用於LTE/A系統之三維定位波束成型法與追蹤

Abstract

在多天線的系統中，若要提升通訊性能，波束成型(Beamforming)是一個常被使用的作法，傳統的波束成型是基地台以掃描的方式，用戶再回傳最佳的波束方向索引，但此方法會造成較長的延遲和增加回傳資訊量。最近，有一個較有效率的方法就被提出，簡稱為以定位為基礎的波束成型，其想法是用戶先利用觀測到達時間差(Observed Time Difference of Arrival, OTDOA)定位法定出自身位置後，回傳所在區域的索引給基地台，基地台再根據此資訊對此方向做波束成型。本論文旨在提升此以定位為基礎的波束成型法效能，首先，為了提升OTDOA的定位精準度，我們對舊有的方法提出許多改進的提案，接著將此方法從二維環境延伸至三維環境中，主要想法為利用陣列天線傳送LTE/A系統規格裡定義的位置參考訊號(PRS)給用戶端，此時所傳送的PRS是帶有方向資訊的，我們提出的方法僅需三個觀測基地台即可定出用戶的三維座標，模擬結果顯示，我們提出的方法可以使系統傳輸量增加了兩倍。最後，我們考慮移動環境中的波束追蹤(bean tracking)問題，我們提出兩個以卡爾曼濾波器(Kalman filter)為基礎的追蹤演算法，模擬結果證明使用兩種追蹤演算法都可以使定位精準度大大的提升。

Beamforming is a commonly used approach to enhance communication performance in multiple-antenna systems. Conventional beamforming relies on a scanning scheme requiring long delay time and heavy overhead. Recently, an effective remedy, referred to as the location-based beamforming, is proposed. In this approach, the user identifies its location with the observed-time-difference-of-arrival (OTDOA) method, reports the region to which it belongs to the BS, and the BS beamforms the signal to that region. This thesis is aimed to enhance the performance of this location-based beamforming method. First, we propose several schemes to improve the localization accuracy of the OTDOA method. Then, we extend the localization method developed for 2D to 3D scenario. The main approach is to transmit directional positioning reference signal (PRS) defined in LTE/A standards to users. With our method, only three BSs are required for the user to locate its position. Simulations show that the proposed method can double the system capacity. Finally, we consider the beam tracking problem in mobile environments. We proposed two Kalman-filter-based tracking algorithms. Numerical results show that both algorithms can greatly enhance the localization performance.