Practical, Real-time, Full-Duplex Wireless Mayank Jain, Jung Il - - PowerPoint PPT Presentation

Practical, Real-time, Full-Duplex Wireless

Mayank Jain, Jung Il Choi, Taemin Kim, Dinesh Bharadia, Kannan Srinivasan, Siddharth Seth, Philip Levis, Sachin Katti, Prasun Sinha

September 22, 2011

1

What full-duplex

2

What full-duplex ... and why?

3

Current wireless radios

• Time Division Duplexing

4

TX/RX TX/RX TX/RX TX/RX

Node 1 Node 2 Node 1 Node 2

Timeslot 1 Timeslot 2

Current wireless radios

• Time Division Duplexing

5

• Frequency Division Duplexing

TX RX RX TX TX/RX TX/RX TX/RX TX/RX

Node 1 Node 2 Node 1 Node 2

Timeslot 1 Timeslot 2

Frequency 1 Frequency 2

Node 1 Node 2

Single channel full-duplex

6

TX RX RX TX

Node 1 Node 2

Single channel full-duplex

➔ Very strong self-interference: ~70dB for 802.11

7

TX RX RX TX

Node 1 Node 2 Self- Interference

Single channel full-duplex

➔ Very strong self-interference: ~70dB for 802.11

8

TX RX RX TX

Node 1 Node 2 Self- Interference

Main idea: cancel self-interference

Combine RF and digital techniques for cancellation

Mobicom’10[1]: Antenna Cancellation + other techniques

9

The story so far...

d d + λ/2 TX1 TX2 RX

[1] Choi et al. “Achieving single channel, full duplex wireless communication”, Mobicom 2010

Mobicom’10[1]: Antenna Cancellation + other techniques

10

The story so far...

d d + λ/2 TX1 TX2 RX

• Does not adapt to channel changes
• Interference pattern can affect intended receivers
• Frequency dependent, narrowband cancellation

[1] Choi et al. “Achieving single channel, full duplex wireless communication”, Mobicom 2010

• New, better RF and digital cancellation techniques
• Adaptive algorithms for auto-tuning cancellation
• Real-time full-duplex MAC layer implementation

11

• RF Cancellation using Signal Inversion
• Adaptive RF Cancellation
• System Performance
• Implications to Wireless Networks
• Looking Forward

Talk Outline

12

• RF Cancellation using Signal Inversion
• Adaptive RF Cancellation
• System Performance
• Implications to Wireless Networks
• Looking Forward

Talk Outline

13

Cancellation using Phase Offset

Self- Interference Cancellation Signal

∑

Cancellation using Phase Offset

15

Self- Interference Cancellation Signal

∑

Self- Interference Cancellation Signal

∑

Frequency dependent, narrowband

Cancellation using Signal Inversion

16

Self- Interference Cancellation Signal

∑

Cancellation using Signal Inversion

17

Self- Interference Cancellation Signal

∑

Self- Interference Cancellation Signal

∑

Frequency and bandwidth independent

Time

18

Xt +Xt/2

• Xt/2

BALUN

BALUN : Balanced to Unbalanced Conversion

Time

19

TX RX TX RF Frontend Xt +Xt/2

• Xt/2

∑ RX RF Frontend Xt +Xt/2

• Xt/2

BALUN

BALUN : Balanced to Unbalanced Conversion

Cancellation Signal

Time

20

TX RX TX RF Frontend Xt +Xt/2

• Xt/2

∑ RX RF Frontend Xt +Xt/2

• Xt/2

BALUN

Over the air attenuation and delay

Time

21

TX RX TX RF Frontend Attenuator and Delay Line Xt +Xt/2

• Xt/2

∑ RX RF Frontend Xt +Xt/2

• Xt/2

BALUN

Signal Inversion Cancellation

Over the air attenuation and delay

+Xt/2

• Measure wideband cancellation
• Wired experiments
• 240MHz chirp at 2.4GHz to measure response

Time

Signal Inversion Cancellation: Wideband Evaluation

22

TX RX

Signal Inversion Cancellation Setup

∑ TX RX

Phase Offset Cancellation Setup

∑ RF Signal Splitter Xt +Xt/2

• Xt/2

Xt +Xt/2 λ/2 Delay

Time

23

Lower is better Higher is better

Time

24

~50dB cancellation at 20MHz bandwidth with balun vs ~38dB with phase offset cancellation.

