009 Interference Management in UMTS Femtocells Low Band

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www.scf.io/ www.smallcellforum.org

RELEASE

DOCUMENT

Interference Management in

UMTS Femtocells

Low-band

February 2013

009.01.02

SMALL CELL FORUM

One scf.io/


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Small Cell Forum supports the wide-scale adoption of small cells. Its mission is

to accelerate small cell adoption to change the shape of mobile networks and

maximise the potential of the mobile internet.

Small cells is an umbrella term for operator-controlled, low-powered radio accessnodes, including those that operate in licensed spectrum and unlicensed carrier-grade

Wi-Fi. Small cells typically have a range from 10 metres to several hundred metres.These contrast with a typical mobile macrocell that might have a range of up to several

tens of kilometres. The term small cells covers femtocells, picocells, microcells andmetrocells.

Small Cell Forum is a not-for-profit, international organisation, with membership opento providers of small cell technology and to operators with spectrum licences for

providing mobile services.

At the time of writing, the Small Cell Forum has 141 members including 68 operators

representing more than 3 billion mobile subscribers 46 per cent of the global total as well as telecoms hardware and software vendors, content providers and innovativestart-ups.

The Small Cell Forum is technology-agnostic and independent. It is not a standards-setting body, but works with standards organisations and regulators worldwide to

provide an aggregated view of the small cell market.

This document forms part of the Small Cell Forums Release One which addresses the

full range of applications for small cells: Home, Enterprise, Metro, Rural. The maintheme of Release One is the Home, and includes the complete body of work operators

will need to know for wide-scale deployment of femtocells intended for home or smalloffice applications. These applications are based typically indoors and involve locations

where a single femtocell is usually sufficient. Both 3GPP and 3GPP2 femtocells areincluded.

Release One also contains works clarifying market needs and addressing barriers to

deployment of enterprise, metro and rural small cells.

The Small Cell Forum Release website can be found here www.scf.io. A description and

roadmap for the release programme can be found here www.scf.io/doc/100

If you would like more information about the Small Cell Forum or would like to

be included on our mailing list, please contact:

Email [email protected]

Post Small Cell Forum, PO Box 23, GL11 5WA UK

Member Services Lynne Price-Walker [email protected]

For a full list of members and further information visit our websitewww.smallcellforum.org


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Report title: Interference Management in UMTS FemtocellsIssue date: 20 February 2013Version: 099.01.02

Scope

This paper [3] provides detailed results of in-depth studies of interference between femtocells andmacrocells deployed in the UMTS low bands around 850/900MHz [2]. An accompanying study is also

available for the UMTS high bands around 2GHz. For a higher level overview of the findings from both ofthese studies, we recommend reading our associated topic brief [1]

Related SCF Publications

[1] Topic brief: Interference Management in UMTS Femtocells, Small Cell Forum, www.scf.io/doc/008

[2] Interference Management in UMTS Femtocells ("High-band"), Small Cell Forum, www.scf.io/doc/003

[3] Interference Management in UMTS Femtocells ("Low-band"), Small Cell Forum, www.scf.io/doc/009


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Executive summary

Femtocells, by virtue of their simultaneous small size, low cost and high performance, are a potentiallyindustry-changing disruptive shift in technology for radio access in cellular networks. Their small size means

that the spectrum efficiency they can attain is much greater than that achievable using macrocells alone.Their low cost means they can be deployed as consumer equipment reducing the capital load andoperating expenses of the host network. And their high performance means that all this can be gained at noloss of service to the customer, and in many cases, owing to the improved link budgets, improved service.

However, for these apparent benefits to translate into real advantage for network operator and consumeralike, we must answer serious questions about the interaction between the femtocell technology and thehost macrocellular radio network into which they are deployed. If femtocells can only achieve their potentialby disrupting the macro network, then they will be relegated to niche deployments, of little overallrelevance to next-generation networks. On the other hand, if the interactions between macro and femtoradio layers can be managed to the benefit of all, then their properties (in terms of lowered cost, improvedspectrum efficiency and link budget and general performance) can be fully realised, and femtocells will findthemselves an essential component of all future radio access network designs.

So, what are these interactions? How can they be managed? What does that all mean for the technology, to

the operator and to the consumer? These are the questions that this paper is helping to answer. In doingso, it has deliberately maintained a tight focus, according to the priorities of its authors. It is exclusivelyconcerned with W-CDMA as an air interface technology (other teams within Small Cell Forum are looking atother air interfaces). This paper is concerned primarily with the 850 MHz band in the United States, but isequally applicable to the 900 MHz band in Europe and elsewhere. It should also be broadly applicable tosimilar bands (eg. 700 MHz). Another study has also been published with similar results for 2 GHz [2]. It isexclusively a theoretical treatment, using link level and system level simulations to draw its conclusions,although we expect to back these conclusions up in due course with trial campaign data. In view of theresidential application that femtocells are addressing, this paper is also concerned with femtocells operatingwith closed user groups. Perhaps most importantly, this paper stands on the shoulders of giants, drawingon the great mass of study work that has already been undertaken by 3GPP RAN4 participants in analysingthese issues, and referencing them for further reading.

The interacting components of the femto-enabled network include femtocells themselves, which can beinteracting in their downlinks with other nearby femtocells and macrocells; macrocells, which interact withnearby femtocells; and users and user equipment (UEs), which, by virtue of intentional radio links tofemtocells and macrocells, may be causing unintentional interactions with both.

In approach, this paper has chosen to look at extreme cases, to complement as far as possible the average or typical scenarios that RAN4 has already studied in 3GPP. In the main, the analysis has shown upinternal contradictions in those extreme cases meaning that they will never occur. For instance: analysingthe case when the UE is operating at full power in its uplink towards a femtocell is shown to occur only whenthe macrocell is nearby in which case the macro downlink signal is so strong that the UE will never selectthe femtocell over the macrocell. This contradiction shows, for instance, that the high noise rise that a UEcould in principle cause will happily never occur. In other cases, the extreme cases are avoided by uplinkpowercapping, or by other techniques recommended in the paper.

With these extreme cases disarmed then, of the many potential interactions between UEs, femtocells andmacrocells, the summary conclusion that we have reached, in common with other studies, is that in order tobe successful, femtocell technology must manage three things:

Femtocell downlink power if femtocells transmit inappropriately loudly, then the cell may belarge, but non-members of the closed user group will experience a loss of service close to thefemtocell. On the other hand, if the femtocell transmits too softly, then non-group members willbe unaffected, but the femtocell coverage area will be too small to give benefit to its users.

Femtocell receiver gain since UEs have a minimum transmit power below which they cannotoperate, and since they can approach the femtocell far more closely than they can a normalmacrocell, we must reduce the femtocell receiver gain, so that nearby UEs do not overload it.This must be done dynamically, so that distant UEs are not transmitting at high power, andcontributing to macro network noise rise on a permanent basis.

UE uplink power since UEs transmitting widely at high power can generate unacceptable noiserise interference in the macro network, we signal a maximum power to the UE (a power cap) toensure that it hands off to the macro network in good time, rather than transmit at too high apower in clinging to the femtocell.


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We have also shown that, with these issues addressed, the net effect of deploying femtocells alongside amacro network is significantly to increase its capacity. In numerical terms, and in terms of the simulatedscenario, the available air interface data capacity is shown to increase by more than a hundredfold with theintroduction of femtocells.


