issues for multi-band multi-access radio circuits in 5g
TRANSCRIPT
Issues for Multi-Band Multi-Access Radio Circuits in 5G Mobile Communication
LABORATORYLABORATORYLABORATORY
Yasushi YamaoAWCC
The University of Electro-Communications
Outline
Background
Requirements for 5G Hardware
Issues for Tx and Rx
Advanced DPD techniques
Post compensation technique for Rx
Reconfigurable BPF
Conclusion
1
From 4G to 5G
2
5G Mobile Communication will be changed to accept the diversity of ;
Different access protocols with wide range of spectrumfrom 700 MHz to more than 6 GHz (~millimeter wave)
Heterogeneous deployment with different cell sizes,
Carrier aggregation (CA) and dual access from UEs,
Cooperated multiple transmission (CoMP), massive MIMOand distributed antenna systems (DSA).
In order to achieve more efficient and flexible use of radioresources, separation of C-plane and U-plane has been studied.
Requirements for 5G Hardware
3
High bandwidth of 10 Gbps or more
Utilizing widely-spread frequency bands from 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 different frequency bands
High Accuracy RF signals are required to increase spectral efficiency
5G hardware is required to be more flexible, accurate,linear and low-cost.
Issues for Transmitter
Nonlinear Compensation Techniques should be developed that can work in a wider bandwidth and multi-band environments.
4
Keeping linearity and power efficiency in a wider unit RF bandwidth of 100MHz or more.
Keeping linearity and power efficiency under concurrent multiband operation
We proposes advanced Digital Predistortion (DPD) techniquescalled SENF and SFFB
Issues for Receiver
Receiver Nonlinearity Compensation technique andreconfigurable RF BPF as pre-selector mitigate the issues.
5
Receiver front-end faces a variety of incoming signals with power of wide dynamic range.Desired signals are not always stronger than others.
Under concurrent multiband operation, near-far problemincreases chance of inter-band modulation called "cross-modulation distortion".
We proposes a Post Compensation technique and Reconfigurable BPF for concurrent dual-band receiver.
PAI
DACDPD QuadMOD
Q
QuadDEMO
LO
ADC
Nonlinear Modeling
with Spectral Extrapolation and DPDTraining
1. Wideband DPD Design Method
6
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) [1].
3-5 times wider bandwidthfor nonlinear output
Iterated Nonlinear
Modeling with Spectral
Extrapolation of Narrowband
Feedback signal
yyΞP ˆl yΞP ˆu
Bl
B
B 3B~5B
~B
SENF DPD Equivalent Baseband Diagram
(1)(2)(3)
PAy
y
Extrapolation
xk( ); polynomial nonlinear function
βx)(k
h
Identification
kP( )
k1( )
k2( )
1
2
P
DPD
yhx ˆ
β
Analog Domain
w1s
w2
h
7
SENF DPD by FPGA
More than 100 MHz Linearization is possible with current FPGAswith 250 Msps ADC by SENF method.
with SENFDPD
Without DPD
RF-DAC2.5 Gsps
QDEM+2 ch ADC250 Msps
RF: 1.75 GHzIn Out
160MHz bandwidth DPDby Xilinx Kintex7 FPGA
8 x 20MHz LTE CA signal (160MHz)
8
SENF DPD by Experiment (1)
More than 300 MHz Linearization is confirmed in Experiment [2].
320MHz feedback bandwidth DPDby measurement set up
16 x 20MHz LTE CA signal (320MHz)
Linearization of signal with 500 MHz and beyond bandwidth will be achieved soon by DPD.
320MHz
9
SENF DPD by Experiment (2)
Proposed DPD can compensate non-continuous CA signal.
4 x 20MHz LTE CA signal (240MHz)
Linearization of 900 MHz and beyond RF bandwidth is achieved by SENF DPD.
