StripComm Interference-resilient Cross-technology Communication in - - PowerPoint PPT Presentation

StripComm

Interference-resilient Cross-technology Communication in Coexisting Environments

Xiaolong Zheng, Yuan He, Xiuzhen Guo

Tsinghua University

Wireless Coexistence

• Heterogeneous devices coexist
• Contention for the shared frequency resource
• Cooperation for smarter service

2

Interconnect Various Technologies

• Cross-technology Communication (CTC)
• Emerging technique
• Enable direct communication between heterogeneous

wireless technologies

3

Frequency (MHz) Frequency (MHz) Frequency (MHz) 1 22MHz 2437 2462

WiFi IEEE 802.11 ZigBee IEEE 802.15.4 Bluetooth IEEE 802.15.1

2412 6 11 2405 2480 2402 2480 Channel Spacing 5MHz 1MHz Channel 11 Channel 26 Channel 2 3 4 5 7 8 9 10 12 13

Existing CTC

• Packet-level CTC
• Manipulating the packet amplitude, packet timing to

build the side channel.

• Require radio silence

4

Energy modulation:

Packet presence  1 Packet absence  0

CTC Zzz... Zzz...

Radio silence for CTC

WiZig Multiple energy levels

Motivation

• However…
• Wireless coexistence
• Hard to keep radio silence for all devices

5

Energy modulation:

Packet presence  1 Packet absence  0

CTC Zzz... Zzz...

Radio silence for CTC Coexisting Interference Coexisting Interference

Coexisting interference will …?

Motivation

• We study the performance of WiZig in an apartment
• A CTC WiFi sender, a CTC ZigBee receiver
• Uncontrolled ambient WiFi devices

6

High SER Low Throughput SNR=CTC signal strength / channel noise + coexisting interference

Motivation

• Insight:
• CTC rely on packet presence/absence, which is easily

corrupted by the interference.

7

0 a/2 a x

(a)

0 a/2a x

(b)

0 a/2a' x

(c)

a/2a x

(d)

aI f(x) f(x) f(x) f(x) TX Symbol 802.11 Sender 802.15.4 Receiver (without interference) Interference 802.15.4 Receiver (with interference) RX symbol RX symbol

1 1 1 1 1 1 1 1 1 1

Time

T1 T2 T5 T4 T3

fN(x) fS(x) fN(x) fS(x) fN(x) fS,I(x) fN(x) fS(x) fI(x)

Interference leads to the false appearance of CTC packet presence

Outline

• Background & Motivation
• Design of StripComm
• Interference-resilient coding
• Interference-aware decoding
• Evaluation
• Conclusion

8

Design

• Goal: Interference-resilient CTC that achieves high

throughput with low error rate even under coexisting interference.

9

StripComm Receiver

RSS Segments Filtered RSS

StripComm PHY Layer

Data Stream

StripComm Sender

Schedule

T* PI, L, I StripComm PHY Layer

Data Stream

1 1 1

Logical Channel Physical Channel

RSS Segmentation Parameter Estimation Interference Cancelation Symbol Demodulation Packet TX Scheduling Symbol Modulation Parameter Selection Link Layer PHY Layer Link Layer PHY Layer Interference Estimation

T, a

Interference-resilient coding Interference-aware decoding

Interference-resilient coding

• Manchester Coding
• Use both packet presence (high) and absence (low) to

encode a symbol

• Symbol 1: high then low
• Symbol 0: low then high

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L 1 1 1 1 1 T Amplitude Energy signal Interference T Amplitude 1 1 1 L K AM CTC StripComm

Interference-resilient coding

• StripComm defines a packet preamble to specify the

start of a CTC packet

• StripComm sender controls the packet length and

transmission timing, based on the encoded CTC symbols.

11

Interference-aware decoding

• Find falling and rising edges, and decode symbols by the “high

then low” and “low then high” patterns of the RSS sequence.

• However, the segments’ amplitude, length, interval can be

corrupted.

12

Overlapped Inserted

Interference-aware decoding

• Use self similarity to strip interference from the

interested signal

13

50% High, 50% Low TH = TL

Interference-aware decoding

• Use self similarity to strip interference from the

interested signal

14

Ti = Ti+1 ISIi = T/2 ISIi = T

Interference-aware decoding

• Use self similarity to strip interference from the

interested signal

15

Packets experience similar channel conditions in a short time, 𝜀𝑗

𝑏 ≈ 𝜀𝑗+1 𝑏

𝑏𝑗 ≈ 𝑏𝑗+1 𝑏𝑗 ≈ 𝑏𝑗+1 𝑏𝑗 ≈ 𝑏𝑗+1 𝜀𝑗

𝑏 ≈ 𝜀𝑗+1 𝑏

𝜀𝑗

𝑏 ≈ 𝜀𝑗+1 𝑏

Interference-aware decoding

• Use self similarity to strip interference from the

interested signal

• Decode the symbols from the processed RSS

sequence (blue sequences)

16

Outline

• Background & Motivation
• Design of StripComm
• Interference-resilient coding
• Interference-aware decoding
• Evaluation
• Conclusion

17

Evaluation

• Setup
• ZigBee: TelosB (raido: cc2420)
• WiFi: commercial laptops, D-ITG traffic generator

USRP/N210

• Environments:
• Office and lab

18

Overall Performance

• Throughput
• When Symbol Error Rate (SER) < 0.01
• WiFi -> ZigBee: 1.1Kbps, 6.5X higher than the state-of-the-art
• ZigBee - > WiFi: 77,8bps, 3.3X higher than the state-of-the-art

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WiFi->ZigBee ZigBee->WiFi Throughput (bps) 1.1K 31.5 77.8 167.8 14.6 10 30 100 200 1000 StripComm FreeBee StripComm FreeBee WiZig WiZig 23.7

6.5 times 34.9 times 3.3 times 5.3 times

Performance under Interference

• SER vs. Interference rate (packets/second)

20

SER Packet size = 50bytes Packet size = 1000bytes

(1) With interference rate increases, SER increases; (2) Stripcomm has a low SER; (3) Interference-resilient coding can conquer partial interference; (4) Interference-aware decoding can solve most of the interference.

Performance under Interference

• Throughput vs. Interference rate (packets/second)

21

Throughput Packet size = 50bytes Packet size = 1000bytes

(1) With interference rate increases, throughput decreases; (2) Stripcomm has relative stable throughput due to the low SER; (3) Interference-aware decoding significantly improves the throughput.

Performance vs. Distance

• Distance between the sender and receiver

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StripComm from WiFi to ZigBee StripComm from ZigBee to WiFi (1) From WiFi to ZigBee, throughput decreases slightly; (2) From ZigBee to WiFi, throughput decreases significantly; (3) StripComm from ZigBee to WiFi is more sensitive to distance than from WiFi to ZigBee due to the high TX power of WiFi.

Conclusion

• We present StripComm, an interference-resilient CTC.
• We design the interference-resilient coding method and

the interference-aware decoding method.

• We evaluate StripComm under various experimental

settings.

• Results demonstrate StripComm can achieve the throughput

up to 1.1Kbps, 6.5X higher than the state-of-the-art.

23

StripComm

Interference-resilient Cross-technology Communication in Coexisting Environments

Thank you! Q & A