7100 RoadmapSystem-level Challenges in the Design of a Wideband RF Transceiver
for LTE and LTE-A
Modulation
FFT Size
UL MIMO
2x2 (Rel-9)
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LTE Rel-8,9,10 and beyond
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Signal Bandwidth: up to 20 MHz
Transceiver Units: 2 RX, 1 TX
Form Factor: double height and double width of a uTCA slot
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Product Managers/End Users
What about phase noise?
Further challenges in LTE-A
Cons:
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2.2 Noise Figure < ?
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 PREFSENS=-97dBm is applied (from 3GPP 36.101).
SNRmin = -1 dB
Pthermal = kTB
NF<7 dB
2.3 EVM Floor <?
EVM results from various RF non-idealities: carrier leakage, IQ imbalance, gain compression, phase noise, frequency error, etc;
Overall EVM floor limits the max achievable T-put!
Given a EVM value, the error power increases linearly with the signal power;
The effect on BLER/T-put may be treated as noise, hence EVM can be converted to SNR;
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1.8%
SNR clamped by the EVM floor.
Note: SNR is defined at the output of the RF front-end, i.e. baseband
LTE requires near 30 dB SNR to achieve the max T-put (150Mbps with 2 layers).
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NF is the differential factor.
EVM is the differential factor.
No effect on T-put.
Consider three RF front-end with different NF and EVM characteristics.
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2.4 TX Blocking
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;
duplex
Transmitter
Receiver
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Consequences:
Cause compression in the RX amplifiers and demodulator
Desensitize the receiver
Solutions:
Application-specific:
- Half-duplex mode for budget handsets;
Advanced techniques:
Single tone measurement
- Input: cos(2π(fc+fm)t)
SIR=41 dB
Desired Region
Integrated Phase Noise Power (15KHz~10MHz): P = -44.1 (dBc)
RMS Phase Error: θRMS = 0.50 (deg)
EVM = 0.88%
Two types of effects:
- Common Phase Error (CPE)
- Inter sub-Carrier Interference (ICI)
Loop BW ↓ lock time ↑
Downlink: 8x8
- L1 data rate 600 Mbps
- ADC Sample data rate:
Uplink: 4x4
- L1 data rate 300 Mbps
- DAC sample data rate:
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2.8 LTE-A: Carrier Aggregation
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
CC for operator-B
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Summary
Introduction to LTE and the Test Mobile: TM500;
How to determine various RF system parameters such as: noise figure, EVM floor, TX leakage, IQ imbalance and phase noise;
Further challenges from LTE-A: high order MIMO and CA;
20 MHz
20 MHz
32%
10%
3%
1%
EVM