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MSK modulation in cc1101

abhishek agarwal
Intellectual 365 points
Other Parts Discussed in Thread: CC1101

hello,

i am configuring cc1101 using msp430 and i am not making use of smartRF studio for getting the register values. i am calculating it directly on the basis of the data mentioned in the data sheet. can you please tell me as to how i can set the value of DEVIATN register for MSK modulation because no data regarding this is given in the data sheet. my project is at a critical stage and i would really appreciate your help.

thank you

regards,

Abhishek

  • 0
    TI__Guru**** 317180 points

    Why don't you use SmartRF Studio? It is the fastest and easiest way to get the wanted settings.

  • 0
    TI__Mastermind 39860 points

    When MSK modulation is enabled, the DEVIATION_M field sets the fraction of symbol period used for phase change.
    DEVIATION_M = 0 means that the phase is changed within 1/8 of a symbol.
    DEVIATION_M = 7 means that the the whole symbol period is used to change phase.
    Higher data rates need faster phase changes.

    From SmartRF Studio you will see that the recommended phase for 500 kbps MSK is 0.

    For lower data rates it is better to use 2(G)FSK with modulation index =0.5 (i.e deviation = data rate/4) instead selecting the MSK modulation format through register  MDMCFG2.

    BTW: using SmartRF Studio to generate the settings are generally a better approach than calculating your own settings.

  • 0 in reply to Sverre
    Intellectual 610 points

    Sverre,

    In SmartRF studio 1.10.3 the settings is not from 0 to 7 ,but from 0 to 255 if I changing manually. So I assume your answer is right with vaules from 0 to 7 (???).

    Also after changing data rate, the Phase transition time is STILL 0 , is it bug or whaT?

    Is in CC1101/CC430 modulation MSK is changing frequency (like in "true" MSK, when frequency is changing in zerocrossing point of carrier) or is phase changing modulation - OffestQPSK witk 1/2 sine shaping (like say datasheets) ?

    Thanks

  • 0 in reply to Mykro Std
    TI__Mastermind 39860 points

    DEVIATN.DEVIATION_M[2:0] has 8 possible combinations: ( 0 to 7)

    0: 1/8 of a symbol period is used for phase change

    1: 2/8 of a symbol period is used for phase change

    2: 3/8 of a symbol period is used for phase change, etc....

    SmartRF Studio does not calculate new values for DEVIATN.DEVIATION_M[2:0] if you change the data rate. The only data rate where we use MSK is for 500 kbps. For other data rates we recommend 2-(G)FSK or OOK/ASK.For other data rates than 500 kbps you should set the deviation to get a modulation index to 0.5 fro MSK signal.

  • 0 in reply to Sverre
    Intellectual 610 points

    Ok, but:

    Why is MSK "only" for 500kbps ? Is there any reasonable argument ? (In datasheet is usable range from 26 to 500 kBaud)

    And why is recommended modulation index 0,5 in use with G(F)SK ?

    Thanks for clarifying.

  • 0 in reply to Mykro Std
    TI__Mastermind 39860 points

    You can use any deviation for (G)FSK as long as the mod index is above approx 0.3. The "recommendation" in the posting is because using GFSK with a mod index = 0.5 gives MSK.

    MSK mod format in CC1101 does not give as good sensitivity as GFSK, mod index = 0.5.

  • 0 in reply to Sverre
    Intellectual 610 points

    So this invoke claim,that (G)FSK with MI=0,5 is "true" MSK  as described in http://www.radio-electronics.com/info/rf-technology-design/pm-phase-modulation/what-is-msk-minimum-shift-keying-tutorial.php  and modulation format in CC1101 called "MSK" is phase shift type of modulations (OQPSK). Mykro