Issues for Multi-Band Multi-Access Radio Circuits in 5G Mobile Communication

Transcription

1 Issues or Multi-Band Multi-Access Radio Circuits in 5G Mobile Communication Yasushi Yamao AWCC The University o Electro-Communications LABORATORY

2 Outline Background Requirements or 5G Hardware Issues or Tx and Rx Advanced DPD techniques Post compensation technique or Rx Reconigurable BPF Conclusion 1

3 From 4G to 5G 5G Mobile Communication will be changed to accept the diversity o ; Dierent access protocols with wide range o spectrum rom 700 MHz to more than 6 GHz (~millimeter wave) Heterogeneous deployment with dierent cell sizes, Carrier aggregation (CA) and dual access rom UEs, Cooperated multiple transmission (CoMP), massive MIMO and distributed antenna systems (DSA). In order to achieve more eicient and lexible use o radio resources, separation o C-plane and U-plane has been studied.

4 Requirements or 5G Hardware High bandwidth o 10 Gbps or more Utilizing widely-spread requency bands rom current UHF to low SHF, high SHF and millimeter waves Low-power/cost small base station and Dual Access to both Macro- and small-cells with dierent requency bands High Accuracy RF signals are required to increase spectral eiciency 5G hardware is required to be more lexible, accurate, linear and low-cost. 3

5 Issues or Transmitter Keeping linearity and power eiciency in a wider unit RF bandwidth o 100MHz or more. Keeping linearity and power eiciency under concurrent multiband operation Nonlinear Compensation Techniques should be developed that can work in a wider bandwidth and multi-band environments. We proposes advanced Digital Predistortion (DPD) techniques called SENF and SFFB 4

6 Issues or Receiver Receiver ront-end aces a variety o incoming signals with power o wide dynamic range. Desired signals are not always stronger than others. Under concurrent multiband operation, near-ar problem increases chance o inter-band modulation called "crossmodulation distortion". Receiver Nonlinearity Compensation technique and reconigurable RF BPF as pre-selector mitigate the issues. We proposes a Post Compensation technique and Reconigurable BPF or concurrent dual-band receiver. 5

7 1. Wideband DPD Design Method Existing DPDs have been designed to eedback ull bandwidth o nonlinear output signal, requiring 3 to 5 times wideband ADC. Iterated Nonlinear Modeling with Spectral Extrapolation o Narrowband Feedback signal B B I Q DPD Nonlinear Modeling with Spectral Extrapolation and DPD Training DAC Band-limited eedback signal ADC ~B Quad MOD LO Quad DEMO PA 3B~5B 3-5 times wider bandwidth or nonlinear output B l With SENF (Spectral Extrapolation o Narrowband Feedback) technique, eedback bandwidth can be same as the signal bandwidth (or even less) [1]. P Ξyˆ l ŷ P Ξyˆ u 6

8 SENF DPD Equivalent Baseband Diagram k( ); polynomial nonlinear unction x k 1 ( ) k ( ) 1 DPD k(x)β Analog Domain PA y k P ( ) P h β ŷ Identiication w 1 s Extrapolation (1) h w hx yˆ (3) () 7

9 SENF DPD by FPGA More than 100 MHz Linearization is possible with current FPGAs with 50 Msps ADC by SENF method. RF: 1.75 GHz In Out QDEM+ ch ADC 50 Msps RF-DAC.5 Gsps with SENF DPD Without DPD 8 x 0MHz LTE CA signal (160MHz) 160MHz bandwidth DPD by Xilinx Kintex7 FPGA 8

10 SENF DPD by Experiment (1) More than 300 MHz Linearization is conirmed in Experiment []. 30MHz 30MHz eedback bandwidth DPD by measurement set up 16 x 0MHz LTE CA signal (30MHz) Linearization o signal with 500 MHz and beyond bandwidth will be achieved soon by DPD. 9

11 SENF DPD by Experiment () Proposed DPD can compensate non-continuous CA signal. 4 x 0MHz LTE CA signal (40MHz) 6 x 0MHz LTE CA signal (80MHz) Linearization o 900 MHz and beyond RF bandwidth is achieved by SENF DPD. 10

