Inter Cell Interference Mitigation through Coordinated Schedulinggssst.iitkgp.ac.in/GSProjects/DIM/DIM_Coordinated_Scheduling_V2.pdf · Coordinated Scheduling Approaches •Coordinated

Inter Cell Interference Mitigation through

Coordinated Scheduling

By

Prabhu Chandhar

Dr. Suvra Sekhar Das

Contents

• Background

• Scheduling Architecture

• Coordinated Scheduling

• State of the Art

• Technical Challenges involved

• Problem Definition

• Work Plan

• Time Plan

• References

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Background

• Inter-Cell Interference (ICI) Mitigation Techniques in LTE

– ICI randomization

– ICI cancellation

– ICI coordination/Avoidance

• Cooperative Multipoint Transmission/Reception

– Coordinated Scheduling and beam-forming

• Data to a User equipment (UE) is transmitted from one of the transmission points

• The scheduling decisions are coordinated to control the interference generated in a set of coordinated cells

– Joint Processing/Transmission

• Data to a UE is simultaneously transmitted from multiple transmission points to improve the received signal quality

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Scheduling Architectures

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Centralized Scheduling Architecture

Scheduler Scheduler

Mobile

MME

Core Network

eNB eNB eNB eNB

Mobile

Mobile

Mobile

Mobile

MobileMobile Mobile

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Distributed Scheduling Architecture

Mobile

MME

Core Network

eNB eNB eNB eNB

Mobile

Mobile

Mobile

Mobile

MobileMobile Mobile

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Scheduler Scheduler SchedulerScheduler

X2 interface

Coordinated Scheduling Approaches

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Coordinated Scheduling Approaches

• Coordinated Scheduling and/or beamforming– Data to a User equipment (UE) is transmitted from one of the transmission points

– The scheduling decisions are coordinated to control the interference generated in a set of coordinated cells

– Inter-cell interference coordination (Distributed Scheduling)

• No information exchange between eNBs

• Interference avoidance through resource usage restrictions imposed by frequency and power planning

• Scheduling cell edge users in different frequency bands

• Examples: Semi static ICI coordination (FFR, SFR, etc)

– PMI coordination (Distributed Scheduling)

• The serving eNB could recommend or restrict the PMIs that will be used by neighboring base stations

– Collision Avoidance Beam-forming (Centralized Scheduling)

• Scheduling is done at master scheduler which locally schedules multiple cells

• Master scheduler decides beams and UEs to be serviced at coordinated cells

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10

Coordinated Scheduling - PRB Coordination

SU /MU- MIMO,

Beam forming, Diversity

eNB1

UE1

UE2

UE3

UE4

UE5

UE6

eNB2

eNB3

Resource Blocks

used by eNB1

Resource blocks

used by eNB2

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Coordinated Beam-Forming

& PMI coordination

Beam forming

eNB 3

UE1UE2

UE3

eNB 1 eNB 2

Interference Avoidance

Beam-forming

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Joint Transmission

Beam forming

eNB 3

UE1UE2

UE3

eNB 1 eNB 2

Joint transmit

Beam-forming

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State of the Art

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State of the Art

Sl. No. Paper Details Contents

1 Kyuho ’ 2009 Authors have formulated utility maximization problem with network wideProportional Fair (PF) as an objective in a multi-cell network with PartialFrequency Reuse (PFR)Proposed online algorithms are based on the inter/intra-handover andcell-site selection in which a metric is changed from the signal strength tothe average throughput.Centralized approach which needs fast information exchange andcomputational complexity

2 Xu Kai ’ 2007 Proposed optimal and sub-optimal inter-cell scheduling strategies basedon the coordinated transmission from the interfering cellsThis paper extends the utility function based multi-user packet schedulingstrategies derived for single cell scenario to multi-cell scenarioCentralized approach

3 Yavuz’ 2009 Proposed a scheduler that allows for opportunistic behavior from a singlesessions point of view but keeps the overall caused interference variation ata low level in order to improve the performance of Link AdaptationIgnores fairness among the users

4 Falconetti’ 2010 A codebook based inter-cell interference coordination scheme has been proposed where, the supporting cells try to use a precoding matrix for which the interference received by selected cell-edge UEs remains acceptable.Methods to solve the conflicts of interest are also discussed

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State of the Art

Sl. No. Paper Details Contents

5 Xinying’ 2009 A signal leakage information based scheme has been proposed fordesigning the precoding vector to reduce the Inter Carrier Interference (ICI).In the proposed method coordinating eNB uses PMIs that would result inminimum interference

6 Jianchi ’ 2010 A large-scale Channel State Information (CSI) for precoding has beenproposed to reduce the over-head involved in the coordination processA coordination scheme has been proposed to determine best groups oftransmission points and coordinated UEs

