[time-nuts] L1 and L2 frequencies
magnus at rubidium.dyndns.org
Thu Jan 15 03:59:37 EST 2015
The traditional GPS has C/A and P(Y) on L1 and P(Y) on L2.
Most Civilian GPSes only uses C/A.
Advanced receivers can also use P(Y) code, since the P-code is known,
the hand-off to P code is known and the way that P-code is encrypted
into Y-code is known (XOR with another code, called A-code or W-code in
different sources). Modern receivers is able to do both code and carrier
phase observations on the P(Y) code signals.
The military goal of this "break-in" is not lost, as those receivers
still rely on the C/A code and that is easy to jam. Also, the "break-in"
comes at a signal quality loss and the advancement of methods have
reduced this loss.
The benefit of dual frequency observation is that ionspheric shift can
be almost completely taken out of the error budget, adjusting both code
and carrier phase observations. Then working on the integer ambiguity
you can get carrier phase observations with accurate pseudo-ranges.
Carrier-phase observations has a much higher precision to them, so that
gives a very high precision and using a good reference network
corrections can be adjusted to give good absolute position.
If civilian receivers where to implement L2C and L5 which now is
becoming common, they would gain quite a bit of precision in a similar
fashion. For car navigation, the GPS would know which lane you are in.
On 01/14/2015 10:40 PM, Brooke Clarke wrote:
> Hi Martyn:
> On each frequency there are a couple or more different codes.
> The Civilian Acess (C/A) code on the L1 frequency is all public
> information and so is the most commonly used.
> But there are classified codes that have a much higher bit rate and
> allow for more accurate position, time and velocity measurements.
> Tom mentioned that there are civilian GPS receivers that make use of the
> L2 frequency, but they do that my using what's called carrier phase
> (that's to say they do not make use of the classified code). This is
> mainly used in surveying applications where, by recording a lot of data
> and post processing, you can get a very precise location.
> When two frequencies are used there's a possibility of removing an error
> related to the total electron count in the path of the signal. The new
> F5 frequency allows for doing that, but as far as I know none of the
> commercial GPS receivers make use of it yet.
> Mail_Attachment --
> Have Fun,
> Brooke Clarke
> Martyn Smith wrote:
>> I have some questions on GPS and GNSS.
>> Do all the civilian GPS receivers only operate on the L1 frequency?
>> Are there any GPS frequency standards out there that use L1 and L2 and
>> that can be purchased by non-military customers?
>> I am playing with the new Lea-M8T receiver.
>> How do I know what satellites are GPS, GLONASS, Galileo etc.
>> >From my understanding GLONASS have different SV numbers but not 100%
>> Any help appreciated.
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