Interference Avoidance in 3GPP FemtocellNetworks Using Resource Partitioning and Sensing

Ismail Guvenc , Moo-Ryong Jeong , Mustafa E. Sahin∗, Huilin Xu , and Fujio WatanabeDOCOMO Communications Laboratories USA, Inc., 3240 Hillview Avenue, Palo Alto, CA, 94304∗Dept. of Electrical Engineering, University of South Florida, Tampa, FL, 33620

Email: {iguvenc, jeong, hxu, watanabe}@docomolabs-usa.com, msahin@mail.usf.edu

Abstract—Interference problems in cochannel femtocell net-works may cause significant performance degradation for certainfemtocell/macrocell users. These problems and potential solutionsare recently being investigated within the 3GPP. The goal of thepresent paper is to review the simulation framework for femtocellnetworks in 3GPP and briefly summarize some of the importantinter-cell interference coordination (ICIC) techniques that havebeen discussed. Then, a new intercell interference avoidance(ICIA) method is proposed for femtocell networks which is basedon resource partitioning and sensing. Different than prior arttechniques, the proposed approach does not require the use ofX2 interface or over-the air signaling, both of which may beinfeasible/costly for femtocells with the available releases of the3GPP.Index Terms— Carrier aggregation, femtocells, ICIC, inter-

ference, HeNB, HNB, macrocell, resource partitioning.

I. INTRODUCTIONFemtocell networks have been recently gaining popularity

for improving the capacity and coverage of next-generationbroadband wireless communication systems. In cochannelfemtocell networks, femtocells aim to reuse the spectrum re-sources of macrocell users. While such cochannel deploymentbrings the advantage of efficient spectrum utilization, it mayalso result in cochannel interference (CCI) problems betweenthe femtocells and the macrocell. In certain scenarios, the CCImay seriously degrade the system performance, and thereforeshould be avoided or mitigated.The interference conditions in a femtocell network greatly

depend on the access mode used by the femtocell network.Closed-access and open-access are two different access optionscommonly used by femtocells. In the closed access mode, themacrocell user equipments (MUEs) that may join a particularfemtocell are restricted to a certain group, while all MUEs areallowed to make hand-off to femtocells without any restrictionfor the open access mode. Even though interference problemsmay be greatly resolved with the open access operation,there may be some other problems such as privacy issues,extra burden on the backhaul of a femtocell’s owner etc. Onthe other hand, for the closed access mode, there may bescenarios where the interference reaches at intolerable levels.As illustrated in Fig. 1, the MUEs that are in the vicinityof a femtocell will be receiving significant interference fromthe femtocell during the downlink (DL) operation, while theywill be causing significant interference to the femtocell duringuplink (UL) operation.In [1], [2], detailed discussion of six different CCI

scenarios between home evolved NodeB (HeNB), evolvedNodeB (eNB), and the user equipments (UEs) have beenpresented, which can be summarized as follows [3]1: 1)HeNB→MUE (DL), 2) HUE→eNB (UL), 3) MUE→HeNB(UL), 4) eNB→HUE (DL), 5) HeNB→HUE (DL), and 6)HUE→HeNB (UL). The interference scenarios captured by1) and 3) are also summarized in Fig. 1 which are due to theMUEs that are close to a HeNB, and these scenarios will alsobe the main focus of the present paper. In order to resolve suchinterference problems, several inter-cell interference coordina-tion (ICIC) and mitigation techniques have been discussed in

1In order to be consistent with the 3GPP terminology, we use the terms UE,eNB, and HeNB in the sequel, which refer to mobile station (MS), macrocellbase station (mBS), and femtocell BS (fBS), respectively.

Fig. 1. Interference scenarios for femtocell/macrocell network in considera-tion. Due to the presence of an MUE in the vicinity of a femtocell, intolerableinterference scenarios may occur when the closed-access option is used.

the 3GPP (see e.g., [4]-[10]). Also, a simulation frameworkhas been developed in the standard for femtocell networks inorder to accurately capture practical interference settings thatmay arise in realistic scenarios [11], [12].The goals of the present paper are three-fold: 1) to present

an overview of the simulation framework for femtocell net-works in 3GPP along with representative simulation results(Section II), 2) to briefly review the available ICIC methodsdiscussed in the 3GPP (Section III), and 3) to introduce andreview an intercell interference avoidance (ICIA) techniquefor femtocell networks that does not require the use of anX2 interface (Section IV). The proposed technique utilizes apre-determined coupling between the UL and DL frequencyresources of the macrocell users. Through resource partitioningand sensing, the macrocell and femtocell users dynamically ad-just their scheduling decisions once the interference conditionsare detected.

