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Backscatter-Aided Hybrid Data Offloading for
Wireless Powered Edge Sensor Networks
Yuze Zou, PhD
School of Electronic Information and Communications
Huazhong University of Science and Technology
IEEE Global Communications Conference
9-13 December 2019
Waikoloa, HI, USA
Revolutionizing Communications
Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks
Introduction
System Model
Energy Minimization for Hybrid Data
Offloading
Numerical Results
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Outline
Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks
Introduction
System Model
Energy Minimization for Hybrid Data
Offloading
Numerical Results
3/18
Outline
Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks
Introduction
4/18Img src: https://www.newgenapps.com/blog/influence-of-iot-on-wearable-technology
MECServer
Cloud Server
Edge Devices
Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks
Communication models in the edge sensor networks
Active Transmission
Relative high transmit rate
High energy consumption
Passive Transmission
Relative low transmit rate
Negligible energy consumption
Introduction
5/18
Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks
Introduction
System Model
Energy Minimization for Hybrid Data
Offloading
Numerical Results
6/18
Outline
Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks
System Model
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𝑆𝑖
𝑆𝑗
⋯
⋯⋯
𝑆𝑁
𝑆1
𝑔𝑖 ℎ𝑁
HAP
Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks
Time Allocation
Each sensor is allocated with fixed slot, say 𝑇/𝑁
Each sensor operate in passive and then active mode
Each sensor harvests energy when others in passive mode
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System Model
Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks
Signal Model Active communications
𝑟𝑎,𝑖 = 𝐵 log2 1 +𝑝𝑎,𝑖 ℎ𝑖
2
𝜎2
Passive communication
𝑟𝑝,𝑖 = 𝑟𝑝
NOTE: 𝑟𝑎,𝑖 > 𝑟𝑝,𝑖 holds true in general.
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System Model
Constant
𝑝𝑎,𝑖 = 𝛽 𝑟𝑎,𝑖≜ 2𝑟𝑎,𝑖/𝐵 − 1 𝜎2/ ℎ𝑖
2⟺ Power
Consumption
Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks
Introduction
System Model
Energy Minimization for Hybrid Data
Offloading
Numerical Results
10/18
Outline
Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks
11/18
Energy Minimization for Hybrid Data Offloading
min𝒕𝒂,𝒕𝒑
𝒊∈𝒩
𝑝0𝑡𝑝,𝑖
s. t. 𝑡𝑎,𝑖 + 𝑡𝑝,𝑖 ≤ 𝑇/𝑁
𝑙𝑎,𝑖 + 𝑙𝑝,𝑖 ≥ 𝐿𝑖
𝑡𝑎,𝑖 ෨𝛽𝑙𝑎,𝑖𝑡𝑎,𝑖
≤ 𝜂
𝑗∈𝒩𝑖
𝑝0𝑔𝑖2𝑡𝑝,𝑗
𝑡𝑎,𝑖 ≥ 0, 𝑡𝑝,𝑖 ≥ 0, 𝑙𝑎,𝑖 ≥ 0
Slot limitation
Task fulfillment
Energy constraint
Energy minimization at HAP
Physical constraint
෨𝛽 𝑟𝑎,𝑖 = 𝛽 𝑟𝑎,𝑖 + 𝑝𝑐,𝑖 denotes the energy consumption of sensor in active mode
𝜂: energy harvesting coefficient, 𝒩𝑖 = 𝒩\ 𝑖𝐿𝑖: total bits to offload of sensor 𝑖, 𝑙𝑎,𝑖 and 𝑙𝑏,𝑖: bits offloaded via active and passive mode, respectively
Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks
Energy Minimization for Hybrid Data Offloading
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Distributed reformulationmin𝒕𝒂,𝒕𝒑
𝒊∈𝒩
𝑝0𝑡𝑝,𝑖
s. t. 𝑡𝑎,𝑖 + 𝑡𝑝,𝑖 ≤ 𝑇/𝑁
𝑙𝑎,𝑖 + 𝑙𝑝,𝑖 ≥ 𝐿𝑖
𝑡𝑎,𝑖 ෨𝛽𝑙𝑎,𝑖𝑡𝑎,𝑖
≤ 𝜂
𝑗∈𝒩𝑖
𝑝0𝑔𝑖2𝑡𝑝,𝑗
𝑡𝑎,𝑖 ≥ 0, 𝑡𝑝,𝑖 ≥ 0, 𝑙𝑎,𝑖 ≥ 0
𝐸𝑖
Sensor 𝑖 is
aware of its
energy supply,
denote by 𝐸𝑖
> This motivates us to optimize sensors’ offloading scheme
in a distributed manner.
Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks
Energy Minimization for Hybrid Data Offloading
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min𝑡𝑎,𝑡𝑝,𝑟𝑎
𝑡𝑝
s. t. C1 𝑡𝑎 + 𝑡𝑝 ≤ 𝑡
C2 𝑡𝑎𝑟𝑎 + 𝑡𝑝𝑟𝑝 ≥ 𝐿
C3 𝑡𝑎𝛽 𝑟𝑎 + 𝑝𝑐𝑡𝑎 ≤ 𝐸
Closed-form solution can be
obtained for each sensor, thus
achieves 𝒪 1 complexity
Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks
Introduction
System Model
Energy Minimization for Hybrid Data
Offloading
Numerical Results
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Outline
Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks
Numerical Results
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HAP’s transmit power: 𝑝𝑡 = 100 mW
Frame length: 𝑇 = 10
Sensor workload: 𝐿 = 10 kbits
Energy harvesting efficiency: 𝜂 = 0.8
Circuit power: 𝑝𝑐 = 1 μW
Passive data rate: 𝑟𝑝 = 5 kbps
Downlink channel gain: 𝑔 2 = −53 dB
Uplink channel gain: ℎ 2 = −60 dB
Noise power: 𝜎2 = −70 dBm
Bandwidth: 𝐵 = 400 kHz
# sensors: 𝑁 = 10
Parameter Settings
Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks
Numerical Results
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The HAP’s energy consumption and
transmit time allocation
Can not offload the
workload in time
Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks
Numerical Results
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Workload and
transmit time
of passive
data
offloading
Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks
Questions & Answers
Thank you !
Q&A
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