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Contents

1. Femtocells, Femtocell Access Points and the Small Cell

Forum .............................................................................. 11.1 What are Femtocell Access Points? ....................................... 1

1.2 What do Femtocells offer? ................................................... 1

1.3 What is the Small Cell Forum? ............................................. 2

2. Introduction .................................................................... 3

2.1 Objectives and Methods of this Paper .................................... 3

3. Previous Work ................................................................. 4

4. Simulation Scenarios and Definitions ............................... 6

5. Abbreviations and Defined Terms .................................... 9

6. Scenario A: Macrocell Downlink Interference to theFemtocell UE Receiver ................................................... 10

6.1 Description ....................................................................... 10

6.2 Analysis ........................................................................... 10

6.3 Extended scenario: HSDPA coverage .................................... 13

6.4 Conclusions ...................................................................... 14

7. Scenario B: Macrocell UE Uplink Interference to theFemtocell Receiver ......................................................... 15

7.1 Description ....................................................................... 157.2 Analysis ........................................................................... 15

7.2.1 HSUPA ............................................................................. 17

7.3 Conclusions ...................................................................... 19

7.3.1 Customer (MUE) impact ..................................................... 19

7.3.2 Customer (FUE) Impact ..................................................... 20

7.3.3 Mitigation techniques ......................................................... 20

8. Scenario C: Femtocell Downlink Interference to theMacrocell UE Receiver .................................................... 21

8.1 Description ....................................................................... 218.2 Analysis ........................................................................... 23

8.3 Scenario analysis and conclusions ....................................... 24

9. Scenario D: Femtocell Uplink Interference to theMacrocell NodeB Receiver .............................................. 25

9.1 Introduction ..................................................................... 25

9.2 Analysis of Scenario D - 12k2 Voice and HSUPA .................... 25

9.2.1 Assumptions ..................................................................... 25

9.2.2 Macro Node B Noise Rise .................................................... 27


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9.3 Conclusions ...................................................................... 29

9.4 Recommendations ............................................................. 29

10. Scenario E: Femtocell Downlink Interference to nearby

Femtocell UE Receiver. .................................................. 3010.1 Description ....................................................................... 30

10.2 Capacity Analysis .............................................................. 30

10.3 Conclusions ...................................................................... 34

11. Scenario F: Femtocell UE Uplink Interference to NearbyFemtocell Receivers ....................................................... 35

11.1 Description ....................................................................... 35

11.2 Analysis ........................................................................... 35

11.2.1 Assumptions ..................................................................... 35

11.2.2 Analysis of Noise Rise received at the Victim AP .................... 3611.3 Conclusions ...................................................................... 38

11.4 Recommendations ............................................................. 39

12. Scenario G: Macrocell Downlink Interference to anadjacent-channel Femtocell UE Receiver ........................ 40

12.1 Description ....................................................................... 40

12.2 Analysis ........................................................................... 40

12.2.1 Assumptions ..................................................................... 40

12.2.2 Simulation Analysis ........................................................... 41

12.2.3 Theoretical Analysis ........................................................... 41

12.3 Conclusions ...................................................................... 42

13. Scenario H: Macrocell UE Uplink Interference to theadjacent channel Femtocell Receiver ............................. 43

13.1 Description ....................................................................... 43

13.2 Analysis ........................................................................... 43

13.2.1 Parameter settings ............................................................ 44

13.2.2 Impact of MUE interference on AMR ..................................... 44

13.2.3 Impact of MUE interference on HSUPA ................................. 4613.3 Conclusions ...................................................................... 49

13.4 Femto System Impact ........................................................ 49

13.5 Mitigation techniques ......................................................... 50

14. Scenario I: Femtocell Downlink Interference to theadjacent channel macrocell UE Receiver ........................ 51

14.1 Description ....................................................................... 51

14.2 Analysis ........................................................................... 51

14.2.1 Parameter settings ............................................................ 52

14.2.2 Impact of Femtocell interference on AMR service ................... 53


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14.2.3 Impact of Femtocell interference on HSDPA .......................... 54

14.3 Conclusions ...................................................................... 56

14.4 Customer (MUE) Impact ..................................................... 56

14.5 Mitigation techniques ......................................................... 5615. Scenario J: Femtocell UE Uplink Interference to the

adjacent channel Macrocell NodeB Receiver .................. 57

15.1 Introduction ..................................................................... 57

15.2 Analysis of Scenario J - 12k2 Voice and HSUPA ..................... 57

15.2.1 Assumptions ..................................................................... 57

15.2.2 Macro Node B Noise Rise .................................................... 59

15.3 Conclusions ...................................................................... 60

16. Downlink and Uplink Scenarios Modelling Power

Control Techniques for Interference Mitigation .............. 6116.1 Modelling of Propagation loss .............................................. 61

16.2 HNB transmit power calibration for 850 MHz ......................... 61

16.3 Simulation results for Dense Urban Deployment .................... 61

16.3.1 Idle Cell Reselection Parameters .......................................... 62

16.3.2 Coverage Statistics at 850 MHz for Calibrated HNB TransmitPower 62

16.3.3 Downlink Throughput Simulations ........................................ 64

16.3.4 Conclusions ...................................................................... 65

16.3.5 Uplink throughput simulations with adaptive attenuation ........ 65

16.3.6 Conclusions ...................................................................... 70

17. Summary of Findings ..................................................... 71

18. Overall Conclusions ....................................................... 78

19. Further Reading ............................................................. 79

19.1 Scenario A ....................................................................... 79

19.2 Scenario B ....................................................................... 79

19.3 Scenario C ....................................................................... 79

19.4 Scenario D ....................................................................... 7919.5 Scenario E ........................................................................ 79

19.6 Scenario F ........................................................................ 80

19.7 Scenario G ....................................................................... 80

19.8 Scenario H ....................................................................... 80

19.9 Scenario I ........................................................................ 80

19.10 Scenario J ........................................................................ 80

19.11 Scenarios Section 16 ....................................................... 81

20. Simulation Parameters and Path Loss Models ................ 82


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20.1 Simulation parameters ....................................................... 82

20.2 Path Loss Models ............................................................... 83

20.2.1 Okumura-Hata .................................................................. 83

20.2.2 ITU-R P.1238 .................................................................... 8320.2.3 System Simulation (Section 16) Path Loss Models.................. 84

References ............................................................................... 85

Tables

Table 3-1 Scenarios ...................................................................................... 5

Table 4-1 Femtocell Deployments in Shared Spectrum ...................................... 6

Table 4-2 Femtocell Deployments in non-Shared Spectrum ................................ 7

Table 4-3 Scenario relationships ..................................................................... 8

Table 6-1 Macro Node B assumptions and transmit EIRP calculation .................. 11Table 6-2 Link budget for the received power from macro Node B to UE ............ 11

Table 6-3 EIRP for the femtocell ................................................................... 11

Table 6-4 Required Ec/No for voice connection ............................................... 12

Table 7-1 Assumptions for Scenario B ........................................................... 15

Table 7-2 MUE link budget at the femtocell receiver ........................................ 16

Table 7-3 FUE transmitter power requirements in order to hold a voice call ........ 16

Table 7-4 Maximum co-channel DL deadzone created by the femtocell for MUEs,based on [R4-070969] and assuming RSSI of -65dBm ...................... 17

Table 7-5 Link budget for HSUPA .................................................................. 17

Table 9-1 Macro Node B noise floor ............................................................... 26Table 9-2 Femto UE TX power 1000 m from macro Node B .............................. 27

Table 9-3 Noise rise calculation for Scenario D (femto UE is transmitting at8.39dBm and 21dBm1000m from a macro Node B for a 12K2 serviceand 2Mbps HSUPA service) ............................................................ 28

Table 9-4 Macro UE Tx power 1,000m away from macro Node B receiver bywindow on a 12K2 voice and 2Mbps HSUPA data service ................... 29

Table 11-1 Femtocell Sensitivity and Noise Rise at AP1 ..................................... 36

Table 12-1 Macrocell Downlink Interference to an adjacent channel Femtocell UEin this worst-case scenario ............................................................ 41

Table 13-1 Uplink radio link-budget for AMR 12.2 kbps RAB ............................... 45

Table 14-1 Maximum Macro NB MUE separation for a given maximumFemtocell transmit power level, when the Femtocell MUE separationis fixed at 5 m ............................................................................. 54

Table 14-2 UE receiver performance requirement (HSDPA), [TS25.101] .............. 55

Table 15-1 Macro Node B noise floor ............................................................... 58

Table 15-2 Femto UE TX power 1000 m from macro Node B .............................. 59

Table 15-3 Noise rise calculation for Scenario D1 (femto UE is transmitting at8.39dBm and 21dBm 1000m from a macro Node B for a 12K2 serviceand 2Mbps HSUPA service) ............................................................ 60

Table 16-1 Parameters for the co-channel idle cell reselection procedure ............. 62

Table 16-2 Pilot acquisition statistics at 850 MHz for dense-urban model with 24active HNBs and calibrated HNB transmit power ............................... 63


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Table 16-3 Coverage statistics for dense-urban model with 24 active HNBs andcalibrated HNB transmit power ....................................................... 63

Table 20-1 Recommended simulation parameters ............................................. 82

FiguresFigure 1-1 Typical femtocell deployment scenario. ............................................. 1

Figure 4-1 Small Cell Forum Scenarios A-J ........................................................ 8

Figure 6-1 Scenario A .................................................................................. 10

Figure 6-2 Received signal strengths at UE, from macrocell and femtocell. .......... 12

Figure 6-3 HSDPA throughput vs. UE to femtocell distance for various femtocellTx powers ................................................................................... 14

Figure 7-1 Scenario B .................................................................................. 15

Figure 7-2 Interference Scenario B, voice call .................................................. 17

