interference MitigationConclusion
3Data rate α Signal quality InformationVoice : 10kbps data rateCan tolerate Low signal qualitycontinuousARPU is low in saturated marketData : Multi Mbps data rateRequire much higher signal qualityBursty in natureARPU is high in saturated marketData rate α Signal quality
4How 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.
5Some small Analysis Data Traffic is Bursty It increases the LAN speedi.e: requires more bandwidthUser requirement: Need same QOS as like in wireline IP connectionMore Bandwidth requirement is nothing but improving spectral efficiency.How can we improve spectral efficiency?
6Use 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 boundUse of smart antennas/MIMO and higher order modulationIncreasing the sectorisation of a cell or reducing the cell size.Shall we consider it as shrinking existing macro cell?
7Macro cell has hierarchical architecture and manual cell planning. This process do not scale to support the millions of smaller cellsDoes not provide ubiquitous (Any where , anytime high speed network access)Ubiquitous requires three components/characteristics:ScalabilityAbility to provide a cost effective architecture that could sustain cellular mobilityThe mechanism that would lace such an architecture into an autonomic paradigm
8The 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.
10i.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 celli.e: individual BW that user can expect is limited.This is called Public bandwidth conceptAcceptable 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
11Incorporating all above concepts into a cell called as FEMTO CELL. Focusing areas includes hot zones, inbuilding,home and enterprise e areasFemtocell deploymentIn secondary frequency bandLower spectral efficiency/areaCochannel deploymentMacrocell and femto cell have deployed in same frequency bandResults in interference issue
12Issues and Challenges Interference mitigation and access control System selection and access controlHandoffsSecurity aspectsLocation detectionNetwork architecture and scalabilityNetwork and frequency planningIntegration with operators core network
13To 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 investigatedAccess methods : open, close and hybrid accessFrequency band allocationTiming and synchronizationSelf organizationSince 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
14Interference 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 interferencesCross layer interferenceSituations in which the aggressor (FAP) and the victim (macro cell user) of interference belong the different network layersCo layer interferenceHere the aggressor(FAP) and the victim(neighbour femto cell user) belong to same network layer
15Proposed methods for overcome interference Interference cancellation techniqueDisregarded due to errors in the concellation processUse of sectoral antennas at FAPReducing interference by decreasing the number of interferersDynamic selection of predefined antenna patternsAll above are hardware based apporach (costly)Interference avoidance (power and subchannel management)Good alternative
16This method can be applied in FAP also Power control algorithms and radio resource management are tools often used in cellular systems to mitigate interferenceIf not users located far from a basestation will be jammed by users in much closer positionsThis method can be applied in FAP alsoEg: 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
19Interference 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 techniqueDownlinkFemto cell carrier selectionDL Transmit power self calibrationUplinkAdaptive attenuation at the femto cellLimiting the transmit power of femto cell users