Significant improvement in wideband cancellation

Lower is better Higher is better

Time

25

• From 3 antennas per node to 2 antennas
• Parameters adjustable with changing conditions

Attenuator and Delay Line TX RX TX RF Frontend Xt +Xt/2

• Xt/2

∑ RX RF Frontend

Other advantages

Time

26

Passive components better than active components

• No gain required
• Saturation can lead to non-linearity
• Passive components are more frequency flat

TX RX TX RF Frontend Attenuator and Delay Line Xt +Xt/2

• Xt/2

∑ RX RF Frontend

• RF Cancellation using Signal Inversion: ~50dB for 20Mhz
• Adaptive RF Cancellation
• Adaptive Digital Cancellation
• System Performance
• Implications to Wireless Networks
• Looking Forward

Talk Outline

27

• Need to match self-interference power and delay
• Can’t use digital samples: Saturated ADC

Adaptive RF Cancellation

28

TX RX Attenuation & Delay Wireless Receiver Wireless Transmitter

RF Cancellation

TX Signal Path RX Signal Path RF Reference

Σ

Balun

• Need to match self-interference power and delay
• Can’t use digital samples: Saturated ADC

Adaptive RF Cancellation

29

RSSI : Received Signal Strength Indicator

TX RX Attenuation & Delay Wireless Receiver Wireless Transmitter

RF Cancellation

TX Signal Path RX Signal Path RF Reference

Σ

Balun

RSSI

• Need to match self-interference power and delay
• Can’t use digital samples: Saturated ADC

Adaptive RF Cancellation

30

Use RSSI as an indicator of self-interference

TX RX Attenuation & Delay Wireless Receiver Wireless Transmitter

RF Cancellation

TX Signal Path RX Signal Path RF Reference

Σ

Balun

RSSI

Control Feedback

31

Objective: Minimize received power Control variables: Delay and Attenuation

TX RX Attenuation & Delay Wireless Receiver Wireless Transmitter

RF Cancellation

TX Signal Path RX Signal Path RF Reference

Σ

Balun

RSSI

Control Feedback

32

Objective: Minimize received power Control variables: Delay and Attenuation

33

➔ Simple gradient descent approach to optimize Objective: Minimize received power Control variables: Delay and Attenuation

34

Off-the-shelf electronically tunable hardware approximation: QHx220 noise canceler

Gain Q Gain I λ/4 Delay

Σ Σ

Interference Sample Signal + Interference Cancellation Signal Clean Signal

35

Off-the-shelf electronically tunable hardware approximation: QHx220 noise canceler

Gain Q Gain I λ/4 Delay

Σ Σ

TX RX Wireless Receiver Wireless Transmitter TX Signal Path RX Signal Path

RSSI

Control Feedback Balun

36

Off-the-shelf electronically tunable hardware approximation: QHx220 noise canceler But ...

• Uses λ/4 delay to generate quadrature

component: Not precise for all frequencies

• Active components for gain: saturation

leading to non-linearities

37

Off-the-shelf electronically tunable hardware approximation: QHx220 noise canceler

38

Typical convergence within 8-15 iterations (~1ms total)

39

40

Saddle Point Recovery from local minimas and saddle points possible, needs more iterations

41

• ~65% converge without going through a local minima
• 98% converge in <20 iterations

• RF Cancellation using Signal Inversion: ~50dB for 20Mhz
• Adaptive RF Cancellation: ~1ms convergence
• System Performance
• Implications to Wireless Networks
• Looking Forward

Talk Outline

42

Digital Cancellation

43

• Measure residual self-interference after RF

cancellation

• Subtract self-interference from received digital

signal

44

Analog Conversion and Shaping

TX Signal

TX Filtering and Digital Conversion

Residual Self-interference

RX Digital Receiver

45

Analog Conversion and Shaping

TX Signal

TX Filtering and Digital Conversion RX

∑

+

• Channel

Model Digital Receiver

Cancellation Signal

Digital Cancellation

Residual Self-interference

46

Digital Interference Cancellation

TX RX Attenuation & Delay RF ➔ Baseband ADC Baseband ➔ RF DAC Encoder Decoder

Digital Interference Reference

RF Cancellation

TX Signal Path RX Signal Path RF Reference

Σ

FIR filter

• RSSI

Control Feedback Channel Estimate

Balun

Bringing It All Together

47

Performance

• ~73 dB cancellation
• WLAN full-duplex:

Yes, with reasonable antenna separation

• Not enough for cellular full-duplex

48

Channel Coherence

~3dB reduction in cancellation in 1-2 seconds ~6dB reduction in <10 seconds

• RF Cancellation using Signal Inversion: ~50dB for 20Mhz
• Adaptive RF Cancellation: ~1ms convergence
• System Performance: ~73dB cancellation
• Implications to Wireless Networks
• Looking Forward

Talk Outline

49

• Breaks a basic assumption in wireless
• Can solve some fundamental problems with

wireless networks today[1,2]

• Hidden terminals
• Network congestion and WLAN fairness

Implications to Wireless Networks

50

[1] Choi et al. “Achieving single channel, full duplex wireless communication”, in Mobicom 2010 [2] Singh et al. “Efficient and Fair MAC for Wireless Networks with Self- interference Cancellation”, in WiOpt 2011

• WARPv2 boards with 2 radios
• OFDM reference code from Rice

University

• 10MHz bandwidth OFDM signaling
• CSMA MAC on embedded processor
• Modified for Full-duplex

Implementation

51

• CSMA/CA can’t solve this
• Schemes like RTS/CTS introduce significant overhead

AP N1 N2

Current networks have hidden terminals

Mitigating Hidden Terminals

52

• CSMA/CA can’t solve this
• Schemes like RTS/CTS introduce significant overhead

AP N1 N2

Since both sides transmit at the same time, no hidden terminals exist Current networks have hidden terminals Full Duplex solves hidden terminals

AP N1 N2

Mitigating Hidden Terminals

53

• CSMA/CA can’t solve this
• Schemes like RTS/CTS introduce significant overhead

AP N1 N2

Since both sides transmit at the same time, no hidden terminals exist Current networks have hidden terminals Full Duplex solves hidden terminals

AP N1 N2

Mitigating Hidden Terminals

54

Reduces hidden terminal losses by up to 88%

Network Congestion and WLAN Fairness

Without full-duplex:

• 1/n bandwidth for each node in network, including AP

Downlink Throughput = 1/n Uplink Throughput = (n-1)/n

55

Network Congestion and WLAN Fairness

Without full-duplex:

• 1/n bandwidth for each node in network, including AP

Downlink Throughput = 1/n Uplink Throughput = (n-1)/n

56

With full-duplex:

• AP sends and receives at the same time

Downlink Throughput = 1 Uplink Throughput = 1

Network Congestion and WLAN Fairness

57

1 AP with 4 stations without any hidden terminals

Throughput (Mbps)

• ughput (Mbps)

Fairness (JFI) Upstream Downstream Fairness (JFI) Half-Duplex 5.18 2.36 0.845 Full-Duplex 5.97 4.99 0.977

Full-duplex distributes its performance gain to improve fairness

• RF Cancellation using Signal Inversion: ~50dB for 20Mhz
• Adaptive RF Cancellation: ~1ms convergence
• Adaptive Digital Cancellation: ~30dB cancellation
• System Performance: ~73dB cancellation
• Implications to Wireless Networks: Collisions, Fairness
• Looking Forward

Talk Outline

58

• Other cancellation techniques

Digital estimation for analog cancellation[1]

59

TX RX RF ➔ Baseband ADC Baseband ➔ RF DAC TX Signal RX Signal

Σ

Baseband ➔ RF DAC Cancellation Signal

[1] Duarte et al. “Full-Duplex Wireless Communications Using Off-The-Shelf Radios: Feasibility and First Results.”, in Asilomar 2010.

• Other cancellation techniques

Digital estimation for analog cancellation[1]

• Non-linear channel response

60

• Other cancellation techniques

Digital estimation for analog cancellation[1]

• Non-linear channel response

Reduce distortion: feedforward amplifiers

61

TX Signal High Power Amplifier

• Other cancellation techniques

Digital estimation for analog cancellation[1]

• Non-linear channel response

Reduce distortion: feedforward amplifiers

62

TX Signal

Estimate Distortion

∑

+ -

High Power Amplifier

• Other cancellation techniques

Digital estimation for analog cancellation[1]

• Non-linear channel response

Reduce distortion: feedforward amplifiers Compensate: non-linear digital cancellation

63

• Other cancellation techniques

Digital estimation for analog cancellation[1]

• Non-linear channel response

Reduce distortion: feedforward amplifiers Compensate: non-linear digital cancellation

• Single antenna solution: circulators

64

TX Signal RX Signal

Circulator

• Other cancellation techniques

Digital estimation for analog cancellation[1]

• Non-linear channel response

Reduce distortion: feedforward amplifiers Compensate: non-linear digital cancellation