6 x 20MHz LTE CA signal (280MHz)
10
2. Concurrent Dual-Band DPD Design
Existing Dual-Band DPDs have two feedback path with two sets of Down Converter and ADC.
DPD1
DPD2
Up Converter
Up Converter
DownConverter
DownConverter
DPDParameterAdjuster
fL1
fL2
x1
x2
v1
v2
y1
y2
CouplerDual Band PA
DAC
DAC
ADC
ADC
f1
f2
High-speed ADCs are expensive!
11
Spectrum Folding Down Converter
SFFB Dual-Band DPD
Spectrum Folding Feedback (SFFB) DPD multiplexes two RF spectra into common IF [3].
ADCDPD
ParameterAdjuster
fL1
fL2
x1
x2
v1
v2
y1
Coupler
= 2
y2
Dual‐BandPA
Up Converter
Up Converter
DownConverter
DAC
DAC
PostProcessing
& PA Modeling
( ,
DPD1
DPD2
f1
f2
Two RF signals are down-converted
into a common IF as a multiplexed
signal. 2
12 fffIF
12
SFFB Down Converter
SFFB Dual-Band DPD
ADCDPD
ParameterAdjuster
fL1
fL2
x1
x2
v1
v2
y1
Coupler
= 2
y2
Dual‐BandPA
Up Converter
Up Converter
DownConverter
DAC
DAC
PostProcessing
& PA Modeling
( ,
DPD1
DPD2
f1
f2 221 ffflo
1.75 GHz 2.75 GHz
0.5 GHz
f1 f2frequency
B1 B2
0 f1 f2
B1 B2
frequency02 1
2f f
max{B1 , B2}
212 ff frequency
max(B1, B2)
Lower RF-band signal spectrum is inverted.
Compensated in baseband byinverting input x1*
1 2( ) ( ) ( )y t y t y t
13
Spectrum Folding Feedback (SFFB) DPD multiplexes two RF spectra into common IF [3].
SFFB Multi-Band ExtensionWith SFFB (Spectral Folding Feedback) technique, multiband signals can be folded into one IF bandwidth.
221
1ffflo
221
1ffflo
f1, f2, f3, f4
221
1ffflo
221
1ffflo
f1 f2 frequency0 f3
0 frequency2
211
ffflo
frequency02
211
ffflo
2
132
fff lo
224
3ffflo
213
2ffflo
f4
234 ff
3 2
2f f
212 ff
0 frequency2
211
ffflo
14
SFFB Dual-Band DPD by Experiment
15
-20 -18 -16 -14 -12 -10 -8 -6 -4 -222
24
26
28
30
32
34
36
Input Power (dBm)
Outp
ut
Pow
er
(dB
m)
1.75GHz
2.75GHz
f1 = 1.75 GHzf2 = 2.75 GHz
AM-AM characteristics of PA
-40 -20 0 20 40-90
-80
-70
-60
-50
-40
-30
-20
-10
Frequency (MHz)
Nor
mal
ized
Pow
er (d
B)
f1 + f2
flo = 2.25 GHz
fIF = 500 MHz
Folded feedback signal without DPD
SFFB Dual-Band DPD by Experiment
16
1.71 1.72 1.73 1.74 1.75 1.76 1.77 1.78 1.79-100
-90
-80
-70
-60
-50
-40
-30
Frequency (GHz)
Pow
er S
pect
ral D
ensi
ty (d
Bm
/Hz)
Without DPDSFFB DPDConv. DPD
2.71 2.72 2.73 2.74 2.75 2.76 2.77 2.78 2.79-100
-90
-80
-70
-60
-50
-40
-30
Frequency (GHz)
Pow
er S
pect
ral D
ensi
ty (d
Bm
/Hz)
Without DPDSFFB DPDConv. DPD
Scenario 1; 10 MHz LTE(1.75 GHz ) + 20 MHz LTE (2.75 GHz)
Scenario 2; 20 MHz LTE (1.75 GHz) + 4 x 20 MHz LTE CA (2.75 GHz)
1.65 1.7 1.75 1.8 1.85-100
-90
-80
-70
-60
-50
-40
-30
Frequency (GHz)
Pow
er S
pect
ral D
ensi
ty (d
Bm
/Hz)
Without DPDSFFB DPDConv. DPD
2.65 2.7 2.75 2.8 2.85-100
