Energy-Efficient Transmission Schemes With Implementation For Radio-Frequency Powered Wireless Networks

Wireless Sensor Network(WSN)is an important part of the Internet of Things(IoT).Traditional WSNs are usually powered by batteries.The difficulty of battery replacement limits the application of WSN.WPCN(Wireless Powered Communications Network)can overcome this bottleneck and provide a solution for sustainable application of WSN.Compared to traditional WSN,WPCN nodes support their perception,computation,communication,and networking by capturing energy from environmental RF signals.Since the energy captured by the WPCN node from the radio is weak,how to transmit data with high energy efficiency has become an important issue that the WPCN needs to solve.This article studies this,the main work and results are as follows:1.Backscatter Communication technology is widely used in WPCN.For the backscatter communication,the large ECD(Energy Consumption Disparity)between reflected bit 0 and bit 1 exists when using FM0 two-phase baseband communication and Miller modulation.The data transmission scheme of generating low-energy codebooks by ECD and then using the codebook for backscatter communication is studied.The fixed-length codebook(that is,the codewords in the codebook are of equal length)is designed,and an EEDDS(Energy-Efficient Data Delivery Scheme)based on a fixed-length codebook is proposed.In the EEDDS scheme,the transmitter and receiver share a fixed-length codebook,and the mapping between the "fixed-length data segment in the original bitstream" and the "codeword in the codebook" is implemented by the codebook.Considering the ECD coefficient,the proportion of high energy consumption bits in the original bit stream,and the channel error rate,the optimization problem model with the goal of maximizing energy saving rate is constructed under the premise of constraining the segmentation delay.The construction process of fixed-length codebook is given and inspired by this process.The greedy algorithm with low computational complexity is used to solve the above optimization problem.The simulation results show that the energy saving rate of the proposed EEDDS scheme is better than the traditional non-coding scheme when the modulation mode has the ECD feature or there are more high energy consumption bits in the original bit stream(such as transmission ASCII code).2.In the EEDDS scheme,the receiver must receive a complete codeword before decoding,and tends to choose a larger segment length,which consumes more node storage space.Aiming at this deficiency of EEDDS scheme,the problem of energy-efficient data transmission using prefix-code is studied.The PCBS(Prefix Code Based Scheme)based on a prefix-free codebook is proposed.The PCBS scheme considers parameters such as ECD coefficient and upper limit of codeword length.Under the constraints of prefix-free features and energy conservation of codewords,an optimization problem model with the goal of minimizing average energy consumption is constructed.In this paper,the genetic algorithm is used to solve this optimization problem.Using the correspondence between binary tree and prefix-free codebook,the binary tree is selected as the chromosome.The selection,crossover,mutation and population iteration of the genetic algorithm are based on the operation of the binary tree,and the energy efficient prefix-free codebook is obtained.The PCBS scheme matches the variable length codewords for each original segment,which is suitable for more general scenarios,further reducing the number of transmissions of high energy consumption bits.It has lower transmission delay,less storage space requirements and higher energy savings.The simulation results show that the segment length of PCBS is lower than the EEDDS scheme.Under the same conditions,the EEDDS scheme has higher energy saving rate and smaller segment length,that is,the PCBS scheme is better than the EEDDS scheme as a whole.3.The codebooks existing in the EEDDS and PCBS schemes occupy a large storage space and thus are difficult to implement on hardware.For the energy-efficient codebook design with extremely limited storage space and the data transmission based on the designed codebook,a hybrid prefix-free code based energy transfer data transmission scheme CBBC(Prefix Code Based Backscatter Communications)is proposed.The CBBC scheme uses two rates to transmit data,and the original data block containing more low energy consumption bits is directly transmitted without using the codebook at one rate,and the original data block containing less low power consumption bits is used at another rate.Fully considering the threshold and ECD coefficients of coding and non-coding,under the constraints of node memory,unit bit time,non-prefix features of codebook and energy saving,an optimization problem model with the goal of minimizing average energy consumption is constructed.The optimization problem is solved by the trimming and expanding operation of the binary tree.In addition,the CBBC scheme was tested on the wireless identification sensing platform WISP(Wireless Identification Sensing Platform)hardware.The experimental results show that with the same energy,the CBBC scheme transmits more than 20% of the data(bits)than the non-encoding scheme.In summary,the CBBC scheme is easy to implement on hardware and has obvious energy-saving effects.It is suitable for passive sensing or backscatter communication scenarios where the node computing power is weak and the storage space is extremely limited.The above solutions can be applied to wireless powered communications network using radio frequency energy harvesting and backscatter communication to improve data transmission energy efficiency at the physical layer.The research results of this paper have important theoretical significance and practical value,which will promote the development of the Internet of Things and the advancement of RF energy supply communication network technology.