適用於一位元量化GPS接收機之新型載波追蹤方法

Abstract

在現代全球定位系統中，軟體接收機（software receiver）為一廣受矚目的技術。有別於一般追蹤程序(tracking process)，本論文探討如何精確估算數控振盪器(NCO)的頻率，以期改善衛星訊號追蹤迴路之效能。針對地面運輸工具的使用環境，我們提出利用特定時間的衛星訊號數據來估算精確的頻率偏移之方法。利用調整NCO初始頻率和相位，從模擬結果顯示載波頻率的誤差可以有效地降低至±10 Hz之內。 在載波頻率精確度大幅提升的同時，必須考慮儲存NCO載波對照表的記憶體空間需求。有別於事先建立的載波對照表，我們提出一種僅使用簡單的數值運算，稱作“虛擬載波對照表”的演算法。利用所提的演算法，我們成功地只使用極少的記憶體空間產生所需的虛擬載波對照表。

It is well known that software receiver is very attractive in modern GPS. In this thesis, we focus on the improvement of the tracking loop performance with the fine frequency estimation for numerical controlled oscillator (NCO). For land vehicle users, we propose a frequency offset measurement scheme that uses the first few data sets to estimate the frequency offset. By adjusting the initial phase and frequency of NCO, the simulation results show that the carrier frequency resolution is within ±10 Hz. Since the frequency resolution has been enhanced, the memory space to store the look-up table of NCO is of concern. Instead of pre-built carrier table, a simple algorithm using numerical operation called “virtual carrier table” generator is proposed. Using the proposed approach, we have successfully generated the virtual carrier table, which requires very small memory space.