具備波束追蹤的第五代行動通訊多用戶波束成形收發系統之設計與實現

Design and Implementation of 5G NR Multi-User MIMO Beamforming Transceiver with Beam Tracking

朱柏彥(Po-Yen Chu)

指導教授 ： 闕志達

國立臺灣大學/電機資訊學院/電子工程學研究所/碩士(2022年)

https://doi.org/10.6342/NTU202200706

摘要

隨著科技不斷演進，無線通訊對於大眾已基本的需求，使得無線連網裝置數量大幅提升。在同時間連網裝置越來越多下，使用傳統的時間分工多重接取(TDMA)、頻率分工多重接取(FDMA)，以及正交分頻多重接取(OFDMA)等技術來傳送不同使用者裝置(User Equipment, UE)的資料，勢必會面臨到有限頻譜資源和時間延遲的問題。因此，利用空間分工多重接取(Spatial Division Multiple Access, SDMA)將不同使用者的資料利用方向性區隔傳送，可以解決先前所面臨的問題。所有使用者可同時間內使用相同頻段，即可提升整體系統的傳輸效能。

本論文基於5G新無線電(NR)標準使用二片賽靈思射頻系統單晶片(Xilinx RFSoC)無線電開發平台實作具備多用戶多輸入多輸出波束成形(Multi-User MIMO Beamforming)十六天線全硬體發射機的基地台(Base Station, BS)。在二片Xilinx RFSoC為二組獨立八天線發射機下, 使用最小變異無失真響應（Minimum Variance Distortionless Response, MVDR）演算法，使基地台最多支援同時傳送7組資料流(data stream)至不同方向上的四位使用者，分別為一個四天線的MIMO UE以及三個MISO UE，而七個資料流在時間及頻率上完全重疊。為了驗證此系統的空間分工多重接取正確性及可行性，本論文成功在真實空氣通道(Over-The-Air，OTA)的環境下驗證波束成形功能，此系統達到空間分工多重接取的效果，將頻譜使用效率提高7倍，峰值傳輸速率(Peak Data Rate)達到508.03 Mbps。

除了實作二組獨立八天線發射機打造而成十六天線全硬體發射機外，也實作使用外部觸發按鍵來同步二片Xilinx RFSoC十六天線發射。同步十六天線發射機使用十六天線波束成形係數設計，可使波束更加集中於發射方向外，也可抑制更多其他方位角上的訊號強度。最終，在OTA下量測波束圖形和同時發射四組資料流給四個UE進行解碼，皆能證明此同步十六天線發射機無論在發射強度和抑制其他方位角上訊號強度的能力皆優於八天線發射機。

多天線陣列不止用於波束成形發射機，也可以實現波束追蹤(Beam Tracking)技術。實際上使用者並非固定不動，所以基地台使用波束成形發射訊號前，必須對使用者進行到達方位角估計(Angle of Arrival)，再有效地將波束往使用者方向發射。因此，本論文使用一片Xilinx RFSoC實作四天線接收機，並與一台控制電腦和一片Xilinx RFSoC的八天線全硬體發射機，組成具有上下行的基地台。使用四天線接收機接收使用者傳送的上行訊號，傳送至電腦進行到達方位角估計。再根據估計方位角，重新計算波束成形係數，傳送至全硬體發射機的波束成形模組內，將下行訊號往正確的方位角發射。當使用者移動後，波束追蹤系統可在3.4秒內將下行訊號指向該使用者的方位角。最終，成功在空氣通道的環境下驗證具有波束追蹤功能的基地台系統，基地台可不停追蹤一個移動使用者的所在方位角，同時利用空間分工多重接取技術，發射四組下行資料流至不同方向上的一個移動式使用者和三個固定方位使用者，且四個使用者皆可解碼成功。

關鍵字

波束成形 ； 波束追蹤 ； 空間分工多重接取 ； 到達方位角估計 ； 賽靈思射頻系統單晶片 ； 空氣通道 ； 多使用者多輸入多輸出 ； 第五代行動通訊新無線電 ； 全硬體正交分頻多工發射機

並列摘要

With the evolution of technology, wireless communication has become a primary demand for the public, resulting in a substantial increase in wireless devices. As more and more devices are connected to the network at the same time, traditional techniques such as Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), and Orthogonal Frequency Division Multiple Access (OFDMA) are used to serve different users. They face the problem of limited spectrum resources and latency. Therefore, Spatial Division Multiple Access (SDMA) can solve the previous issues by transmitting data to different users using the direction. All users could use the same frequency band simultaneously, and the transmission performance of the overall system can be improved.

