Interference mitigation

and diversity antennas for

femtocells

Yue Gao (Frank)

Email: yue.gao@eecs.qmul.ac.uk http://www.eecs.qmul.ac.uk/~yueg/

21 May 2013 The 8th International Workshop on Small Cell and HetNet

Outline • Overview Interference Scenarios in Femtocell networks

• TV White Space and geolocation database model

• Cross-tier Interference Mitigation in Suburban

Femtocell Deployment

• Dual-mode diversity antenna for Femtocell base stations

• Ray tracing channel model for an indoor scenario

2

Interference Scenarios in Femtocell networks

Index Aggressor Victim Interference

Type

Transmission

Mode

1 Macro UE Femto BS Cross-tier Uplink

2 Macro BS Femto UE Cross-tier Downlink

3 Femto UE Macro BS Cross-tier Uplink

4 Femto BS Macro UE Cross-tier Downlink

5 Femto UE Femto BS Co-tier Uplink

6 Femto BS Femto UE Co-tier Downlink

Current solutions: Fractional frequency reuse and resource partition; Power control of HeNBs; Collaborative frequency scheduling;

3

TV White Space (TVWS) • Digital Switchover (DSO) • Location-dependent availability • Cognitive access methods

Beacon Spectrum sensing Geo-location database

• Use cases Machine-to-Machine Communications Short Range Wireless Access Network Wireless Regional Access Network

4

Motivation • Obtaining locally available TVWS information

using cognitive access method.

• Utilizing locally available TVWS for Femtocell networks.

Designing appropriate resource allocation schemes

based on the available TVWS to reduce the interference in Femtocell networks in different deployment scenarios.

5

Geo-location Database Model

• Adopt power control strategy to dynamically determine the maximum allowable transmit power for CR stations

• Build up the Geo-location database Model 1) Establishing the DTV Station database 2) Calculation of available TVWS channels 3) Calculation of associated maximum allowable transmit

power

6

Geo-location Database Model • The proposed power-control database model is more

efficient in obtaining TVWS information than the keep-away region model, e.g. more available TVWS channels obtained with various maximum allowable transmit power.

Available TVWS information in Glasgow (NS595655) by power-control model

Channel No. 30 42 45 48 49 51 52 55 56 59

Max. EIRP

(watts) 4 0.128 0.119 4 0.108 4 4 4 4 4

Available TVWS information in Glasgow (NS595655) by keep-away region model

Channel No. 30 48 51 52 55 56 59

Max. EIRP

(watts) 4 4 4 4 4 4 4

7

TVWS Geo-location Database Model • Mobile Phone Application of Geo-location Database Models

Android app can be downloaded from http://www.eecs.qmul.ac.uk/~yueg/#_Software_tools 8

Cross-tier Interference Mitigation in Suburban Femtocell Deployment

• The proposed system architecture • The Geo-location database model to obtain locally

available TVWS information • A novel resource allocation scheme using the locally

available TVWS to mitigate the downlink cross-tier interference between Macro UEs and nearby Femtocells. Femtocell Classification Resource Allocation

9

Simulation set-up

Parameter Assumption Femtocells per macrocell 5

Femto UEs per femtocell 2

Number of Macro UEs 50

Macrocell Radius 288m

Femtocell Radius 12m

Wall Penetration Loss 10dB/20dB

System Bandwidth 10MHz

Total No. of RBs 50

RB Bandwidth 180kHz

Total eNB Transmit Power 46dBm

HeNB Transmit Power 20dBm

Thermal Noise -174dBm/Hz

SINR Threshold -8dB

Minimum Distance between UE and eNB

35m

Minimum Separation between UE and HeNB

20cm 10

NGR Number of location: TQ360823

Channel No. 29 50 56 58

Maximum Allowable

EIRP(watts) 4.000 4.000 0.315 4.000

Available TVWS information results from Geo-location database (Simulated location: Queen Mary, University of London)

Simulation parameters

Cross-tier Interference Mitigation in Suburban Femtocell Deployment

• The proposed scheme reduced the cross-tier interference significantly.

