Achieving Single Channel Full-Duplex Wireless Communication Jung Il - - PowerPoint PPT Presentation

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Achieving Single Channel Full-Duplex Wireless Communication Jung Il - - PowerPoint PPT Presentation

Oct 01, 2022 387 likes •1.06k views

Achieving Single Channel Full-Duplex Wireless Communication Jung Il Choi, Mayank Jain, Kannan Srinivasan, Philip Levis and Sachin Katti 1 Can a wireless node transmit AND receive at the same time on a single band? 2 Can a wireless node

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SLIDE 1

Achieving Single Channel Full-Duplex Wireless Communication

Jung Il Choi, Mayank Jain, Kannan Srinivasan, Philip Levis and Sachin Katti

1

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SLIDE 2

Can a wireless node transmit AND receive at the same time on a single band?

2

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SLIDE 3

Can a wireless node transmit AND receive at the same time on a single band?

3

Status quo: NO

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SLIDE 4

Current wireless radios

  • In-band half-duplex
  • Full-duplex through other dimensions
  • E.g. different frequencies
  • Bandwidth is a precious resource

4

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SLIDE 5

Why not full-duplex on the same band?

5

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SLIDE 6

Why not full-duplex on the same band?

  • Very strong self-interference
  • ~70dB stronger for 802.15.4
  • Analog to Digital converter (ADC) saturates

TX RX

6

TX RX

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SLIDE 7
  • Digital cancellation: Subtracting known interference

digital samples from received digital samples. ZigZag[1], Analog Network Coding[2] etc.

  • Hardware cancellation: RF noise cancellation circuits with

transmit signal as noise reference Radunovic et al.[3]

Existing Techniques

7

[1] Gollakota et al. “ZigZag Decoding: Combating Hidden Terminals in Wireless Networks”, ACM SIGCOMM 2008 [2] Katti et al. “Embracing Wireless Interference: Analog Network Coding”, ACM SIGCOMM 2007 [3] Radunovic et al. , "Rethinking Indoor Wireless: Lower Power, Low Frequency, Full-duplex", WiMesh (SECON Workshop),, 2010

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SLIDE 8
  • Digital cancellation: Subtracting known interference

digital samples from received digital samples. ZigZag[1], Analog Network Coding[2] etc. Ineffective if ADC is saturated

  • Hardware cancellation: RF noise cancellation circuits with

transmit signal as noise reference Radunovic et al.[3]

Existing Techniques

8

[1] Gollakota et al. “ZigZag Decoding: Combating Hidden Terminals in Wireless Networks”, ACM SIGCOMM 2008 [2] Katti et al. “Embracing Wireless Interference: Analog Network Coding”, ACM SIGCOMM 2007 [3] Radunovic et al. , "Rethinking Indoor Wireless: Lower Power, Low Frequency, Full-duplex", WiMesh (SECON Workshop),, 2010

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SLIDE 9

These are not enough 25dB +15dB < 70dB

  • Digital cancellation: Subtracting known interference

digital samples from received digital samples. ZigZag[1], Analog Network Coding[2] etc. ~15dB Ineffective if ADC is saturated

  • Hardware cancellation: RF noise cancellation circuits with

transmit signal as noise reference Radunovic et al.[3] ~25dB

Existing Techniques

9

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SLIDE 10

Our innovation: Antenna Cancellation

d d + λ/2 TX1 TX2 RX

10

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SLIDE 11

Our innovation: Antenna Cancellation ~30dB self-interference cancellation

Enables full-duplex when combined with Digital (15dB) and Hardware (25dB) cancellation.

d d + λ/2 TX1 TX2 RX

11

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SLIDE 12

Can a wireless node transmit AND receive at the same time on a single band?

