Receiver Hardware Considerations INTRODUCTION(1) Chương này bàn về các phần cứng của người nhận. Kể từ khi thiết kế cơ bản của máy thu GPS trong cuốn sách này là định hướng phần mềm, phần cứng được trình bày ở đây là khá đơn giản. Thông tin duy nhất cần thiết cho một máy thu phần mềm là các dữ liệu lấy mẫu. Những dữ liệu lấy mẫu hoặc số hóa sẽ được lưu trữ trong bộ nhớ để được xử lý. Đối với xử lý sau kích thước bộ nhớ định độ dài của dữ liệu ghi lại. Một tối. | Fundamentals of Global Positioning System Receivers A Software Approach James Bao-Yen Tsui Copyright 2000 John Wiley Sons Inc. Print ISBN 0-471-38154-3 Electronic ISBN 0-471-20054-9 CHAPTER SIX Receiver Hardware Considerations INTRODUCTION This chapter discusses the hardware of the receiver. Since the basic design of GPS receiver in this book is software oriented the hardware presented here is rather simple. The only information needed for a software receiver is the sampled data. These sampled or digitized data will be stored in memory to be processed. For postprocessing the memory size dictates the length of data record. A minimum of 30 seconds of data is needed to find the user position as mentioned in Section . In real-time processing the memory serves as a buffer between the hardware and the software signal processing. The hardware includes the radio frequency RF chain and analog-to-digital converter ADC . Thus the signal processing software must be capable of processing the digitized data in the memory at a real-time rate. Under this condition the size of the memory determines the latency allowable for the signal processing software. This chapter will include the discussion of the antenna the RF chain and the digitizers. Two types of designs will be discussed. One is a single channel to collect real data and the other is an in-phase and quadrature phase I-Q channel to collect complex data. In both approaches the input signals can be either down-converted to a lower intermediate frequency IF before digitization or directly digitized at the transmitted frequency. The relation between the sampling frequency and the input frequency will be presented. Some suggestions on the sampling frequency selection will be included. Two hardware setups to collect real data will be discussed in detail as examples. The impact of the number of digitized bits will also be discussed. A digital band folding technique will be discussed that can alias two or more narrow .