12 . Concurrent Dual-Band DPD Design Existing Dual-Band DPDs have two eedback path with two sets o Down Converter and ADC. x 1 x DPD1 DPD v v 1 DAC DAC Up Converter L1 Up Converter 1 Dual Band PA Coupler L DPD Parameter Adjuster y 1 y ADC ADC Down Converter Down Converter High-speed ADCs are expensive! 11

13 SFFB Dual-Band DPD Spectrum Folding Feedback (SFFB) DPD multiplexes two RF spectra into common IF [3]. x 1 DPD1 v 1 DAC Up Converter 1 L1 Dual Band PA Coupler x DPD v DAC Up Converter (, DPD Parameter Adjuster y 1 y Post Processing & PA Modeling L IF ADC 1 Down Converter = Spectrum Folding Down Converter Two RF signals are down-converted into a common IF as a multiplexed signal. 1

14 SFFB Dual-Band DPD x 1 Spectrum Folding Feedback (SFFB) DPD multiplexes two RF spectra into common IF [3]. DPD1 v 1 DAC Up Converter 1 B 1 B B 1 B x DPD v DAC L1 Up Converter L Dual Band PA Coupler lo 1.75 GHz.75 GHz (, 1 requency max(b 1, B ) max{b 1, B } y 1 DPD Parameter Adjuster y Post Processing & PA Modeling ADC Down Converter SFFB Down Converter = GHz Lower RF-band signal spectrum is inverted. y() t y () t y () t * 1 requency requency Compensated in baseband by inverting input x 1 13

15 SFFB Multi-Band Extension With SFFB (Spectral Folding Feedback) technique, multiband signals can be olded into one IF bandwidth. 1,, 3, 4 lo 1 1 lo 1 1 lo 1 1 lo requency 0 lo lo 1 1 lo 3 1 lo requency 0 lo requency 0 lo 1 1 requency 14

16 SFFB Dual-Band DPD by Experiment AM-AM characteristics o PA Output Power (dbm) GHz.75GHz = 1.75 GHz =.75 GHz Input Power (dbm) IF = 500 MHz Normalized Power (db) lo =.5 GHz Frequency (MHz) Folded eedback signal without DPD 15

17 SFFB Dual-Band DPD by Experiment Scenario 1; 10 MHz LTE(1.75 GHz ) + 0 MHz LTE (.75 GHz) Power Spectral Density (dbm/hz) Without DPD SFFB DPD Conv. DPD Power Spectral Density (dbm/hz) Without DPD SFFB DPD Conv. DPD Frequency (GHz) Frequency (GHz) Scenario ; 0 MHz LTE (1.75 GHz) + 4 x 0 MHz LTE CA (.75 GHz) Power Spectral Density (dbm/hz) Without DPD SFFB DPD Conv. DPD Power Spectral Density (dbm/hz) Without DPD SFFB DPD Conv. DPD Frequency (GHz) Frequency (GHz) 16

18 3. Cross-Modulation due to Multi-Band Access Near-ar problem increases chance o inter-band modulation Far & weak L,P L 0 90 ADC ADC I Q EVM (%) macro BS H,P H Near & strong LNA L Synthesized Oscillators H ADC I P -0-0 H (dbm) P L (dbm) (a) EVM or L 10 emto/ micro macro / / repeater Sel-Generated Distortion Inter-band modulation 0 90 Sel-Generated Distortion ADC Q EVM (%) P H (dbm) P L (dbm) 0 10 L H L H H L (b) EVM or H Not Cared 17

19 Post-Compensation o Receiver Nonlinearity L y L s L x L (n) x H (n) DDC or ω L ADC 3rd IM y L y L c' 30 LNA 3rd CM c' 3 DDC or ω H ADC y H y H y L 5th IM c' 50 digital domain Channel Filter s L (n) Compensator or y L (n) H y L (n) y H (n) Time Alignment y L 4 y L 5th CM y H y L y L 5th CM y H 4 y L c' 5 c' 54 Channel Filter s H (n) Compensator or y H (n) By polynomial y H Q-1 y L c' Q,Q-1 Compensator diagram or y L Blind & Adaptive Nonlinear Compensation method is necessary [4]. 18

