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A Leaner Carrier for the New 5G Air InterfaceKilian Roth, Cecilia Carbonelli, Michael Faerber, Josef A. Nossek
Glasgow
11 May 2015
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Motivation of a leaner carrier
Improved spectral efficiency and cell edge throughput
More flexible control channel allocation
Reduced reference overhead
Reduced interference
Reduced common reference symbols
Improved base-station interference coordination
Reduced base-station power consumption
Micro-sleep of RF front-end possible
Possible evolutionary solution for 5G waveform
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Open aspects of 3GPP discussion
Sufficient tracking performance in challenging scenarios
Frequency offset tracking
Timing offset tracking
Standalone operation
Broadcast channel transmission scheme
Channel estimation broadcast channel
Control channel resource allocation
Uplink HARQ ACK/NACK
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Lean carrier frame structure
4Time
Freq
uen
cysubframe with common reference symbolscontrol channel
data channel
sync symbols
broadcast channel
demodulation reference symbols
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Timing and frequency offset estimation
5
Estimation of frequency and timing offset
Based on correlation of reference symbols
Common reference symbols and synchronization symbols
Demodulated reference symbol
𝐷𝑘,𝑙 = 𝑒𝑗φ𝑙(ε𝑓)𝑒𝑗φ𝑘(ε𝑡)𝐻𝑘,𝑙 +𝑊𝑘,𝑙𝑋𝑘,𝑙
∗
φ𝑙 ε𝑓 = 2π𝑙ε𝑓 𝑁+𝑁𝑔
𝑁, φ𝑘 ε𝑡 = −
2π𝑘ε𝑡
𝑁
Symbol correlation
ε𝑓 =< 𝐷𝑘,𝑙𝐷𝑘,𝑙+𝐿
∗
−2π𝐿(1+𝑁𝑔
𝑁), ε𝑡 =
< 𝐷𝑘,𝑙𝐷𝑘+𝐾,𝑙∗
−2π𝐾/𝑁
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Offset Tracking Loop
6
Estimation
delay
Loop Filter+Compensa
tion
εεC
ε
Compensated offset
Estimated offset
εC
Different loop filters possible
FIR filter
IIR filter
Adaptive filter or other algorithms possible
Simple IIR filter optimized for each scenario separately is used
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Frequency offset tracking fixed offset 200 Hz
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Frequency-offset tracking High Speed Train (HST)
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Timing offset tracking fixed offset 1μs
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Broadcast Channel Description
10
Purpose of Broadcast channel
Primary channel to access system information
Enable initial cell access
Assumptions
Same payload
Same reserved area
Design challenges in LCT
No Tx-Div possible
No channel estimation averaging across subframes
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Broadcast channel CE options
11
Frequency filtering
Timefiltering
sync symbols
common reference symbols
broadcast channel
CE based on common reference symbols and/or sync symbols
Synchronizations symbols CE advantages
More reference symbols
Simpler and less MMSE filters
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Broadcast channel BLER ETU 70Hz low correlation
12
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Standalone Lean carrier aspects
13
Resource allocation of control channel
Flexibility simplicity tradeoff
Common search space allocation limited by broadcast information bits
Allocation should enable base-station control channel interference coordination
Uplink HARQ ACK/NACK in control channel
Reduced overhead because HARQ bits not protected by FEC
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Conclusion
14
Parameter estimation for a lean carrier
Frequency offset tracking feasible
Timing offset tracking feasible
Minor impact of reduced reference symbols
Throughput performance equal improvement compared to LTE
More flexible control overhead
Reduced reference overhead
Broadcast channel performance
BLER comparable to LTE/LTE-A
Improvement by synchronization symbols usage possible
Possible candidate for a 5G waveform
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in cooperation with
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Control channel resource allocation
16
Control Channel PRBSubframe PRB
eNodeB 1 eNodeB 2 eNodeB 1 eNodeB 2 eNodeB 1 eNodeB 2
a) b) c)