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CC1101 : Query regarding PQT algorithm

Vikas Javkar
Prodigy 120 points
Other Parts Discussed in Thread: CC1101

Hi ,

We are trying to understand preamble quality threshold (PQT) calculation algorithm of CC1101 RF chip.

In the CC1101 following descrption is given on page

The preamble quality estimator increases an internal counter by one each time a bit is
received that is different from the previous bit, and decreases the counter by eight each time
a bit is received that is the same as the last bit.

From above description it is clear that whenever 2 similar bits are received, PQT estimator algorithm reduces PQT counter by 8. But does that mean, counter will go in negative. For example suppose preamble quality is counter is zero now and after receiving 010101, chip received 11 or 00, PQT counter becomes (0-8 = -8) ?

( We are using wake-on-radio mode of CC1101 with period of 5sec. RX time configured is 100msec. Boards wakes up on preamble and transmitter generate preamble for  8sec. To avoid false wake-up, we are using PQT level setting which is set to 1. So we want to understand what will be the ideal RX time with use of PQT level 1, to have guaranteed board wake-up from WOR).

Thanks in advance

- Vikas Javkar

  • 0
    TI__Mastermind 39860 points

    The counter will not go negative. 0-1-0-1 will give a count of 3, if a 1 is next received the counter will be reset to 0.

  • 0 in reply to Sverre
    Prodigy 120 points

    Thanks Sverre for your quick reply.

    I have another query related to PQT

    We are using wake-on-radio mode of CC1101 with period of 5sec. RX time configured is 100msec. Boards wakes up on preamble and transmitter generate preamble for  8sec. To avoid false wake-up, we are using PQT level setting which is set to 1. So we want to understand what will be the ideal RX time with use of PQT level 1, to have guaranteed board wake-up from WOR mode?


    Thanks in advance

    - Vikas

  • 0 in reply to Vikas Javkar
    TI__Guru* 86131 points

    Hi

    It is not possible to say anything about the RX timeout as I do not know anything about your data rate, but with PQT = 1 you need to be able to receive a minimum of 5 preamble bits for preamble quality to be reached. The best thing you can do it to set up your transmitter to transmit preamble continuously. On your receiver, strobe SRX and monitor how long time it takes from the radio is in RX state (GDOx = LNA_PD Inverted is asserted) until the preamble quality reached signal is asserted (IOCFGx.GDOx_CFG=8.)

    BR

    Siri

  • 0 in reply to Siri
    Prodigy 230 points

    What are the repercussions of using the default PQT value of 000?

    According to the datasheet, a sync word is always accepted in this case.  I'm working with a data packet format that uses a preamble that is not "0xAA" formatted. 

    From what the datasheet says, it sounds like I should be able to receive the packet based on sync bytes alone.  Is this correct?

  • 0 in reply to Kelly Hawkins
    TI__Mastermind 39860 points

    Using the sync word as an RX qualifier only, and not in combinaton with PQT nor Carrier Sense, is perfectly alright and what we use in most of our examples. Makes sure the sync word has good auto correlation properties. Using 4 byte sync word reduces the likelihood of false sync word detection compared to using 2 byte.