-90
-80
-70
-60
-50
-40
-30
Frequency (GHz)
Pow
er S
pect
ral D
ensi
ty (d
Bm
/Hz)
Without DPDSFFB DPDConv. DPD
3. Cross-Modulation due to Multi-Band Access
17
LNASynthesized Oscillators
macro BS
femto/ macro /repeater
L
H
L
I
Q
090
HI
Q090
ADC
ADC
ADC
ADC
Near-far problem increases chance of inter-band modulation
Near & strong
Far & weak
Inter-band modulationSelf-Generated
Distortion
Self-GeneratedDistortion
Not Cared
L HHL 2LH 2
-20-10
010
-20
-10
0
100
5
10
15
20
PL (dBm)P
H (dBm)
EV
M (
%)
-20-10
010
-20
-10
0
100
5
10
15
20
PL (dBm)P
H (dBm)
EV
M (
%)
,PL
,PH
(a) EVM for L
(b) EVM for H
micro /
Post-Compensation of Receiver Nonlinearity
18
DDC for ωL
sL(n)
LNA
Channel Filter
xH(n)xL(n)
Compensatorfor yL(n)
yH(n)
yL(n)Time
Alignment
sH(n)Channel
FilterCompensator
for yH(n)
L
H
DDC for ωH
digital domain
ADC
ADC
Compensator diagram for yL
yL sL
|yL|2yL
|yH|2yL
|yL|4yL
|yH|4yL
|yH|2|yL|2yL
c'30
c'32
c'50
c'52
c'54
yH
|yH|Q-1yL
c'Q,Q-1
3rd IM
3rd CM
5th IM
5th CM
5th CM
Blind & Adaptive Nonlinear Compensation method is necessary [4].
Bypolynomial
How to Determine Compensator Coefficients?
19
Minimization
DesiredSignal Band
0 Frequency Shift
Proposed algorithm determines the compensator coefficients so as to minimize outband spectra power for each band.
This works successfully because nonlinearity generates both inband and outband components and they are correlated.
The key is separation filter that eliminates the in-band signaland maximizes SNR of outband distortion detection.
Experimental Results
20
2320 2330 2340 2350 2360 2370 2380-80
-70
-60
-50
-40
-30
Frequency (MHz)
Pow
er
Spectr
al D
ensity (
dB
)
2620 2630 2640 2650 2660 2670 2680-70
-60
-50
-40
-30
-20
-10
Frequency (MHz)
Pow
er
Spectr
al D
ensity (
dB
)
Uncompensated
3rd order
5th order
7th order
Power levels of L and Hin (a)/(b) are -10 dBm and 6 dBm, respectively.
(a) Output spectra at L (b) Output spectra at H
(c) EVM for L signal (d) EVM for H signal
7th-order compensation presents the best results.
Proposed compensator improves EVM in both bands.Maximum acceptable input power increases more than 4 dB.
f1 = 2.35 GHzf2 = 2.65 GHz
4. Reconfigurable RF BPF
21
Reconfigurable BPF can adapt the receiver flexibly to the change of access channels and prevent unexpected cross-modulation distortions in multi-band/multi-access operation.
Example of nonlinear output spectrum under concurrent dual-band operation.Some of them locate near the operating band.
Frequency (GHz)
Pow
er (
dBm
)
SHF Dual-band Reconfigurable BPF Low SHF (< 6 GHz) reconfigurable BPF and High SHF wideband
BPF are integrated for concurrent dual-band access.