12

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SLIDE 13

Can a wireless node transmit AND receive at the same time on a single band? YES, IT CAN! Full-duplex prototype achieves 92% of the throughput of an “ideal” full-duplex system

13

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SLIDE 14
  • Design of Full-Duplex Wireless
  • 3 Techniques: Antenna, Hardware and

Digital Cancellation

  • Analyzing Antenna Cancellation
  • Performance Results
  • Implications to Wireless Networks
  • Limitations of Design, Future Work

Talk Outline

14

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SLIDE 15
  • Design of Full-Duplex Wireless
  • 3 Techniques: Antenna, Hardware and

Digital Cancellation

  • Analyzing Antenna Cancellation
  • Performance Results
  • Implications to Wireless Networks
  • Limitations of Design, Future Work

Talk Outline

15

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SLIDE 16

Three techniques give ~70dB cancellation

  • Antenna Cancellation (~30dB)
  • Hardware Cancellation (~25dB)
  • Digital Cancellation (~15dB)

16

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SLIDE 17

Attenuator

Antenna Cancellation: Block Diagram

d d +

λ/2

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

17

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SLIDE 18

Hardware and Digital Cancellation

* Radunovic et al. , "Rethinking Indoor Wireless: Lower Power, Low Frequency, Full-duplex", MSR Tech Report, 2009

Digital Cancellation

  • Subtract known transmit samples from received

digital samples Hardware Cancellation

  • Use existing interference

cancellation circuits (QHx220)*

18

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SLIDE 19

Bringing It Together

QHX220

ADC

Hardware Cancellation

TX Signal

Antenna Cancellation

19

RX

Digital Cancellation

∑

TX Samples

+

  • Clean RX samples

RF Baseband

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SLIDE 20

Bringing It Together

QHX220

ADC

Hardware Cancellation

TX Signal

Antenna Cancellation

20

RX

Digital Cancellation

∑

TX Samples

+

  • Clean RX samples

RF Baseband

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SLIDE 21

Bringing It Together

QHX220

ADC

Hardware Cancellation

TX Signal

Antenna Cancellation

21

RX

Digital Cancellation

∑

TX Samples

+

  • Clean RX samples

RF Baseband

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SLIDE 22

Bringing It Together

QHX220

ADC

Hardware Cancellation

TX Signal

Antenna Cancellation

22

RX

Digital Cancellation

∑

TX Samples

+

  • Clean RX samples

RF Baseband

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SLIDE 23

Our Prototype

23

Antenna Cancellation Hardware Cancellation Digital Interference Cancellation

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SLIDE 24
  • Design of Full-Duplex Wireless
  • 3 Techniques: Antenna, Hardware and

Digital Cancellation

  • Analyzing Antenna Cancellation
  • Performance Results
  • Implications to Wireless Networks
  • Limitations of Design, Future Work

Talk Outline

24

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SLIDE 25
  • 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

Antenna Cancellation: Performance

25

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SLIDE 26
  • 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

Antenna Cancellation: Performance

26

Only TX1 Active

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SLIDE 27
  • 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 Only TX2 Active Both TX1 & TX2 Active

Antenna Cancellation: Performance

27

Null Position

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SLIDE 28
  • 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 Only TX2 Active Both TX1 & TX2 Active

Antenna Cancellation: Performance

28

~25-30dB

Null Position

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SLIDE 29

Sensitivity of Antenna Cancellation

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Amplitude Mismatch between TX1 and TX2 Placement Error for RX

dB Reduction Limit (dB) Reduction Limit (dB) Error (mm)

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SLIDE 30

Sensitivity of Antenna Cancellation

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dB Reduction Limit (dB) Reduction Limit (dB) Error (mm)

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

Amplitude Mismatch between TX1 and TX2 Placement Error for RX

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SLIDE 31

Sensitivity of Antenna Cancellation

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dB Reduction Limit (dB) Reduction Limit (dB) Error (mm)

  • 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

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SLIDE 32

Bandwidth Constraint

A λ/2 offset is precise for one frequency

32

fc

d d + λ/2 TX1 TX2 RX

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SLIDE 33

Bandwidth Constraint

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

33

fc

fc+B fc -B

d d + λ/2 TX1 TX2 RX

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SLIDE 34

Bandwidth Constraint

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

34

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

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SLIDE 35

Bandwidth Constraint

35

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

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

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SLIDE 36

Bandwidth Constraint

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2 . 4 G H z 5 . 1 G H z 3 M H z