Figure 7-3 HSUPA simulation, Scenario B. E-DPDCH Ec/No compared to

throughput for RFC3 ..................................................................... 18Figure 7-4 Throughput for HSUPA. 70% max bit rate for all FRCs ....................... 19

Figure 8-1 Illustration of the interference analysis for Scenario C ....................... 21

Figure 8-2 Path loss model ........................................................................... 22

Figure 8-3 TX power needed for 12.2 kbps for MUE (1000 metres away and 100metres away respectively) ............................................................. 23

Figure 8-4 MUE throughput with HSDPA for locations at 1,000 and 100 metresrespectively ................................................................................. 24

Figure 9-1 Interference Scenario D ................................................................ 25

Figure 10-1 Scenario E. Adjacent femto with UEs connected to each AP ................ 30

Figure 10-2 Apartments Plan Flats layout ....................................................... 31

Figure 10-3 Macrocell location relative to the house where the femtos are located . 31

Figure 10-4 Dedicated carrier: CDF of HSDPA throughput ................................... 33

Figure 10-5 Shared carrier: CDF of HSDPA throughput ....................................... 33

Figure 11-1 Illustration of the Interference Scenario F ........................................ 35

Figure 12-1 Illustration of the Interference Scenario G ....................................... 40

Figure 12-2 CPICH Ec/Io for Femto .................................................................. 41

Figure 13-1 Illustration of the interference Scenario H ........................................ 43

Figure 13-2 Minimum separation between Femtocell and MUE to avoid blocking,for a given MUE ........................................................................... 46

Figure 13-3 E-DPDCH Ec/No variation as a function of MUE transmit power level ... 47

Figure 13-4 Required average FUE transmit power level to meet HSUPAthroughput requirements. ............................................................. 48

Figure 13-5 E-DPDCH Ec/No variation as a function of MUE transmit power level ... 49

Figure 14-1 Illustration of the Interference Scenario I ........................................ 51

Figure 14-2 Macro Node B signal strength relative to the interfering femtocellsignal strength measured at the MUE, required for successfuldecoding of AMR .......................................................................... 53

Figure 14-3 Maximum MNB - MUE separation as a function of femtocell MUEseparation, assuming AMR voice service .......................................... 54

Figure 14-4 Maximum macrocell-MUE separation as a function of femtocell-MUE

separation, for reception of HSDPA ................................................. 55


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Figure 15-1 Interference Scenario J ................................................................. 57

Figure 16-1 In variance of HNB calibrated Tx Power in the two frequencies ........... 63

Figure 16-2 DL user throughput distribution under different minimum powers,User Throughput Distributions, 10 MUEs, 24 HUEs ............................ 64

Figure 16-3 Magnified version of Figure 1-2 showing outage statistics .................. 65Figure 16-4 HUE uplink throughput distribution ................................................. 66

Figure 16-5 MUE uplink throughput distribution ................................................. 67

Figure 16-6 Transmit power distribution ........................................................... 68

Figure 16-7 Transmit power distribution ........................................................... 69

Figure 16-8 UE uplink throughput distributions in 850 MHz. There are, in total, 34UEs per macrocell, of which 24 UEs migrate to MNB in the No HNBscase. HNB deployment increases the system capacity significantly. ..... 70


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Report title: Interference Management in UMTS FemtocellsIssue date: 20 February 2013Version: 099.01.02 1

1. Femtocells, Femtocell Access Points and the Small Cell Forum1.1 What are Femtocell Access Points?Femtocell Access Points (FAPs) are low-power radio access points, providing wireless voice and broadbandservices to customers primarily in the home environment. The FAP provides cellular access in the home andconnects this to the operators network through the customers own broadband connection to the Internet.

FAPs usually have an output power less than 0.1 Watt, similar to other wireless home network equipment,and they allow a small number (typically less than 10) of simultaneous calls and data sessions at any time.By making the access points small and low-power, they can be deployed far more densely than macrocells(for instance, one per household). The high density of deployment means that the femtocell spectrum is re-used over and over again, far more often than the re-use that the macro network (with its comparativelylarge cells) can achieve. Trying to reach the same levels of re-use with macrocellular technology would beprohibitively expensive in equipment and site acquisition costs. By using femtocells, the re-use, spectrumefficiency, and therefore the aggregate capacity of the network can be greatly increased at a fraction of themacrocellular cost.

A typical deployment scenario is shown in Figure 1-1.

Figure 1-1 Typical femtocell deployment scenario.

1.2 What do femtocells offer?Zero-touch installation by end user: femtocells are installed by the end user without intervention from the

operator. The devices will automatically configure themselves to the network, typically using NetworkListen capabilities to select settings that minimise interference with the macro network.

Moveability: The end user may move their femtocells for example, to another room, or, subject tooperator consent, to another location entirely.

Backhaul via the end users fixed broadband connection: Femtocells will use the subscribers broadbandconnection for backhaul, which typically will be shared with other devices in the home.

Access control the Closed User Group: The operator and/or end user will be able to control which mobiledevices can access the femtocell. For example, subscribers may be able to add guest phone numbers via aweb page.

Supports a restricted number of simultaneous users: Femtocells will support a limited number (typically,fewerthan ten) of simultaneous calls and data sessions.


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Femtozone (homezone) tariffs: Mobile services accessed through the femtocell may be offered at a cheaperrate than the same services on the macro network. End users are advised when services are accessed viathe femtocell, either by an advisory tone, or a display icon or some other means, so they know when thefemto-tariffs apply.

Ownership: Various ownership models are possible for example, end users may own their femtocells, just

as they own their mobile phones, or the operator may retain ownership, with end users renting theequipment (like a cable modem).

Small cell size/millions of cells in the network: The femtocell network can easily extend to millions ofdevices.

Femto as a service platform: Novel mobile services can be made available on the femtocell. For example, afemtocell-aware application on the mobile handset could automatically upload photos to a website when theuser enters the home, and download podcasts.

1.3 What is the Small Cell Forum?The Small Cell Forum is the only organisation devoted to promoting small cell technology worldwide. It is anot-for-profit membership organisation, with membership open to providers of small cell technology and to

operators with spectrum licences for providing mobile services. The Forum is international, representingaround 140 members from three continents and all parts of the femtocell industry, including:

major operators, major infrastructure vendors, specialist femtocell vendors, and vendors of components, subsystems, silicon and software necessary to create femtocells.

The Small Cell Forum has three main aims:

to promote adoption of femtocells by making information available to the industry and thegeneral public,

to promote the rapid creation of appropriate open standards and interoperability for femtocells,and

to encourage the development of an active ecosystem of femtocell providers, to deliver ongoinginnovation of commercially and technically efficient solutions.

The Small Cell Forum is technology agnostic and independent. It is not a standards setting body, but workswith standards organisations and regulators worldwide to provide an aggregated view of the small cellmarket. A full current list of Small Cell Forum members and further information is available atwww.smallcellforum.org.


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2. Introduction2.1 Objectives and Methods of this PaperThe benefits of femtocells are not straightforward to realise. While network operators will see significantcapacity gains, and end users can expect higher performance, to achieve this the radio layer must becarefully managed. The management of the radio interference between the Macro and Femto Layers is a keyindustry concern addressed by this paper.

Interference adversely affects the capacity of a radio system and the quality of the individualcommunication links on that system. Adding capacity is always based on a trade-off between interference,quality and capacity. Hence, there is a need for interference management techniques to minimiseinterference that might otherwise counteract the capacity gains and degrade the quality of the network.

1. The principal objectives of this study are: To develop an industry position on the interference risks from femtocell deployments. To recommend mitigation techniques and any necessary associated RF parameters and

performance requirements, to ensure minimal disruption to the macro network or other

femtocells.2. To achieve these objectives, this paper develops detailed interference scenarios for evaluation

and inclusion in the interference management assessment. The scenarios will cover worst-casedeployment conditions and assess the respective system impact.

3. An immediate focus is to develop the assessment for W-CDMA, and in doing so devise a processthat should be consistent with alternative radio technologies.

4. Two main steps were identified in order to accomplish the above goal: First, a baseline set of interference analysis conclusions for UMTS femtocells, based on

3GPP RAN4 interference studies, was required. This would be supplemented with specificanalysis of identified micro scenarios, their likelihood, and potential impact. Interferencemitigation techniques should also be considered on the understanding that vendorindependence be preserved wherever possible.

