Integrated RoF Network Conceptfor Heterogeneous / Multi-Access
5G Wireless System
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Yasushi YamaoAWCC
The University of Electro-Communications
Outline
GoalCreate concept of 5G smart backhaul network withRoF transmission and develop enabling technologiesfor it
Outline Background
Backhaul NW with RoF Transmission
Nonlinearity Issues in Analog RoF Transmission
Advanced DPD technique
Optical Power Supply
Conclusion 1
From 4G to 5G
2
5G Radio Access Network Architecture will be changed to accommodate the diversity of ;
Different access protocols with wide range of spectrumfrom 700 MHz to more than 6 GHz (~28 GHz?)
Heterogeneous deployment with different cell sizes,
Carrier aggregation (CA) and dual access from UEs,
Cooperated multiple transmission (CoMP), massive MIMOand distributed antenna systems (DSA).
Separation of C-plane and U-plane is being studiedto achieve more efficient and flexible use of radio resources.
Requirements for Backhaul NW
3
High bandwidth of 10 Gbps or more
Accommodate different protocols such as 4G, 5G, WLAN that have different bandwidth and carrier frequencies
Adaptation to CA, Dual Access, CoMP, MIMO, DSA
Support C-plane separation architecture
Heterogeneous cell deployment support
5G backhaul NW should be more flexible, scalable and smartto enable RAN virtualization.
Backhaul NW with RoF Transmission
4
Radio over Fiber (RoF) technology will provide advantages of;
Simple and Transparent
High bandwidth (~10GHz/ each λ) Low loss
Optical power supply capability
Transparent RF signal transmission in the NW is importantto make the NW as simple as possible with scalability.
Can it accommodate concurrent multi-band operationin the heterogeneous environment ?
Can it support C-plane separation architecture and RANvirtualization/reconfiguration?
Proposed RoF Backhaul NW
5
WDM RoF networks Pico & Femto BTSs with Macro BTS.
Macro BTS(RoF Center)
RRM
TRxRF MODEM
Distr. ANT(RoF Terminal)
TRx
Pico BTS(RoF Terminal)
TRx
Femto BTS(RoF Terminal)
TRx
OpticalIP NW
> 4 MIMO TxInter‐band CA
Femto BTS(RoF Terminal)
TRx
2‐4 MIMO TxIntra‐ band CA
2‐4 MIMO TxIntra‐ band CA
4‐8 MIMO TxInter‐ & Intra‐ band CA
WDM‐PON
Optical/ Electrical Converter
E/O+OpPS
Macro BTSRRM
Distr. ANT(RoF Terminal)
TRx
WDM RoF Fiber
OpPS: Optical Power SupplyRRM: Radio Resource ManagerCA: Carrier Aggregation
> 10W < 10W
~ 0.2W
~ 0.2W
Macro Cell
Proposed WDM Assignment
6
Optical wavelengths λ0 ~ λm are assigned to;
λ0: C-plane info. for each cell including assignment of carriers.λ11: RoF MIMO stream 1 for the 1st group of carriers.λ12: RoF MIMO stream 2 for the 1st group of carriers.
λ21: RoF MIMO stream 1 for the 2nd group of carriers.λ22: RoF MIMO stream 2 for the 2nd group of carriers.
f
CR6 CR7C-PL
λ0
Ex. Down stream WDM signals can be broadcast to BTSs inside Macro Cell.Each BTS choose necessary streams according to C-plane information.
CR5CR4CR3CR1 CR2
λ
RoFsignals
Two Types of RoF for Mobile NW (1)
7
Digital RoF is currently used in 3G/4G networks.
12 bit/100 Msps= 1.2 Gbps
For 400 MHz 5G signal, 24 Gbps transmission/channel
Considering 8 MIMO transmissions, 192 Gbps is required!WDM (Wave Length Multiplexing) is mandatory.
x 60
Common fIF= 30 MHz
Up Conv.
RFnBPF×
IFD-A PA
SM FiberO/EDown Conv.
to IF
×IF
BPFIF
A-D
MUX
Down Conv. to IF
× IFBPF
IFA-D
RF120MHz
BW E/O
RFn20MHz
BW
Optical transmission
RFCOM
B.
Up Conv.
RF1BPF×
IFD-A PA
DE MUX
BW around 10 GHz(without WDM)
Optical transmission rate
~ 1.2 n Gbpsfor n RF channels
of 20 MHz BW
Two Types of RoF for Mobile NW (2)
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Analog RoF does not increase the bandwidth.Only the highest RF frequency is limited by RoF bandwidth.
It has no ADC/DAC nor up/down converters.
RF1800 MHz
RF21500 MHz
SM Fiber
O/EE/O
Optical TransmissionRFn
6000 MHz
RF1BPF PA
RFCOMB.
