[IGS-RTWG-91] Re: Positions Against Phase Alignment

"Dr. Gerhard Wübbena" gerhard.wuebbena at geopp.de
Tue Jan 29 07:37:30 PST 2013


Dear Ken,

I do not agree with your interpretation, that "the only useful and 
reliable observations would be the reference signals on each frequency".

If you transmit untouched observables, i.e. the observables as obtained 
from the proprietary receiver formats, and if your application requires 
"phase alignment" you need the phase shift message only in very limited 
scenarios.

You *do not need *a phase shift message

  * If you have only phase observable per GNSS and frequency,
  * if you have more than one phase observable for a frequency and if
    you have overlapping satellites, i.e. both or all phases are
    simultaneously tracked for the same satellites. In this case a
    direct comparison of the phases yields the information about
    necessary shifts.

In the majority of scenarios these cases will be the default. I.e. you 
will have all the necessary information from the stream with untouched 
observables.

Currently, there is only one scenario where a phase shift message is 
needed if your application requires alignment. This is the tracking of 
L2P and L2C without overlapping satellites. However, the alignment of 
L2C is difficult in case of Flex Power (to be expected with L2C-IOC in 
2014/15?). The current MSM-CDV does not support alignment in this case, 
but it is defined in our proposal (see below).

In our joint MSM proposal with Alberding, BKG and DLR (attached, in case 
you did not receive it) we defined the phase shift message to be 
optional, because it is not needed in most cases and in order to allow 
the generation of MSM streams by converter software if the phase shifts 
are unknown to the converter. We think this is a better solution 
compared to the necessity to throw away observations by the converter or 
to violate the standard (this will make the standard unreliable). The 
decision to throw away or to use observations should not be taken by a 
converter software but by the receiving application. The receiving 
application might not require alignment or might know through other 
means how to do the alignment for the specific streams.

The current MSM-CDV gives you ambiguous phase observations unless you 
define a mandatory phase shift message. However, such a message is not 
defined in the CDV. With the CDV definition you will not be able to 
restore the original observations, you may loose continuity of phases, 
interfrequency and code-carrier biases (as used for MW-combinations) 
will become ambiguous and may experience discontinuities. In case of 
Flex Power you will have aligned or non-aligned phases and you have no 
way to identify it. This will result in ambiguous and unreliable 
streams. Not really an acceptable method in my opinion!

Best Regards

Gerhard


-- 
Dr.-Ing. Gerhard Wübbena                                   #
Geo++ GmbH, Steinriede 8, D-30827 Garbsen, Germany         ###
phone +49- 5131-4689-0, fax +49- 5131-4689-99              #####
Latitude: N52°25'51" Longitude: E009°36'30"                #######
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Geschäftsführer/President: Dr.-Ing. Gerhard Wübbena        #############

Am 29.01.2013 14:01, schrieb MacLeod, Ken:
> Hi Loukis,
>
> The Geo++ paper proposes that one can encode data in MSM format and NOT make an effort to phase align the data (no mandatory phase alignment message).   In this case the only useful and reliable observations would be the reference signals on each frequency.  Not really an acceptable method in my opinion.
>
> I think we can work with unaligned MSM phase as long as there was a mandatory phase alignment message, since RINEX 3.02 can accommodate this method and we have the information required to align the phase obs in RT.
>
> We will see what happens Thursday and Friday.
>
> Regards
>
> Ken
> ________________________________
> From: igs-rtwg-bounces at igscb.jpl.nasa.gov [igs-rtwg-bounces at igscb.jpl.nasa.gov] on behalf of Loukis Agrotis [loukis at symban.co.uk]
> Sent: January 29, 2013 6:49 AM
> To: RTWG
> Subject: [IGS-RTWG-89] Positions Against Phase Alignment
>
> Dear Colleagues,
> Please see attached two papers taking positions against phase alignment at the RTCM meeting taking place this week in San Diego. The IGS has previously taken a position in favour of phase alignment. The outcome of the meeting may well be that the MSM formats are approved by majority of the people present, but in case there is another stalemate, I believe that there should be a serious discussion to see how a compromise could be achieved as soon as possible.
>
> Best Regards,
> Loukis
>
>
>
> _______________________________________________
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> IGS-RTWG at igscb.jpl.nasa.gov
> http://igscb.jpl.nasa.gov/mailman/listinfo/igs-rtwg
>

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