Integrated RoF Network Concept for Heterogeneous / Multi-Access 5G Wireless System

Transcription

1 Integrated RoF Network Concept for Heterogeneous / Multi-Access 5G Wireless System Yasushi Yamao AWCC The University of Electro-Communications LABORATORY

2 Goal Outline Create concept of 5G smart backhaul network with RoF transmission and develop enabling technologies for it Outline Background Backhaul NW with RoF Transmission Nonlinearity Issues in Analog RoF Transmission Advanced DPD technique Optical Power Supply Conclusion 1

3 From 4G to 5G 5G Radio Access Network Architecture will be changed to accommodate the diversity of ; Different access protocols with wide range of spectrum from 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 MIMO and distributed antenna systems (DSA). Separation of C-plane and U-plane is being studied to achieve more efficient and flexible use of radio resources. 2

4 Requirements for Backhaul NW 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 Heterogeneous cell deployment support Support C-plane separation architecture 5G backhaul NW should be more flexible, scalable and smart to enable RAN virtualization. 3

5 Backhaul NW with RoF Transmission Radio over Fiber (RoF) technology will provide advantages of; High bandwidth (~10GHz/ each λ) Simple and Transparent Low loss Transparent RF signal transmission in the NW is important to make the NW as simple as possible with scalability. Optical power supply capability Can it accommodate concurrent multi-band operation in the heterogeneous environment? Can it support C-plane separation architecture and RAN virtualization/reconfiguration? 4

6 Proposed RoF Backhaul NW WDM RoF networks Pico & Femto BTSs with Macro BTS. RRM Macro BTS Optical IP NW 4 8 MIMO Tx Inter & Intra band CA TRx RF MODEM RRM Macro BTS (RoF Center) > 10W < 10W TRx WDM RoF Fiber E/O + Op PS 2 4MIMO Tx Intra band CA Pico BTS (RoF Terminal) TRx Femto BTS (RoF Terminal) ~ 0.2W WDM PON > 4 MIMO Tx Inter band CA 2 4MIMO Tx Intra band CA Macro Cell ~ 0.2W TRx Femto BTS (RoF Terminal) Optical/ Electrical Converter OpPS: Optical Power Supply RRM: Radio Resource Manager CA: Carrier Aggregation TRx Distr. ANT (RoF Terminal) TRx Distr. ANT (RoF Terminal) 5

7 Proposed WDM Assignment Optical wavelengths λ 0 ~ λ m are assigned to; λ 0 : C-plane info. for each cell including assignment of carriers. λ 11 : RoF MIMO stream 1 for the 1st group of carriers. λ 12 : RoF MIMO stream 2 for the 1st group of carriers. RoF signals λ 21 : RoF MIMO stream 1 for the 2nd group of carriers. λ 22 : RoF MIMO stream 2 for the 2nd group of carriers. λ 0 C- PL λ CR1 CR2 CR3 CR4 CR5 Ex. Down stream WDM signals can be broadcast to BTSs inside Macro Cell. Each BTS choose necessary streams according to C-plane information. CR6 CR7 f 6

8 Two Types of RoF for Mobile NW (1) Digital RoF is currently used in 3G/4G networks. RF1 20MHz BW RFn 20MHz BW IF BPF Down Conv. to IF Common f IF = 30 MHz IF BPF Down Conv. to IF x60 IF A-D IF A-D MUX E/O 12 bit /100 Msps = 1.2 Gbps SM Fiber Optical transmission IF D-A For 400 MHz 5G signal, 24 Gbps transmission/channel RFn BPF Up Conv. Considering 8 MIMO transmissions, 192 Gbps is required! WDM (Wave Length Multiplexing) is mandatory. O/E BW around 10 GHz (without WDM) DE MUX Optical transmission rate ~ 1.2 n Gbps for n RF channels of 20 MHz BW IF D-A RF1 BPF Up Conv. PA PA RF COM B. 7

9 Two Types of RoF for Mobile NW (2) Analog RoF does not increase the bandwidth. Only the highest RF frequency is limited by RoF bandwidth. RF1 800 MHz RF MHz RFn 6000 MHz RF COMB. E/O SM Fiber Optical Transmission O/E BW around 10 GHz (without WDM) RF1 BPF RFn BPF PA PA RF COMB. to ANT It has no ADC/DAC nor up/down converters. Hardware cost will be significantly reduced. However, multicarrier signal is vulnerable for Nonlinear transmission. 8