II. FEMTOCELL NETWORKS SIMULATION FRAMEWORK IN3GPP STANDARDIZATION

In order to study the interference scenarios between macro-cells and femtocells, certain simulation settings and assump-tions have been specified in [11] for frequency division duplex(FDD) type of femtocell networks. This simulation frameworkhas then been extended to heterogenous networks to definea realistic simulation environment for relays, picocells, anddistributed antenna systems in [12]. Since femtocell relatedassumptions in [12] are mostly aligned with [11], in this sec-tion, we will review the simulation assumptions for femtocellnetworks described in [11] and provide some representativeresults.The simulation assumptions and parameters for the macro-

cell system and the femtocell system discussed in [11] aresummarized in Table I and Table II, respectively. As shown in

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TABLE IMACROCELL SYSTEM ASSUMPTIONS AND PARAMETERS [11].

Parameter AssumptionCellular layout Hexagonal grid, 3 sectors per site, reuse 1Inter-site distance 500 m or 1732 mNumber of sites 19 (57 cells) or 7 (21 cells)Carrier frequency 2 GHzShadowing standard devia-tion

8 dB

Shadowing correlation 0.5 (between cells), 1 (between sectors)Wall penetration loss 10 dB or 20 dBBS antenna gain after cableloss

14 dBi

BS noise figure 5 dBNumber of BS antennas 2 Rx, 2 TxUE antenna gain 0 dBiUE noise figure 9 dBNumber of UE antennas 2 Rx, 1 TxTotal BS Tx power 46 dBmMaximum UE Tx power 23 dBmIntercell interference mod-elling

Explicit modelling

Traffic model Full buffer with 10 UEs per sectorUE distribution UEs dropped uniformly within coverageMinimum distance betweenUE and the eNB

35 m

UE speeds 3 km/hFading model Ray based or correlation matrix basedDL receiver type MRC (single stream) or MMSE (multiple

streams)UL receiver type MRC

TABLE IIFEMTOCELL SYSTEM ASSUMPTIONS AND PARAMETERS [11].

Parameter AssumptionFemtocell spectrum assignment Cochannel or dedicated channelMinimum HUE-HeNB separation 20 cmNumber of HeNB Tx antennas 1Number of HeNB Rx antennas 2HeNB antenna gain 0 dBi, 3 dBi, or 5 dBiExterior wall penetration loss 10 dB or 20 dBLognormal shadowing standard de-viation

4 dB

HeNB noise figure 8 dBMin/max HeNB Tx power 0/20 dBmCarrier bandwidth 10 MHzNumber of resource blocks (RBs)for PUCCH

4

Number of symbols for PDCCH 3

Table I, either a 19-site (57 cells) or a 7-site (21 cells) archi-tecture is considered in order to account for the interferencein neighboring cells. While omnidirectional azimuth antennapattern is assumed for UEs and HeNBs, the azimuth antennapattern used by the eNB is given by [11], [12], [13]

A(θ) = −min³12(θ/θ3dB)

2, Am

´, (1)

where θ3dB = 70 degrees, Am = 20 dB, and antenna bore-sight points towards flat side of the cell. There are differentsets of path-loss models specified for different links in [11].On the other hand, the following simplified path loss model istypically utilized for the distance dependent path loss from anHeNB to a UE (based on ITU-R M1225 single floor indooroffice model) [12]

L = 127 + 30 log10R , (2)

where R is the transmitter-receiver distance in kilometers, andthe central frequency is 2 GHz.An example SINR distribution using the antenna pattern

specified in (1) is illustrated in Fig. 2(a) for three cells (one

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Fig. 2. SINR map with the antenna pattern specified in (1).

