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    Current measurements

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    • felixdonkers
      felixdonkers last edited by

      Today we’ve been doing some current measurements using an SODAQ NB-IoT board with an uBlox SARA-N211-02B (with v6.57 firmware). We notice some ‘strange’ behavior that might be related to the network. See the two pictures below. The first one is when transmitting 32 bytes, this is what I observe:

      • sleep mode (~3 seconds)

      • connection mode (~200 msec)

      • transmit mode (~200 msec)

      • receive mode (~22 seconds)

      • idle mode (~1 second)

      • eDRX mode (~27 seconds)

      0_1516035518472_transmit_32byte.PNG

      Now with 512 bytes I see a lot more, which a cannot explain:

      • connection mode ? (from t=~3 until t=~23 seconds)

      • transmit mode ? (from t=~24 until t=~35 seconds), i.e. 11 seconds for 512 bytes?

      • a second transmit mode ? (from t=~56 until t=~58 seconds), why ?

      0_1516035645343_transmit_256bytes.PNG

      Can this 512 byte transfer behavior be explained ?

      A 1 Reply Last reply Reply Quote 1
      • M
        Maad last edited by

        I rise similar question.
        I had cases were it took up to 2 minutes to transmit 32 bytes and actually the data size did not matter all the time, I got a delay in receiving the data for up to 2 min!.
        what could it be ?and why?

        1 Reply Last reply Reply Quote 0
        • A
          Andre Rodenburg @felixdonkers last edited by

          @felixdonkers Dear Felix,

          How did you meassure the current? Did you use a shunt resistor or another method?

          felixdonkers 1 Reply Last reply Reply Quote 0
          • T
            techniek last edited by

            @felixdonkers hi Felix,

            The network experts tel me that NB-Iot has a devides a packet into variable length segments, dempending on the quality of the transmission channel…

            3gpp specs that might shed some light… for the deternmined…
            http://www.3gpp.org/ftp/Specs/archive/45_series/45.820/45820-d10.zip

            1 Reply Last reply Reply Quote 0
            • felixdonkers
              felixdonkers @Andre Rodenburg last edited by

              @andre-rodenburg We used the SODAQ board, cut one of the traces to the uBlox modem and put a 1 ohm resistor in series to measure the current consumption. Since the SIM is also powered by the modem, that current is also included.

              1 Reply Last reply Reply Quote 0
              • A
                Andre Rodenburg last edited by

                Heb zelf ook een stroommeting gedaan:

                alt text

                Er gebeurt dit: (denk ik)

                • Modem is in PSM (+NPSMR = 1)
                • Ik stuur +NMGS=3,“AABBAA”
                • Modem wordt uit zichzelf wakker (+NPSMR = 0)
                • Verstuurd het bericht (TX piek)
                • Luisterd naar inkomend verkeer? (RX)
                • Nog een paar RX- pieken?
                • PSM is weer actief (+NPSMR = 1)

                Op de spectrum analyzer is het volgende te zien, het NB-IoT signaal (QPSK modulatie!) met een beetje spiegeling door de lokale oscillator:
                alt text

                Wat interessant is is dat elke +NMGS TX- piek wordt opgevolgd met een tweede TX- piek met een lagere intensiteit 20 seconden later:
                alt text
                Iemand enig idee wat dit is?

                1 Reply Last reply Reply Quote 0
                • T
                  techniek last edited by

                  Ik vermoed dat de 3 piekjes momenten zijn waarop het device nog luistert naar een paging request.

                  1 Reply Last reply Reply Quote 0
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