7 Jing ’ 2010 A joint PF scheduling algorithm has been for CoMP-SU-MIMOThe proposed algorithm treats the cell-edge UEs and cell-center UEsequally in every TTI without partitioning the frequency band for CoMPoperation

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Technical Challenges

• Fraction of frequency band allocation for coordination

• Selection of users for cooperation

• Selection of eNBs for cooperation

• Space-Time-Frequency Scheduling for Multi-Cell MU-MIMO

• Feedback Reduction

• PMI conflict issues

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Problem Definition

• Existing single cell Packet scheduling strategies for OFDMA networks are based on utilityfunction that maximizes system throughput.

• The existed coordination strategies for multi-cell scenario are based on centralizedscheduling approach

• The aim of this work is to develop a less complex integrated packet scheduling and ICIcoordination strategy for OFDMA based Single Frequency Networks with the followingobjectives

– Maximize the total system throughput

– Maintain network wide fairness among the users

– Reduced information exchange between the BSs

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Objectives

• Development of integrated packet scheduling and ICI coordination strategy thatimprove the system throughput and maintain network wide fairness among theusers

• Development of PMI coordination methods for SU-MIMO, MU-MIMO schemes

• Design of feedback reduction mechanisms which will reduce the amount ofsignaling involved in coordination process

• Design of Space-Time-Frequency Scheduling for Multi-Cell MU-MIMO scenario

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Work Plan

• System level simulation framework considering 3GPP-LTE being developed

(2 months)

• Investigation on existing Packet scheduling (PS) strategies in single cell scenario for

OFDMA networks (3 months)

• Investigation on existing ICI coordination techniques for multi-cell OFDMA networks

(3 months)

• Design of integrated packet scheduler and ICI coordination for coordinated

scheduling between two neighbouring cells (7 months)

• Design of integrated PS and ICI coordination for coordinated scheduling between

three neighbouring cells (3 months)

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Time Plan

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Activity 2012 2013

Simulation

Framework

Investigation

of existing PS

Investigation

of existing ICI

techniques

Algorithm

Development for 2

cells

Algorithm

Development for 3

cells

References

1. Kyuho Son; Song Chong; Veciana, G.; , "Dynamic association for load balancing and interference avoidance in multi-

cell networks," Wireless Communications, IEEE Transactions on , vol.8, no.7, pp.3566-3576, July 2009

2. Xu Kai; Tao Xiaofeng; Wang Ying; Zhang Ping; , "Inter-Cell Packet Scheduling In OFDMA Wireless Network," Vehicular

Technology Conference, 2007. VTC2007-Spring. IEEE 65th , vol., no., pp.3115-3119, 22-25 April 2007

3. Fodor, G.; Koutsimanis, C.; , "A Low Intercell Interference Variation Scheduler for OFDMA Networks," Communications,

2008. ICC '08. IEEE International Conference on , vol., no., pp.3078-3084, 19-23 May 2008

4. Falconetti, L.; Hoymann, C.; , "Codebook based Inter-Cell Interference Coordination for LTE," Personal Indoor and

Mobile Radio Communications (PIMRC), 2010 IEEE 21st International Symposium on , vol., no., pp.1769-1774, 26-30 Sept.

2010.

5. Xinying Gao; Anxin Li; Kayama, H.; , "Low-complexity downlink coordination scheme for multi-user CoMP in LTE-

Advanced system," Personal, Indoor and Mobile Radio Communications, 2009 IEEE 20th International Symposium on , vol.,

no., pp.355-359, 13-16 Sept. 2009

6. Jianchi Zhu; Xiaoming She; Xiang Yun; Lan Chen; Otsuka, H.; , "A Practical Design of Downlink Coordinated Multi-Point

Transmission for LTE-Advanced," Vehicular Technology Conference (VTC 2010-Spring), 2010 IEEE 71st , vol., no., pp.1-6,

16-19 May 2010

7. Jing Liu; Yongyu Chang; Qun Pan; Xin Zhang; Dacheng Yang; , "A Novel Transmission Scheme and Scheduling

Algorithm for CoMP-SU-MIMO in LTE-A System," Vehicular Technology Conference (VTC 2010-Spring), 2010 IEEE 71st ,

vol., no., pp.1-5, 16-19 May 2010.

8. Heath, R.W.; Tao Wu; Soong, A.; , "MIMO Spatial Mode Adaptation at the Cell Edge Using Interferer Spatial

Correlation," Vehicular Technology Conference, 2009. VTC Spring 2009. IEEE 69th, vol., no., pp.1-6, 26-29 April 2009.

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