site), where an inter-site distance of 500 m is considered. Ifa link-quality based cell selection method is considered, theUEs are associated to the cell with the best SINR. Then, theresulting coverage area (neglecting the shadowing effects) forthe SINR map in Fig. 2(a) is illustrated in Fig. 2(b), wherethe coverage area of each cell is marked with a differentcolor. Fig. 2(b) also illustrates two different cell/site coveragearea models: 1) A large hexagon that corresponds to thecoverage area of an omnidirectional antenna pattern, and 2)Three different smaller hexagons that attempt to capture thecoverage area due to the specific antenna pattern in (1)2. Itis observed that the latter structure more accurately representsthe coverage area for the antenna pattern given in (1).In 3GPP, both suburban and urban settings are considered

for femtocell deployment modelling [11], [12]. For suburbanHeNB deployments, a house size of 12× 12 m is considered.Number of active HUEs per femtocells is one, and houseswith HeNBs are uniformly distributed within the macrocellcoverage area. Distribution of HUEs within a HeNB house,and distribution of a HeNB within a HeNB house are alsorandom uniform, both being subject to minimum separationconstraints. While all the MUEs are assumed to be indoorsin [14] for suburban settings, probability of an HUE beingoutdoors (e.g., in backyard) is set to a certain value (e.g., 10%).For dense-urban HeNB modeling, on the other hand, two

different simulation models are specified. The dual stripe

2See e.g., [13], Section 8.3 for a more detailed discussion of these twodifferent cell layouts.

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Fig. 3. Downlink SNR at femtocells for a) sub-urban and b) urban scenarios.

model considers that there are two stripes of apartments, whereeach stripe has 2 by N apartments. The size of each apartmentis 10 m by 10 m and a street of size 10 m exists between thetwo stripes of apartments. Each femtocell block has L floors(L being a random number between 1 and 10), and there areM blocks per sector (e.g.,M = 1). The femtocell deploymentratio, femtocell activation ratio, and probability of MUE beingindoors (e.g., 80%) are three different parameters between 0and 1 that capture the characteristics of the environment. Itis assumed in [14] that there is only one HUE per femtocellwhich is dropped randomly within the femtocell area. Otherthan the dual stripe model, [11] also specifies a simple 5× 5grid model with a single-floor building, where each buildingis composed of 25 apartments of size 10 m× 10 m.An example for the DL SNRs from different HeNBs scat-

tered around a macrocell network is illustrated in Fig. 3(a) forthe suburban simulation model, and in Fig. 3(b) for the urbansimulation model, respectively (M = 1 block is considered persector in the urban scenario simulations). While the HeNBsare clustered around the building block for the urban scenario(four HeNBs within each strip), they are more uniformlydistributed around the cell for the sub-urban scenario. Sincethere are multiple neighboring apartments within each strip(2 × N , with N = 10 in Fig. 3(b)), due to wall penetrationloss, SNR level is considerably stronger at the apartment wherethe HeNB is present, compared to the neighboring apartmentsin the strip without any apartments.The cumulative distribution functions (CDFs) of the UE

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Fig. 4. Downlink SINR CDF of (a) macrocell, and (b) femtocells. Impactof wall loss on capacity CDFs for a given deployment are also illustrated.

SINRs and throughputs carry critical importance to assessthe overall performance of the system. Even if the mean(or median) SINR of the users in the macrocell and/or thefemtocells may be large, it is not exceptable if certain usersare observing interference levels that may yield outages. TheCDF, rather than average system performance, is thereforea critically useful tool in order to understand the overallimprovement in the system, outage behavior of the UEs,fairness characteristics of the scheduler, impact of frequency(or component carrier (CC)) assignment method on the overallsystem, effectiveness of the interference cancellation methodemployed, etc.In Fig. 4 and Fig. 5, representative results for the DL

SINR and DL throughput CDFs of the MUEs and HUEsare shown for the suburban scenario for 10 dB and 20 dBwall loss (WL) values. Two CCs are used in the simulations,which are assigned to macrocell and femtocells dependingon the cochannel or dedicated channel spectrum assignmentmethods as specified in Table II. In the cochannel approach(Fig. 6(a)), femtocell and macrocell use both of the CCs; thismakes more bandwidth available for both tiers, but results incochannel interference problems. Dedicated channel allocation(Fig. 6(b)), on the other hand, allocates a different CC to eachtier. Note that apart from the inter-femtocell interference thatis observed when dedicated channel allocation is used, thereis an additional macrocell-femtocell interference factor whenthe cochannel allocation is used. As far as the distributions of

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Fig. 5. Downlink throughput CDF of (a) macrocells and (b) femtocells.