RFnBPF PA
to ANT
BW around 10 GHz(without WDM)
RFCOMB.
Hardware cost will be significantly reduced.
However, multicarrier signal is vulnerable for Nonlinear transmission.
Example;
Mach-Zehnder (MZ) optical intensity modulatorType: T • MZH1.5-10PD-ADC-S-Y-Z
Optical Modulator E/O Characteristic
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50
0.10.20.30.40.50.60.70.80.9
11
Input DC voltage (V)
Out
put o
ptic
al in
tens
ity (m
W)
V
biasV
9
MZ modulator has sinusoidal E/O characteristic that causesintermodulation distortion (IM) due to odd-order nonlinearity.
Direct Laser Diode modulator has more complicated E/O characteristic that produces both even- and odd-order nonlinearity.
High PAPR multicarrier signal suffers from E/O nonlinearity
Nonlinear Compensation of Analog RoF
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Ultra-Wideband Digital Predistortion can solve nonlinearity of E/O converters.
It keeps the simple structure of analog RoF.In the near future, digital hardware processing technologies will allow ultra-wideband operation of DPD.
RF1RF2
RFn
Digital RF
COMB.O/E
RF1BPF
RFnBPF
E/O
O/E
DPD
A-DD-A
DigitalBB signal withcarrier info.
Optical Transmission
WDM design that considers DPD bandwidth is still necessary.
WDM Assignment Grouping
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RoF signals are grouped to satisfy the bandwidth of DPD.
λ0: C-plane info. for each cell including assignment of carriers.λ11: RoF MIMO stream 1 for the 1st group of carriers.λ12: RoF MIMO stream 2 for the 1st group of carriers.
λ21: RoF MIMO stream 1 for the 2nd group of carriers.λ22: RoF MIMO stream 2 for the 2nd group of carriers.
f
CR6 CR7C-PL
λ0
Ex.
CR5CR4CR3CR1 CR2
1st carrier group 2nd carrier group
λ
RoFsignals
Wideband DPD Design Method
12
Existing DPDs have been designed to feedback full bandwidth of nonlinear output signal, requiring 3 to 5 times wideband ADC.
Band-limited feedback signal
With SENF (Spectral Extrapolation of Narrowband Feedback) technique, feedback bandwidth can be same as the signal bandwidth or even less.
3-5 times wider bandwidthfor nonlinear output
Spectral Extrapolation of
Narrowband Feedback signal
yyΞP ˆl yΞP ˆu
Bl
B
B 3B~5B
SENF DPD Design Example
13
More than 100 MHz Linearization is possible with current FPGAsby SENF method.
with SENFDPD
Without DPD
RF-DAC2.5 Gsps
QDEM+ADC
250 Msps
RF: 1.75 GHzIn Out
100MHz bandwidth DPDby Xilinx Kintex7 FPGA
8 x 20MHz LTE multicarrier signal (160MHz)
400 MHz and beyond linearization will be achieved shortly by DPD.
Power Supply via Optical Fiber
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Power supply via optical fiver makes it easy to deploy femto cells.
Max. input optical power for Single-mode fiber ~ 1W /fiberfor Multi-mode fiber > 5W /fiber
9 μm core50~62 μm core
(2) MMF-WDM type
DC supply~ 640 mW
O/EWDME/ORF signal1550 nm
830 nm, 4WHigh PowerLaser Diode 830 nm, 2W
Photonic PowerConverter
WDM
1550 nm
RF signalRoF+Power
DC bias
MMF 500m
Efficiency ~32%
(1) Separate SMF type
DC supply~ 360 mW
/fiber
Photonic PowerConverter
O/EE/ORF signal 1550 nm RF signal
DC bias
SMF 2km
Efficiency ~28%
High PowerLaser Diode 1480 nm SMF 2km
1.8 W/ fiber 1.3 W/ fiber
Conclusions
Propose WDM RoF backhaul network architecture with a C-plane / carrier group wavelength assignment scheme.
Wideband Analog RoF transmission is considered to reduce hardware costs.
Ultra-Wideband Digital Predistortion technique such as SENFcan solve nonlinearity of E/O converters.
Optical power supply will help to deploy femto cells.
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[1] Y. Ma, Y. Yamao, Y. Akaiwa, and K. Ishibashi, "Wideband Digital PredistortionUsing Spectral Extrapolation of Band-Limited Feedback Signal", IEEE Trans.Circuit and Systems-I, 2014. (available in IEEE Explore)
[2] J. Sato and M. Matsuura, “Radio-over-fiber transmission with optical powersupply using a double-clad fiber,” Proc. CLEO-PR & OECC/PS 1013, TuPO-8,2013.
This work is supported by the Ministry of Internal Affairs and Communications (MIC) of Japan under the SCOPE Program #135003118 in Year 2013.
Acknowledgement
References
Thank you for listening!
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