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IEEE Global Communications Conference Ba Backscatter kscatter-Ai Aided ded Hy Hybrid id Da Data ta Offl Offloa oadin ding g fo for Wi Wirel eless ess Po Powe wered ed Ed Edge ge Se Sens nsor or Ne Netw tworks orks Yuze Zou, PhD School of Electronic Information and Communications Huazhong University of Science and Technology 9-13 December 2019 Waikoloa, HI, USA Revolutionizing Communications

Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks Ou Outline tline  Introduction  System Model  Energy Minimization for Hybrid Data Offloading  Numerical Results 2/18

Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks Ou Outline tline  Introduction  System Model  Energy Minimization for Hybrid Data Offloading  Numerical Results 3/18

Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks In Introduct troduction ion Cloud Server MEC Server Edge Devices Img src : https://www.newgenapps.com/blog/influence-of-iot-on-wearable-technology 4/18

Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks In Introduct troduction ion 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 5/18

Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks Ou Outline tline  Introduction  System Model  Energy Minimization for Hybrid Data Offloading  Numerical Results 6/18

Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks Sys System tem Model Model HAP 𝑇 1 ⋯ 𝑕 𝑗 ℎ 𝑂 𝑇 𝑗 ⋯ ⋯ 𝑇 𝑂 𝑇 𝑘 7/18

Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks Sys System tem Model Model  Time Allocation  Each sensor is allocated with fixed slot, say 𝑈/𝑂  Each sensor operate in passive and then active mode  Each sensor harvests energy when others in passive mode 8/18

Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks System Sys tem Model Model  Signal Model  Active communications 𝑏,𝑗 = 𝐶 log 2 1 + 𝑞 𝑏,𝑗 ℎ 𝑗 2 𝑠 𝜏 2 𝑞 𝑏,𝑗 = 𝛾 𝑠 ⟺ 𝑏,𝑗 Power ≜ 2 𝑠 𝑏,𝑗 /𝐶 − 1 𝜏 2 / ℎ 𝑗 2 Consumption  Passive communication 𝑠 𝑞,𝑗 = 𝑠 Constant 𝑞 NOTE : 𝑠 𝑞,𝑗 holds true in general. 𝑏,𝑗 > 𝑠 9/18

Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks Ou Outline tline  Introduction  System Model  Energy Minimization for Hybrid Data Offloading  Numerical Results 10/18

Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks En Ener ergy gy Mi Mini nimization mization fo for r Hy Hybr brid id Da Data ta Offload Offloading ing min 𝑞 0 𝑢 𝑞,𝑗 ෍ Energy minimization at HAP 𝒖 𝒃 ,𝒖 𝒒 𝒋∈𝒪 Slot limitation s. t. 𝑢 𝑏,𝑗 + 𝑢 𝑞,𝑗 ≤ 𝑈/𝑂 𝑚 𝑏,𝑗 + 𝑚 𝑞,𝑗 ≥ 𝑀 𝑗 Task fulfillment 𝑚 𝑏,𝑗 𝑢 𝑏,𝑗 ෨ 2 𝑢 𝑞,𝑘 𝛾 ≤ 𝜃 ෍ 𝑞 0 𝑕 𝑗 Energy constraint 𝑢 𝑏,𝑗 𝑘∈𝒪 𝑗 𝑢 𝑏,𝑗 ≥ 0, 𝑢 𝑞,𝑗 ≥ 0, 𝑚 𝑏,𝑗 ≥ 0 Physical constraint ෨ 𝛾 𝑠 𝑏,𝑗 = 𝛾 𝑠 𝑏,𝑗 + 𝑞 𝑑,𝑗 denotes the energy consumption of sensor in active mode 𝜃 : energy harvesting coefficient, 𝒪 𝑗 = 𝒪\ 𝑗 𝑀 𝑗 : total bits to offload of sensor 𝑗 , 𝑚 𝑏,𝑗 and 𝑚 𝑐,𝑗 : bits offloaded via active and passive mode, respectively 11/18

Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks En Ener ergy gy Mi Mini nimization mization fo for r Hy Hybr brid id Da Data ta Offload Offloading ing  Distributed reformulation min 𝑞 0 𝑢 𝑞,𝑗 ෍ 𝒖 𝒃 ,𝒖 𝒒 𝒋∈𝒪 s. t. 𝑢 𝑏,𝑗 + 𝑢 𝑞,𝑗 ≤ 𝑈/𝑂 Sensor 𝑗 is 𝑚 𝑏,𝑗 + 𝑚 𝑞,𝑗 ≥ 𝑀 𝑗 aware of its 𝑚 𝑏,𝑗 energy supply, 𝑢 𝑏,𝑗 ෨ 2 𝑢 𝑞,𝑘 𝛾 ≤ 𝜃 ෍ 𝑞 0 𝑕 𝑗 𝐹 𝑗 𝑢 𝑏,𝑗 denote by 𝐹 𝑗 𝑘∈𝒪 𝑗 𝑢 𝑏,𝑗 ≥ 0, 𝑢 𝑞,𝑗 ≥ 0, 𝑚 𝑏,𝑗 ≥ 0 > This motivates us to optimize sensors’ offloading scheme in a distributed manner. 12/18

Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks En Ener ergy gy Mi Mini nimization mization fo for r Hy Hybr brid id Da Data ta Offload Offloading ing 𝑢 𝑏 ,𝑢 𝑞 ,𝑠 𝑏 𝑢 𝑞 min s. t. C1 𝑢 𝑏 + 𝑢 𝑞 ≤ 𝑢 C2 𝑢 𝑏 𝑠 𝑏 + 𝑢 𝑞 𝑠 𝑞 ≥ 𝑀 C3 𝑢 𝑏 𝛾 𝑠 𝑏 + 𝑞 𝑑 𝑢 𝑏 ≤ 𝐹 Closed-form solution can be obtained for each sensor, thus achieves 𝒫 1 complexity 13/18

Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks Ou Outline tline  Introduction  System Model  Energy Minimization for Hybrid Data Offloading  Numerical Results 14/18

Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks Nume Numerical rical Resu Results lts  Parameter Settings Downlink channel gain: 𝑕 2 = −53 dB HAP’s transmit power: 𝑞 𝑢 = 100 mW Uplink channel gain: ℎ 2 = −60 dB Frame length: 𝑈 = 10 Noise power: 𝜏 2 = −70 dBm Sensor workload: 𝑀 = 10 kbits Energy harvesting efficiency: 𝜃 = 0.8 Bandwidth: 𝐶 = 400 kHz Circuit power: 𝑞 𝑑 = 1 μW # sensors: 𝑂 = 10 Passive data rate: 𝑠 𝑞 = 5 kbps 15/18

Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks Nume Numerical rical Resu Results lts Can not offload the workload in time The HAP’s energy consumption and transmit time allocation 16/18

Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks Nume Numerical rical Resu Results lts Workload and transmit time of passive data offloading 17/18

Y. Zou et al. Backscatter-Aided Hybrid Data Offloading for Wireless Powered Edge Sensor Networks Q&A Q&A Qu Ques estion tions & An s & Answ swers ers Tha Thank nk yo you u ! 18/18