- 學位論文
適用於第五代行動通訊新無線電的多用戶多輸入多輸出波束成形下行發射機之設計與實現
Design and FPGA-based Implementation of 5G NR Multi-User MIMO Beamforming Downlink Transmitter
摘要
隨著科技的進步以及時代的演進，近年來大眾對於無線連網裝置的依賴程度越來越高，除了單位時間內所需的資料傳輸速率提高以外，在同一時間內連網的裝置數量也越來越多。而在傳統的無線通訊系統中，不同使用者的資料通常是利用時間或是頻率的分隔來達到多重接取的效果，例如時間分工多重接取(TDMA)、頻率分工多重接取(FDMA)，以及正交分頻多重接取(OFDMA)。但礙於同一個時間內無線通訊頻譜的總量是有限的，所以若連網裝置的數量持續增加，勢必會遇到物理資源不敷使用的情況。因此也就必須利用其他類型的多重接取，例如：空間分工多重接取(Spatial Division Multiple Access, SDMA)將不同使用者所傳送的資料分隔開來。 在現今無線通訊系統多元的應用需求下，5G NR規格多元且彈性，讓系統實作更具挑戰性。而本論文基於現有波束成形的理論，選擇使用性價比及開發彈性非常高的軟體無線電開發平台Xilinx RFSoC，並參考5G NR規範實作具備多使用者多輸入多輸出波束成形(Multi-User MIMO Beamforming)功能的全硬體OFDM發射機。最多支援同時傳送4組data streams給位在不同方向上的3個UEs，其中包含一個MIMO UE，兩個MISO UEs。並且為了提高資料傳輸的效率，我們利用全硬體OFDM發射機實時地將使用者要傳送的原始binary data經過一連串的處理，轉換成可由天線發射的射頻類比訊號。 另外，因為波束成形需要控制各個通道之間的訊號相位差，但實際使用儀器實作時會遇到各個發射通道存在隨機相位差的問題。為了克服這個問題，本論文使用一套訊號相位校正方法，並且經過多次實驗後確定，在目前常見的兩種軟體定義無線電平台上(NI USRP、Xilinx RFSoC)，皆能夠有效地將儀器內部各個通道的隨機相位差消除掉。 最後，為了驗證本論文所設計的整套系統的正確性及可行性，我們選擇在空氣通道(Over-The-Air)的環境下使用本系統同時傳送三部不同的影片檔案給三個位在不同方位上的使用者，其中各個使用者的資料在時間及頻率上完全重疊。最後三部大小約為11 MB的影片檔案在接收端解碼後皆可達到Block Error Rate = 0，並順利在接收端將影片重新播放出來。成功利用波束成形的技術達到空間分工多重接取(Spatial Division Multiple Access, SDMA)的效果。
並列摘要
As modern technology evolves, people have been asking for more from wireless internet devices. Not only the data transmission rate has risen, but the amount of devices connected to the internet at the same time has increased as well. In traditional wireless communication systems, data of different users are usually separated in time or frequency domain to achieve the purpose of multiple access. For instance, TDMA, FDMA, and OFDMA are all schemes for multiple access. However, since the total spectrum is limited, the physical resources become more and more scarce as the number of internet devices keeps rising. As such, we need to adopt other more advanced multiple access techniques. One such scheme is the Spatial Division Multiple Access, SDMA. There are countless wireless communication applications nowadays, and the diversity and flexibility of the 5G-NR specification renders 5G system implementation even more challenging. In this thesis, a full hardware multi-user MIMO (MU-MIMO) beamforming OFDM transmitter is designed and implemented in FPGA. This design is based on existing beamforming theory and 5G-NR waveforms, and the transmitter hardware is implemented on a cost-effective and flexible software-defined radio (SDR) platform, Xilinx RFSoC. This transmitter is capable of transmitting up to 4 data streams simultaneously toward 3 UEs locating at different angular positions, with one of them a MIMO UE and the other two MISO UEs. In order to enhance data transmission efficiency, we developed the OFDM transmitter circuit to convert the binary data streams to RF beamformed signals and transmit in real-time the signals with eight antennas. Beamforming involves the control of signal phase difference between each channel. Unfortunately, the phase difference between each channel of the RFSoC board varies randomly. In this thesis, we proposed a phase alignment approach to solving this problem. This phase calibration approach is shown to be effective on two SDR platforms (NI USRP and Xilinx RFSoC) after extensive experimentation. We transmitted three different video files toward three UEs locating on different positions under the over-the-air (OTA) environment to verify the correctness and feasibility of the whole system. The signals carrying data for three users completely overlap in the time and frequency domain. In the end, the three video files that are each about 11 MB can be decoded correctly with zero Block Error Rate and be played successfully at the receiving users’ computer. This experiment demonstrated the effectiveness and efficiency of the FPGA-based SDR platform for the Spatial Division Multiple Access (SDMA) system.
參考文獻
延伸閱讀
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