GPS接收器於ARM-based FPGA平台上的實現

Abstract

近年來通訊技術的進步，使得全球定位系統(Global Positioning System)的應用日益廣泛，但一般商用GPS操作環境必須在高度18000公尺以下、速度不能超過515公尺/秒、加速度須在4g以下，無法應用在比較特殊的用途，像高動態導航，且一般商用GPS接收機是由ASIC和一般用途處理器(general- purpose processor)所組成，GPS接收機上ASIC和燒錄在ROM上的軟體出廠後就無法更改，故本研究選擇自行設計一個GPS接收機。

本研究GPS訊號的處理流程參考GPL-GPS[11], Namuru[12]等架構。平台的選擇上使用了Altera公司生產的ARM-based FPGA，因為在同一個晶片上擁有一般用途處理器ARM cortex-A9和FPGA，能同時實現硬體和軟體的方式實現所需的訊號處理，利用FPGA來取代ASIC的功能，低成本並且架構完全開放能隨更改來適應不同的狀況，且Altera在設計軟體方面發展齊全，讓處理器和FPGA的連接介面實現上更加容易，這樣的優點提供一個很好的發展平台。

本研究所設計的接收機擁有12個頻道，能夠同時並且即時追縱12個GPS衛星，論文中會詳細的介紹軟體/硬體的實現架構和模擬結果，最後再接上天線接收當下的衛星訊號驗證最後的結果，結果顯示，在接上天線接收實際衛星訊號，可以成功鎖定7顆衛星號，並完成定位功能，TTFF(time to first fix)約60秒，輸出頻率10Hz。

In recent years, advances in communications technology enable the global positioning system (GPS) being used widely. The regulations confine the commercial GPSR applications to the cases such as: height is lower than 18,000 meters, speed is lower than 515 m / s, and acceleration is smaller than 4g. Therefore, it can’t be applied to applications such as high dynamic and high altitude navigations. Besides, commercial GPSRs are made by ASIC and general purpose processor technology. The algorithms in the ASIC cannot be overwritten after it is shipped out of the factory. The goal of this research is develop a GPSR suitable for the high dynamics applications. Therefore, we must start it by building a GPSR on a platform which we have the fully control of the hardware and software.

There are many GPSR algorithms that can be found in literature. We chose the one which combines GPL-GPS [11], the work from Namuru [12], and other researchers. We also chose an ARM-based FPGA platform from Altera company, which composes of FPGA and ARM processor. The reason for using ARM-based FPGA platform is because it can realize the designated signal-processing algorithms using both hardware (FPGA) and software (ARM) to satisfy the needs of computation speed and coding flexibility. The Altera company provides very a good software development environment for composing/ debugging the codes for FPGA and ARM. It is very convenient for researchers to get started with.

In this project, we developed a GPSR that has 12 channels to track satellite signal simultaneously. The architecture of the signal processing, implementation of software/ hardware, Matlab simulations, and experimental results are all described in detail. The experimental results show that the developed receiver can successfully lock GPS signals from seven satellites, TTFF (time to first fix) is about 60 seconds, and the output frequency is of 10Hz.