• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 1 answer
  • Subscribers 54 subscribers
  • Views 1154 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

CC1352P: SimpleLink LongRange Mode information

Vsevolod Elantsev4
Intellectual 2810 points
Part Number: CC1352P

Hi team,

Do we have a documantation what is SimpleLink Long Range Mode?

Can you provide an information about packet content, preamble length, sync word etc?

How information is translated to radio symbols? Is the sync word is translated with DSSS and FEC or the sync word is raw?

I set preamble length to 32 byte in SmartRF studio and get CRC errors on RX side. Why?

I set TX side to LongRange Mode and Rx side to usual mode 2GFSK, 5kHz deviation, same sync and preamble. But I can't recieve any data.

Best Regards, Vsevolod.

  • 0
    TI__Genius 9215 points
    Hi Vsevolod,

    The coding scheme is data bits => convolutional encoder => direct sequence spreader (DSSS) => GFSK modulator => GFSK signal

    A convolutional encoder of rate ½ is followed by a direct sequence spreader (DSSS) with variable spreading length. The output of that module is finally fed to the 2-(G)FSK modulator. The Direct Sequence Spreader (or Direct Sequence Spread-Spectrum, DSSS) assigns a known bit pattern to each of the incoming bits to the module. In the CC13xx Long Range modes, the spreader length can be configured to be [1, 2, 4, 8].

    DSSS ‘0’ ‘1’
    1 0 1
    2 00 11
    4 1100 0011
    8 11001100 00110011

    The relationship between data rate (i.e. the actual amount of information bits available to the higher protocol layers) and the symbol rate (i.e. the actual modulation rate used in the radio) can be expressed as: Data Rate = Symbol Rate / (2*DSSS).

    SimpleLink long-range mode (SLRM) uses no preamble. Instead, it uses a hard-coded 64-bit sync word (SW) that is repeated M+1 times. The first M times, the inverted SW is sent. The final repetition is as specified. The SW in SLRM is as mention hard-coded (0xCCC3_C3CC_C33C_3333, LSB first) and cannot be modified by users. The number of repetitions (M) is configured through the .preamConf.nPreamBytes variable of CMD_PROP_RADIO_DIV_SETUP. The default value is 2.

    This mean that in Smart RF Studio you need to use Long Range mode on both the transmitter and the receiver to make SLRM work.

    Best Regards,
    Reidar
  • 0 in reply to R.M
    TI__Intellectual 2810 points
    Hi Reidar,
    I use 2.5kbps LRM with PacketTx example. I removed delay and RF_yield.
    I want to create as short LRM packet as possible. In best choise - transmit only sync words to use it like preable detection. We need to detect transmission in the air for LRM mode as fast as possible.

    I remove CRC and variable length, set pktLen=1
    RF_cmdPropTx.pktLen = PAYLOAD_LENGTH; // 1
    RF_cmdPropTx.pPkt = packet; // 0x00
    RF_cmdPropTx.pktConf.bUseCrc = 0;
    RF_cmdPropTx.pktConf.bVarLen = 0;
    RF_cmdPropTx.startTrigger.triggerType = TRIG_NOW;
    RF_cmdPropTx.startTrigger.pastTrig = 1;
    RF_cmdPropTx.startTime = 0;
    RF_cmdPropTx.pktConf.bFsOff = 0;

    It looks like we should have only 1 data byte payload (8 byte coded).

    The packet packet duration is around 16.5ms (330 symbols). In this number we have 3pcs SW = 192symbols, 64symbols for 1 byte payload. And around 74 additional symbols can you tell me what are these symbols and how we can remove them?

    When I try to send 0 bytes of payload the packet packet duration is increased, why?
    Is it OK to use M = 1, just to send the only one SW and the one inverted SW? What will happends with the sensitivity?
  • 0 in reply to Vsevolod Elantsev4
    TI__Genius 9215 points
    Hi Vsevolod,

    We will look into this and get back to you.

    Best Regards,
    Reidar
  • 0 in reply to R.M
    TI__Genius 9215 points

    Hi Vsevolod,

    The package format for LRM is illustrated in the figure below:

    The modem automatically insert seven termination bits at the end of the payload to be able to terminate the sequence. These termination bits can not be removed.

    The number of symbols (nsymbols) and the total packet duration (tpd, in us) for LRM is given by:
    nsymbols = (M+1)*64 + N*8*2*DSSS + 7*2*DSSS
    tpd = 1e6*(nsymbols/fsym)
    where M is the number of SW repetitions, N the number of payload bytes and fsym the symbolrate in Hz.

    Example for 1 Byte Payload and M=2:
    3 * 64 + 1*8*2*4 + 7*2*4 = 312 symbols

    It is not recommended to use less SW that what's default in SmartRF Studio (M=2).

    I need to look more into why you are seeing longer packet duration with N = 0.

    Best Regards,

    Reidar

  • 0 in reply to R.M
    TI__Genius 9215 points
    Hi Vsevolod,

    The minimum payload length in LRM is 3 Bytes (inc eventually any CRC). This is related to the fact that the data is coded and it needs a certain size to be able to do the FEC encoding and decoding properly.

    Best Regards,
    Reidar
  • 0 in reply to R.M
    TI__Intellectual 2810 points
    Reidar, thanks a lot for the explanation!