Capacity Analysis Of Frequency Shift Based Ambient Backscatter Communication System

With the development of science and technology,The Internet of Things is getting more popular in people's lives,however,there are still much technique bottleneck need to be settled,such as communication problem between wearable devices,battery replacement difficulties in implanted devices.Recently the newly proposed backscattering techniques can solve these problems to a certain extent.The low cost and low energy consumption properties of backscattering technology has attracted more and more attention in the field of Internet of things.Backscatter communication system enables communication between low power devices by reflecting or absorbing the carrier signal.There will be interference between backscatter signals and the carrier signal during the backscatter process inevitably.To cancel self-interference from the wireless carrier without specific hardware,ambient backscatter systems usually adopt to shift the carrier signal to another frequency band and keep the backscattered signals away from primary carrier signal.In this paper,we analyze the effect of frequency shift size on ambient backscatter system capacity performance.And we discuss the feasibility of the OFDM-based capacity expanding method on ambient backscatter system.Finally,we build prototype backscatter system,consisting of a FPGA facilitated backscatter tag and WARP board as the transceiver.We give emphasis to the hardware and software design of WARP,and conduct experiments with various frequency shift step sizes to analyze the effect of frequency shift size on system performance,and verify that the capacity of ambient backscatter communication system with OFDM-based capacity expanding method in 802.11 g transmissions is 48 times larger than which of frequency-shift based ambient backscatter communication system without any capacity expanding method in 802.11 b transmissions.