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SLIDE 37

Bandwidth Constraint

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2 . 4 G H z 5 . 1 G H z 3 M H z

  • WiFi (2.4GHz, 20MHz): Max 47dB reduction
  • Bandwidth⬆ => Cancellation⬇
  • Carrier Frequency⬆ => Cancellation⬆
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SLIDE 38

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

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SLIDE 39

10 20 30

  • 30 -20 -10

10 20 30

  • 30
  • 20
  • 10

x axis (meters) y axis (meters)

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Equal Transmit Power Deep Nulls at 20-30m

Unequal Transmit Power

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

  • Different transmit powers for two TX helps

10 20 30

  • 30 -20 -10

10 20 30

  • 30
  • 20
  • 10

x axis (meters) y axis (meters)

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SLIDE 40

10 20 30

  • 30 -20 -10

10 20 30

  • 30
  • 20
  • 10

x axis (meters) y axis (meters)

40

Equal Transmit Power

Unequal Transmit Power

10 20 30

  • 30 -20 -10

10 20 30

  • 30
  • 20
  • 10

x axis (meters) y axis (meters)

  • 52 dBm
  • 58 dBm
  • 52 dBm
  • 100 dBm

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

  • Different transmit powers for two TX helps
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SLIDE 41

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

  • Different transmit powers for two TX helps
  • Diversity gains in indoor environments
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SLIDE 42
  • Design of Full-Duplex Wireless
  • 3 Techniques: Antenna, Hardware and

Digital Cancellation

  • Analyzing Antenna Cancellation
  • Performance Results
  • Implications to Wireless Networks
  • Limitations of Design, Future Work

Talk Outline

42

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SLIDE 43
  • 802.15.4 based signaling on USRP nodes
  • Two nodes at varying distances placed in an
  • ffice building room and corridor

Experimental Setup

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SLIDE 44
  • Full-duplex should double aggregate throughput

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Half-Duplex :- Nodes interleave transmissions

Node 1 ! 2

Node 2 ! 1

Node 1 ! 2

Node 2 ! 1

Full-Duplex :- Nodes transmit concurrently

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SLIDE 45

Median throughput 92% of ideal full-duplex

Throughput

0.2 0.4 0.6 0.8 1.0

50 100 150 200 250 300 CDF Throughput (Kbps) Half-Duplex Full-Duplex Ideal Full-Duplex

1.84x

45

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SLIDE 46

0.2 0.4 0.6 0.8 1.0

50 100 150 200 250 300 CDF Throughput (Kbps)

Throughput

Half-Duplex Full-Duplex Ideal Full-Duplex

1.84x

46

Performance loss at low SNR

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SLIDE 47

Little loss in link reliability: 88% of half-duplex on average

Link Reception Ratio

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0.25 0.50 0.75 1.00 10 20 30 40 Packet Reception Ratio SNR (dB) Half-Duplex Full-Duplex

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SLIDE 48

0.25 0.50 0.75 1.00 10 20 30 40 Packet Reception Ratio SNR (dB)

Link Reception Ratio

Half-Duplex Full-Duplex

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  • Loss at High SNR: Due to spurious signal peaks in USRP

Loss at High SNR

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SLIDE 49

0.25 0.50 0.75 1.00 10 20 30 40 Packet Reception Ratio SNR (dB) Half-Duplex Full-Duplex

Link Reception Ratio

  • Loss at High SNR: Due to spurious signal peaks in USRP
  • Loss at low SNR: Due to imprecisions in prototype

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Loss at Low SNR

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SLIDE 50
  • Design of Full-Duplex Wireless
  • 3 Techniques: Antenna, Hardware and

Digital Cancellation

  • Analyzing Antenna Cancellation
  • Performance Results
  • Implications to Wireless Networks
  • Limitations of Design, Future Work