Fig. 6. Different CC assignment approaches: (a) Cochannel CC assignment,(b) Dedicated channel CC assignment, (c) Escape carrier at the macrocell [9].

the 50 UEs within the macrocell are concerned, all the MUEsand the HUEs (one per each of the 8 HeNBs) are assumed tobe located indoors [11]3.Results in Fig. 4(a) show that with cochannel deployment,

certain MUEs may observe SINRs as low as −50 dB, whilelowest SINRs observed by the MUEs in dedicated channeldeployment are on the order of −20 dB for WL= 10 dBand −30 dB for WL= 20 dB. The low SINRs for cochanneloperation typically belong to the MUEs that are located closeto the femtocells and observing high interference levels dueto closed-access operation. The HUE SINR CDFs in Fig. 4(b)show that the cochannel approach yields worse SINRs com-pared to the dedicated channel approach for the femtocell

3Note that the probability of MUEs being indoors and probability of HUEsbeing outdoors may have significant impact on the capacity CDFs in practice,which will not be investigated here.

TABLE IIIREVIEW OF IMPORTANT ICIC TECHNIQUES IN 3GPP RAN.

Ref. Notes[4] The eNB reserves a certain number of resource blocks during DL

transmissions. Then, it transmits a DL high interference indicator(DL-HII) message over X2 to HeNBs that may possibly interfereto MUEs

[5] HUEs associated with a HeNB report their signal to interferenceratio (SIR) over each sub-band to the HeNB. Then, HeNB mayrequest/grant/deny resources from/to other HeNBs, which necessi-tates the use of X2 interface.

[6] The femtocell detects the resource block allocation of eNB throughsensing the spectrum, assuming that scheduling decisions do notchange at the macrocell for a certain period of time (requires X2interface).

[7] The resource blocks are partitioned by scheduling cell-center andcell-edge users on dedicated spectrum resources.

[8] The coordination information is relayed by the MUE that is closeby to a femtocell. To achieve this for an MUE, measurement reportsare used for communicating with the eNB and UL transmissionsare used for communicating with the HeNB.

[9] The MUEs are dedicated a CC (referred as the “escape carrier”)which is not used by the femtocell network (see e.g., Fig. 6(c)).Any MUE which is close by to a femtocell is scheduled withinthis escape carrier based on interference sensing.

[10] The victim MUEs in the vicinity of a femtocell are detected by theHeNB using the characteristics of Zadoff-Chu sequences.

users as well. On the other hand, the SINRs of the HUEsare observed to be significantly larger compared to the SINRsof the MUEs.The throughput CDFs for the MUEs and HUEs correspond-

ing to the SINR CDFs in Fig. 4 are shown in Fig. 5. Inorder to obtain the throughput values from the SINR values,the mapping tables presented in the Table A-2 of [15] areused, which attempt to capture effective 3GPP performancefor a given SINR (note that after a certain SINR, the capacityreaches a maximum limit). Moreover, the bandwidth perconnected user is evaluated for each cell in order to scalethe throughput corresponding to each user with its allocatedbandwidth [14]. The CDF results in Fig. 5 show that whilethe SINR CDFs of the cochannel option are worse in Fig. 4,due to the larger available bandwidth per UE, cochanneloperation typically yields better throughput for most of theMUEs and HUEs compared to the dedicated channel option.On the other hand, it is also observed that cochannel operationresults in outage for about 23% and 14% of the MUEsfor WL= 10 dB and WL= 20 dB, respectively, which aretypically the MUEs in the vicinity of femtocells. On the otherhand, outage that is observed with dedicated channel operationis considerably lower. Therefore, despite the large potentialgains that may be obtained with cochannel deployment offemtocells, resulting cochannel interference problems shouldbe appropriately mitigated to prevent outages for low-SINRusers, which will be discussed in the next two sections.III. REVIEW OF FEMTOCELL ICIC TECHNIQUES IN 3GPPThere have been several contributions in the 3GPP that

