本文關(guān)鍵詞： LPWAN DSSS LECIM PHY 捕獲 頻偏估計(jì) 低信噪比　出處：《安徽大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：低功耗廣域網(wǎng)(LPWAN:Low Power Wide Area Network),是專門為實(shí)現(xiàn)低功耗、遠(yuǎn)距離、低速率、大連接的物聯(lián)網(wǎng)應(yīng)用而設(shè)計(jì)。電氣和電子工程師協(xié)會IEEE(Institute of Electrical and Electronics Engineers)針對這一需求在低速率無線個(gè)域網(wǎng)上制定了 EEE802.15.4k標(biāo)準(zhǔn)。該標(biāo)準(zhǔn)主要適用于低功耗關(guān)鍵基礎(chǔ)設(shè)施監(jiān)控(LECIM:Low Energy Critical Infrastructure Monitoring)網(wǎng)絡(luò)的應(yīng)用。本文基于IEEE 802.15.4k標(biāo)準(zhǔn)的直接序列擴(kuò)展頻譜系統(tǒng)的低功耗關(guān)鍵基礎(chǔ)設(shè)施監(jiān)控網(wǎng)絡(luò)(DSSS LECIM:Direct Sequence Spread Spectrum LECIM),對其物理層(Physical Layer)收發(fā)鏈路各模塊的關(guān)鍵技術(shù)進(jìn)行了深入研究,設(shè)計(jì)并搭建了整個(gè)基帶收發(fā)鏈路。實(shí)際工程應(yīng)用中由于低成本的限制,一般采用普通的廉價(jià)的晶振,晶振的頻率漂移高達(dá)40PPM(parts per million)以上。晶振的頻率漂移將引起接收性能的惡化,這對接收端在低信噪比環(huán)境下正確恢復(fù)出發(fā)送的數(shù)據(jù)造成了一定的難度,因此對物理層接收機(jī)鏈路中同步技術(shù)的研究具有非常重要的學(xué)術(shù)價(jià)值以及實(shí)際應(yīng)用意義。針對上述問題,論文首先針對基帶接收機(jī)在低信噪比環(huán)境下存在隨機(jī)頻偏的長碼字捕獲技術(shù)進(jìn)行研究。主要以基于快速傅里葉變換(FFT:Fast Fourier Transformation)運(yùn)算的時(shí)頻域二維搜索捕獲和基于差分處理捕獲算法兩個(gè)方面進(jìn)行研究,傳統(tǒng)的捕獲算法都不能滿足LECIM網(wǎng)絡(luò)的應(yīng)用需求。本論文提出一種基于差分處理的M階自相關(guān)偽碼同步改進(jìn)算法。先將接收信號和偽碼相乘以消除偽碼信息,然后進(jìn)行M階差分自相關(guān)消除載波頻偏信息同時(shí)對噪聲有一定的抑制。最后和傳統(tǒng)的幾種差分捕獲算法在相同條件下進(jìn)行仿真驗(yàn)證。實(shí)驗(yàn)結(jié)果表明本論文提出改進(jìn)算法的抗噪性能更加優(yōu)越,其捕獲性能有4-5dB的改善,很大程度上改善了信噪比,提高了基帶系統(tǒng)的接收靈敏度,故更適應(yīng)于低信噪比條件下工作。其次,對實(shí)現(xiàn)超低信噪比環(huán)境下的高精度頻偏估計(jì)技術(shù),主要研究了利用FFT運(yùn)算以及基于時(shí)域上的經(jīng)典Fitz算法�；诮�(jīng)典Fitz算法,提出了對信號先進(jìn)行預(yù)處理再進(jìn)行相關(guān)運(yùn)算的策略。該項(xiàng)處理在不縮小頻偏估計(jì)范圍的前提下,能通過有偏自相關(guān)并迭代的方法抑制噪聲,從而實(shí)現(xiàn)了在低信噪比環(huán)境下的頻偏估計(jì)問題。該算法可以大大的提高估計(jì)性能,并且隨著預(yù)處理次數(shù)增加而提高估計(jì)精度。該方法穩(wěn)定可靠,非常適合應(yīng)用于IEEE802.15.4k標(biāo)準(zhǔn)下超長碼字、低'信噪比、遠(yuǎn)距離通信、超高接收靈敏的應(yīng)用需求。最后,基于MATLAB平臺搭建整個(gè)基帶系統(tǒng),分別對接收端的頻偏糾正模塊以及信道編譯碼模塊進(jìn)行相應(yīng)現(xiàn)場可編程門陣列FPGA(Field Programmable Gate Array)功能的實(shí)現(xiàn)。通過分析結(jié)果驗(yàn)證了模塊實(shí)現(xiàn)的正確性。
[Abstract]:Low power WAN: low Power Wide Area Network is designed to achieve low power consumption, long range, low speed. The association of electrical and electronic engineers, IEEE(Institute of Electrical and Electronics engineers, has developed a EEE802.15.4k standard for this demand on low-rate wireless personal area networks. The standard is mainly suitable for low-power critical infrastructure. In this paper, the low power critical infrastructure of direct sequence spread spectrum system based on IEEE 802.15. 4k standard, DSSS LECIM:Direct Sequence Spread Spectrum LECIMIMM, is used to monitor the physical layer of the physical layer. An in-depth study was carried out. The whole base-band transceiver link is designed and built. Due to the limitation of low cost in practical engineering application, the ordinary cheap crystal oscillator is generally used, and the frequency drift of the crystal oscillator is up to 40 PPM parts per million. The frequency drift of the crystal oscillator will cause the