Transcript 7100 Roadmap - Microwave & RF
System-level Challenges in the Design of a Wideband RF Transceiver for LTE and LTE-A
Dr. Jin Wang
Senior Algorithm Engineer Aeroflex Test Solutions Stevenage, UK www.aeroflex.com
Aeroflex Company Confidential
Agenda
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1. Design Objectives
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2. Design Challenges
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3. Summary
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4. Q&A www.aeroflex.com
1.1 3GPP LTE Air Interface Overview
Modulation Signal Bandwidth Signal PAPR (Crest Factor) FFT Size Sub-Carrier Spacing DL MIMO UL MIMO Max Data Rate DL: OFDM UL: DFTS-OFDM 1.4,3,5,10,15,20 MHz DL: ~11 dB, UL: ~8 dB 2048 (Normal CP) 15 kHz (Normal CP) 2x2 (Rel-8) 4x4, 4x2 (Rel-9) 2x2 (Rel-9) DL: 150~300 Mbps UL: 50~100 Mbps www.aeroflex.com
1.2 Product Overview: TM500
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Industry Standard Base Station Tester for LTE and HSPA
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LTE Rel-8,9,10 and beyond
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From RF to Protocol Layers www.aeroflex.com
1.3 Wideband Radio Card
▼ ▼ ▼ ▼
Operating Frequencies: 400MHz~4GHz Signal Bandwidth: up to 20 MHz Transceiver Units: 2 RX, 1 TX Form Factor: double height and double width of a uTCA slot www.aeroflex.com
1.4 Translate System Req. to RF Req.
System Engineers Receiver Sensitivity Maximum Throughput System Bandwidth MIMO Hand-over … Product Managers/End Users Noise Figure EVM Floor Filter Spec.
LO Phase Noise LO Settling Time … RF Engineers
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2. RF Design Challenges
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Homodyne or Heterodyne?
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What’s the minimum requirement on Noise Figure?
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What’s the minimum requirement on EVM floor?
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The biggest blocker might be your own TX!
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Do we need to worry about IQ imbalance?
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What about phase noise?
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Further challenges in LTE-A www.aeroflex.com
2.1 Homodyne or Heterodyne?
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Homodyne (direct conversion/zero-IF) Pros: - fewer processing stages - No image frequency problem - Mainstream design in recent years Cons: - IQ imbalance - DC offset or carrier leakage www.aeroflex.com
2.2 Noise Figure < ?
(I)
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Max noise figure allowed depends on the RX sensitivity requirement, e.g.
3GPP requires that no less than 95% of maximum throughput is achieved on a reference measurement channel (BW=10MHz) when minimum input power of P REFSENS =-97dBm is applied (from 3GPP 36.101).
100 90 80 70 60 50 40 30 20 10 0 -2 -1.8
-1.6
-1.4
-1.2
SNR (dB) -1 -0.8
-0.6
SNR min = -1 dB
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2.2 Noise Figure (Cont’d)
P REFSENS SNR P N = P thermal + NF NF P thermal = kTB NF<7 dB
(II) NF = P REFSENS – P thermal – SNR min
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2.3 EVM Floor
EVM E E
rms
Error Level
rms
Signal Level SNR 20 Log( EVM ) (dB) ▼
EVM results from various RF non-idealities: carrier leakage, IQ imbalance, gain compression, phase noise, frequency error, etc;
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Overall EVM floor limits the max achievable T-put!
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Given a EVM value, the error power increases linearly with the signal power;
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The effect on BLER/T-put may be treated as noise, hence EVM can be converted to SNR; www.aeroflex.com
2.3.1 EVM Floor, Noise Figure and SNR
SNR clamped by the EVM floor.
Noise Figure=7dB, EVM Floor=1.8% 50
SNR increases with the input signal power.
40 1% 30 3%
1.8%
20 10% 10 0 -10 -130 -120 -110 -100 -90 RSRP (dBm/sc) -80 -70 Noise limited EVM limited Combined -60 -50 Note: SNR is defined at the output of the RF front-end, i.e. baseband 32%
LTE requires near 30 dB SNR to achieve the max T-put (150Mbps with 2 layers).
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2.3.2 EVM Floor, Noise Figure and T-put
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Consider three RF front-end with different NF and EVM characteristics.
No effect on T-put.
EVM is the differential
50
factor.
40 1% 30 3%
NF is the differential factor.