address potential cochannel interference problems for fem-tocell networks. As discussed in Fig. 1, one of the criticalinterference scenarios arise when there is an MUE in thevicinity of a femtocell; due to the closed-access policy, sucha MUE is not allowed to make a hand-off to the femtocell.A short summary of ICIC techniques that aim to address

interference problems in such settings is presented in Table IIIbased on the recent related contributions in the 3GPP [4]-[10] (see also [16], [17] and the references therein). Notethat the techniques discussed by [4]-[7] in Table III requirethe use of X2 interface between the HeNBs and the eNBfor coordination purposes. X2 interface is already used forICIC purposes between different eNBs in the earlier releasesof the standard [4]. However, even though it may be consideredas a possible extension in future releases, X2 interface isnot currently available for the HeNBs in the latest releases

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of the 3GPP. Moreover, implementation of X2 interface maybe costly. Therefore, alternative ICIC techniques that do notrely on the X2 interface are essential for ensuring satisfactoryperformance of femtocells in the absence of any X2 interface.Techniques such as those presented in [8]-[10] do not

require the use of the X2 interface. However, [8] requiresextra signalling overhead for communication of the messagesover the MUE (where MUE relays the coordination messagesbetween the eNB and HeNB), or, overhead due to broadcastingof coordination messages directly by the eNB. While [9] doesnot require use of X2 interface or transmission of any coor-dination messages, the drawback of this approach is that thecertain frequency resources are always restricted for femtocellsregardless of whether there is any interfering MUE close to thefemtocell or not. This results in poor spectrum utilization forHUEs in the absence of any macrocell interference. In [10],the victim MUEs are detected at the femtocell in order toprevent interference to them; however, how to mitigate bothDL and UL interference for the HUEs and the MUEs is notdescribed. Even if the victim MUEs are accurately sensed, ittypically requires coordination messages between the HeNBsand the eNB to prevent all relevant CCI problems.IV. INTERFERENCE AVOIDANCE THROUGH RESOURCE

PARTITIONING AND SENSINGIn this section, we propose an X2-free ICIA mechanism

for femtocell networks that relies on accurate sensing of thespectrum at MUEs and HeNBs and coupling of the DL/ULmacrocell scheduling decisions. At the macrocell-side, theMUEs sense the spectrum during DL and detect whetherthere are any interfering HeNBs in the vicinity. If there areany HeNBs interfering to the MUEs, the eNB appropriatelyreschedules these victim MUEs by restricting the DL spectrumresources that may be utilized by them within a certainresource partition. Subsequently, the UL spectrum resourcesof the victim MUEs are also restricted to a certain resourcepartition that is a known function of the DL resource partitionused by the same MUEs.Note that such a coupling of the scheduling resources at the

macrocell during the DL and UL carries critical importance forthe femtocells, which enables them to obtain the DL schedul-ing information of the victim MUEs from the UL sensingresults. Moreover, the coupling of DL/UL transmissions ofMUEs and restricted scheduling of MUEs are only performedfor the victim MUEs; the scheduling of the MUEs which arenot interfered by the femtocell are performed in a conventionalway.After the re-scheduling of the victim MUEs at the macro-

cell, UL spectrum sensing is performed at the HeNB. If anyhigh-power MUEs are detected, the resources utilized by theseMUEs are released during the HeNB UL, giving priority tothe macrocell for accessing these resources. Moreover, theHeNB uses the pre-determined mapping rule to obtain theDL spectrum resources used by the victim MUEs from ULsensing results, and avoids scheduling its HUEs within theseDL resources as well.The proposed approach may have two variations depend-

ing on the granularity of scheduling resources: 1) carrier-aggregation based approach, and 2) resource partitioning basedapproach, both of which will be discussed next through simpleexamples.A. Carrier Aggregation ApproachConsider an example scenario as in Fig. 7(a), where there

are three CCs that may be utilized by the macrocell andfemtocell users. In order to better benefit from the multiuserdiversity, the eNB and the HeNBs may schedule their userswithin any of these CCs based on the channel qualities and raterequirements. If all the CCs are used in a cochannel mannerby macrocell and femtocell users, there may be significantinterference problems as discussed before. In the proposedapproach, first, the MUEs sense DL interference from HeNBs.If the interference conditions have changed for any of theMUEs, they record the IDs of close-by HeNBs that are causing

