Baseband Hardware Designs in Modernised GNSS Receivers - Global Navigation Satellite Systems: Signal,Theory and Applications - page 34

Antenna

RF Front end
(Down-
converter +
ADC)

PVT
Solu tion

Digital
Baseband
(Correlator)

Processing
(Software)

Fig. 1. Typical architecture of a GNSS receiver

5. To provide recommendations and guidelines for the design of a low power, high
performance, affordable multi-GNSS baseband hardware.
This chapter substantially draws on one of the authors' conference papers published in ISCAS
2010 (Shivaramaiah & Dempster, 2010).

2. GNSS receiver and baseband hardware

2.1 GNSS receiver architecture

Fig. 1 shows the typical architecture of a GNSS receiver. Each signal from a different frequency
band is down-converted and passed through an Analog-to-Digital-Converter (ADC) to obtain
the Intermediate Frequency (IF) samples. The baseband signal processing hardware (widely
known as the correlator) is usually implemented in hardware. With the help of feedback
control algorithms (implemented either as a part of the digital hardware or as a part of
the processing in software), the baseband circuit provides accurate estimates of the delay,
phase and frequency of the carrier and spreading code in the received signal (tracking). The
baseband circuit is also used for the initial coarse estimates of these parameters (acquisition).
The processing, usually implemented in software, computes the Position-Velocity-Time (PVT)
solution (Braasch & van Dierendonck, 1999; Kaplan & Hegarty, 2006; Parkinson & Spilker,
1995).

2.2 Generic baseband architecture for the tracking process in a GNSS receiver

This section describes a generic architecture for the GNSS baseband that allows the basic
functionality of tracking the signal. Though the same architecture can be used for the signal
acquisition process, the signal acquisition is not the focus here. The GNSS baseband hardware
in its usual definition is comprised of all the signal processing circuits bounded on the input
side by the sampled and digitised IF signal, and on the output side by the received signal
measurements (carrier phase, code phase, navigation data bits, signal strength, etc.). Fig.
2 shows the functional diagram of generic GNSS baseband hardware for a single signal
component. The functionality of each block is described in detail elsewhere in the literature
(e.g. Kaplan & Hegarty (2006)) and will be discussed briefly here.

The baseband functionality can be broadly divided into two parts.
1. Core Correlator Hardware
The core hardware is responsible for correlating the input signal with the local replica and
producing the correlation values.