-80 -70 -60 -50 -40 -30 -200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

MUE Total Interference (dBm)

CD

FEmpirical CDF

TraditionalProposedDRP

70 percentile

11

Cross-tier Interference Mitigation in Suburban Femtocell Deployment

• The proposed scheme performed better in the scenarios of more dense Femtocell distribution or smaller Macrocell.

F. Peng, N. Wang, Y. Gao, L. Cuthbert and X. Zhang, “Geo-location Database based TV White Space for Interference Mitigation in LTE Femtocell Networks,”The Fourteenth International Symposium on a World of Wireless, Mobile and Multimedia Networks, IEEE WoWMoM 2013, 4-7 June 2013, Madrid , Spain. (To be appear)

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Summary for Cross-tier Interference Mitigation in Femtocell networks

• TVWS in a Geo-location database to address the downlink cross-tier interference in LTE femtocell networks.

• The proposed scheme can reduce the downlink interference suffered by Macro UEs by more than 3dB and 2.5dB at the 70% percentile of the CDF diagram in comparision with the traditional all-shared scheme and the dynamic resource partitioning scheme, respectively.

• The proposed scheme had better performance in the scenarios of dense femtocell distribution and small macrocells.

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Dual-mode diversity antenna for Femtocell base stations

14

-30

-20

-10

0

10

20 30

210

60

240

90270

120

300

150

330

180

0

-30

-20

-10

0

10

20 30

210

60

240

90270

120

300

150

330

180

0

Simulated 3D radiation patters

Measured and simulated 2D radiation patters

• The diversity antennas were modelled and optimised in CST Microwave studio.

Y. Gao, S. Wang, O. Falade, X. Chen, C. G. Parini and L. G. Cuthbert, "Mutual coupling effects on pattern diversity antennas for MIMO femtocells," Hindawi International Journal of Antennas and Propagation, special issue on "Mutual Coupling in Antenna Arrays", DOI:10.1155/2010/756848, Volume 2010 (2010).

Fabrication and measurement

15

Ground plane

Radiator

160

160

Shorting post

Broadside mode feeding (S11)

Z

X

Y

Conical mode SMA feeding (S22)

Broadside mode feeding (S11)

Hybrid ring

prototype

Anechoic chambers

S-parameters

16

1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5-40

-35

-30

-25

-20

-15

-10

-5

0

Frequency/GHz

Am

plitu

de/d

B

Measured S11Simulated S11Measured S22Simulated S22

1.5 2 2.5

-20

-15

-10

-5

0

Frequency/GHz

Am

plitu

de/d

B

Measured S12Simulated S12

1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5-45

-40

-35

-30

-25

-20

-15

-10

-5

0

Frequency/GHz

Am

plitu

de/d

B

46.1 12

4.1

Port 4

Port 2Port 3

2.320.7

26

Port 1 with a chip resistor

Design 2

Design 1

Ray tracing channel model simulation set-up

Material Permittivity Conductivity Thickness

Concrete (Wall, floor and ceiling)

5.820 0.0596 0.3 m

Wood (Door) 2.5 0.0033 0.05 m

Glass (Window) 6 0.00278 0.005 m

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Material properties used at 2.1 GHz

Antenna Types for FAP Mutual coupling levels

Dual ideal dipole antennas No coupling

Dual dipole antennas (λ/4) -8.5dB coupling

Proposed antenna design 1 -12dB coupling

Proposed antenna design 2 -30dB coupling

Mutual coupling levels of the antennas

Ray tracing channel model simulation set-up

18

45 metres

16 metres

Y

XCorridor Offices and Labs

Rx3

FAPReceivers

Rx4

RoomB

RoomA

Rx2

Rx1FAP

Channel capacity formulaiton

†2( ) log det nC I HH

nρρ = +

02

0

θ π τ

=

= ⋅ ⋅∑ k k

Mj j f

ij kk

h P e e

kP kθ kτ

1,1 1,2

2,1 2,2

h hH

h h

=

A 2 x 2 MIMO system’s capacity can be calculated as

where H is the normalized n x n channel matrix, I is the identity matrix and ρ is the SNR. With a narrowband assumption, the channel response H is given by