20 10 0 -10 -130 -120 -110 -100 -90 RSRP (dBm/sc) -80 NF=4dB,EVM=1% NF=7dB,EVM=1.8% NF=7dB,EVM=3% -70 -60 -50 10% 32%
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2.4 TX Blocking
TX Max Power: ~ 23 dBm
Transmitter
duplex
Receiver
RX REFSENS: ~ -97 dBm ▼ ▼
The TX power can be 120 dB higher than the RX power; The TX and RX frequency separation can be as small as 30 MHz; www.aeroflex.com
2.4 TX Blocking (Cont’d)
Consequences:
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Particularly serious for wideband transceivers
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Cause compression in the RX amplifiers and demodulator
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Desensitize the receiver Limit the max TX power allowed Solutions:
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Application-specific:
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- Block-tolerant front-end; - TX Power back-off for lab operations; - Half-duplex mode for budget handsets; Advanced techniques: - Adaptive interference cancellation duplexer www.aeroflex.com
2.5 IQ Imbalance
ε: Amplitude error θ: Phase error
Wanted Signal
x
RF (
t
)
I
(
t
) cos(
c t
)
Q
(
t
) sin(
c t
),
x LPF
(
t
) cos( ) cos( )
x L
(
t
)
j
j
sin( sin( ) )
I I
(
t
(
t
) )
jQ
(
t jQ
(
t
) )
x
*
L
(
t
)
Image Signal www.aeroflex.com
2.5.1 Self-Interference induced by IQ Imbalance
140 X: 4.8
Y: 134.9
120 X: -4.8
Y: 93.87
100 80
SIR=41 dB
60 40 20 -80 -60 -40 -20 0 Freq (MHz) 20 40 60 80
Single tone measurement - Input: cos(2 π(f c +f m )t) - Output Expected : cos(2 πf m t)+j sin(2 πf m t) www.aeroflex.com
2.5.2 SIR of IQ Imbalance
6 20 18 20
Desired Region
5 22 4 24 3 26 2 30 28 26 22 24 20 22 20 18 1 40 38 36 34 32 30 28 24 22 20 26 0 0 1 2 3 7 8 9 10 4 5 6 Amplitude Error (%) SIR 10log10 2 2 10log10 1 2 2 tan tan 2 2
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2.6 LO Phase Noise
P
f
1
f
2
L
(f) df
rms EVM 180 180 2
P
(deg) rms 100 %
Source: Analog Devices® ADF4350 datasheet Integrated Phase Noise Power (15KHz~10MHz): P = -44.1 (dBc) RMS Phase Error: θ RMS = 0.50 (deg) EVM = 0.88% www.aeroflex.com
2.6.1 Phase Noise on OFDM Constellation
1.5
1 0.5
0 -0.5
-1 -1.5
-1.5
CPE dominated
Loop Bandwidth=10kHz -1 -0.5
0 0.5
1 1.5
▼ ▼ ▼
Two types of effects: - Common Phase Error (CPE) - Inter sub-Carrier Interference (ICI) CPE can be easily corrected, ICI not Loop BW ↓ lock time ↑
1.5
1 0.5
0 -0.5
-1 -1.5
-1.5
ICI dominated
Loop Bandwidth=40kHz -1 -0.5
0 0.5
1 1.5
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2.7 LTE-A: High Order MIMO
Downlink: 8x8 - 8 RX processing chains – high density - L1 data rate 600 Mbps - ADC Sample data rate: 30.72MSamp/s x (2x16 bits/sample)x8 = 7.86 Gbps Uplink: 4x4 - 4 TX processing chains – high density - L1 data rate 300 Mbps - DAC sample data rate: 30.72MSamp/s x (2x16 bits/sample)x4 = 3.93 Gbps www.aeroflex.com
2.8 LTE-A: Carrier Aggregation
Contiguous CA N*300kHz 20 MHz 20 MHz 20 MHz Band 3 20 MHz Band 4 20 MHz ~ 40 MHz Non-contiguous CA 20 MHz CC for operator-B 5 MHz N*100 kHz 20 MHz 10 MHz 10 MHz Band 7 15 MHz Band 3 Band 4 N*300 kHz Non-contiguous aggregated CC for operator-A Band 7
LTE-A allows up to 5 component carriers. Each component carrier can be 1.4, 3, 5, 10, 15 and 20 MHz. The maximum aggregated system bandwidth is 100 MHz. The three possible carrier aggregation types are: - Intra-band contiguous carrier aggregation - Intra-band non-contiguous carrier aggregation - Inter-band carrier aggregation www.aeroflex.com
LTE-A in the News
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World-record 1.4 Gbps in LTE-Advanced demo (03/2012 source: http://4g-portal.com ) - 5 component carriers - 20MHz 4x4 MIMO each - and TM500!
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TM500 supports the development of multiband lightRadio ® technology.
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Summary
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Introduction to LTE and the Test Mobile: TM500;
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How to determine various RF system parameters such as: noise figure, EVM floor, TX leakage, IQ imbalance and phase noise;
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Further challenges from LTE-A: high order MIMO and CA; www.aeroflex.com