Fig. 7. Carrier aggregation approach for interference avoidance (see alsoFig. 1): (a) Before ICIA, and (b) After ICIA.

large interference to each MUE. Then, the eNB makes atable of victim MUEs corresponding to each HeNB-ID. Forexample, for the scenario illustrated in Fig. 1, an examplevictim MUE table includes MUE-3 as a victim of Femto-A,and MUE-1 and MUE-2 as a victim of Femto-B.In the next step, if any of the MUEs are being significantly

interfered by a certain HeNB during the DL, the eNB re-schedules all the MUEs which are in the vicinity of thisHeNB (obtained from the victim MUE table discussed above)within a single CC. Again, considering the example scenarioin Fig. 1, and the initial CC allocations in Fig. 7(a), theeNB assigns MUE-1 and MUE-2 to the same CC, and MUE-3 to a different CC. This way, the eNB may still dedicatethe same amount of DL bandwidth to macrocell users withinthe selected CC; however, since a narrower total bandwidthbecomes available for scheduling decisions, multiuser diversitygain will be diminished. During the UL, for the same UEs,the eNB uses the same CC that it uses during the DL (or usesa mapping function that is known to HeNBs).At the femtocell side, the HeNB senses the spectrum during

the UL transmissions of MUEs. When a HeNB detects stronginterference at certain CC(s), it may judge that there are victimMUEs within its coverage. The HeNB may then avoid usingthe detected CC(s) during the UL as long as the interferenceconditions persist. As for the DL, the HeNB utilizes the DL-to-UL mapping rule used by the eNB; based on the obtained ULsensing results, the HeNB determines the DL CC(s) used byclose-by MUEs, and avoids using their CC(s) during femtocellDL.

B. Resource Partitioning ApproachA similar method may also be used in the resource par-

titioning based approach, where a certain CC may be parti-tioned into smaller chunks that may be independently usedby macrocell and the femtocells. Again, consider an examplescenario as in Fig. 8 for the DL/UL resource allocationsfor macrocell and femtocell users. Consider that there are16 resource blocks (RBs) per macrocell user in the DL, while10 RBs per macrocell user in the UL. On the other hand,femtocell users fully use all the available spectrum.In such a setting, the macrocell and the femtocell may

use the steps similar to those discussed in Section IV-Afor the carrier aggregation based approach. The difference isthat the MUEs at the macrocell are scheduled to resourcepartitions that are a subset of the CCs. A certain resourcepartition includes all the MUEs which are in the vicinityof the same HeNB. For example, in Fig. 9(b), one resourcepartition includes resource blocks of MUE-1 and MUE-2 thatare in the vicinity of HUE-A, while another separate resourcepartition includes the resource blocks of MUE-3 which isin the vicinity of HUE-B. Once the HeNBs detect the ULtransmissions of the MUEs within their vicinity, they can avoidusing these UL resource partitions for scheduling their ownHUEs. Using the known mapping function, they may alsoobtain the DL scheduling information of the MUEs, and avoidscheduling HUEs to these resource partitions during the DLas well. Note that in a practical setting, the size of the UL andDL resource partitions may be different. The pre-determinedmapping function may be configured to consider asymmetric

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Fig. 8. Resource partitioning approach for ICIA before interference avoidance(see also Fig. 1): (a) Uplink, (b) Downlink.