Secondly, a recommendation for a common set of behaviours (RF parameters and/or testcases) that can be derived by any UMTS femtocell was required. This is so that the

femtocell can configure itself for minimal disruption to either the macrocell layer or otherdeployed femtocells.5. 5. We focus exclusively on the Closed User Group model. This is the most likely residential

deployment model, and restricts the pool of allowed users to a small group authorised by theoperator or the owner of the femtocell. Non-authorised subscribers may suffer coverage andservice impairment in the vicinity of a closed-access femtocell (the so-called deadzone), whichis important to assess.

6. The study will also investigate methods of controlling the impact of deploying large numbers offemtocells on the macro network. For example, different scrambling codes and adaptive powercontrols may be used to manage the interference in the network.

7. This paper has limited itself in scope, according to perceived priorities, as follows: It is exclusively concerned with W-CDMA as an air interface technology (other teams within

Small Cell Forum are looking at other air interfaces). It is concerned primarily with the 850 MHz band in the United States, but is equally

applicable to the 900 MHz band in Europe and elsewhere. It should also be broadlyapplicable to similar bands (eg. 700 MHz).

It is exclusively a theoretical treatment, using link level and system level simulations todraw its conclusions, although we expect to back up these conclusions in due course withexperiment.

8. The femtocells have been modelled in terms of three power classes (10dBm, 15dBm, 21dBm) or(10mW, 30mW, 125mW), although not all cases examine all three classes.

9. In approach, this paper has chosen to look at extreme cases of general industry concern, tocomplement as far as possible the RAN4 scenarios already studied in 3GPP. In the main, theanalysis has shown up internal contradictions in those extreme cases meaning that they willnever occur in practice. Such contradictory analyses are then followed up with less extreme,more realistic scenarios, where the interference effects and their mitigation can be modelled andanalysed.


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3. Previous WorkAnalysis in this problem space has already been carried out as part of the 3GPP Home Node B study item.

3GPP RAN4 concluded their study into the radio interface feasibility of Home Node B (aka femtocells) at

RAN#39 in March 2008. Their results are presented in [TR25.820]. Part of their study included the analysisof anticipated interference scenarios covering a range of HNB deployments. A summary of their findings ispresented in Table 4-1 below.

The scenarios for this paper are defined in Section 4.

Scenario

(this

paper)

25.820

scenario

id

Summary of RAN4 conclusions

A 4 Macrocell DL interference can generally be overcome, as long as thefemtocell has sufficient transmit dynamic range.

B 3 The femtocell receiver must reach a compromise between protectingitself against uncoordinated interference from the macro UEs, andcontrolling the interference caused by its own UEs towards the MacroLayer. Adaptive uplink attenuation can improve performance, butconsideration must also be given to other system issues like theassociated reduction in UE battery life.

C 2 Downlink interference from a closed-access femtocell will result incoverage holes in the macro network. In co-channel deployments thecoverage holes are considerably more significant than when thefemtocell is deployed on a dedicated carrier. A number of models arepresented for controlling maximum femtocell transmission power, but itis acknowledged that no single mechanism alone provides a definitivesolution. Open access deployment should also be considered as a

mitigating option.

D 1 Noise rise on the Macro Layer will significantly reduce macroperformance; consequently, the transmit power of the femto UE shouldbe controlled. A number of mechanisms to achieve this are presented,generally providing a compromise between macro and femtocellperformance. Again, open access deployment should be seen as amitigating option in the co-channel case.

E 6 This scenario has received less coverage than the macro interferencecases, but it is noted that the performance of Closed Subscriber Group(CSG) femtocells is significantly degraded unless interference mitigationtechniques are used. This is generally a similar problem to macro DLinterference in the co-channel scenario.

F 5 It is difficult to avoid co-channel interference between CSG femtocells,and this limits the interference reductions achieved by deploying thefemtocell on a separate carrier from the macro network. Again,interference management techniques are required to manage femto-to-femto interference.

G 4 Macrocell DL interference can generally be overcome, as long as thefemtocell has sufficient transmit dynamic range.


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Scenario

(this

paper)

25.820

scenario

id

Summary of RAN4 conclusions

H 3 The femtocell receiver must reach a compromise between protecting

itself against uncoordinated interference from the macro UEs, andcontrolling the interference caused by its own UEs towards the MacroLayer. This is generally an easier compromise to arrive at with adjacent-channel deployments than it is with co-channel.

I 2 Downlink interference from a closed-access femtocell will result incoverage holes in the macro network. In adjacent-channel deploymentsthe coverage holes are considerably easier to minimise and control thanwhen the femtocell is deployed on the same carrier as the Macro Layer.A number of models are presented for controlling maximum femtocelltransmission power; all except the fixed maximum power approachare generally acceptable.

J 1 Noise rise on the Macro Layer will significantly reduce macroperformance; consequently, the transmit power of the Femto UE shouldbe controlled. A number of mechanisms to achieve this are presented,generally providing a compromise between macro and femtocellperformance. Adjacent-channel deployments can generally beaccommodated.

Table 3-1 Scenarios

In addition to the previous 3GPP analysis work, the Small Cell Forum conducted an earlier study coveringthe same scenarios at 2 GHz [FF08]. For this study at 850 MHz, several changes were made to thesimulation parameters used in that earlier 2 GHz study:

Wall loss was reduced from 20 to 10dB, to reflect greater building penetration at 850 MHz. Macro basestation antenna height was increased from 25 to 30 metres, to reflect the higher

antenna heights (larger cell size) typical in North American deployments. The minimum distance from a macro basestation was increased from 30 to 1,000 meters, to

again reflect typical North American deployment scenarios where cells are larger andbasestations are not typically located in residential areas. This also allowed us to eliminate theuse of the ITU P.1411 propagation model, and to use the Okumura-Hata model, simplifying theanalysis work.


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4. Simulation Scenarios and DefinitionsThe Small Cell Forum has identified 10 stretch scenarios that explore the limits of operation of femtocellsand femtocell subscriber equipment.

The scenarios are summarised in the following tables and figure.

Scenario Description

Macrocell Downlink Interferenceto the Femtocell UE Receiver (A)

A femtocell UE receiver, located on a table next to theapartment window, is in the direct bore sight of a macrocell(1 km distance). The macrocell becomes fully loaded, whilea femtocell UE is connected to the femtocell at the edge ofits range.

Macrocell Uplink Interference tothe

Femtocell Receiver (B)

A femtocell is located on a table within the apartment.Weak coverage of the macro network is obtainedthroughout the apartment. A user UE1 (that does not haveaccess to the femtocell) is located next to the femtocell

and has a call established at full power from the UE1device. Another device UE2 has an ongoing call at the edgeof femtocell coverage.

Femtocell Downlink Interferenceto the Macrocell UE Receiver (C)

UE1 is connected to the macro network at the edge ofmacro coverage. It is also located in the same room as afemtocell (to which it is not allowed to access). Thefemtocell is fully loaded in the downlink.

Femtocell Uplink Interference tothe

Macrocell Node B Receiver (D)

UE1 is located next to the apartment window, in direct boresight of a macrocell (1 km distance). UE1 is connected tothe femtocell at the edge of its range, and is transmittingat full power.

Femtocell Downlink Interferenceto

Nearby Femtocell UE Receivers(E)

Two apartments are adjacent to each other. Femtocells(AP1 and AP2) are located one within each apartment. Theowner of AP2 visits their neighbours apartment, and is onthe edge of coverage of their own femtocell (AP2) but veryclose (


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Scenario Description

Macrocell Downlink Interferenceto the adjacent-channel FemtocellUE Receiver (G)

A femtocell UE is located on a table next to the apartmentwindow, in direct bore sight of a macrocell (1 km distance).The macrocell becomes fully loaded, while a femtocell UE is

connected to the femtocell at the edge of its range.

Macrocell Uplink Interference tothe adjacent-channel FemtocellReceiver (H)

A femtocell is located on a table within the apartment.Weak coverage of the macro network is obtainedthroughout the apartment. A user (that does not haveaccess to the femtocell) is located next to the femtocell andhas a call established at full power from the UE1 device.Another device UE2 has an ongoing call at the edge offemtocell coverage.

Femtocell Downlink Interferenceto the adjacent-channel MacrocellUE Receiver (I)

Two users (UE1 and UE2) are within an apartment. UE1 isconnected to a femtocell at the edge of coverage. UE2 isconnected to the macrocell at the edge of coverage, andlocated next to the femtocell transmitting at full power.

Femtocell Uplink Interference tothe adjacent-channel MacrocellNodeB Receiver (J)

A femtocell is located in an apartment, in direct bore sightof a macrocell (1 km distance). UE1 is connected to thefemtocell at the edge of coverage, but next to the widow thus, in the direct bore sight of the macrocell antenna.