deterioration of the receiving performance. This makes it difficult for the receiver to recover the transmitted data correctly in the environment of low SNR. Therefore, the research of synchronization technology in physical layer receiver link has very important academic value and practical application significance. In this paper, the long codeword acquisition technology of baseband receiver with random frequency offset in low signal-to-noise ratio (SNR) environment is studied, mainly based on time-frequency domain two-dimensional search acquisition and difference based on fast Fourier transform (FFT) operation. Two aspects of processing capture algorithm are studied. The traditional acquisition algorithm can not meet the application requirements of LECIM network. In this paper, an improved M-order autocorrelation pseudo-code synchronization algorithm based on differential processing is proposed. The received signal and pseudo-code are multiplied to eliminate the pseudo-code information. Then M-order differential autocorrelation is carried out to eliminate carrier frequency offset information and the noise is suppressed. Finally, simulation results are carried out under the same conditions as some traditional differential acquisition algorithms. The experimental results show that this paper proposes a new method. The anti-noise performance of the feedforward algorithm is more superior. The acquisition performance is improved by 4-5dB, which greatly improves the signal-to-noise ratio (SNR) and the reception sensitivity of the baseband system, so it is more suitable for working under the condition of low SNR. Secondly, the high precision frequency offset estimation technology in the ultra-low SNR environment is realized. This paper mainly studies the use of FFT operation and the classical Fitz algorithm based on time domain. Based on the classical Fitz algorithm, the strategy of preprocessing the signal first and then performing the correlation operation is put forward. This process does not reduce the range of frequency offset estimation. The frequency offset estimation problem in low SNR environment is realized by using biased autocorrelation and iterative method to suppress noise. The proposed algorithm can greatly improve the estimation performance. And the estimation accuracy is improved with the increase of preprocessing times. This method is stable and reliable, which is very suitable for the application of IEEE802.15.4k standard, such as ultra-long codewords, low 'signal-to-noise ratio (SNR), long distance communication, super high receiver sensitivity. Finally, Based on the MATLAB platform, the whole baseband system is built, and the frequency offset correction module and the channel coding and decoding module are implemented respectively. The implementation of the corresponding FPGA(Field Programmable Gate array function is verified by the analysis results.
【學(xué)位授予單位】：安徽大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TP393.2

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