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LTE-Advanced Field TrialCoordinated Multipoint Reception
Uwe Dtsch, Bell Labs
July-2010
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Motivation
Coordinated multipoint transmission / reception (CoMP)
Candidate technology for LTE-Advanced (a.k.a. network MIMO)
Enhance cell edge spectral efficiency
More consistent QoS throughout the network
Enhanced user experience
CoMP particularly promising in UL
UE transmit power limitation at cell edge
Coherent combining can be realized w/o changes of LTE air interface and
w/o changing the total number of antennas in the network
Significant UL throughput gains observed in simulations
Objectives:
Prove feasibility of UL CoMP in realistic LTE environment
Quantify macro-diversity gains of UL CoMP in the field
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UL CoMP basic principle
Exchange over X2 interface
CoMP with 3 sites
CoMP with 2 sites
Exchange over X2 interface
UL signal from one user isreceived in multiple cells
Radio resources allocatedmultiple times, i.e. multi-userMIMO over multiple cells
Coherent combining of ULsignals in a central unit
Transfer of I/Q samples orsoft bits to the central unit
Over X2 interface or using adistributed RF architecture
LTE eNB
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Framework
Field trials within EASY-C research project
UL CoMP drive test conducted in Berlin testbed
Partners in Berlin trial: Alcatel-Lucent Bell Labs: LTE eNB central processing
Deutsche Telekom Laboratories (T-Labs): antenna sites, fiber links, van
Fraunhofer Heinrich Hertz Institute (HHI): Berlin testbed
Kathrein: remote radio heads
EASY-C research project:
Key technologies for next generation cellular networks
Funded by German government
Partners from academia and industry
Mobile network operators: T-Mobile and Vodafone
Two testbeds in Berlin and Dresden www.easy-c.com
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LTE UL CoMP setup (4Rx)
Architecture: Central processing unit + two distributed
remote radio heads (RRH) with two crosspolarized antennas each
1st RRH on T-Labs building 2nd RRH on Technical University Berlin
About 570m distance between RRH sites
RRHs connected via CPRI optical fibre links
Length of fibre links ~3km
System parameters: 2.6GHz carrier
5 MHz bandwidth
UL peak data rate = 8.5 Mbps (16QAM SIMO)
LTE eNodeB
CentralProcessingUnit
2.5Gbps CPRI fibre links
~3km length
RemoteRadioHeads
+
antennas
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UL COMP Lab measurements with 2Rx and 4 Rx for fading profile
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
-5 0 5 10 15 20 25 30 35
UL SINR per path [dB]
UL
Throughput[kBit/s]
4Rx
2Rx
LTE eNodeB
2.5GbpsCPRI fibre
links
RRHs
FadingEmulator(Spirent)
Rx1
Rx2
Rx3
Rx4
Measurement Set up
Tx1
Test mobile
Splitter1:4
Main results:
Gains confirmed
increased received energy for 4RX vs. 2RX 3dB
plus diversity gain depending from fadingchannel
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
0 5 10 15 20 25 30 35
(estimated) UL SINR [dB]
UL
Throughput[kBit/s]
4Rx
2Rx
3dB+ diversity gain
diversity gain
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Field Test Berlin
T-Labs TU Berlin
Heinrich Hertz Institute
T-Labs
HHI
TUB
Optical fiber network
~570m distance
User equipmentcarried in van
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Consistency Check : Static user @ cell edge
static field measurement matches lab data
approximately 4 dB gain in SINR
80 % throughput gain
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
0 5 10 15 20 25 30 35
(estimated) UL SINR [dB]
UL
Throu
ghput[kBit/s]
4Rx
2Rx
diversity gain
2 Rx TLabs
2 Rx TUB
4 Rx TLabs
4 Rx TLabs
Simulated a cell edge situation:
- Static UE was positioned outside HHI (cell edge position, no velocity)
- Lab measurements for comparison
2 Rx TLabs/TUB
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Determination of serving cell
HHI
1Tx2Rx
T-LabsTUB
2Rx 2Rx UL SIR T-Labs > UL SIR TUB
2Rx UL SIR TUB > UL SIR T-Labs
Mapping of strongest Cell for drive route
T-labs site dominates
Handovers would not be toofrequent
UL
SIR(d
B)
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UL Throughput gain of Macro Diversity compared to 2Rx Handover
1Tx2Rx
T-Labs
HHI
TUB
2Rx
Serving Cell TUB
Significant MacroDiversity gaincompared toHandover Scenariowith 2 Rx for SIRthreshold 0 dB
Throughput[kBit/s]
Position
Serving Cell TUB
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TLabs Site: Macro Diversity compared to 2Rx Handover
Serving Cell: TLabs
Significant throughput improvementwith Macro Diversity compared to
Handover Scenario with 2 Rx for SIRthreshold 0 dB
Serving Cell: TLabs
Significant improvement of UL SINR forthe Macro Diversity Case
SINR gains, but throughput limited by modulation 64 QAM would help here
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Field Test Berlin
T-Labs TU Berlin
Heinrich Hertz Institute
T-Labs
HHI
TUB
Optical fiber network
~570m distance
User equipmentcarried in van
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Throughput improvement
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Throughput improvement
TUB
2Rx
1Tx
2Rx
HHI
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Throughput and SNR improvement
Throughput CDFs show the
improvement in throughput
and SINR
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Summary
Industrys first live field test of CoMP in LTE network
Feasibility of UL CoMP in realistic LTE environment has been proven
Central processing with distributed RRHs (>500m apart) Digital Baseband transmission over optical fibers of ~3km length
UL coherent combining validated for MMSE receiver
No issues with optical transmission delay
Receiver can handle delay spread and alignment of timing advance
Quantitative results of test:
Significant UL throughput enhancements observed for user at cell edge
Potential improvement identified for 64 QAM modulation
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www.alcatel-lucent.comwww.alcatel-lucent.com
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