Table 4-2 Femtocell Deployments in non-Shared Spectrum

In addition to these extreme scenarios, we include shared-spectrum system level simulations specificallymodelling the mitigation of downlink interference and uplink noise rise by power control techniques(Section 15). These simulations also model the effect of femtocells on the total throughput and capacity ofthe network.

The relationship between these scenarios and those already studied in RAN4 is summarised in the followingtable and figure.


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Victim

Femto UE DLRx

Femto AP ULRx

Macro UE DLRx

Macro

NodeB UL Rx

Neighbour

Femto UE DLRx

Aggressor

Macro NodeB

DL Tx

A, G

4

Macro UE

UL Tx

B, H

3

Femto AP

DL Tx

C, I

2

E

6

Femto UE

UL Tx

D, J

1

Neighbour Femto UE

UL Tx

F

5

Table 4-3 Scenario relationships

AF are the interference scenarios for co-channel deployments

GJ are the interference scenarios for adjacent-channel deployments

16 are the equivalent interference scenario IDs used in the 3GPP HNB analyses [TR25.820]

The following diagram illustrates and summarises the Small Cell Forum Scenarios A-J:

Figure 4-1 Small Cell Forum Scenarios A-J


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5. Abbreviations and Defined TermsThroughout this paper a number of abbreviations are used to identify various system elements andparameters. The most frequently used are presented here for quick reference. However, a more extensivelist has been produced and is available under separate cover.

AP Access Point

BER Bit Error Rate (or Bit Error Ratio) the proportion of the total number of bits received that aredecoded wrongly

BS Base Station (assumed to be a wide-area BS, as defined in [TS25.104], unless otherwisestated)

EIRP Equivalent Isotropic Radiated Power a measure of the transmitted power in a particulardirection that takes account of the antenna gain in that direction

FAP Femto AP, also known as the femtocell

FUE Femto UE, also called the Home UE (HUE)

HUE Home UE, also called the femto UE (FUE)

HNB Home NodeB

MNB Macro NodeB

MUE Macro UE

QoS Quality of Service

UE User Equipment (handset, data terminal or other device)

RAN Radio Access Network

RAT Radio Access Technology

RSCP Received Signal Code Power

RTWP Received Total Wideband Power

LOS Line-Of-Sight

P-CPICH Primary Common Pilot Channel

Victim Is a radio node (macro node-B, or femto access point) whose receiver performance iscompromised by interference from one or more other radio nodes (the Aggressor).Alternatively, the Victim may be a radio link, whose quality is degraded by unwanted

interference from Aggressor nodes

Aggressor Is a radio node (either macro node-B, femto access point or UE) whose transmissions arecompromising the performance of another radio node (the Victim), or which are contributing tothe degradation of quality of a (Victim) radio link

Deadzone Is an area where the quality of service is so poor as a result of interference that it is notpossible to provide the demanded service. Deadzones are also characterised by the fact that inthe absence of any interference, a normal service would be possible.

Deadzones are often specified in terms of the path loss to the Aggressor transmitter. A 60dB deadzone inthe femtocell is, therefore, a region around the femtocell where the path loss to the FAP is less than 60dB.


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6. Scenario A: Macrocell Downlink Interference to the FemtocellUE Receiver

6.1 DescriptionA UE is located on a table next to the apartment window that is 1km distance away from a macrocell. Themacrocell is operating at 50% load, while the UE is connected to the femtocell (ie. FUE) at the edge of itsrange. In this scenario the Victim link is the downlink from the femtocell to the FUE, while the Aggressortransmitter is the downlink from the macrocell. This interpretation of Scenario A is summarised in Figure 6-1.

Figure 6-1 Scenario A

6.2 AnalysisThe objective of the analysis of this scenario is to work out the services that can be delivered to a femto UEwhen it is on the edge of the femtocell the femtocell itself being positioned, as required by the scenario,1km from the macro. The analysis strategy for this scenario is broken down as follows:

The first task is to determine the range of the femtocell as defined by the pilot power. This gives us themaximum range at which the UE can detect and decode the femto beacon, and therefore camp on to it.Secondly, we work out the services that can be offered by the femtocell at the edge of its coverage, giventhat interference level. The first step is accomplished by the following sequence:

Assume a given P-CPICH transmit power for both macro and femto; then find the power due to the macro at the distance given by the scenario (1km); then find the distance from the femto at which the ratio of femto power to macro power is sufficient

for the UE to detect the femtocell. This distance is the range of the femtocell as defined by thepilot power the maximum range at which a UE can detect the femtocell and camp on to it.

The second step (to work out the services that can be offered at this range) is accomplished as follows:

For voice, work out how much dedicated channel power is required to sustain a voice call, giventhe interference level calculated in the first step, and reconcile that with the total amount ofpower available to give the number of voice calls that may be sustained.

For data, work out the Ec/Io that can be achieved by allocating all the remaining power to theHSDPA downlink shared channel, and derive a throughput from that, given an industry standardrelationship between Ec/Io and throughput.

Assumptions for the macrocell are as defined in [FF09] with variant values shown in Table 6-1, which showsthe transmit EIRP of the macrocell. The link budget for the macrocell is defined in Table 6-2.


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Value Units Comments

Macro Node B utilisation as percentage of totalpower

50 %

Macro Node B maximum Tx power 43 dBm Ptx_max

Macro Node B Tx power 40 dBm Ptx_m= Ptx_max +10*log(0.5)

Antenna gain 17 dBi Gm

Feeders and cable losses 3 dB Lc

Tx EIRP 54 dBm EIRP_m=Ptx_m+Gm-Lc

Table 6-1 Macro Node B assumptions and transmit EIRP calculation

Value Unit Comments

Distancemacro nodeBto UE

1000 m d_mu

Height macro

nodeB antenna

30 m hb

Height UE fromground

1.5 m hM

Path loss 125.75 dB PL_m is calculated from the Okumura-Hata Model, + 5dBwindow loss

UE antennagain

0 dBi Gue

UE connectorand bodylosses

3 dBi Lc_u

Macro nodeBreceived powerat UE

-79.75 dBm Prx_m=eirp_m-PL_m+Gue-Lc_u

Table 6-2 Link budget for the received power from macro Node B to UE

The value Prx_m in Table 6-2 is the power due to the macrocell at the scenario distance (1km), and takesaccount of the propagation, plus an allowance for the window loss (5dB).

The femtocell assumptions are presented in Table 6-3. Note that three types of femtocell are assumed withthe defined femto transmit power classes (10dBm, 15dBm and 21dBm).

Value Unit Comments

Femtocell max transmit power 10 dBm Ptx_f for the three power classes modelled

15

21

Femtocell antenna gain 0 dBi Gf (same as UE)Femtocell feeders/connectorlosses

1 dB Lc_f

Maximum transmit EIRP 9 dBm eirp_f=Ptx_f+Gf-Lc_f, for the three powerclasses modelled14

20

P-CPICH power relative tomaximum power

10 % pcp_pctage

P-CPICH transmit EIRP -1 dBm Eirp_pcp_f = eirp_f * pcp_pctage

4

10

Table 6-3 EIRP for the femtocell


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In order to complete the calculation of position of the cell edge according to P-CPICH, we calculate the P-CPICH power at the UE and compare it to the power at the UE due to the macrocell. Note that in thisscenario we are fixing the UE at the window and moving the femtocell location so the macrocell power isconstant at the value calculated in Table 6-2. We use the indoor propagation model ITU-R P.1238, assuminga residential building and same floor operation, the femtocell characteristics from Table 6-2 as well as thesame UE characteristics as in Table 6-2. Figure 6-2 shows the femtocell P-CPICH power received at the UE,

and the power at the UE from the macrocell as taken from Table 6-2.

In order for the FUE to detect the femtocell and camp onto it, the P-CPICH Ec/No must be sufficient. It isassumed that a level of -18 dB will be adequate in this respect. To find the range of the femtocell we needto find the distance below which the P-CPICH power is less than 18 dB below the power from the macrocell.By observing in Figure 7-2 where the P-CPICH power exceeds the bounds on the macro interference powerminus 18 dB, it can be seen that even at the 10 dBm transmit power, the FAP has a range of more than 100m. It is to be noted that this does not necessarily mean that a UE 100m away from the FAP will select theFAP in idle mode. Rather, it means that if the UE is already connected to this FAP, it can still sustain theconnection at this distance

Figure 6-2 Received signal strengths at UE, from macrocell and femtocell.

Further, it can be seen that, based on Table 6-4, voice services are readily achievable at the edge ofcoverage, since they require about the same Ec/No as the minimum CPICH Ec/No assumed above.

