| Recently,spread spectrum communication systems have been widely used in long-distance and low-power transmission of Internet-of-Things.A smart meter,which is a key terminal smart grid device,is based on the technical standard of a low-power wide-area network and uses spread spectrum technology in its physical layer chip design.To ensure that the smart meter wireless transmission system receives the correct information,the spread spectrum signal should be synchronized prior to receiving.However,during smart meter application,the spread spectrum signal synchronization algorithm has the following issues.The high-sensitivity system requires signal captures with a low signal-to-noise ratio(SNR);however,the output gain of the existing capture algorithm is insufficient.Tracking loop how to set the phase detector and loop filter,balance frequency offset estimation range,stability,and convergence rate indicators.Due to the drawbacks of traditional algorithms in engineering applications,we developed a new algorithm to effectively solve the above problems in this study.The primary research content and results are as follows:(1)The receiver signal synchronization design scheme is proposed.The design scheme of weak signal acquisition algorithm and tracking algorithm of intelligent meter is proposed based on the spread spectrum communication principle and the research of satellite signal synchronization algorithm.(2)A new equilibrium incoherent cumulative partial matched filter Fourier transform(PMF-FFT)algorithm is developed.The existing incoherent cumulative PMF-FFT algorithms cannot account for SNR requirements and computational complexity due to the limited length of spread spectrum codes and amount of data.Thus,a new balanced incoherent cumulative PMF-FFT algorithm with the advantages of this kind of algorithms is proposed and simulated.The results demonstrate that the detection probability of the new algorithm is higher than that of the existing two incoherent cumulative PMF-FFT algorithms,and the output gain is larger under the same amount of computational data.(3)A new steady state tracking loop phase detector algorithm based on direct sequence spread spectrum-offset quadrature phase shift keying(DSSS-OQPSK)signal is proposed.A new phase detector algorithm for the carrier tracking loop of DSSS-OQPSK signal is designed,which reduces about 1/2 of the calculation data compared with the existing algorithm.To solve the problem of insufficient frequency range of loop carrier tracking,the loop gain and equivalent noise bandwidth are adjusted to make the loop tracking frequency offset range reach the maximum residual frequency offset after acquisition on the premise of ensuring stable tracking.(4)The improved capture algorithm and tracking algorithm is verified.The acquisition algorithm and tracking algorithm are implemented in the software radio innovation practice platform,and the test results verify the feasibility of the algorithm in the physical platform.Thus,in this study,we improved the capture algorithm and designed the tracking algorithm so that the signal synchronization algorithm can not only achieve the low SNR and other working targets but also achieve low-power consumption requirements.The issues encountered during the process of DSSS-OQPSK signal capture and tracking are addressed within the framework of the intelligent meter automatic dual-mode communication protocol,allowing the signal to be accurately de-expanded and demodulated. |
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