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CC1101 MSK for IEEE 802.15.4f

Andrew Bradford
Prodigy 80 points
Other Parts Discussed in Thread: CC1101

There are many discussions of using MSK modulation on CC1101 which usually result in the answer being that for data rates below 500 kbps to simply use 2-FSK with deviation set to 0.5 to achieve MSK.  For IEEE 802.15.4f, MSK is the specified modulation for the 433 MHz PHY at 250, 100, and 31.25 kbps data rates.

In this case, is the MSK modulation implemented by CC1101 required or will 2-FSK with deviation set to 0.5 produce a continuous phase FSK (effectively MSK) waveform?

If MSK modulation used by CC1101 would be required in order to obtain continuous phase FSK, how exactly is the MSK modulation used by CC1101 "inverted" as specified in the data sheet?  And why is the bandwidth, when using Smart RF Studio to continuous transmit random modulated data at 250 kbps, of MSK wider than 2-FSK with 0.5 deviation?  I would expect them to be the same.

  • 0
    Prodigy 80 points

    Regarding the MSK spectrum being wider than 2-FSK spectrum, my measurements were done with DEVIATION_M set to 0.  Setting DEVIATION_M to 7 for MSK results in spectrum that is the same as 2-FSK.

  • 0
    Prodigy 80 points

    Regarding using a deviation of 0.5, that is not entirely the correct way to state the situation.

    The difference between the +1 and -1 symbols should be equal to half of the data rate.  My statement of a deviation of 0.5 above meant that the difference between the +1 and -1 symbols is half the data rate.

    For example, a data rate of 250 kbps would result in the +1 and -1 symbols being separated by 125 kHz.  As CC1101 radios specify deviation, this would be set into the DEVIATN register as 62.5 kHz (or as close as is possible given the constraints of the register) deviation from carrier when in 2-FSK mode.