Value Unit Comments

Chiprate 3.84e6 cps W

Bitrate of AMR voice call 12.2 kbps R

Eb/No requirement for voiceconnection

+7 dB Eb/No

Ec/No requirement for voiceconnection

-18 dB Ec/Io=Eb/No-10*log10(W/R)

Table 6-4 Required Ec/No for voice connection


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Similarly for HSDPA, assuming that 80% of the femtocell power is reserved for HSDPA services (9dB aboveP- CPICH), the HSDPA Ec/No will be at least -1.8 dB (@ 100m from HNB), which corresponds to > 1.5 Mbps,according to the translation equation in [R4-080149].

6.3 Extended scenario: HSDPA coverageThe HSDPA throughput at the UE as a function of the distance between the HNB and the window is analysedby employing the rate mapping equation presented in reference [R4-080149]. The HSDPA max data rate ispresented as a function of average HS-DSCH SINR.

In this work, SINR is calculated using the formula in [Hol06]:

Equation 6-1

where:

SF16 is the spreading factor, PHS-DSCH is the received power of the HS-DSCH, summing over all active HS-PDSCH codes, Pown is the received own-cell interference, is the downlink orthogonality factor (assumed to be 1, fully orthogonal), Pother is the received other-cell interference, Pnoise is the received noise power (here it is assumed that the UE Noise figure is 7dB).

Assuming:

The femtocell transmit powers are 10dBm, 15 dBm and 21 dBm, with 80% allocated to HS-DSCH And employing the path loss assumptions of the previous section The UE is still assumed to be 1 km away from the macrocell.

The HSDPA throughput for the FUE at different distances from the femtocell is shown in Figure 6-3.


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Figure 6-3 HSDPA throughput vs. UE to femtocell distance for various femtocell Tx powers

It can be seen from Figure 6-3 that the maximum HSDPA throughput can be expected up to 25 m away

from the femto, even at the 10 dBm transmit power.

6.4 ConclusionsThe scenario that has been analysed in this section examines the case of the UE being located in front of awindow overlooking a macrocell that is 1 km away. Assuming standard models and parameters, it is shownthat, even at 10 dBm transmit power, the femtocell is able to comfortably provide voice to the UE when thefemtocell is located as far as 100 m away, and maximum HSDPA throughput can be expected up to 25 maway.


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7. Scenario B: Macrocell UE Uplink Interference to the FemtocellReceiver

7.1 DescriptionA femtocell is located on a table within the apartment. Weak coverage of the macro network is obtainedthroughout the apartment. A user that does not have access to the femtocell (MUE) is located next to thefemtocell. Another user device (FUE) is connected to the femtocell and has an ongoing call at the edge offemtocell coverage. The scenario is depicted in Figure 7-1. In this case the Victim receiver belongs to thefemtocell access point (FAP), and the Aggressor transmitter is that of the nearby MUE.

Figure 7-1 Scenario B

7.2 AnalysisThe general assumptions for the analysis of this scenario are presented in Figure 7-1. The link budget forthe MUE is shown in Table 7-2; note that three separation distances between the MUE and the femtocell aretaken into account (5, 10 and 15m).

Value Unit Comments

Voice call service rate 12.2 kbps R

Chip rate 3.84 Mbps W

Processing gain 24.98 dB PG=10*log10(W/R)

Required Eb/No for voicecall

8.3 dB Eb/No (performance requirement in[TS25.104] for AWGN channel, nodiversity)

Frequency 850 MHz Fc (Band V)

Table 7-1 Assumptions for Scenario B


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Value Unit Comments

MUE uplink transmittedpower

21 dBm Ptx_mue (power class 4)

UE antenna gain 0 dBi Gue

Connectors/body loss 3 dB Lue

MUE Tx EIRP 18 dBm eirp_mue=Ptx_mue+Gue-Lue

Distance MUE-femtocell 5, 10, 15 m d_mue

MUE-femtocell path loss 50.16 (@5m)

58.59(@10m)

63.52 (@15m)

dB PL_mue, Indoor to indoor pathloss model , where d=d_mue,f=fc

Femtocell antenna gain 0 dBi Gf

Femtocell feeders/connectorlosses

1 dB Lf

Uplink power received bythe femtocell from MUE atdifferent MUE-femtocellseparation distances

-33.16(@5m)

-41.59(@10m)

-46.52(@15m)

dBm Prx_mue=eirp_mue-PL_mue+Gf- Lf

Table 7-2 MUE link budget at the femtocell receiver

In Table 7-3, the FUE's minimum transmitted power requirement for holding a voice call is calculated. Notethat the power is well within the FUE's capabilities, even at the largest separation distance.

Value Units Comments

Distance between FUEand femtocell

15 m d_fue

Path loss 63.51 dB PL_fue

Indoor to indoor path loss model(d=d_fue, f=fc)

Eb/N0 requirements

for a voice call

8.3 dB Eb/No_fue [TS25.104]

Processing Gain 24.98 dB PG_fue

Noise power -103 dBm PN from [TS25.942]

FUE received power inorder to obtainrequired Eb/N0 fordifferent MUEdistances (d_mue)

-49.84 (@5m)

-58.27(@10m)

-63.20 (@15m)

dBm Prx_fue is calculated from equation[Hol06]:

FUE transmittedpower requirementsfor different MUEdistances (d_mue)

17.68 (@5m)

9.25 (@10m)

4.32 (@15m)

dBm Ptx_fue=Prx_fue-Gue+Lue+PL_fue-Gf+Lf

Table 7-3 FUE transmitter power requirements in order to hold a voice call

The values calculated in Table 7-3 for the transmitted power of the FUE required are the same as the onecalculated for the 1900Mhz study. The reason for this is that the reduction on frequency affects both FUEand MUE in the same way. Moreover, as the MUE is near to the femtocell, the affect of Noise Power is smallin the calculation of Prx_fue.

In Figure 7-2, the results are interpolated for different UE distances and power levels.

Note that the plot includes the downlink deadzones created by the femtocell, which affects the MUE.Downlink deadzone assumptions are summarised in Table 7-4.


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DL Tx power Maximum co-channelDL

deadzone

MUE-femtocell distance(using ITU-

P.1238 indoor path loss model)

10dBm 60dB 11.3m

15dBm 65dB 17m

20dBm 70dB 25.7m

Table 7-4 Maximum co-channel DL deadzone created by the femtocell for MUEs, based on

[R4-070969] and assuming RSSI of -65dBm

Within these zones, the MUE will be re-directed to another WCDMA frequency or Radio Access Technology(RAT) by the macrocells, or the call may be dropped. In both case the interference level in the femtocellreduces, and the uplink power requirements will relax.

Figure 7-2 Interference Scenario B, voice call

7.2.1 HSUPAIn this section the affects of HSUPA are analysed. The link budget is shown in Table 7-5.

Value Unit Comments

FUE uplink transmitted power 21 dBm Ptx_fue

UE antenna gain 0 dBi Gue

Connectors/body loss 3 dB LueFUE Tx EIRP 18 dBm eirp_fue=Ptx_fue+Gue-Lue

Distance FUE-femtocell 5 m d_fue

FUE-femtocell path loss 50.16 dB PL_fueIndoor to indoor path lossmodel(d=d_fue, f=fc)

MUE distance from femtocell 21 dBm Ptx_mue

MUE-femtocell separation

MUE power at femtocell (see Table7-2 for d_mue=10)

Noise level

E-DPDCH Ec/No

10

-41.59

-103

-2.57

mdBm

dBmdB

d_mue

Prx_mue

N0

Table 7-5 Link budget for HSUPA


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The simulation results in Figure 8-3 show the E_DPDCH Ec/No for two cases:

FUE is at 5m from the femtocell FUE is at 15m from the femtocell.

In both cases, it is expected that the MUE is transmitting at maximum power (21dBm).

Figure 7-3 shows the fixed-reference channel (FRC) #3 (see [TS25.104], Pedestrian A channel model) forthe following requirements for E-DPDCH to be met:

Ec/No of 2.4dB: provides R30% of max information bit rate Ec/No of 9.4dB: provides R70% of max information bit rate.

Note that DL deadzones are not taken into account. However, the grey area in the figure represents themaximum extent (11.3m) of the DL deadzone for a femtocell transmitting at +10dBm. This distance wouldreduce if the FAP was not loaded in the downlink.

Note also that the indoor to indoor path loss model, ITU-R P.1238, may underestimate the true path lossoutside 15-20m range, as it is likely that other physical features (such as furniture, walls and buildings) willaffect radio propagation (this is particularly true in dense urban areas.). A larger path loss reduces MUEinterference, which, in turn, allows greater FUE throughput (linked to an increase in FUE-DPDCH Ec/No).

