| The logging cable telemetery system play s a significant role in the current field of petroleum logging due to its many characteristics,such as high stability,tensile strength,and high transmission rate.The development of advanced technology has put forward a higher requirement for the transmission rate and anti-interference ability of the cable remote transmission system.Aiming at the above problems,this paper introduces new coding and modulation techniques to study more promising transmission schemes.Aiming at the inaccuracy of the cable’s cable channel characteristics,this thesis establishes the non-uniform cable equivalent model,proposes a calculation method of crosstalk characteristics based on segmented circuits,and analyzes the crosstalk characteristics of cable cores under different working modes.The simulation results reveal that this equivalent modeling method possesses a simple structure as well as high modeling accuracy.Furthermore,the calculation method of crosstalk characteristics based on this model can effectively speculate the interference between the cable cores in different working modes.In order to improve the transmission rate of the system,it is proposed to apply the Sparse Code Multiple Access(SCMA)technology to the cable communication system.Moreover,the feasibility of applying this technology to cable communication system is explored,and the transmission model of SCMA technology based on one-core is established.According to the idea of orthogonal dimension expansion,a high-dimensional codebook design method is proposed.The simulation results show as follows:(1)Because of the non-orthogonality between users and resources,the transmission rate increased by 1.5 times.(2)the system possesses good anti-noise performance.(3)This technology is slightly better than the baseband modulation technology in terms of the anti-sampling frequency deviation.(4)the optimization algorithm based on orthogonal dimension expansion decreases encoded peak-to-average power ratio.(5)Meanwhile,the peak-to-average power ratio of this technology is significantly higher than that of baseband modulation technology.For the problem mentioned in the(5)above,this thesis puts forward a codebook optimization algorithm for reducing the peak-to-average power ratio of the code,analyzes the relationship among codebook parameters,users’ codebook rotation phase and peak-to-average power ratio as well as the relationship among codebook parameters,users’ codebook rotation phase,and bit error rate.Furthermore,it establishes a estimation model of the bit error rate on resource nodes.The simulation results show as follows:(1)Symbol constellation radius influence the minimum euclidean distance and PAPR(peak-to-average ratio)of the code,and rotating phases of users’codebooks influence code distribution.(2)The optimized codebook achieves a lower peak-to-average power ratio of resource nodes compared with the existing lattice and circular codes.(3)The estimation model bit error rate on the resource node can accurately estimate the bit error performance of the system.Moreover,as the uniformity of the improves,its accuracy directly relate to code word distribution and scope radius.To further reduce PAPR and increase unti-frequency deviation interference,an optimal wavelet tree transmission scheme based on SCMA technology is established,and the relationship between sampling frequency deviation and basis function as well as wavelet tree structure is analyzed.Based on the above relationship model,it is proposed to apply the first derivative R’φ of the basis function correlation function to describe the influence of the sampling frequency deviation on the basis function.On the basis of the cable channel,the interference filter coefficient Dl,m[n]is utilized to describe the relationship between synchronization interference and the system tree structure.The theoretical analysis and simulation reveal as follows:(1)It can reduce the influence from sampling frequency offset with optimal wavelet base and tree structure;(2)The optimal wavelet packet transmission scheme based on SCMA technology possesses great advantages in many aspects,such as anti-synchronization deviation interference and peak-to-average power ratio.(3)Because of the optimized tree structure and variable rate,it is significant for logging cable systems with narrow bandwith and full duplex communication. |
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