Talk Outline

50

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SLIDE 51

The prototype gives 1.84x throughput gain with two radios compared to half-duplex with a single radio So what? PHY gains similar to 2x2 MIMO

51

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SLIDE 52

The prototype gives 1.84x throughput gain with two radios compared to half-duplex with a single radio So what? PHY gains similar to 2x2 MIMO True benefit lies beyond the physical layer

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SLIDE 53
  • Breaks a basic assumption in wireless
  • Can solve some fundamental problems with

wireless networks today

  • Hidden terminals
  • Primary detection in whitespaces
  • Network congestion and WLAN fairness
  • Excessive latency in multihop wireless

Implications to Wireless Networks

53

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SLIDE 54
  • CSMA/CA can’t solve this
  • Schemes like RTS/CTS introduce significant overhead

AP N1 N2

Current networks have hidden terminals

Mitigating Hidden Terminals

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SLIDE 55
  • 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

55

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SLIDE 56

Primary Detection in Whitespaces

Secondary transmitters should sense for primary transmissions before channel use

Time

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Primary TX (Wireless Mics) Secondary TX (Whitespace AP)

Primary sensing

Primary TX (Wireless Mics) Secondary TX (Whitespace AP)

Traditional nodes may still interfere during transmissions

Interference

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SLIDE 57

Primary Detection in Whitespaces

Secondary transmitters should sense for primary transmissions before channel use

Time

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Primary sensing

Primary TX (Wireless Mics) Secondary TX (Whitespace AP)

Full-duplex nodes can sense and send at the same time

Primary sensing

Primary TX (Wireless Mics) Secondary TX (Whitespace AP)

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SLIDE 58

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

58

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SLIDE 59

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

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With full-duplex:

  • AP sends and receives at the same time

Downlink Throughput = 1 Uplink Throughput = 1

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SLIDE 60

Long delivery and round-trip times in multi- hop networks Solution: Wormhole routing

N1 N2 N3 N4

N1 N2 N3 N4 N1 N2 N3 N4

Time Time

Half-duplex

Time

Full-duplex

Reducing Round-Trip Times

60

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SLIDE 61
  • Design of Full-Duplex Wireless
  • 3 Techniques: Antenna, Hardware and

Digital Cancellation

  • Analyzing Antenna Cancellation
  • Performance Results
  • Implications to Wireless Networks
  • Limitations of Design, Future Work

Talk Outline

61

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SLIDE 62
  • Bandwidth Constraint

Working on a frequency independent signal inversion technique

  • Time-varying wireless channel

Auto-tuning of the hardware cancellation circuit

  • Multi-path

Estimate and incorporate in digital cancellation: Some existing work does this

  • Single stream

Extension to MIMO-like systems

62

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SLIDE 63

Summary

  • Prototype for achieving in-band full-duplex wireless
  • Constraints of current prototype can be overcome

with some neat ideas and careful engineering

  • Rethinking of wireless networks
  • We’ve discussed some applications like mitigating

hidden terminals and WLAN fairness

  • Many more possibilities

63

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SLIDE 64

From 3 antennas to 2 antennas ! solves bandwidth problem

Demo on Wednesday

64

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SLIDE 65

Summary

  • Prototype for achieving in-band full-duplex wireless
  • Constraints of current prototype can be overcome

with some neat ideas and careful engineering

  • Rethinking of wireless networks
  • We’ve discussed some applications like mitigating

hidden terminals and WLAN fairness

  • Many more possibilities

65

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SLIDE 66

Summary

  • Prototype for achieving in-band full-duplex wireless
  • Constraints of current prototype can be overcome

with some neat ideas and careful engineering

  • Rethinking of wireless networks
  • We’ve discussed some applications like mitigating

hidden terminals and WLAN fairness

  • Many more possibilities

66

PS: We’re looking for jobs starting mid-2011 :)

Kannan: Academic Mayank and Jung IL: Industrial Research