20 How to Determine Compensator Coeicients? Proposed algorithm determines the compensator coeicients so as to minimize outband spectra power or each band. Minimization 0 Frequency Shit Desired Signal Band This works successully because nonlinearity generates both inband and outband components and they are correlated. The key is separation ilter that eliminates the in-band signal and maximizes SNR o outband distortion detection. 19

21 Experimental Results Power Spectral Density (db) Uncompensated 3rd order 5th order 7th order Frequency (MHz) (a) Output spectra at L Power Spectral Density (db) Frequency (MHz) (b) Output spectra at H 1 =.35 GHz =.65 GHz Power levels o L and H in (a)/(b) are -10 dbm and 6 dbm, respectively. 7th-order compensation presents the best results. Proposed compensator improves EVM in both bands. (c) EVM or L signal (d) EVM or H signal Maximum acceptable input power increases more than 4 db. 0

22 4. Reconigurable RF BPF Reconigurable BPF can adapt the receiver lexibly to the change o access channels and prevent unexpected cross-modulation distortions in multi-band/multi-access operation. Power (dbm) Frequency (GHz) Example o nonlinear output spectrum under concurrent dual-band operation. Some o them locate near the operating band. 1

23 SHF Dual-band Reconigurable BPF Low SHF (< 6 GHz) reconigurable BPF and High SHF wideband BPF are integrated or concurrent dual-band access. High SHF wideband BPF section IC Resonator ISC Resonator OC DIP DIP IC Reconig. Resonator1 ISC Reconig. Resonator OC Low SHF Reconigurable BPF section DIP: Diplexer IC: Input Coupling circuit ISC; Inter-Stage Coupling circuit OC: Output Coupling circuit

24 -stage 3-bit Low-SHF Reconigurable BPF OPEN OPEN l 3 l 3 l 1 SW l 1 3 SW 6 SW 1 SW SW 4 SW l 5 l l 0 l 0 L in L out Z g V g L inter L cut L cut l 1 l 1 SHORT SHORT 1st stage nd stage Z L S 1 (db) Center Frequency; 3.1 to 4.6 GHz Insertion loss; 1.0~.1 db High SHF BPF and diplexers are under design process Frequency (GHz) 3

25 Conclusions 5G hardware is required to be more lexible, accurate, linear and low-cost. For Txs, advanced DPD techniques called SENF and SFFB are proposed. - SENF saves eedback bandwidth, which enables wider compensation bandwidth. - SFFB enables simple eedback or concurrent dual-band operation. For concurrent dual-band Rxs, Post Compensation technique and Reconigurable BPF are proposed. The results will contribute to improve practical perormance o the 5G system. 4

26 Related Works 1) Y. Ma, Y. Yamao, Y. Akaiwa, K. Ishibashi, Wideband digital predistortion using spectral extrapolation o band-limited eedback signal, IEEE Trans. Circuit and Systems-I, vol. 61, no. 7, pp , July 014. ) Y. Ma and Y. Yamao, Experimental results o digital predistorter or very wideband mobile communication system, Proc. IEEE VTC015-Spring, 6PB-, Glasgow, UK, May ) Y. Ma and Y. Yamao, Spectra-olding eedback architecture or concurrent dual-band power ampliier predistortion, IEEE Trans. Microw. Theory & Tech., Vol. 63, No. 10, pp , Oct ) Y. Ma, Y. Yamao, K. Ishibashi and Y. Akaiwa, "Adaptive compensation o inter-band modulation distortion or tunable concurrent dual-band receivers," IEEE Trans. Microw. Theory & Tech., vol.61, no.1, pp , Dec ) R. Kobayashi, T. Kato, K. Azuma and Y. Yamao, Design and Fabrication o Two-Stage Three-Bit Reconigurable Bandpass Filter Using Brunch Line-Type Variable Resonator, IEICE Trans. Electronics, Vol. E98-C, No. 7, pp , July

27 Acknowledgement A part o this work is supported by the Ministry o Internal Aairs and Communications (MIC) o Japan under the program R&D or the realization o 5G mobile communication system". Thank you or listening! LABORATORY 6