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

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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

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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

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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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