60GHz無線個人區域網路中基於波束編碼簿之波束成形相關技術改良

Abstract

在本篇論文中，主要是討論適用於60 GHz無線個人區域網路(WPAN)高速、高輸出的系統之波束成形技術，並以IEEE 802.15.3c中基於編碼簿之波束成形為主，提出多種與波束成形相關的技術改良其效能。在802.15.3c原始的編碼簿為了減低射頻端電路設計複雜度，是採用90度的相位解析度，而在本文中將探討有限地提高編碼簿相位解析度時的效能，並發現可以使用維度較小的編碼簿提供即可比802.15.3c中維度較大編碼簿較好的效能。802.15.3c的編碼簿是對固定天線間距所設計，因此在不同頻段下會造成增益損失，當訊號方向接近水平時損失可能高達3 dB。本文提出只需知道所使用通道頻段即可對編碼簿做補償的方法，讓修改後的編碼簿在固定天線間距下，也能於不同頻段時能有與在理想頻段時類似的效能。另外本文提出了一種新的波束搜尋法，與所有現有搜尋法相比只需要傳送最少次的訓練序列數，即可達到最佳波束對搜尋的目的。最後提出了兩種基於編碼簿估測訊號方向的波束成形技術，在流程中只需知道訊雜比即可將波束調整到需要的指向。並實際套用於OFDM與60 GHz通道環境中，發現所提出的波束成形只需使用最低複雜度的符元式波束成形架構，即可提供與複雜度較高的混合式波束成形相仿甚至在某些情況下有更好的效能。

In the thesis, we discuss the beamforming techniques in order to realize high speed, and reliable transmission for millimeter-wave 60GHz wireless personal area networks (60GHz WPANs). Based on the beam codebook in IEEE 802.15.3c, we proposed some techniques and their analyses for enhancing the beamforming performance. Firstly, the original codebooks in 802.15.3c are generated with 90 degree phase resolution in order to simplify the RF circuit design. We modified codebooks by raising phase resolution finitely and analyzed the performance of them. We discovered that using modified codebooks with fewer antennas could provide better performance than originals with more antennas. Secondly, codebooks are designed for the fixed antenna spacing. Therefore, it maybe has gain loss in different frequency band which could be approximate 3 dB loss when the beam is closed to the horizontal. We proposed a compensation method which only needs the information of the frequency of transmitted bands. After compensation, the performance of modified codebooks in different bands would be approximate to originals in the ideal band. In addition, we proposed a new beam searching process. Comparing to existing searching processes, our method needs the least number of training sequence to find the best beam pairs. Finally, we propose two beamforming schemes based on using codebooks to estimate direction of signals. In these methods, we only need to know SNR of different beam pairs and it would adjust the beam to the desired direction. By simulation results in OFDM and 60 GHz systems, the proposed schemes, which use symbol-wise beamforming with the lowest complexity, could provide similar performance to the hybrid beamforming, which has more complexity, and even have better performance under some conditions.