Research On Throughput Enhancement Technologies For Backscatter Communications

Backscatter communication is considered as one of the practical solutions to support the vision of the Internet of Everything due to its low power consumption and low cost.The key is that the backscatter device transmits the information by reflecting the radio frequency signal in the environment,thus eliminating the need for radio-frequency analog components.However,due to limited hardware resources and cascaded channel fading,the data rates of existing backscatter schemes in narrow-band,wide-band,and multi-antenna transmission scenarios are constrained by the challenges of the long symbol period,insufficient subcarriers,and difficult channel estimation,respectively.These challenges hinder the further development and application of backscatter.To address the above challenges,this thesis deeply studies the throughput enhancement technologies of backscatter communication from the time,frequency,and space domains,respectively.Extensive experiments verify the superior performances of the proposed solutions in terms of throughput.The main contributions are summarized as follows:1.From the time domain perspective,a time interval modulation solution assisted by the sliding-window detection is proposed for narrow-band backscatter to deal with the challenge of the long symbol period.Specifically,variable-length time interval symbols and fixedlength anchor symbols are introduced,respectively.Multiple information bits are carried by changing the length of the time interval symbols to improve the data rate,and the anchor symbols are used to ensure long-distance transmission.Further,the methods to enhance transmission reliability are discussed.Moreover,a frequency adjustment method is proposed to eliminate the frequency discontinuity of anchor symbols at the receiver.A sliding windowbased detection algorithm is designed to locate anchor symbols in the frequency domain.The experimental results show that the proposed solution can improve the throughput by up to8.6 times in the outdoor scenario.2.From the frequency domain perspective,a multi-carrier signal emulation scheme assisted by a high-order impedance network is proposed for wide-band backscatter to face the challenge of insufficient subcarriers.Specifically,a high-order impedance network,including in-phase and quadrature paths,is designed.Hence,the time-domain variation of reflection coefficients is used to emulate orthogonal frequency division multiplexing(OFDM)signals to improve the data rate.Furthermore,an efficient mapping between available reflection coefficients and OFDM signals is established,and a time-domain oversampling-based modulation method for OFDM is provided to reduce signal emulation errors.The experimental results show that the proposed solution realizes OFDM with 64 subcarriers on a backscatter device,and the throughput can reach 25.1 Mbps.3.From the space domain perspective,a spatial multiplexing scheme assisted by the equivalent channel is proposed for multi-antenna backscatter to solve the challenge of channel estimation.Specifically,the equivalent channel containing a cascaded backscatter channel and backscatter information is introduced,thereby avoiding the high complexity of separating and estimating the cascaded channel.Besides,a low-overhead estimation method for the equivalent channel is proposed.Furthermore,a maximum likelihood detection algorithm based on subcarrier redundancy is designed,where multi-carrier excitation signals are leveraged to enhance transmission reliability.The experimental results show that the proposed solution can support the transmission of a six-antenna backscatter device,significantly improving the system throughput.This thesis focuses on the narrow-band,wide-band,and multi-antenna transmission scenarios in backscatter communication,and proposes corresponding throughput enhancement solutions from the time,frequency,and space domains,respectively.The proposed solutions may provide technical support for practical applications of backscatter communication in scenarios such as smart cities,smart homes,and wearable devices.