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CC1150: RRC-shaped QPSK with CC1101/CC1150/CC13xx

Joao Crespo
Prodigy 20 points
Part Number: CC1150
Other Parts Discussed in Thread: CC1101, , CC1352R, CC1310

Dear E2E members,

I was redirected to this forum by TI Customer support. We are looking at possibilities to implement square-root raised cosine (RRC) pulse shaped QPSK transmission (100 ksymbols/second) for the sub-Ghz region (center frequency around 400.0 MHz), and I have come across CC1150(tx only)/CC1101. As long as I could find, TI does not supply any IC doing RRC-shaped QPSK directly, so my question is: using the "Asynchronous Transparent Transmit" mode, is it possibly to have access to the sent I/Q samples directly, so that we can implement our own modulation? If not, does TI have another IC which could do this at a low cost (<= $2 pp for on the order of 100k units), either directly or giving access to the I/Q samples (or using the IC in any other way to obtain RRC-shaped QPSK)?

Also, I would like to hear your thoughts on the CC13xx family, e.g. CC1310 or CC1352R: can I implement "custom" RRC QPSK with these?

Thanks in advance!

  • 0
    TI__Mastermind 36375 points

    Joao, 

    Is there a detailed, public, specification that describes this modulation in detail? 

    In general I would say the older CC11xx series devices, CC1101 or CC1150 will not be able to do this.

    However, there is a reasonable chance that the CC13xx series of products can do this, but I need to know more details about the modulation.

    Regards,
    /TA

  • 0 in reply to TA12012
    Prodigy 20 points

    Dear TA,

    Thank you for your fast reply. Root-raised cosine shaping is, in fact, a very classical shaping procedure which can be found in a vast amount of literature (e.g. A. Goldsmith, Wireless Communications, Cambridge University Press 2005, Sects. 5.3.2 and 5.5), or simply wikipedia (here and here). The idea is that you transmit

    Re{ z(t) exp(j w0 t) }

    with a complex baseband z(t) given by a train of pulses with amplitudes +-1 +- j (depending on the symbols to transmit), convolved with the filter on wikipedia. The digital implementation of this is that you take your symbols z(n) in {-1-j, -1+j, 1-j, 1+j}, n = 0, 1, 2, 3, ... , upsample them by some factor (say SPS), and filter the result by a sampled version of the filter on wikipedia (sampling rate SPS samples / symbol).

    Can you get access to the complex baseband z(n) on TI13xx, i.e., the I/Q samples which are going to be transmitted? Then this would be straightforward to implement.

    Best regards,

    João Crespo

  • 0 in reply to Joao Crespo
    TI__Mastermind 36375 points
    Joao,

    Actually our CC13xx does not use a IQ chain for TX, we have what we call a polar modulator. It is capable of producing any constant envelope signal you want. And OQPSK in the way you are showing is constant envelope, we can do this with a patch on CC13x2.

    On the RX side you can access IQ data in realtime and make your own demodulator.

    Regards,
    /TA