Figure 7-3 HSUPA simulation, Scenario B. E-DPDCH Ec/No compared to throughput for RFC3

The results in Figure 7-3 are mapped to the TS 25.104 throughput model for pedestrian A no receiverdiversity. The results are shown in Figure 7-4. Here, it is noted how interference from the MUE has a strongaffect on throughput; however, it should be noted that the simulation assumes an MUE transmitting atmaximum power (on the edge of the macrocell).


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Figure 7-4 Throughput for HSUPA. 70% max bit rate for all FRCs

7.3 ConclusionsBased on link budget calculations, the affects of uplink interference from one UE on the macrocell and a UEon the femtocell have been analysed; in this work it is assumed that the same frequency is used by theMacro and Femto Layer.

In the analysis, it was assumed a femtocell serving an FUE on the physical edge of the cells (assumed to be15m away) with a 12.2kbps AMR speech call; while a co-channel interference MUE is in the proximity of thefemtocell. The analysis results showed that in order to be able to maintain the uplink connection betweenthe FUE and femtocell, the transmitted power requirements are within the capability of the UE.

Additionally, the performance of HSUPA on the femto-FUE link has been analysed in the presence of uplinkinterference from the Macro UE. By simulation, it has been found that in order to obtain HSUPA throughputof at least 2.8Mbps with a category 6 UE, the FUE needs to be near to the femtocell (5m) and transmit at apower level greater than 15dBm if the MUE is within 15m of the femtocell.

However, such analysis must take into account the downlink deadzone created by the femtocell. High powerfrom the femtocell, in order to maintain the downlink, will interfere with the macrocell signal at the MUE,and will force the macrocell to handover the call to another WCDMA frequency or RAT; or, if none of theseare possible, the MUE call may be dropped.

7.3.1 Customer (MUE) impactFrom the point of view of the MUE, the femtocell is a source of interference to the macrocell. However, themacro network can already cope with re-directing UEs to other WCDMA frequencies or RAT if a user isaffected by high interference.

Those locations with no coverage from alternative WCDMA frequencies or RATs may be adversely affectedby poor Eb/No levels, leading to dropped calls.


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Due to femtocells, the macrocell may also be affected by an increase of uplink interference as femto-UEsincrease power levels in order to achieve required quality levels. This may be limited by capping themaximum power level transmitted by FUEs, or limiting uplink throughput.

7.3.2 Customer (FUE) ImpactThe minimum separation between MUE and femtocell has a strong affect on the capability to offer therequired QoS to the femtocell user. However, the FUE has enough power to sustain a voice call while theMUE is in the coverage range of the femtocell. The downlink deadzone sets a minimum separation betweenMUE and femtocell meaning that the FUE transmit power is always within its capability.

For HSUPA, the user is required to go closer to the femtocell in order to be provided with the bestthroughput. Simulation has shown that at 5m from the femtocell, good throughput can be achieved forMUEs further away than 12m.

7.3.3 Mitigation techniquesAvailability of alternative resources (a second carrier, or underlay RAT) for handing off or reselecting macro-users is the best way to provide good service when macro-users are in the proximity of femtocells.


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8. Scenario C: Femtocell Downlink Interference to the MacrocellUE Receiver

8.1 DescriptionIn this scenario, MUE is connected to the macro network at the edge of coverage (RSCP


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Figure 8-2 Path loss model

The maximum indoor path loss is shown to be more than 90 dB in some locations. The minimum outdoorpath loss from an indoor Femto can be less than 60 dB. This will be a challenge for operators to balancegood indoor coverage while not causing excessive outdoor interference.

Studied in this section is a macrocell user (MUE) at cell edge, located in an apartment where an activefemtocell is operating with full capacity. Analysis is given for the following case:

For the MUE to detect the macrocell and camp on it, or to maintain a call, the P-CPICH Ec/No must besufficient. We assume a -20 dB threshold ie. the received P-CPICH RSCP from the macro must be no morethan 20dB below the Rx P-CPICH RSCP of the femto. It is assumed that cell-edge PCPICH RSCP for themacro is -103 dBm, and so we can infer that the femto PCPICH RSCP must be lower than -83dBm for theMUE to camp on the macrocell. (Note that techniques for facilitating cell re-selection, such as the use ofhysteresis, cell re-selection parameters, HCS, HPLMN, etc, are not discussed here, and are beyond thescope of this paper; the discussion in this paper is on the generic aspect of triggers for cell re-selectiononly.)

We have assumed two scenarios for the location of the femto relative to the macrocell: 100 metres and

1,000 metres away from the macro have been used. We have found that when the femto is deployed in anarea in close proximity to the macrocell (ie. 100 metres away), the maximum output power of the femtoshould be increased beyond 100 mW in order to ensure operation in high coverage. Therefore, when we

study the 100 metres case, we assume the femto is able to radiate up to 125 mW, while maximum outputpower is limited to 20 mW when the femto is deployed further away (ie. 1,000 metres).

Figure 8-3 shows the statistics of the MUE performance when located near the femto in the abovementioned two cases.

1. Femto being 100 metres away from macrocell2. Femto being 1,000 metres away from macrocell.


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8.2 AnalysisMacrocell configuration:

Macrocell site-to-site distance: 100 or 1,000 metres Antenna height: 25 m Antenna gain: 18 dBi Frequency carrier in 850 MHz band Output power of the macro Node B: 20 Watts Town size: 500m radius.

Femto location configuration:

House size: 8.3X17.5 (m2) Houses cover 70% of the area Wall penetration loss: 12 dB CPICH power is 10% of max output power.

The following figures show the required power (as a proportion of the total macrocell power) needed tosupport a voice call at 12.2 kbps within the house in the two deployment scenarios.

Figure 8-3 TX power needed for 12.2 kbps for MUE (1000 metres away and 100 metres awayrespectively)

It is evident that the required power for a well-sustained call at 12.2 kbps is higher in the following twocases:

When the MUE is at the edge of the macrocell (i.e. 1,000 metres away) and is behind thebuilding where the femto is deployed. In this case the MUE requires the macrocell to transmit theradio link at a higher power to compensate for the high path loss affecting the macro signal andthe interference from the femtocell.

When the MUE is in close proximity to the femtocell and the MUE is located inside the house. Inthis case the wall loss is adding additional attenuation to the macro signal.

The following figures show the macro HSDPA throughput within the house in the two deployment scenarios(based on how far the femto is from the macro).


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Figure 8-4 MUE throughput with HSDPA for locations at 1,000 and 100 metres respectively

8.3 Scenario analysis and conclusionsIn the scenario presented in this section, the performance of MUE attached to the macrocell is shown to beaffected by the femtocell in some locations. This can be mitigated by the use of adaptive power control onfemto. Results show that in some cases the MUE might experience deadzone when in close proximity tothe femto. One firm conclusion from this analysis is that adaptive power control is necessary for thefemtocells. Femtocells will require higher output power when the femtocell is deployed in locations near thecentre of the macrocell.

Adaptive power control on the femtocell mitigates interference by offering just the required transmit poweron the femto, based on the level of interference from macro. However, it is shown that a macrocell UE(MUE) might not receive an adequate signal level from the macro to compensate for the femto interference.This is evident in all places in close proximity to the femto when the macro and femtocells share the samecarrier.

It is also concluded that there is no apparent and fundamental performance change whether 850 MHz or2100 MHz is used for the carrier.

In general, if a macro network is designed to provide fixed coverage in terms of cells radius, then themacrocell requires lower output power when operating at 850 MHz. Therefore, the interference level seen bya femto is the same, regardless of the carrier frequency.

It is shown that the femto is an effective vehicle for delivering a good carrier re-use. Furthermore,femtocells are an efficient technique for delivering the high-speed data offered by HSPA to femto users. Thiscan be compared with the macrocell case, where cell radius is larger, resulting in the distribution of thepotential bandwidth of the HSDPA to a larger number of users. It is also well known that HSPA throughput isaffected by the location of the UE; the closer the UE to the centre of the cell, the higher the throughput.This leads us to conclude that small cells like femtocells are an optimum complementary technique formacrocells for addressing high-data usage.


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9. Scenario D: Femtocell Uplink Interference to the MacrocellNodeB Receiver

9.1 IntroductionThis document provides an analysis of Femtocell Uplink Interference from femtocell mobiles (FUEs) to aMacrocell NodeB Receiver.

The scenario being investigated is as follows: An FUE is located next to the apartment window that is insight of a rooftop macrocell (approximately 1,000 m in distance), as shown in Figure 10-1. At the sametime, the FUE is connected to the femtocell at the edge of its range, and is transmitting at full power.

