OFDM 系統在60 GHz 頻帶之非直視傳輸： 混合式波束形成和全雙工中繼器

Abstract

IEEE802.15.3c系統是一適合高速之上網或高畫質之影音傳輸的規格，但操作的頻段是在免執照的 60 GHz，此頻段的通道對訊號之衰減性高且載波之穿透性低，因此其所需的傳送功率大且傳輸須直視的環境(LOS)，如何在非直視環境(NLOS)下做低功率的傳輸是一大挑戰。本篇論文的目的即是研究60GHz 系統中LOS/NLOS 之傳輸技術。我們使用平面陣列天線(planar antenna array)以及波束形成(beamforming)技術來補償損耗的方法。首先依據IEEE 802.15.3c的編碼簿，我們提出了一種新的波束搜尋法，可快速的達到搜尋出最佳波束對的目的，同時也提出一另一方法可以在LOS變動為NLOS時，仍然能夠可快速的搜尋出最佳波束對。此外，我們也使用全雙工(full-duplex)中繼器來克服NLOS的問題，並改善傳統半雙工系統吞吐量減半的問題。在全雙工(full-duplex)中繼器中，接收機會受到傳送機的干擾，稱之為為迴音(echo)，為了使迴音(echo)干擾消除且同時不影響原本的陣列天線的場型，我們設計了一個混合波束形成器的迴音消除器，有效的消除了迴音。

IEEE 802.15.3c system offers data rates of multiple Gbit/s for applications such as high speed internet access or high quality video streaming. However, it is operated in unlicensed 60GHz band, the propagation loss is high and signal penetration is low. Thus, 60GHz transceivers require high transmission power, and can only be properly operated in LOS environments. This thesis aims to develop LOS/NLOS transmission technologies for 60GHz systems. To solve the problem, we use a hybrid planar antenna array conducting beamforming. First, based on the codebook in IEEE 802.15.3c, we propose a new beam matching method which can find the best transmit and receive beamforming pair quickly. The method is also extended such that it is able to find the beamforming pair shortly after the environment changes from LOS to NLOS. Then, we propose another method, using full-duplex relays, to solve the NLOS problem. In a full-duplex relay, transmitted signal will interfere its received signal, a phenomenon called echo. We then design an echo canceller to suppress echo signal without affecting the original antenna pattern. It is shown that the echo is effectively canceled.