Microwave IC & System Lab

Antenna and RF Self-interference Cancellation

in Full Duplex Systems

Byung-Wook Min (민병욱), Ph.D.

bmin@yonsei.ac.kr

Assistant ProfessorElectrical and Electronic EngineeringYonsei University

Microwave IC & System Lab

Outline

• Full Duplex Radio System

• Self-Interference

• Antenna Self-Interference Cancellation

• RF Self-Interference Cancellation

• System Budget and RX Dynamic Range

• Array Pattern and Extending MIMO System

• To Study

Microwave IC and Systems

What is Full Duplex System? Todays Communication System

1. TDD(Time-Division Duplex)

- ProsConsume single frequency resources

- ConsThroughput is half than FDD

2. FDD (Frequency-Division Duplex)- ProsThroughput is double than TDD

- ConsConsume double frequency resources

Q : Is it possible to make new systemthat have both Pros of TDD andFDD?

Full Duplex Radio

A : No. Such a system will suffer from Self Interference (SI).So, the key point to make FD is achieving Self Interference Cancellation (SIC).

Microwave IC and Systems

FDD/TDD System Block Diagram

TDD – T/R Switch

FDD – Duplexer

XWhy Duplexer?Self interference (SI)!

How to blockTX(PA) to RX(LNA)using same freq. in FD.

ADC

ADC

MODEM

I

Q

DAC

DAC

MODEM

I

Q

PA

ADC

ADC

MODEM

I

Q

DAC

DAC

MODEM

I

Q

PA

Microwave IC and Systems

State of the Art RFIC

Off chip T/R-Band switch, duplexer, PA and on-chip LNAFor FDR, TX an RX PLL (VCO) can be shared.

TX D

PLL

RX

Fra

c-N

PLL

DIG

ITA

L

DC

-CAL

Microwave IC and Systems

RX Path Linearity

LNA mode

Gain (dBV/V)

NF (dB)In-band

IIP3 (dBm)

In-bandIIP2

(dBm)

G0 50 2.3 -38 -12

G1 42 2.8 -32 -6

G2 36 3.3 -10 15

G3 25 14 -4 27

G4 14 20 1 27

G5 3 33 1 50

RX Linearity (dBm)

Input Power (dBm)

NF (dB)

RX Gain (dB)

RX SI

We have to bring the SI down,to the worst linear power level of RX pathbefore the active RX path (LNA).

SIC at the RF Front-Endor increased RX path linearity(trade-off NF and power consumption)

Microwave IC and Systems

Two Antennas?

ADC

ADC

MODEM

I

Q

DAC

DAC

MODEM

I

Q

PA

> -15 dBNot a relay.

LTE TX power PAVG=23 dBm, SI >8 dBm saturates RX.LTE RX sensitivity -106.4 dBm

Microwave IC and Systems

Rice FD System

Now cancel SI

Antenna Isolation + RF(?) SIC = -31 dBExperiment-Driven Characterization of

Full-Duplex Wireless Systems, Ashutosh Sabharwal, Rice (2012)

Better

Microwave IC and Systems

Stanford FD System I

Antenna Isolation + RF SIC= -42dBPractical, Real-time, Full Duplex Wireless, Sachin Katti, Stanford(2011)

Microwave IC and Systems

Stanford FD System II

Antenna SIC (-30dB) + RF SIC (-20 dB)Achieving Single Channel, Full Duplex Wireless Communication,

Sachin Katti ,Stanford(2010)

-180o

BW Issue!Not a MIMOBeam pattern?

Microwave IC and Systems

Princeton SIC

Double Antenna SIC: TX (-25 dB) + RX (-20 dB)MIDU: Enabling MIMO Full Duplex, Ehsan Aryafar, Princeton(2012)

-180o

Beam pattern?

Microwave IC and Systems

Circulator?

> -20 dB

Not enough, but comparable to antenna isolation

ADC

ADC

MODEM

I

Q

DAC

DAC

MODEM

I

Q

PA

Microwave IC and Systems

Circulator3 port device to make power flow only in a specific direction (Circulating), usually made by ferrite material which is impossible to be integrated.

Microwave IC and Systems

Non-Ferrite Based Circulator

ANT

RX

TX

DA (TWA) based quasi circulator

Signal canceling based circulator

Microwave IC and Systems

Stanford FD System III

RF SIC (-60dB) + Digital SIC (-50dB) = -110dB (enough?)Full Duplex Radios, Dinesh Bharadia, Stanford(2013)

RF SIC (Circulator + RF SIC)

Sampling Cancellation

Digital SIC

We can do whatever we want using DSP.

(RX+αTX) - αTX = RX ?

(RX+αTX) - αTX = RX+αTX !!!

(Non-linearity of the RX chain!)

What if increasing RX linearity?

