ITU-R WP 5D Meeting – Dresden

Qualcomm-Germany LTE-Advanced Activities

Jamshid Khun-Jush

15 October 2009

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Optimized utilization of resources

Plug-n-Play Relays, Picos, Femtos, RRH

LTE-Advanced Goals

Robust network deployment

Resource PartitioningCoordinated Multi-Point Tx

HeterogeneousNetworks

Higher Peak User Rate

DL MIMO up-to 8x8UL MIMO up-to 4x4

InterferenceManagement

Higher OrderMIMO

Flexible utilization ofResources

Multi-Carrier,Inter-Band Aggregation

CarrierAggregation

Flexible & Faster Network

Deployment

improved Spectral

Efficiency & Fairness

Greater Flexibility with Wideband

Deployment

Ubiquitous & cost effective

broadband

• Candidate features should provide:• enhanced user experience

• improved spectral efficiency

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Heterogeneous Network Deployment Vision

• Network expansion due to varying traffic demand & RF environment– Resulting in change of network topologies

– Cell-splitting of traditional macro-centric planned deployments is complex and iterative

– Indoor coverage and need for site acquisition add to the challenge

• Future network deployments based on Heterogeneous Networks (HNs)– Deployment of Macro eNBs for initial coverage only

– Addition of Pico/Home eNBs and Relay stations for incremental capacity growth & richer user experience

• Improved in-building coverage and flexible site acquisition with low power base stations• Relays provide coverage extension with no incremental backhaul expense

Need for Flexible and Low-Cost Network Deployment Using Mix of Macro, Pico,

Relay, RRH and Home eNBs

MacroHNB

Core Network

Internet

RelayPico

Backhaul

Relay Backhaul

Pico Pico

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Heterogeneous Network Performance Improvement

• Strong interference scenarios exist in heterogeneous networks– CSG cells and unplanned deployments will lead to higher interference

• Inter-cell fairness becomes more important in dense HNs – Large variability in loading across small cells– Need to equalize performance of users with similar QoS requirements

• “Intelligent UE association” requires more protection against interference– In LTE Rel-8, a UE associates with an eNB with the best DL signal– UE association with an eNB with a weaker SINR is required under certain conditions

• Resulting in a better spectral efficiency and network capacity

• ⇒ Advanced Interference Management (AIM) techniques required– Provides robust performance– Improves inter-cell fairness in heterogeneous network– Enables gains in spectral efficiency

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Macro Network Performance Improvement

• Average Spectral efficiency and cell edge user throughput to be improved compared to LTE Rel. 8 in the order of 40% (TR 36.913 & R1-072444)

• Inter-cell interference is the bottleneck– In frequency reuse 1/1 the SINR values at cell edge are about -10 dB

• ⇒ Advanced Interference Management techniques required

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LTE Release 8 Interference Management

• Capabilities:– X2 backhaul based– eNBs indicate resources on which

they intend to generate high UL or DL interference in other cells

– eNBs indicate UL interference levels (low/medium/high) on each resource block

– eNBs can advertise TX power on different resource blocks of DL

X2

LTE Core Network

• Limitations:– Interference indications and Tx power advertisements are too coarse (binary/ternary)

– Semi-static resource reservation insufficient for bursty traffic– Response to the interference indicator messages is left unspecified

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Advanced Interference Management in LTE-A

• Coordinated Multipoint (CoMP) transmission techniques are considered as promising candidates for efficient IM to improve both cell edge and system throughput

• Examples of CoMP– Scheduling Coordination (SC) between cells with data transmission over one radio leg

– Joint processing/transmission (JP/T) with data transmission over multiple radio legs (referred to also as Network MIMO)

Joint Processing/Transmission(JP/T) CoMP

Coordinated Scheduling (CS) CoMP

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Qualcomm-Germany LTE-A Research Activities

• Research Work On CoMP

– Both Macro and Heterogeneous Networks considered– Joint Processing/Transmission

• MAC architecture

• Cell clustering

• Coherent transmission and pre-coding

• 3GPP compliant

– Scheduling Coordination• Interference avoidance & reduction strategies in spatial domain

– Related Topics• Channel estimation and “reference signal” design for multiple legs

• IMT-Advanced Evaluation– WINNER+: External Evaluation Group of ITU-R WP 5D

• Evaluation of LTE-A as an IMT-Advanced proposal

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Basic Idea of JP/T CoMP

• The same information is transmitted from multiple cells to the target UE

• Cooperation across X2 interface to exchange scheduling information

• Challenges (1 and 2 valid for CS CoMP as well)1. Appropriate cluster strategy

• Which sectors should cooperate?

2. Joint scheduling to efficiently allocate network resources across sectors

• How should the PRBs be allocated across the sectors

3. SINR losses for JP/T CoMP• What is the impact of multiple legs

on channel estimation?

Master Slave

Gains achieved by applying over the air combiningI. Power gainII. Interference reductionIII. Frequency diversity

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JP/T CoMP Architecture

• A cluster consists of a set of sectors

• One preconfigured master sector in each cluster

• One HARQ entity per UE per cluster

• All HARQ entities located in the MAC of the master sector

• A central scheduler in the master sector manages all resources of a cluster

• The master sector distributes scheduling information to the transmission points over X2

Transmission Point 1

= Anchor Sector Transmission Point 2

= Slave Sector

Master Sector

Transmission Point 1

= Anchor Sector = Master Sector

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CS-CoMP: BS Coordination Beam Selection

• Problem: Strong interference if adjacent cells transmit at the same time/frequency to the same location

• Goal: Avoid interference in the spatial domain• Idea: Identify worst interferer, avoid “collision”

– LTE Rel. 8: Codebook of six pre-coding matrices defined for 2Tx (4 rank 1, 2 rank 2)

– Prevent interferers from using “most destructive” pre-coding matrices, i.e. further restrict codebook for interferers

• Properties: + full bandwidth available at each eNB+ no impact on air interface- impact on multiuser diversity

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Conclusions

• LTE-Advanced Goals– Flexible and Faster Network Deployment

• Heterogeneous Networks

– Better Coverage and Improved Spectral efficiency (Cell Edge and Average)• Robust Interference Management

– Greater Flexibility with Wideband Deployments• Wider Bandwidth by Carrier Aggregation Across Bands

– Ubiquitous & Cost Effective Broadband• Higher Peak User Rate by Higher Order DL and UL MIMO

• Qualcomm-Germany performs research on the LTE-Advanced features– Participation in the current and future funded projects

• According to a current Press Release, EC has allocated 18 Million Euro to such activities

– Development of concepts for Coordinated Multi-Point Transmission in the context of Easy-C project

– Evaluation of LTE-Advanced as an IMT-A proposal in the context of WINNER+ project