Navman 11 - Manual (Page 6)

6 MN002000A © 2004 Navman NZ Ltd. All rights reserved. Proprietary information and specifications subject to change without notice.
1.0 Introduction
This document provides technical information
common to the entire Navman Jupiter series.
Navman’s Jupiter series of Global Positioning
System (GPS) receivers are single-board,
12 parallel-channel receiver engines. Each
board is intended as a component for an Original
Equipment Manufacturer (OEM) product.
GPS satellites, in various orbits around the Earth,
broadcast Radio Frequency (RF) ranging codes
and navigational data messages. The Navman
Jupiter series GPS receivers continuously track all
‘visible’ satellites and decode all available signals
from them, producing a highly accurate and robust
navigation solution.
The Jupiter series receivers are designed for high
performance and maximum flexibility in a wide
range of OEM applications including handhelds,
panel mounts, sensors, and in-vehicle automotive
products. These highly integrated digital receivers
incorporate two custom SiRF devices that have the
SiRF Jupiter chip set: the RF1A and the Scorpio
Digital Signal Processor (DSP). The combination
of custom devices minimises the receivers’ size
and satisfies harsh industrial requirements.
1.1 Product overview
1.1.1 Description
The receivers require DC power and a GPS signal
from a passive or active antenna. To provide
the lowest total system cost with minimal power
consumption, each of the receivers provides
only those components that are required for the
majority of applications (e.g. if a passive antenna
can be used with a short cable, no pre-amplifier is
required).
The all-in-view tracking of Jupiter series receivers
provides robust performance in applications that
require high vehicle dynamics or that operate
in areas of high signal blockage, such as dense
urban centres. By continuously tracking all visible
GPS satellites and using all of the measurements
to produce an ‘over-determined’ and ‘smoothed’
navigation solution, the Jupiter receiver provides
a solution that is relatively immune to blockage
induced position jumps that can occur in other
receivers with fewer channels.
The 12-channel architecture provides rapid Time-
To First Fix (TTFF) under all start-up conditions.
The best TTFF performance is normally achieved
when time of day and current position estimates
are provided to the receiver. However, the flexible
Jupiter signal acquisition system takes advantage
of all available information to provide a rapid TTFF.
Acquisition is guaranteed under all initialisation
conditions as long as available satellites are not
obscured.
To minimise TTFF following a power interruption,
each of the Jupiter receivers can accept external
voltage to maintain power to the Static Random
Access Memory (SRAM) and Real-Time Clock
(RTC) for periods following the loss of primary
power. The use of external voltage assures the
shortest possible TTFF following a short power
interruption. The OEM may extend the operation
of the RTC by providing stand-by power on a
connector pin, in which case a short TTFF is
achieved by using the RTC time data and prior
position data from the receiver’s Electrical
Eraseable Programmable Read-Only Memory
(EEPROM).
The Jupiter series supports two dimensional
(2D) operation when less than four satellites are
available or when required by operating conditions.
Altitude information required for 2D operation is
determined by the receiver or may be provided by
the OEM.
The Jupiter receivers contain two independent
serial ports, one of which is configured for primary
input and output data flow using the National
Marine Electronics Association (NMEA) 0183
format or Navman binary message format. The
second port is used to receive Differential GPS
(DGPS) corrections in the Radio Technical
Commission For Maritime Services (RTCM)
SC-104 format. The receivers support DGPS
operations for improved accuracies over standard
GPS.
A complete description of the serial data interface
for the entire Jupiter series of GPS receivers is
contained in this document.
For applications that require timing synchronisation
to GPS accuracies, the Jupiter receivers provide
an output timing pulse that is synchronised to
one second Universal Time Coordinated (UTC)
boundaries.
1.1.2 Receiver architecture
Figure 1-2 illustrates the internal architecture of
the Jupiter receivers. Each receiver is designed
around two custom SiRF devices that contain most
of the required GPS functionality.
1. The RF1A, which contains all the RF down-
conversion and amplification circuitry, and
which presents sampled data to the Scorpio
device.