Based on the 5G New Radio (NR) standard, we use the two Xilinx RFSoC radio development platforms to implement Multi-User MIMO Beamforming with sixteen antennas to build the base station (BS). With two Xilinx RFSoCs as two sets of independent eight-antenna transmitters, the base station supports up to seven groups of data streams to be transmitted simultaneously in different directions using the Minimum Variance Distortionless Response (MVDR) algorithm. The four users include one four-antenna MIMO UE and three MISO UEs. The seven data streams overlap entirely in the time and frequency domain. To verify the correctness and feasibility of the SDMA in this system, we successfully demonstrated the beamforming in the Over-The-Air (OTA). This system achieves the effect of SDMA. The spectrum efficiency increases seven times, and the peak data rate reaches 508.03 Mbps.

In addition to implementing two sets of independent eight-antenna transmitters to build a 16-antenna full-hardware transmitter, we also implement the synchronous 16-antenna transmitter on two Xilinx RFSoCs by using the external trigger button. Synchronous 16-antenna transmitters are adopted with 16-antenna beamforming coefficients, making the beam more concentrated to the transmitting direction and suppressing the signal power in other azimuth angles. Finally, measuring the beam pattern in OTA and simultaneously transmitting four sets of data streams to four UEs for decoding prove that the synchronous 16-antenna transmitter is superior in both transmission power at beam direction and suppression the intensity at other azimuth angles than eight-antenna transmitters.

Multi-antenna arrays are not only used for beamforming transmitters but also Beam Tracking technology. Because the user is not stationary, the base station must estimate the Angle of Arrival (AoA) of the user and then transmits the beam toward the user. Therefore, we build the base station with one Xilinx RFSoC as a four-antenna receiver for uplink signals and one Xilinx RFSoC as eight-antenna full-hardware transmitter for downlink signals. A four-antenna receiver is used to receive the uplink signal sent by the user and calculate the azimuth angle of arrival by the computer. Then, according to the angle of arrival, the downlink beamforming coefficient is recalculated and sent to the beamforming module in the all-hardware transmitter to transmit the downlink signal to the correct azimuth angle. When the user moves, the beam tracking system could transmit the downlink signal to the user's azimuth within 3.4 seconds. In the end, the base station system with beam tracking was successfully verified in OTA. The base station keeps track of the azimuth angle of the movable user and transmits four sets of downlink data streams to different users by SDMA at the same time. Four downlink data serve one movable user and three beam-fixed users, and four users can decode successfully.

並列關鍵字

Beamforming ； Beam Tracking ； Spatial Division Multiple Access (SDMA) ； Angle of Arrival Estimation (AoA Estimation) ； Xilinx RFSoC ； Over-The-Air (OTA) ； Multi-User MIMO (MU-MIMO) ； 5G NR ； hardware OFDM transmitter

參考文獻

[1] Ericsson, “Mobile data traffic growth outlook,” ericsson.com, para. 4. Nov. 2019. [Online]. Available: https://www.ericsson.com/en/mobility-report/reports/november-2019/mobile-data-traffic-outlook [Accessed Jan. 14, 2022].

[2] ITU, “IMT Vision – Framework and overall objectives of the future development of IMT for 2020 and beyond.” [Online]. Available: https://www.itu.int/dms_pubrec/itu-r/rec/m/R-REC-M.2083-0-201509-I!!PDF-E.pdf [Accessed Jan. 14, 2022]

[3] ITU, “Setting the Scene for 5G: Opportunities Challenges.” [Online]. Available: https://www.itu.int/dms_pub/itu-d/opb/pref/D-PREF-BB.5G_01-2018-PDF-E.pdf [Accessed Jan. 14, 2022]

[4] NCC, 行動寬頻業務5G釋照電子式競價系統-最新競價結果[Online]. Available: https://mbb5g.ncc.gov.tw/ [Accessed Jan. 14, 2022]

[5] Keysight, “Understanding the 5G NR Physical Layer.” [Online]. Available: https://www.keysight.com/upload/cmc_upload/All/Understanding_the_5G_NR_Physical_Layer.pdf [Accessed Jan. 14, 2022]