• Single antenna solution: circulators
• Device precision: 1 ps resolution for delay line

65

• Other cancellation techniques

Digital estimation for analog cancellation[1]

• Non-linear channel response

Reduce distortion: feedforward amplifiers Compensate: non-linear digital cancellation

• Single antenna solution: circulators
• Device precision: 1 ps resolution for delay line
• Going mobile: Higher cancellation, faster adaptation

66

• Other cancellation techniques

Digital estimation for analog cancellation[1]

• Non-linear channel response

Reduce distortion: feedforward amplifiers Compensate: non-linear digital cancellation

• Single antenna solution: circulators
• Device precision: 1 ps resolution for delay line
• Going mobile: Higher cancellation, faster adaptation
• MIMO full-duplex

67

68

Access Point networks

Full-duplex Networking

69

Access Point networks Cellular networks

Cell Basestation Relay

Full-duplex Networking

70

Access Point networks Multi-hop Networks Cellular networks

Cell Basestation Relay

Full-duplex Networking

71

Access Point networks Multi-hop Networks Secure Networks[1,2] Cellular networks

Cell Basestation Relay

Full-duplex Networking

[1] Gollakota et al. “They Can Hear Your Heartbeats: Non-Invasive Security for Implantable Medical Devices.”, in Sigcomm 2011. [2] Lee et al. “Secured Bilateral Rendezvous using Self-interference Cancellation in Wireless Networks”, in IFIP 2011.

72

Access Point networks Multi-hop Networks Secure Networks[1,2] Cellular networks

Cell Basestation Relay

Full-duplex Networking

[1] Gollakota et al. “They Can Hear Your Heartbeats: Non-Invasive Security for Implantable Medical Devices.”, in Sigcomm 2011. [2] Lee et al. “Secured Bilateral Rendezvous using Self-interference Cancellation in Wireless Networks”, in IFIP 2011.

?

73

Thank You Questions?

Backup

74

• RF Cancellation using Signal Inversion: ~50dB for 20Mhz
• Adaptive RF Cancellation: ~1ms convergence
• Adaptive Digital Cancellation
• System Performance
• Implications to Wireless Networks
• Looking Forward

Talk Outline

75

Digital Cancellation

76

• Create a precise “digital replica” of the self-

interference signal using TX digital samples

• Subtract self-interference replica from received

digital signal Requires ADC not saturated: RF cancellation

77

OFDM processing

Signal Band

78

OFDM processing

Sub-bands

79

OFDM processing

Channel Distortion

80

OFDM processing

Channel Distortion Equalization

OFDM processing

81

ADC RX

RF Mixer

Carrier Frequency Carrier Frequency Offset Correction Packet Detect FFT Engine Channel Estimation Equalization Demapping

Channel Distortion Equalization

Step 1: Estimation

82

Self-interference Sounding

Preamble Training Sequence

Self-interference Estimate

FIR Filter

ADC RX

RF Mixer

Carrier Frequency Carrier Frequency Offset Correction Packet Detect FFT Engine Channel Estimation Equalization Demapping IFFT

Estimation includes effect of RF cancellation

Step 2: Cancellation

83

ADC RX

RF Mixer

Carrier Frequency Carrier Frequency Offset Correction Packet Detect FFT Engine Channel Estimation Equalization Demapping

TX Signal

+-

Self-interference Estimate

FIR Filter

IFFT

Cancellation Signal

Step 2: Cancellation

84

ADC RX

RF Mixer

Carrier Frequency Carrier Frequency Offset Correction Packet Detect FFT Engine Channel Estimation Equalization Demapping

TX Signal

+-

Self-interference Estimate

FIR Filter

IFFT

Cancellation Signal

30dB Cancellation

• RF Cancellation using Signal Inversion: ~50dB for 20Mhz
• Adaptive RF Cancellation: ~1ms convergence
• Adaptive Digital Cancellation: ~30dB cancellation
• System Performance
• Implications to Wireless Networks
• Looking Forward

Talk Outline

85

Attenuator

Phase Offset Cancellation: Block Diagram

d d +

λ/2

TX1 TX2 RX RX RF Frontend Digital Processor TX RF Frontend Power Splitter

86

• 60
• 55
• 50
• 45
• 40
• 35
• 30
• 25

5 10 15 20 25

RSSI (dBm)

Position of Receive Antenna (cm)

TX1 TX2

Only TX1 Active

Phase Offset Cancellation: Performance

87

• 60
• 55
• 50
• 45
• 40
• 35
• 30
• 25

5 10 15 20 25

RSSI (dBm)