, and are the received power, phas and time delay of the k-th ray respectively. M is the total number of rays. So that for a 2 x 2 MIMO case, channel realization the H matrix can be built as

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Channel capacity for different receivers at Room A and B

20

Rx1 at Room A Rx2 at Room A

1 1. 5 2 2. 5 3 3. 5 4 4. 5 5 5. 50

0. 1

0. 2

0. 3

0. 4

0. 5

0. 6

0. 7

0. 8

0. 9

1

Channel Capacity (bit/sec/Hz)

Pro

b. x

< a

bsci

ssa

SI SODual i deal di pol ePr oposed Desi gn 1Pr oposed Desi gn 2

0 1 2 3 4 5 6 70

0. 1

0. 2

0. 3

0. 4

0. 5

0. 6

0. 7

0. 8

0. 9

1

Channel Capacity (bit/sec/Hz)

Pro

b. x

< a

bsci

ssa

SI SODual i deal di pol ePr oposed Desi gn 1Pr oposed Desi gn 2

Rx3 at Room B Rx4 at Room B

0 1 2 3 4 5 6 70

0. 1

0. 2

0. 3

0. 4

0. 5

0. 6

0. 7

0. 8

0. 9

1

Channel Capacity (bit/sec/Hz)

Pro

b. x

< a

bsci

ssa

SI SODual i deal di pol ePr oposed Desi gn 1Pr oposed Desi gn 2

2 2. 5 3 3. 5 4 4. 5 50

0. 1

0. 2

0. 3

0. 4

0. 5

0. 6

0. 7

0. 8

0. 9

1

Channel Capacity (bit/sec/Hz)

Pro

b. x

< a

bsci

ssa

SI SODual i deal di pol ePr oposed Desi gn 1Pr oposed Desi gn 2

Summary for the diversity antennas

• Two pattern diversity antennas operating from 1.68GHz to 2.5GHz for femtocell base stations with mutual coupling of -12dB and -30dB, respectively.

• The channel capacity of the proposed Design 2 with very low mutual coupling (-30dB) is close to that of an ideal dipole array without mutual coupling in most cases.

• The exception case from the results shows that the channel capacity not only depends on the mutual coupling levels but also on the propagation environment.

• A mutual coupling of -12dB is a reasonable level to maintain a good channel performance and there is no need to obtain a very low mutual coupling in Design 2 at the expense of the diversity antenna performance, such as impendence bandwidth and compactness.

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Special issue on Base Station Antennas for Small Cell or Large-Scale Multiple-Antenna Systems- 1

• International Journal of Antennas and Propagation

• A comprehensive antenna system with beamforming, gain, polarization, patterns for effective enhancement of performance is required.

• This call for papers aims to have papers with feasible and great potential antenna designs for the base station in a small cell or large-scale multiple-antenna systems. Potential topics include, but not limited to:

– Multiband and broadband antennas – Reconfigurable antennas – Multisystem array antennas – High directivity beamforming antennas – Flexible compact antennas – Bendable reconfigurable array antennas – Ultrawideband antennas – Smart and semi-smart antenna design – Low profile compact antennas – Circular polarized and dual polarized antennas – Multibeam adaptive base station antennas – Low mutual coupling effect array antennas

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http://www.hindawi.com/journals/ijap/si/502524/cfp/

Special issue on base station antennas - 2

• Lead Guest Editors – Yue GAO (Frank), EECS, Queen Mary University of London, UK; – Cyril LUXEY, EPIB, University Nice Sophia-Antipolis, France; – Zhaobiao LV, China Unicom Research Institute, China.

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Manuscript Due October 25, 2013

First Round of Reviews January 17, 2014

Publication Date March 14, 2014

Before submission authors should carefully read over the journal's Author Guidelines, which are located at http://www.hindawi.com/journals/ijap/guidelines/. Prospective authors should submit an electronic copy of their complete manuscript through the journal Manuscript Tracking System at http://mts.hindawi.com/