[LinuxPPS] Using GPS for automotive applications

[Neal Probert]

VII
---
This is a US-DOT funded project with involvement from most of the 
automotive companies and a dozen other suppliers/vendors.  There are a 
number of experimental public, safety and private applications being 
developed.

    http://www.its.dot.gov/vii/

Most of work we're doing is still research and development, working to 
get the cost of GPS units down and find ways to improve accuracy and 
precision in the moving vehicle.

DSRC is basically a WiFi link at 5.9Ghz.  We're using Linux because it's 
a hell of a lot cheaper and easier to add a new network protocol stack 
to an open source operating system.

The VII testing in taking place in Farmington Hills/Novi in the Detroit, 
Michigan area.  Another test area is in California.

GPS
---
DoD has removed all dilution from the satellite signals.  There is a new 
generation of satellites (block III) going up in the next decade or so 
that drastically improves the accuracy and precision.  That implies new 
GPS receivers, of course.

The DGPS signal is sent from a local DGPS base station to the traffic 
lights which is broadcast to the test vehicles.  At this point in time, 
it's not a significant improvement.  We're probably looking at using 
each traffic light as a virtual reference station in the future.

Automotive
----------
Most automotive GPSes use the speed input from the vehicle, so they can 
do a little dead reckoning.  Most consumer grade GPSes are often based 
on the ARM chipset, so only support single precision floating point 
math.  So SiRF and u-Blox, even with corrections, aren't good enough.

For VII, we're doing 100 msec extrapolations based on vehicle speed, 
acceleration and yaw available from the vehicle's CAN bus.  A lot of 
information is available from modern vehicles because it's used for 
anti-lock brakes, traction control systems, vehicle dynamics control, ...

Some folks are adding an IMU which helps in cases where you need dead 
reckoning in the urban canyon.  Spend a little more money we can get 
higher quality (a lot more money in the case of the Applanix) positioning.

Linux Kernel
------------
The PPS integration is important for DSRC radio synchronization and 
keeping the OS clock in sync.

So I'm looking at waiting on the 2.6.26 kernel, so it looks like I'll 
need to be patching the latest Ubuntu kernels to get what I need.

So, yes, it would be very handy and helpful to get this integrated into 
the kernel as soon as possible.  It would be a huge win for Linux.

PPS Interface
-------------
The simplest way I can see interfacing the PPS is through a MAX232 chip 
into the serial port's DCD input.  Right?


Keywords to Google: VII, DSRC, 802.11p, IEEE 1609, SAE J2735


-- 

             *** ProbeStar Telematics, LLC.  ***
  Automotive, Mobile and Embedded Communications Consulting

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