10 Optical Modulator E/O Characteristic Output optical intensity (mw) V V bias Input DC voltage (V) Example; Mach-Zehnder (MZ) optical intensity modulator Type: T MZH1.5-10PD-ADC-S-Y-Z High PAPR multicarrier signal suffers from E/O nonlinearity MZ modulator has sinusoidal E/O characteristic that causes intermodulation 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. 9

11 Nonlinear Compensation of Analog RoF Ultra-Wideband Digital Predistortion can solve nonlinearity of E/O converters. RF1 RF1 BPF RF2 RFn Digital BB signal with carrier info. Digital RF COMB. A-D DPD D-A E/O O/E Optical Transmission O/E RFn BPF It keeps the simple structure of analog RoF. In the near future, digital hardware processing technologies will allow ultra-wideband operation of DPD. WDM design that considers DPD bandwidth is still necessary. 10

12 WDM Assignment Grouping RoF signals are grouped to satisfy the bandwidth of DPD. λ 0 : C-plane info. for each cell including assignment of carriers. λ 11 : RoF MIMO stream 1 for the 1st group of carriers. λ 12 : RoF MIMO stream 2 for the 1st group of carriers. RoF signals λ 21 : RoF MIMO stream 1 for the 2nd group of carriers. λ 22 : RoF MIMO stream 2 for the 2nd group of carriers. Ex. λ 0 C- PL λ CR1 CR2 CR3 CR4 CR5 CR6 CR7 f 1st carrier group 2nd carrier group 11

13 Wideband DPD Design Method Existing DPDs have been designed to feedback full bandwidth of nonlinear output signal, requiring 3 to 5 times wideband ADC. B 3B~5B Band-limited feedback signal 3-5 times wider bandwidth for nonlinear output Spectral Extrapolation of Narrowband Feedback signal B B l With SENF (Spectral Extrapolation of Narrowband Feedback) technique, feedback bandwidth can be same as the signal bandwidth or even less. P Ξyˆ l ŷ P Ξyˆ u 12

14 SENF DPD Design Example More than 100 MHz Linearization is possible with current FPGAs by SENF method. RF: 1.75 GHz In Out QDEM +ADC 250 Msps RF-DAC 2.5 Gsps with SENF DPD Without DPD 100MHz bandwidth DPD by Xilinx Kintex7 FPGA 8 x 20MHz LTE multicarrier signal (160MHz) 400 MHz and beyond linearization will be achieved shortly by DPD. 13

15 Power Supply via Optical Fiber Power supply via optical fiver makes it easy to deploy femto cells. Max. input optical power for Single-mode fiber ~ 1W /fiber for Multi-mode fiber > 5W /fiber (1) Separate SMF type 9 μm core 50~62 μm core RF signal 1550 nm SMF 2km O/E RF signal E/O DC bias (2) MMF-WDM type RF signal DC bias High Power Laser Diode E/O 1550 nm High Power Laser Diode WDM 1480 nm SMF 2km 1.8 W/ fiber 1.3 W/ fiber 830 nm, 4W RoF+Power MMF 500m WDM 830 nm, 2W Photonic Power Converter Efficiency ~28% 1550 nm O/E Photonic Power Converter Efficiency ~32% DC supply ~ 360 mw /fiber RF signal DC supply ~ 640 mw 14

16 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 SENF can solve nonlinearity of E/O converters. Optical power supply will help to deploy femto cells. 15

17 Acknowledgement This work is supported by the Ministry of Internal Affairs and Communications (MIC) of Japan under the SCOPE Program # in Year References [1] Y. Ma, Y. Yamao, Y. Akaiwa, and K. Ishibashi, "Wideband Digital Predistortion Using Spectral Extrapolation of Band-Limited Feedback Signal", IEEE Trans. Circuit and Systems-I, (available in IEEE Explore) [2] J. Sato and M. Matsuura, Radio-over-fiber transmission with optical power supply using a double-clad fiber, Proc. CLEO-PR & OECC/PS 1013, TuPO-8,

18 Thank you for listening! LABORATORY 17