Fig. 9. Resource partitioning approach for ICIA after interference avoidance(see also Fig. 1): (a) Uplink, (b) Downlink.

sizes of the resource partitions. Alternatively, as shown inFig. 9(b), partial overlap between the DL transmissions ofHeNB and eNB may be allowed, which still provides partialgains compared to when no cochannel interference avoidancetechnique is utilized.An example timeline for the proposed interference avoid-

ance scheme is illustrated in Fig. 10. First, based on thereceived packets from the HeNB DL transmissions, the DLinterference is detected at the MUE. This is followed by noti-fication of HeNB-IDs to the eNB, updating of the interferencetable at the eNB, resource partitioning and DL scheduling, DLto UL mapping, and UL scheduling at the eNB. The victimMUE with updated resource allocation may then be sensed bythe HeNB (that is in the vicinity of the victim MUE), whichperforms resource partitioning and rescheduling of its usersduring UL, UL-to-DL mapping, and rescheduling of its usersduring DL.The sensing during the DL and the UL may be based on

the interference over thermal noise (IoT), or using some moresophisticated techniques. The IoT approach has the drawbackthat it becomes difficult to detect whether the interferenceis from a single dominant interferer, or, multiple weakerinterferers. An improved victim MUE detection algorithmbased on autocorrelation and peak to average power ratiocharacteristics of the received signal have been investigatedin [10], which reports probability of missed detection valuessmaller than 10−4 for medium and high SNRs.

V. CONCLUDING REMARKSIn this paper, 3GPP simulation assumptions and parameters

for femtocell networks are briefly summarized, and some ofthe relevant standard contributions for femtocell ICIC arereviewed. SINR and throughput CDF simulations for cochan-nel and dedicated channel macrocell/femtocell networks are

Fig. 10. An example timeline for the proposed interference avoidancescheme.

presented in the DL based on the recommended simulationmethodology in the standard. Finally, an X2-free ICIA methodis introduced which relies on resource partitioning, sensing,and coupling of DL/UL resources. Future work includesperformance assessment of the proposed approach and itscomparison with other femtocell ICIC techniques available inthe literature.

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[3] Vodafone, “LTE-FDD HeNB interference scenarios,” 3GPP StandardContribution (R4-091976), May 2009.

[4] NTT DOCOMO, “Downlink interference coordination between eNodeBand home eNodeB,” 3GPP Standard Contribution (R4-093203), Aug.2009.

[5] CMCC, “Downlink interference coordination between HeNBs,” 3GPPStandard Contribution (R4-092872), Aug. 2009.

[6] IIIT, “Interference mitigation for HeNBs by channel measurements,”3GPP Standard Contribution (R4-093196), Aug. 2009.

[7] Motorola, “Femtocell and macrocell interference coordination based onSFR,” 3GPP Standard Contribution (R4-093092), Aug. 2009.

[8] ——, “HeNB interference management,” 3GPP Standard Contribution(R1-101121), Feb. 2010.

[9] Nokia Siemens Networks, “Macro+HeNB performance with escapecarrier,” 3GPP Standard Contribution (R1-101453), Feb. 2010.

[10] picoChip Designs, Kyocera, “Victim UE aware downlink interferencemanagement,” 3GPP Standard Contribution (R1-100913), Jan. 2010.

[11] Alcatel-Lucent, picoChip Designs, Vodafone, “Simulation assumptionsand parameters for FDD HeNB RF requirements,” 3GPP StandardContribution (R4-092042), May 2009.

[12] 3GPP, “Further advancements for E-UTRA physical layer aspects,”3GPP Technical Report (3GPP TR 36.814), Nov. 2009.

[13] ITU, “Guidelines for evaluation of radio interface technologies for IMT-Advanced,” Report ITU-R M.2135, 2008.

[14] CATT, “Interference analysis for various het-net scenarios,” 3GPPStandard Contribution (R4-100033), Jan. 2010.

[15] 3GPP, “E-UTRA; radio frequency (RF) system scenarios,” 3GPP Tech-nical Report (3GPP TR 36.942), Dec. 2009.

[16] ——, “Evolved universal terrestrial radio access (E-UTRA); FDD HomeeNode B (HeNB) radio frequency (RF) requirements analysis,” 3GPPTechnical Report (3GPP TR 36.921), Apr. 2010.

[17] ——, “Evolved universal terrestrial radio access (E-UTRA); TDD HomeeNode B (HeNB) radio frequency (RF) requirements analysis,” 3GPPTechnical Report (3GPP TR 36.922), Apr. 2010.

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