Re: [Discuss-gnuradio] XM on GR

[Andy Walls]

Just to be clear, Sirius is different than XM (even though they merged).  The 
lower edge of the 12.5 MHz XM allocation is at 2332.5 MHz, IIRC.  The upper 
edge of the 12.5 MHZ Sirius allocation is there as well.

Sirius does have patents on hierarchical modulation, which I'm guessing they 
would use in the Sirius band.

Regards, 
Andy

On April 10, 2016 5:36:08 PM EDT, Chris Kuethe <address@hidden> wrote:
>Thanks to Steve for hitting me with a clue-stick. For anyone else
>playing along at home, the Sirius patch antenna has an integrated amp
>and takes inline power - a fact that I did not see anywhere.
>
>This test was done with a hackrf tuned to 2.3265GHz, 20Msps, 8MHz
>analog filter - there is clearly something interesting going on when
>inline power is enabled with the "bias=1" argument.
>
>On Sat, Apr 9, 2016 at 6:32 AM, Andy Walls
><address@hidden> wrote:
>>
>>
>> On Fri, Apr 8, 2016 at 10:48 AM, Andy Walls
><address@hidden>
>> wrote:
>>>
>>>
>>> >         The audio codec is proprietary and not documented anywhere
>AFAIK
>>> > so
>>> >         even if you demod the bitstream, you won't be able to do
>much
>>> > with it.
>>>
>>> > Thank you all for the conversation, it is pretty interesting. 
>That
>>> > makes sense
>>> > that they have a proprietary protocol, it's a shame though.  Is
>the text
>>> > that
>>> > comes through encoded in a proprietary way?
>>> >
>>> > Does anyone know what the frequency of channel 1 is on (I'd like
>to see
>>> > if I
>>> > can even see the signal popping up above the noise)?
>>> >
>>> > ~Jason
>>>
>>> The XM center freqs are shown here:
>>>
>>>
>>>
>https://www.rohde-schwarz.com/us/technologies/satellite-broadcast/xm-satellite/xm-satellite-technology/xm-satellite-technology_55613.html
>>>
>>> The Sats are QPSK, the terrestrial is COFDM.
>>>
>>> That page also states the audio codec for voice programming is AMBE,
>and
>>> AAC+ for all other programming.
>>>
>>>
>>> The XM radio patents give you a lot of clues:
>>>
>>>
>https://www.google.com/search?tbo=p&tbm=pts&hl=en&q=inassignee:%22Xm+Satellite+Radio+Inc.%22
>>>
>>> Images 4 and 6 of this one:
>>>
>>>
>https://www.google.com/patents/US7020217?dq=inassignee:%22Xm+Satellite+Radio+Inc.%22&hl=en&sa=X&ved=0ahUKEwj5ycbeoP_LAhXEXh4KHWSdDeA4HhDoAQgwMAM
>>> Image 4 of this one:
>>>
>>>
>https://www.google.com/patents/US6510317?dq=inassignee:%22Xm+Satellite+Radio+Inc.%22&hl=en&sa=X&ved=0ahUKEwikn4Ogof_LAhVIJx4KHYaYCt44KBDoAQhTMAg
>>>
>>> And maybe the most useful I've skimmed:
>>>
>>>
>https://www.google.com/patents/US7123875?dq=inassignee:%22Xm+Satellite+Radio+Inc.%22+MCM&hl=en&sa=X&ved=0ahUKEwidqpT1of_LAhUFXh4KHXqIDuEQ6AEIKjAC
>>> Images 1, 5, and 6.
>>>
>>> This particular patent also indicates that after the demod, RS
>decoder,
>>> viterbi decoder, and deinterleaver, that an MPEG TS *might* be the
>>> transport multiplex.
>>>
>>> The images show that the decryption happens after all the FEC and
>>> deinterleaving is handled and also after SL (service layer)
>decoding.
>>> The I2C connected external NVRAM is likely where the program
>decryption
>>> key is stored (inside of a tamper boundary), according to other
>internet
>>> pages from 7 years ago.
>>>
>>> So I'm guessing you have to totally demodulate and decode one of the
>SAT
>>> or terrestrial channels, and then dig around in a (hopefully MPEG)
>>> transport stream to find your unencrypted "Channel 1"
>>>
>>
>> The STA400A datasheet gives a lot of good information about the XM
>signal
>> characteristics, bit rate, RCC filter bandwidth, code rates and
>puncturing,
>> proper order of FEC blocks, etc.:
>>
>> http://www.chipfind.net/datasheet/pdf/stmicroelectronics/sta400a.pdf
>>
>> Enough info to give one half a chance of getting the demodulation
>correct.
>> It also talks a little bit about the frame structure.
>>
>> This MAXIM 2140 App Note has a yet another picture of the spectrum
>> allocation, that also shows Sirius' and WCS' allocations in context:
>>
>> http://pdfserv.maximintegrated.com/en/an/AN3851.pdf
>>
>> I also found a Sirius patent that talks about an overlay modulation,
>but it
>> wasn't clear to me if it was being applied to the XM satellite
>signals.
>>
>> Regards,
>> Andy
>>
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