Position of Receive Antenna (cm)

TX1 TX2

Only TX2 Active

88

Only TX1 Active

Phase Offset Cancellation: Performance

• 60
• 55
• 50
• 45
• 40
• 35
• 30
• 25

5 10 15 20 25

RSSI (dBm)

Position of Receive Antenna (cm)

Null Position

TX1 TX2

89

Only TX1 Active Only TX2 Active Both TX1 & TX2 Active

Phase Offset Cancellation: Performance

• 60
• 55
• 50
• 45
• 40
• 35
• 30
• 25

5 10 15 20 25

RSSI (dBm)

Position of Receive Antenna (cm)

Null Position

TX1 TX2

90

~25-30dB

Only TX1 Active Only TX2 Active Both TX1 & TX2 Active

Phase Offset Cancellation: Performance

91

What about attenuation at intended receivers? Destructive interference can affect this signal too!

• Different transmit powers for two TX helps

Single Transmit Antenna

Two Transmit Antennas

10 20 30

• 30 -20 -10

10 20 30

• 30
• 20
• 10

x axis (meters) y axis (meters)

• 52 dBm
• 58 dBm

10 20 30

• 30 -20 -10

10 20 30

• 30
• 20
• 10

x axis (meters) y axis (meters)

• 52 dBm

Sensitivity of Phase Offset Cancellation

92

Amplitude Mismatch between TX1 and TX2 Placement Error for RX

dB Cancellation (dB) Cancellation (dB) Error (mm)

Higher is better Higher is better

Amplitude Mismatch between TX1 and TX2 Placement Error for RX

dB Cancellation (dB) Cancellation (dB) Error (mm)

93

30dB cancellation < 5% (~0.5dB) amplitude mismatch < 1mm distance mismatch

Sensitivity of Phase Offset Cancellation

94

• Rough prototype good for 802.15.4
• More precision needed for higher power systems (802.11)

Amplitude Mismatch between TX1 and TX2 Placement Error for RX

dB Cancellation (dB) Cancellation (dB) Error (mm)

Sensitivity of Phase Offset Cancellation

Bandwidth Constraint

95

fc

d d + λ/2 TX1 TX2 RX

A λ/2 offset is precise for one frequency

Bandwidth Constraint

A λ/2 offset is precise for one frequency not for the whole bandwidth

96

fc

fc+B fc -B

d d + λ/2 TX1 TX2 RX

Bandwidth Constraint

A λ/2 offset is precise for one frequency not for the whole bandwidth

97

fc

fc+B fc -B

d d + λ/2 TX1 TX2 RX d2 d2 + λ+B/2 TX1 TX2 RX d1 d1 + λ-B/2 TX1 TX2 RX

Bandwidth Constraint

A λ/2 offset is precise for one frequency not for the whole bandwidth

98

fc

fc+B fc -B

d d + λ/2 TX1 TX2 RX d2 d2 + λ+B/2 TX1 TX2 RX d1 d1 + λ-B/2 TX1 TX2 RX

WiFi (2.4G, 20MHz) => ~0.26mm precision error

Bandwidth Constraint

99

2.4 GHz 5.1 GHz 300 MHz fc Edge frequency

Bandwidth Constraint

100

• WiFi (2.4GHz, 20MHz): Max 47dB reduction
• Bandwidth⬆ => Cancellation⬇
• Carrier Frequency⬆ => Cancellation⬆

2.4 GHz 5.1 GHz 300 MHz

Mitigating Hidden Terminals

101

0.5 0.6 0.7 0.8 0.9 2000 4000 6000 8000 Data Load (Kbps) Packet Reception Ratio Full Duplex Half Duplex

0.5 0.6 0.7 0.8 0.9 2000 4000 6000 8000

Mitigating Hidden Terminals

102

Data Load (Kbps) Packet Reception Ratio Full Duplex Half Duplex

• Full-duplex reduces hidden terminal related losses by 88% at 2 Mbps

Mitigating Hidden Terminals

103

0.700 0.775 0.850 0.925 1.000 2000 4000 6000 8000 Data Load (Kbps) Fairness (JFI) Full Duplex Half Duplex

• Full-duplex reduces hidden terminal related losses by 88% at 2 Mbps
• At higher loads, half-duplex improves PRR at the expense of fairness

0.5 0.6 0.7 0.8 0.9 2000 4000 6000 8000 Data Load (Kbps) Packet Reception Ratio Full Duplex Half Duplex