Receiver Hardware Considerations - Fundamentals of Global Positioning System Receivers: A Software Approach - page 105

CHAPTERSIX

Receiver Hardware
Considerations

6.1 INTRODUCTION ( 1 )

This chapter discusses the hardware of a GPS receiver. Since the basic design
of GPS receiver in this topic 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 5.5. 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