Figure 9-1 Interference Scenario D

In this analysis the impact to the macro Node B is measured by the sensitivity degradation, also referred toas noise rise (or relative increase in uplink Received Total Wide Band Power (RTWP)), experienced by themacro Node B, due to the femto UE. The impact is considered relative to the impact a macro UE will have ona macro Node B from the same location as the femto UE. The rest of this document is structured as follows:

In Section 9.2, analysis of Scenario D described in [Law08] is presented, including theassumptions used. The analysis shows that the femto UEs impact on the macro Node B is noworse that the impact a macro UE from the same location would cause.

In Section 9.4, a mitigation technique is suggested that would always ensure there is minimalimpact to macro Node Bs due to femtocell UEs.

9.2 Analysis of Scenario D - 12k2 Voice and HSUPAAn analysis of this scenario is presented, based on link budget calculations. The analysis looks at the noiserise at the Macro Node B antenna connector due to the femtocell UE in the described scenario.

9.2.1 AssumptionsA macro Node B with a noise floor based on the assumption that the sensitivity of the Wide macro Node Bfor 12k2 voice service at the time is equal to -121 dBm (ie. the 3GPP reference sensitivity level for a 12k2voice service on a Wide Area Node B at the antenna connector [TS25.104]). This sensitivity captures both

the loading and noise figure of the macro Node B. The noise floor calculation is shown in Table 9-1.


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Value Units Comment

Sensitivity @

antenna connector -121 dBm Pue_rec

3GPP reference sensitivity level for

Wide Area Node B

UE Service Rate 12.20 kbps R

Chip rate 3.84 MHz W

UE Processing Gain 24.98 dB PG = 10*log(W/R)

Required EbNo 8.30 dB EbNo

DCH performance without rx diversity

(see [FF09])

noise floor -104.32 dB nf_ant = Pue_rec +PG -EbNo

Table 9-1 Macro Node B noise floor

Next, the factors that could lead the femto UE to transmit at a power higher than expected are considered.This will occur if the femto UE is at the femtos cell edge, and if the femtocell experiences a noise rise, or itsreceiver is experiencing a blocking effect, caused by one of the following:

A co-channel macro UE. An adjacent channel macro UE. Another femto UE located very close (~1m Free Space Loss) to the femtocell eg. a laptop with

a 3G data card doing a data upload on the same desk as the femtocell.

Subsequently, for the purposes of this scenario, the following assumptions are made:

The femto is operating under extreme conditions, experiencing a total noise rise equivalent to70% loading in the uplink.

A 21 dBm class femto1 is used in the scenario that can provide a coverage path loss of up to 120dBs (path loss estimate based on minimum RSCP sensitivity of UE of -111 dBm and an 11 dBmCPICH transmit power and assumption of negligible downlink interference from surrounding NodeBs).

Based on these assumptions, the link budget in Table 9-2 estimates the likely femto UE uplink transmissionpower at the femtocell edge of coverage for a 12K2 voice service and a 2Mbps HSUPA service.

1

Under the same RF conditions a 21 dBm class femto cell will provide larger downlink coverage than a15dBm class or a 10dBm class femto2 Under the same RF conditions, a 21 dBm class femtocell will provide larger downlink coverage than a


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Value

12K2

Voice

2Mbps

HSUPA

Units Comments

Frequency 850.00 850.00 MHz F

Bandwidth 3.84 3.84 MHz BThermal NoiseDensity

-174.00 174.00 dBm/Hz tnd

Receiver NoiseFigure

8.00 8.00 dB NF

Receiver NoiseDensity

-166.00 -166.00 dBm/Hz rnd = tnd +NF

Receiver NoisePower

-100.16 -100.16 dBm rnp =rnd +10*log(B*1e6)

Loading 70.00 70.00 % L

Noise Rise due to

Loading 5.23 5.23 dB IM = -10*log(1-L/100)

Femto ReceiverNoise

Floor-94.93 -94.93 dBm trnp =rnp +IM

Femto UEService Rate

12.2 kbps R

Chip rate 3.84 MHz W

Femto UEProcessing

Gain24.98 dB PG = 10*log(W/R)

Required EbNo 8.30 dB EbNo

DCH performancewithout rx diversity

[FF09]

Required EcNo -16.68 0 dB

EbNo PG for 12K2

Typical EcNo to achieveHSUPA rates of ~ 2Mbps[Hol06]

MinimumRequired

Signal Level forFemto

UE

-111.61 -94.93 dB Pfmin = trnp +EcNo

Femto UE Pathloss to

Femto120 120 dB DLcov

Femto UE TxPower

8.39 21 dBm Pfue = min(21, max ((Pfmin+ DLcov), -50)

Table 9-2 Femto UE TX power 1000 m from macro Node B

9.2.2 Macro Node B Noise RiseThe noise rise caused to the macro by a femto UE transmitting at 8.39dBm for a 12K2 voice service and21dBm for a 2Mbps HSUPA service was calculated, using the link budget in Table 10-3, as 1.44 dB and 9.12dB respectively. Assuming that a macro UE is at the same location as the femto UE by the window (pathloss of 130.77dB from the macro, see Ltot in Table 10-3), Table 10-4 shows that a macro UE operating fromthe same location as the femto UE will be transmitting at 9.94 dBm, and 21dBm if on a 12k2 voice serviceand 2Mbps HSUPA data service respectively and, hence, will lead to the same amount of noise rise as thefemto UE.


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Value

12K2

Voice

2Mbps

HSUPA

Units Comments

Node B Antenna Gain 17 17 dBi Gant [FF09]

Feeder/Connector Loss 3 3 dB Lf

Noise Floor at antenna

connector -104.32

-104.32 dBm nf_ant Table 9-1

Femto UE Tx Power 8.39 21 dBm Pfue

UE Antenna Gain 0 0 dBi Gmant

Femto UE Tx EIRP 8.39 21 dBm

Pfue_eir

p =Pue Gmant +m

Window/Wall Loss 5 5 dB Lw

Path loss to Macro NodeB

130.77 130.77

dB Ltot =1000m Okumura-Hata(Node B

at30m and mobile at 1.5m)

Femto UE Interference@

macro antenna-108.38

-95.77 dB Pfue_rec = Pfue_eirp Ltot + Gant Lf

Rise above noise floor -4.06 8.55 dB R Pfue_rec- nf_ant

Noise rise 1.44 9.12 dB NR =10*log( 1+ 100.1*R))

Table 9-3 Noise rise calculation for Scenario D (femto UE is transmitting at 8.39dBm and

21dBm1000m from a macro Node B for a 12K2 service and 2Mbps HSUPA service)

Value Value Units Comments

12K2 HSUPA

Frequency 850 850 MHz

Bandwidth 3.84 3.84 MHz B

Thermal Noise Density -174.00 -174.00 dBm/Hz tnd

Receiver Noise Figure 5.00 5.00 dB NF

Receiver Noise Density -169.00 -169.00 dBm/Hz rnd = tnd + NF

Receiver Noise Power -103.16 -103.16 dBm rnp =rnd +10*log(B*1e6)

Loading 50.00 50.00 % L

Noise Rise due to Loading 3.01 3.01 dB IM =-10*log(1-L/100)

Macro Receiver NoiseFloor

-100.15 -100.15 dBm trnp = rnp +IM

Required EcNo

-16.68

0.00 dB EcNo

= EbNo - PG for 12k2(see EbNo

in Table 9-2)

Typical EcNo to achieveHSUPA

rates of ~ 2Mbps[Hol06]

Fade Margin 10 10 dB m

Antenna gain 17 17 dBi Gant

Feeder/Connector Loss 3 3 dB Lf

Minimum Required Signal -120.83


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Value Value Units Comments

Level -104.15 dB Pfmin = Trnp Gant +Lf +EcNo+ m

Macro UE Path loss to

macro

130.77

130.77 dB DLcov

=1000m Okumura-Hata(Node B

at 30m and mobile at1.5m)

+Lw

Macro UE Tx Power

9.94

21 dBm Pfue

= min(21, max ((Pfmin+ DLcov),

-50)

Table 9-4 Macro UE Tx power 1,000m away from macro Node B receiver by window on a12K2 voice and 2Mbps HSUPA data service

9.3 ConclusionsThe following conclusions can be drawn:

It is unlikely that a femto UE will be transmitting at maximum power, due to the relativelysmaller coverage of the femto compared to the macro.

When the femto is operating under extreme loading conditio

009 Interference Management in UMTS Femtocells Low Band

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