22
Low SHF Reconfigurable BPF section
DIP
Resonator ResonatorIC OCISC
DIP
Reconfig.Resonator1
Reconfig.Resonator2
IC OCISC
High SHF wideband BPF section
DIP: Diplexer IC: Input Coupling circuitISC; Inter-Stage Coupling circuit OC: Output Coupling circuit
2-stage 3-bit Low-SHF Reconfigurable BPF
23
SHORT
OPEN
l21 SW3
Lin
SW1 SW2
SW6
SW4 SW5
SHORT
OPEN
Zg
Vg
l21
Lcut
Linter Lcut
Lout
ZL
l22l20 l20
l22
l23 l23
l1 l1
1st stage 2nd stage
-40
-30
-20
-10
0
1 2 3 4 5 6
f1f2
f3f4
f8f7f6f5
|S21
| (dB
)
Frequency (GHz)
Center Frequency; 3.1 to 4.6 GHzInsertion loss; 1.0~2.1 dB
High SHF BPF and diplexers are underdesign process.
Conclusions
5G hardware is required to be more flexible, accurate, linear and low-cost.
For Txs, advanced DPD techniques called SENF and SFFB are proposed.
- SENF saves feedback bandwidth, which enables wider compensation bandwidth.
- SFFB enables simple feedback for concurrent dual-band operation.
For concurrent dual-band Rxs, Post Compensation technique and Reconfigurable BPF are proposed.
24
The results will contribute to improve practical performance of the 5G system.
Related Works
25
1) Y. Ma, Y. Yamao, Y. Akaiwa, K. Ishibashi, “Wideband digital predistortion using spectral extrapolation of band-limited feedback signal,” IEEE Trans. Circuit and Systems-I, vol. 61, no. 7, pp. 2088-2097, July 2014.
2) Y. Ma and Y. Yamao, “Experimental results of digital predistorter for very wideband mobile communication system,” Proc. IEEE VTC2015-Spring, 6PB-2, Glasgow, UK, May 2015.
3) Y. Ma and Y. Yamao, “Spectra-folding feedback architecture for concurrent dual-band power amplifier predistortion,” IEEE Trans. Microw. Theory & Tech., Vol. 63, No. 10, pp. 3164-3174, Oct. 2015.
4) Y. Ma, Y. Yamao, K. Ishibashi and Y. Akaiwa, "Adaptive compensation of inter-band modulation distortion for tunable concurrent dual-band receivers," IEEE Trans. Microw. Theory & Tech., vol.61, no.12, pp.4209-4219, Dec. 2013.
5) R. Kobayashi, T. Kato, K. Azuma and Y. Yamao, “Design and Fabrication of Two-Stage Three-Bit Reconfigurable Bandpass Filter Using Brunch Line-Type Variable Resonator,” IEICE Trans. Electronics, Vol. E98-C, No. 7, pp. 636-643, July 2015.
Thank you for listening!
LABORATORYLABORATORYLABORATORY
26
A part of this work is supported by the Ministry of Internal Affairs and Communications (MIC) of Japan under the program “R&D for the realization of 5G mobile communication system".
Acknowledgement
2-Stage 3-bit Reconfigurable BPF in UHF Bandopen
l23
SW3
SW1 SW2
l20
l21 l22
L01 L12Rinl1
short
V
open
l23
SW6
SW4 SW5
l20
l21 l22
L23
l1
short
RoutLT1 LT2
(From APMC2012, Kaohsiung Taiwan)
27
|S21
| (dB
)
1.0 2.0 3.0 4.0 5.0
5
f6
10152025303540
00
f7 f8f5
f2 f3 f4f1
Frequency (GHz)
fiCenter frequency
(GHz)Insertionloss (dB)
Band width(MHz)
f1 2.01 0.90 505f2 2.09 0.81 542f3 2.13 0.90 520f4 2.24 0.92 528f5 2.38 0.94 548f6 2.44 0.93 552f7 2.72 0.96 574f8 2.80 0.98 567