StripComm. Interference-resilient Cross-technology Communication in Coexisting Environments. Tsinghua University. Xiaolong Zheng, Yuan He, Xiuzhen Guo

Transcription

1 StripComm Interference-resilient Cross-technology Communication in Coexisting Environments Xiaolong Zheng, Yuan He, Xiuzhen Guo Tsinghua University

2 Wireless Coexistence Heterogeneous devices coexist Contention for the shared frequency resource Cooperation for smarter service 2

3 Interconnect Various Technologies Cross-technology Communication (CTC) Emerging technique Enable direct communication between heterogeneous wireless technologies WiFi IEEE Channel Frequency (MHz) ZigBee IEEE MHz Channel Spacing 5MHz Frequency (MHz) Channel 11 Channel 26 Bluetooth IEEE Frequency (MHz) MHz Microwave Ovens 3

4 Existing CTC Packet-level CTC Manipulating the packet amplitude, packet timing to build the side channel. Require radio silence CTC Energy modulation: Packet presence 1 Packet absence 0 Zzz... Radio silence for CTC Zzz... WiZig Multiple energy levels 4

5 Motivation However Wireless coexistence Hard to keep radio silence for all devices Coexisting interference will? CTC Coexisting Interference Zzz... Energy modulation: Packet presence 1 Packet absence 0 Radio silence for CTC Zzz... Coexisting Interference 5

6 Motivation We study the performance of WiZig in an apartment A CTC WiFi sender, a CTC ZigBee receiver Uncontrolled ambient WiFi devices High SER Low Throughput SNR=CTC signal strength / channel noise + coexisting interference 6

7 Motivation Insight: CTC rely on packet presence/absence, which is easily corrupted by the interference. Time T 1 T 2 T 3 T 4 T 5 f(x) f N(x) f S(x) TX Symbol Sender Receiver (without interference) RX symbol a/2 a x (a) f(x) f(x) f N(x) f S(x) 0 a/2a x (b) f N(x) f S,I(x) Interference Receiver (with interference) RX symbol a/2a' x (c) f(x) f N(x) f S(x) f I(x) 0 a/2 a a I x (d) Interference leads to the false appearance of CTC packet presence 7

8 Outline Background & Motivation Design of StripComm Interference-resilient coding Interference-aware decoding Evaluation Conclusion 8

9 Design Goal: Interference-resilient CTC that achieves high throughput with low error rate even under coexisting interference. StripComm Sender Link Layer StripComm Receiver Link Layer Data Stream StripComm PHY Layer Interference Estimation P I, L, I Parameter Selection T* Symbol Modulation Logical Channel Data Stream StripComm PHY Layer Symbol Demodulation Filtered RSS Interference Cancelation T, a Parameter Estimation Packet TX Scheduling Schedule PHY Layer Physical Channel Segments RSS Segmentation RSS PHY Layer Interference-resilient coding Interference-aware decoding 9

10 Amplitude Amplitude 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 K Energy signal L Interference AM CTC L T StripComm T 10

11 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

12 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. Overlapped Inserted 12

13 Interference-aware decoding Use self similarity to strip interference from the interested signal T H = T L 50% High, 50% Low 13

14 Interference-aware decoding Use self similarity to strip interference from the interested signal T i = T i+1 ISI i = T/2 ISI i = T 14

15 Interference-aware decoding Use self similarity to strip interference from the interested signal a i a i+1 δ a a i δ i+1 a i a i+1 a δ i a δ i+1 Packets experience similar channel conditions in a short time, δ a a a i a i+1 i δ i+1 15

16 Interference-aware decoding Use self similarity to strip interference from the interested signal Decode the symbols from the processed RSS sequence (blue sequences) 16

17 Outline Background & Motivation Design of StripComm Interference-resilient coding Interference-aware decoding Evaluation Conclusion 17

18 Evaluation Setup ZigBee: TelosB (raido: cc2420) WiFi: commercial laptops, D-ITG traffic generator USRP/N210 Environments: Office and lab 18

19 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 WiFi->ZigBee FreeBee WiZig times 6.5 times StripComm 1.1K ZigBee->WiFi FreeBee 14.6 WiZig times 3.3 times StripComm Throughput (bps)

20 SER Performance under Interference SER vs. Interference rate (packets/second) 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. 20

21 Throughput Performance under Interference Throughput vs. Interference rate (packets/second) (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. Packet size = 50bytes Packet size = 1000bytes 21

22 Performance vs. Distance Distance between the sender and receiver 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. 22

23 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

24 StripComm Interference-resilient Cross-technology Communication in Coexisting Environments Thank you! Q & A