【摘要】：移動通信在近三十多年來發(fā)展迅速,尤其3GPP提出的“準4G”標準LTE更是近幾年的研究熱點。為提高頻譜利用率,LTE中采用了OFDM技術,然而OFDM技術對時頻偏差的敏感,使時頻同步技術成為LTE通信過程中一個巨大的挑戰(zhàn)。本文基于Linux系統(tǒng)中的開源軟件無線電平臺GNU Radio與USRP研究LTE中的上下行同步過程。論文首先分析了LTE的基帶傳輸技術基礎。包括LTE中的上下行調制傳輸方式、基本的幀結構以及相應物理信道的處理流程,此外還介紹了LTE中為解決時頻偏差而引入的導頻信號序列,包括主輔同步序列(PSS, SSS)和參考符號序列(RS)。其次在分析時頻偏差對系統(tǒng)影響的基礎上分別研究并設計了上下行同步方案。第一、設計下行時頻同步方案,主要包括利用PSS與SSS序列完成定時粗同步與頻率粗同步,完成小區(qū)搜索功能；利用RS信號進行信道估計與均衡,同時利用信道估計結果進行系統(tǒng)殘余定時偏差、殘余頻率偏差的估計,并完成時頻誤差調整及補償,以此完成下行追蹤過程的同步。第二、設計上行同步方案,主要包括在eNB側利用上行SRS進行上行時間提前量的估計,并通過TA指令控制UE側進行樣點調整以完成上行定時同步；此外,在UE側還通過頻偏預補償來完成上行頻率同步。第三、設計上下行之間的同步方案,在UE側以下行定時同步為基礎計算下行接收時刻表,作為上行發(fā)送時刻的基準,并結合TA過程使所有UE發(fā)送數據到達eNB的幀起始時刻一致,完成上下行間同步。第四、針對GNU Radio平臺給出LTE中系統(tǒng)同步的整體流程。最后使用C++語言在GNU Radio平臺上實現(xiàn)了本文提出的LTE系統(tǒng)同步方案,并分別在室內無線環(huán)境與萊斯仿真信道下進行測試。測試結果表明：第一、在無線傳輸環(huán)境中,下行捕獲時間在0.35s～0.45s之內,并且穩(wěn)定工作后子幀處理時間約為0.25ms～0.31ms,證明本論文設計的同步方案能夠完成并保證接收數據的正確、實時處理；第二、在無線環(huán)境中,系統(tǒng)殘余定時偏差與殘余頻率偏差均在5ms內完成收斂；第三、在多徑仿真信道中,SNR為0dB時,定時位置誤檢概率低于10%,殘余定時偏差小于10-2,殘余頻率偏差小于10-3,并且SNR為6dB時定時位置檢測無差錯。
[Abstract]:Mobile communication has developed rapidly in recent 30 years, especially the "quasi-4G" standard LTE proposed by 3GPP is a hot research topic in recent years. In order to improve the spectrum efficiency, OFDM technology is used in LTE. However, the sensitivity of OFDM technology to time-frequency deviation makes time-frequency synchronization technology become a great challenge in the process of LTE communication. In this paper, based on the open source software radio platform GNU Radio and USRP in Linux system, the uplink and downlink synchronization process in LTE is studied. Firstly, the basis of baseband transmission technology of LTE is analyzed. It includes the uplink and downlink modulation transmission mode in LTE, the basic frame structure and the processing flow of the corresponding physical channel. In addition, the pilot signal sequence introduced in LTE to solve the time-frequency deviation is also introduced, including the primary and auxiliary synchronization sequence (PSS, SSS) and the reference symbol sequence (RS). Secondly, based on the analysis of the influence of time-frequency deviation on the system, the uplink and downlink synchronization schemes are studied and designed. Firstly, the downlink time-frequency synchronization scheme is designed, which mainly includes using PSS and SSS sequences to complete timing rough synchronization and frequency rough synchronization, completing cell search function, using RS signal to estimate and equalize the residual timing deviation and residual frequency deviation, and completing the adjustment and compensation of time-frequency error, so as to complete the synchronization of downlink tracking process. Secondly, the uplink synchronization scheme is designed, which mainly includes the estimation of uplink time advance by using uplink SRS on the eNB side, and the sample point adjustment through TA instruction to complete uplink timing synchronization; in addition, the uplink frequency synchronization is completed by frequency offset pre-compensation on the UE side. Thirdly, the synchronization scheme between uplink and downlink is designed, and the downlink receiving schedule is calculated on the basis of row timing synchronization below UE side, which is used as the reference of uplink transmission time, and the frame starting time of all UE transmission data arriving at eNB is consistent with TA process, and the synchronization between up and down lines is completed. Fourth, the overall process of system synchronization in LTE is given for GNU Radio platform. Finally, the synchronization scheme of LTE system proposed in this paper is implemented on GNU Radio platform with C language, and tested in indoor wireless environment and Rice simulation channel respectively. The test results show that: first, in the wireless transmission environment, the downlink acquisition time is within 0.35s~0.45s, and the subframe processing time after stable operation is about 0.25ms 鈮，

本文編號：2503861