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**Senior Algorithm Engineer Aeroflex Test Solutions Stevenage, UK**

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 Aeroflex Company Confidential

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Agenda 1. Design Objectives 2. Design Challenges 3. Summary 4. Q&A

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**1.1 3GPP LTE Air Interface Overview**

Modulation DL: OFDM UL: DFTS-OFDM Signal Bandwidth 1.4,3,5,10,15,20 MHz Signal PAPR (Crest Factor) DL: ~11 dB, UL: ~8 dB FFT Size 2048 (Normal CP) Sub-Carrier Spacing 15 kHz (Normal CP) DL MIMO 2x2 (Rel-8) 4x4, 4x2 (Rel-9) UL MIMO 2x2 (Rel-9) Max Data Rate DL: 150~300 Mbps UL: 50~100 Mbps

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1.2 Product Overview: TM500 Industry Standard Base Station Tester for LTE and HSPA LTE Rel-8,9,10 and beyond From RF to Protocol Layers

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**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

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**1.4 Translate System Req. to RF Req.**

System Engineers Receiver Sensitivity Maximum Throughput System Bandwidth MIMO Hand-over … Noise Figure EVM Floor Filter Spec. LO Phase Noise LO Settling Time … Product Managers/End Users RF Engineers

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**2. RF Design Challenges Homodyne or Heterodyne?**

What’s the minimum requirement on Noise Figure? What’s the minimum requirement on EVM floor? The biggest blocker might be your own TX! Do we need to worry about IQ imbalance? What about phase noise? Further challenges in LTE-A

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**2.1 Homodyne or Heterodyne?**

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

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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 ). (I) SNRmin = -1 dB

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**(II) NF = PREFSENS – Pthermal – SNRmin**

2.2 Noise Figure (Cont’d) PREFSENS SNR PN = Pthermal + NF NF<7 dB NF Pthermal = kTB (II) NF = PREFSENS – Pthermal – SNRmin

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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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**2.3.1 EVM Floor, Noise Figure and SNR**

SNR clamped by the EVM floor. SNR increases with the input signal power. 1.8% LTE requires near 30 dB SNR to achieve the max T-put (150Mbps with 2 layers). Note: SNR is defined at the output of the RF front-end, i.e. baseband

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**2.3.2 EVM Floor, Noise Figure and T-put**

Consider three RF front-end with different NF and EVM characteristics. No effect on T-put. EVM is the differential factor. NF is the differential factor.

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**2.4 TX Blocking Transmitter Receiver duplex TX Max Power: ~ 23 dBm**

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;

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**2.4 TX Blocking (Cont’d) Consequences:**

Particularly serious for wideband transceivers Cause compression in the RX amplifiers and demodulator Desensitize the receiver Limit the max TX power allowed Solutions: Application-specific: - Block-tolerant front-end; - TX Power back-off for lab operations; - Half-duplex mode for budget handsets; Advanced techniques: - Adaptive interference cancellation duplexer

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**2.5 IQ Imbalance Wanted Signal ε: Amplitude error θ: Phase error**

Image Signal

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**2.5.1 Self-Interference induced by IQ Imbalance**

SIR=41 dB Single tone measurement - Input: cos(2π(fc+fm)t) - Output Expected : cos(2πfmt)+j sin(2πfmt)

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2.5.2 SIR of IQ Imbalance Desired Region

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2.6 LO Phase Noise Source: Analog Devices® ADF4350 datasheet Integrated Phase Noise Power (15KHz~10MHz): P = (dBc) RMS Phase Error: θRMS = 0.50 (deg) EVM = 0.88%

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**2.6.1 Phase Noise on OFDM Constellation**

CPE dominated ICI dominated Two types of effects: - Common Phase Error (CPE) - Inter sub-Carrier Interference (ICI) CPE can be easily corrected, ICI not Loop BW ↓ lock time ↑

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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

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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 - Inter-band carrier aggregation

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LTE-A in the News World-record 1.4 Gbps in LTE-Advanced demo (03/2012 source: ) - 5 component carriers - 20MHz 4x4 MIMO each - and TM500! TM500 supports the development of multiband lightRadio® technology.

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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;

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