GPS receiver modules ease
overall system design
Max Bucher
Product Manager, Embedded systems
µ-blox ag
The focus in this presentation is on the advantages of the use of
GPS receiver modules for the design of new and innovative
products. Very short design cycles, increasing cost pressure and
the use of many different base technologies are the main challenges for the system integrator. Modular solutions enable designers and system integrators to meet the window of opportunity while enhancing the functionality of their systems. A few
sample applications are discussed.
1 Introduction
The rapid development of mobile communication and the upcoming new networks (GPRS, UMTS) that allow mobile data
communication at data rates up to the speed of land based networks. The increasing bandwidth and higher processing power
of mobile devices enable new applications that need more functionality of the device. This paper shall show that modular solutions help to meet the more and more stringent time frames
for the development of very complex systems.
Common conception is that modules are very well fitted for
systems with moderate complexity and no too stringent space
and power requirements. Very often the pricing of modules is
not considered to be competitive with a chipset solution. In the
following we would like to show, that miniaturized modules
can be a very cost-effective and good solution for a system integrator.
2 Markets and Applications
The on-going conversion of communication and mobile computing creates new products and services. This opens great opportunities as well for service providers, system integrators and
network providers. Companies from different markets like
mobile communication or mobile computation are expanding
their product portfolio to enter these markets. Meeting the
timeframe to enter these markets is crucial.
The design of portable devices such as smart phones, PDAs
and Handheld computers needs a very strongly integrated system with very low power consumption and small size. These
products also combine very different functionalities and thus
require various design competencies. The system integrator
needs to have a very deep insight in RF design, high-speed
digital design as well as software engineering for embedded
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systems and user interface. Moreover the overall complexity of
these systems will increase in the very near future. The still
increasing need for miniaturization and low power consumption introduces even bigger challenges.
Make or buy
One of the questions a system integrator is faced with is: is it
more cost effective to implement all the functional block (subsystems) himself, or would it be more efficient to buy modular
solutions for some sub-systems.
3 Miniature Flight recorder - an Application Examples
The Project
One of the most fascinating topics in bird research is the navigation capabilities of birds, especially homing pigeon. Ornithologists all over the world are trying to figure out how these
birds navigate and what sense of orientation enables them to
find their way home from places as far as 200 miles away. You
might think: “Why should we bother? What does this have to
do with ITS systems? We basically want to know where our
trucks are!”
At first sight behavioral studies of birds might not have too
much in common with fleet management and traffic technology. But the technical challenges implementing a miniature
flight recorder are very well suited to demonstrate the advantages of the integration of a complete system on a GPS receiver
module. Size and weight restrictions require an extraordinary
high level of integration, which results in reduced external component count. A welcome side effect is a considerable reduction of the total system cost.
A GPS receiver basically consists of a RF front-end, a
correlator ASIC and a small processor system with SRAM and
FLASH (see Figure 1). The solution of the equations to calculate the position in real-time requires a powerful processor.
Therefore the processor will be idle most of the time, if the
position information is not required at the highest frequency
possible. A cost-effective system design will take account of
this and uses the free resources, in order to minimize external
component count while maintaining or even enhancing system
functionality.
Picture 2: Pigeon with flight recorder mounted
Figure 1: Blockschematic of the GPS receiver
Miniature Flight recorder
Prof. Dr. Lipp, head of the research group for Neuroanatomy
and Behavior at the University of Zurich brought up the idea of
a miniature GPS flight recorder. His research group is internationally known for their behavioral studies on homing pigeons.
They were looking for a device to get a new edge on their research regarding the orientation and navigational skills of homing pigeons. Until now there where only simple flight recorders, which were based on a compass. These could only record
the headings during the flight. With a GPS receiver much more
detailed data could be collected. Through the analysis of this
data they hoped to get better insight on the behavioral patterns
and cognitive skills of pigeons. In a joint project of the Institute
for Anatomy of the University of Zurich and the Electronics
Lab of the ETH Zurich a flight recorder for homing pigeons
was developped. The idea was to attach a small box to the back
of the bird that captures and records position, altitude and time.
Once the bird has returned home the recorded data is transferred to a PC for analysis.
Basically the flight recorder would consist of a power supply (battery or accumulator), GPS receiver, GPS antenna and a
datalogger (Picture 1). This is an example of a minimal system
with harsh size and power consumption constraints.
Using a standard ‘off-the-shelf’ GPS receiver module with
a special software extension (integrated datalogger) allowed to
realize a highly integrated system within very short time.
With its weight of 8g and the measurements of 30mm x
30mm the GPS-MS1E-DL from µ-blox was the ideal candidate for this application. Power consumption was a major concern, as in most mobile applications. The GPS-MS1E-DL supports a power save mode. In this power save mode the receiver
acquires a position, stores it to the FLASH and automatically
shuts down. This process takes about 1 sec. During the rest of
the period the system remains in stand-by at a power consumption of 500µA. Using a position up-date period of 5s the GPSMS1E would operate up to 8h on a CR3 battery. This battery
type proved to be the one with the best capacity/weight ratio.
To reach the highest integration possible for the antenna a ceramic patch antenna with a ground plane directly on the PCB
was used.
The whole receiver is packaged into an ultra-light composite housing. The battery, the GPS receiver and the ceramic patch
antenna contributes the most to the weight of the total system.
The weight of the complete system including battery, antenna
and housing is currently 36g (see table).
Table 1: Weight budget
Picture 1: Picture of flight recorder
A pigeon is capable of carrying about 40g of weight for
several hours, which is what they usually carry as food during a
flight. Therefore the total weight of the system was not to exceed 40g. The size is determined by the size of the back of a
pigeon. A module of 40mm x 60 mm would fit on the bird’s
back. (Picture 2) Due to these mechanical constraints the highest possible level of integration was mandatory.
The data logger
The GPS-MS1E-DL contains 1024kBytes FLASH memory of
which 700kBytes are available for custom use. These free resources can be used to implement a datalogger directly on the
GPS receiver. This internal datalogger can write position information, altitude, velocity, time and number of satellites used
for navigation to the on-board FLASH. After a flight the recorded data is downloaded to a PC through a serial interface.
There the data is visualized and analyzed. The size of a regular
data record is 9 x 16bit words. The datalogger is configured
through the serial interface. A configuration software lets you
set the logging interval as well as filter parameters define
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whether a position fix should be stored to the FLASH or not.
This filter minimizes the number of stored positions, while
maintaining enough information to reconstruct a trace. The filter checks the minimum distance between two logs before storing a data record. This prevents the receiver to fill the FLASH,
if the tracked object is moving very slowly or even standing
still. A data compression algorithm further increases the number of data records that can be stored in the FLASH. Data is
compressed by only storing the difference to the last position.
Using all these features the datalogger is able to store up to
100’000 data records. Furthermore the datalogger offers the
possibility to store the states of the (12) digital IOs together
with a time tag. This allows the storage time and position of
external events like starting an engine or pushing a panic button.
It flies...
For the first test flights the pigeons were trained with dummy
units of the same size and weight as the flight recorder. After
that training period the birds did not seem to take any notice of
the additional weight anymore and first flights of 2-5km (see
Picture 3) showed very encouraging results. For the first time
ever recording the flight of birds over long distances (>100km)
were made possible.
Picture 3: Recorded path
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Author’s contact details
Max Bucher
µ-blox ag
Z¸rcherstrasse 68
CH-8800 Thalwil, Switzerland
Phone: (41-1) 722 74 63
Fax: (41-1) 722 74 47
E-mail: max@u-blox.ch
Web site: www.u-blox.ch