目前已經有愈來愈多的學術應用與商務產業開始利用全球導航衛星系統進行定位、導航、校時的服務。而各類使用者對定位系統的定位效能的需求也相對提升。然而在都市高樓林立定位環境下，傳統的接收機設計時常會出現衛星訊號失鎖的情形或者受到多重路徑定位誤差。有鑑於此，一直以來有許多研究探討著如何設計出較為穩定的訊號追蹤演算法。傳統衛星訊號追蹤演算法使用電碼鎖相迴路與相位鎖相迴路對每一個衛星分別進行訊號追蹤，當成功追蹤後再將導航資訊傳遞給導航處理器進行使用者之定位。向量追蹤法不同於傳統衛星訊號追蹤法為其單使用一個迴路即可同時追蹤每一個衛星並同時估測使用者位置。此向量追蹤法之迴路為利用擴展卡曼濾波器(Extended Kalman filter, EKF)來進行估測，並且將每一個通道之鑑別器輸出值當作濾波器輸入觀測量，藉由所有衛星之鑑別器輸出，濾波器即可以成功估測使用者位置。向量追蹤法的優點為可以集中所有衛星訊號的強度進而增加濾波器增益值。正因為此種特性，向量追蹤法相當適合使用於低衛星訊號信噪比的環境中，而這也正是傳統衛星追蹤演算法較不能支援的環境。目前尚未有研究討論與評估向量追蹤法在多重路徑干擾環境下的效能，有鑑於此，本論文的第一個目標為分析向量追蹤法是否能力消減由多重路徑所造成的影響。為了增進向量追蹤法於消減多重路徑誤差的效能，本論文的第二個目標為提出一新的組合：向量追蹤法整合基於鑑別器設計的多重路徑消減演算法，並且評估其效能。其中，本論文所使用的向量追蹤迴路為向量電碼延遲鎖相迴路(vector delay lock loop, VDLL)而整合基於鑑別器設計的多重路徑消減演算法為頻閃相關器(Strobe correlator)。
本論文首先使用直接訊號消減法進行兩種環境的模擬：訊號中斷與非視線訊號接收(non-line-of-sight reception)。此模擬的目的為驗證本論文研發的向量追蹤法確實具備有消減多重路徑干擾的能力。根據模擬結果顯示，向量追蹤法不但有能力在訊號中斷時繼續銜接並提供定位服務，並且也展現出偵測非視線訊號接收情形的潛力。接著本論文將嘗試於兩個不同的都市環境，台灣成功大學校區與日本東京市區，收集全球定位系統中頻訊號，並對向量追蹤法與本論文提出的新組合，向量追蹤法整合基於鑑別器設計的多重路徑消減演算法，進行測試。此實驗可以分為靜態實驗與動態實驗，兩個實驗皆可證明確實受到多重路徑干擾。根據實驗結果首先可以發現，相對於傳統追蹤迴路，向量追蹤迴路可以估測出更穩定並且準確的電碼頻率(code frequency)。這個特性可以減少多重路徑干擾對於向量追蹤迴路的影響，進而減少多重路徑所造成的定位誤差。另外，根據實驗定位結果顯示，將頻閃相關器整合於向量追蹤迴路可以進一步提高向量追蹤法消減多重路徑影響的能力。最後，本論文也發展一基於相關器設計的蒙地卡羅模擬器以對本文提出的新整合演算法進行接收機敏感度(receiver sensitivity)的檢測。模擬結果顯示，相對於整合頻閃相關器於傳統追蹤迴路，整合其於向量追蹤迴路可以獲得2.26 dB-Hz的增進。有鑑於上述之實驗與模擬結果，本論文總結向量追蹤迴路具備對於多重路徑干擾的抵抗力，並且此演算法不需要使用額外的感測器。

This dissertation focuses on the application of the pedestrian positioning without external aiding in radio frequency difficult environments. Multipath interference and non-light-of-sight (NLOS) reception are major error sources when using Global Navigation Satellite System (GNSS) in an urban environment. Buildings and dense foliage reflect and diffract the signals, and receiver-based multipath and NLOS mitigation would be a strong candidate. Traditionally, this mitigation technique involves applications of different discriminator designs to mitigate multipath, and these discriminator designs can reduce the pseudorange multipath error when the receiver’s precorrelation bandwidth is sufficient. However, these discriminator design not only decrease the receiver’s sensitivity but also not helpful to mitigate NLOS reception at all. New approaches to multipath and NLOS mitigation are therefore needed. A promising approach to minimize the effect of multipath interference is the vector tracking loop. In comparison to the conventional tracking loop, the vector tracking loop replaces the delay lock loop (DLL) and the phase lock loop (PLL) with an Extended Kalman filter (EKF) to track the GNSS signals. This EKF of the vector tracking loop not only tracks the signals but also calculates the user positions. By combining the tracking and positioning tasks, the vector tracking loop can use the user motion determined from the stronger GNSS signal to predict the code phase and maintain lock of the weaker signals. The vector tracking loop also has the potential to mitigate the effects of multipath interference and NLOS reception. However, the degree to which this could be achieved has not yet being shown. Therefore, the first objective of this dissertation is to investigate the immunity against multipath effect generated by the vector tracking loop. The second objective is to maintain the multipath mitigation capability from the discriminator-based method and avoid the loss of sensitivity by proposing an integration scheme of the discriminator-based multipath mitigation technique and the vector-based tracking loop.
In this dissertation, a Strobe correlator is used as the discriminator-based multipath mitigation algorithm and a vector delay lock loop (VDLL) is used as the vector tracking algorithm. This VDLL replaces the individual DLLs but retains conventional PLLs to separate the carrier phase of each signal. This work uses an 8-state EKF with adaptive tuning to estimate the user position and maintain code phase. The EKF’s adaptive tuning algorithm uses the variance of the measurement innovation to determine the assumed measurement noise covariance.
This work adopts our Matlab-based GPS software-defined receiver as the research platform and implements the vector tracking algorithm. This work initially applies a signal cancellation method to simulate the scenarios of signal termination and the NLOS reception. The method can help to test the capabilities of the developed vector tracking loop. Then, it compares the positioning performance of the conventional and the vector tracking loops by means of a common set of the intermediate frequency (IF) signals recorded at the Tzu-Chang campus of the National Cheng Kung University and the urban canyon of Tokyo city. Both static and dynamic signals are collected in a challenging urban environment subject to multipath interference. Further, the comparison analyze of performance of the standalone conventional tracking (CT) method, the CT with Strobe correlator method, the standalone vector tracking (VT) method, and the VT with Strobe correlator method (the proposed combination) are presented in this dissertation.
The experimental results show that the VT method generates more stable code numerical controlled oscillator (NCO) frequency than that of CT method does. This characteristic can reduce the impact of multipath interference which reflected in a smaller positioning error while using VT. According to the experiment results, the Strobe correlator further enhances the multipath mitigation ability of the vector tracking loop in terms of the position solutions as well as the capability to detect the multipath effects. Finally, a correlator-based Monte-Carlo simulator is developed to evaluate the proposed receiver architecture sensitivity. In comparison to the conventional tracking loop, the simulation results show that the proposed integration scheme is able to achieve a maximum 2.26 dB improvement in terms of the tracking threshold probability of 50% with seven satellites in view. In conclusion, the VT method provides resistance against multipath interference for a GPS receiver without any external aiding and hence its performance is further enhanced by the integration of the discriminator-based multipath mitigation algorithm.

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