-Power consumption much more than PA

-Linearity-Noise trade-off

-ADC????TX

RX+ αTX

RX+αTX

Noise?

Microwave IC and Systems

Required Total SIC for LTE

TX Power = 23 dBm

RX Sensitivity = 106 dBm

Peak to average power ratio of modulation ~ 10 dB

Total SIC for LTE = 23 dBm + 10 dB – 106 dBm ~ 140 dB

Let’s see whether current RF system has some margin!

Microwave IC and Systems

Avago LTE Duplexer

min 43 dB TX-RXisolation

TXRX-50 dB

Microwave IC and Systems

Avago PCS/Cell Dualband DuplexerRXTX

TXRX-47 dB

TXRX-55 dB

RXTX Band5 Band25

min 40 dB IsolationEnough SIC?NO! FTX=FRX

21 MHz

?

Microwave IC and Systems

PA Output Spectrum

Center Freq.=782 MHz Freq.=751 MHz w/ 30 MHz offset

@15 MHz offset -56 dBc @30 MHz offset -75 dBc

Additional ~60 dB SIC required!

Microwave IC and Systems

LTE UE Spectrum Emission Mask

ACLRorSEM!

23 dBm-(-36 dBm)60 dB lower TX at ~ 20 MHz offset.

Microwave IC and Systems

Stanford SIC Power Budget

Stanford WIFI SIC Plan: total 110 dB60 dB Analog SIC and 50 dB Digital SIC with 60 dB dynamic range

If we achieve 100 dB (+10 dB PAPR) SIC before LNA,We may use the existing transceiver.Do the SIC as much as possible and increase the RX linearity.

peak to averagepower ratio.

noteasyReceiver.

LTE caseRX: -106 dBm RXTX: -27 (=23+10-60) dBmDynamic range:~79 dBADC Burden

Microwave IC and Systems

Half Duplex System Budget

ADC

ADC

MODEM

I

Q

DAC

DAC

MODEM

I

Q

PA

24 dBm (avg)

0 dBm

33 dBm (peak)

-106 dBm

-20 dBm (avg)

-107 dBm23 dBm (avg)

-125 dBA

-43 dBA

-18 dBS

-25 dBm

10 MHz

-50 dBA

TIA

TIA PGA

PGA

-7 dB

77 dBZ 30 dB-70 dBrejection

-132 dBA-25 dBm

FDR system cannot rely on the baseband filter!!!

Microwave IC and Systems

Full Duplex System Budget

SolutionEliminate PGA ADC dynamic range (70 dB + PARR required)Use BB analog SIC I/Q phase difference TX and RX LO phase control/match

Heterodyne receiver

Microwave IC and Systems

ADC Linearity

ADC BW and Dynamic range

Current 12bit ADC ENOB=1020log(210)=60 dB Antenna/RF/Analog SIC ~ 80 dB

World best at 10 MHz ADC (for 20 MHz LTE) 80~85 dB dynamic range. Antenna/RF/Analog SIC required at least 60 dB.

Receiver is a gain block, and ADC sees the most burden!

TX leakage

RXsignal

RX+TX

Microwave IC and Systems

Beam Pattern?

Same signal two antennas Beam pattern!!!!

Microwave IC and Systems

Two Antenna Beam PatternWe need to consider array factor!!!

-9 -6 -3 0 3 6

60

120

30

150

0

180

30

150

60

120

90 90

λ/2Null No radiation

-9 -6 -3 0 3 6

60

120

30

150

0

180

30

150

60

120

90 90

3λ/4

6 dB gain?

Microwave IC and Systems

-9 -6 -3 0 3 6

60

120

30

150

0

180

30

150

60

120

90 90

Bring Antenna Closer

λ3

λ3 TX2TX1

TX w/ Φ=180

TX w/ Φ=0

r=1 cm, λ~12 cm@ 2.5 GHz0.666λ

0.167λ

-9 -6 -3 0 3 6

60

120

30

150

0

180

30

150

60

120

90 90

No null loss

RXRX TX2TX1

TX w/ Φ=180

TX w/ Φ=0

Microwave IC and Systems

Extending to MIMO: Antenna SIC

T1T3

T2

R1 R3

R2

Using Different polarization?

UsingDigital MIMO techniquefor SIC?(ex. T1, T2 beam formingto set a null to R)

Not very far field region

Microwave IC and Systems

Extending to MIMO: RF SIC

RF SIC is getting complicated….(Better to get all SIC from antenna!)M MIMO requires M2 RF SIC circuit.

Microwave IC and Systems

Stanford 3x3 MIMO Results

Simpler RF SIC circuitbut still M2 circuit.

Microwave IC and Systems

To Communication System...

- Inter-device interference & 스케줄링- Backward compatibility FD 시스템 운용- Near Field를 고려한 MIMO SIC

RF

Microwave IC & System Lab

감사합니다.