I'm transmitting a 16-QAM signal using an NI 2920 USRP. Here is a snapshot of the front panel that is seen (on LabVIEW) -

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I'm trying to figure out the bit rate from the given details. The symbol rate is given to be 125k. For 16-QAM, each symbol must be encoded using 4 bits. Does this mean that the bit rate is simply 125k*4 = 500kbps? Do parameters such as the IQ sampling rate and samples per symbol make a difference to the bit rate?


1 Answer 1


Yes, bit rate is simply the amount of bits transported, so it's the number of symbols per second times the number of bits per symbol, as you noted. No surprises.

Note that any real-world system has a high chance to have channel coding, which means the info bitrate is a different one than the code bit rate.

Edit: ah with your picture it's clear. There's no channel decoder, so no channel codes involved.

  • \$\begingroup\$ Is there a way that I can figure out which channel code is being used in this particular LabVIEW program (it's an example program that came pre-installed)? The block diagram has no mention of which type of channel code is being used. \$\endgroup\$
    – V-Red
    Commented Mar 31, 2017 at 16:26
  • \$\begingroup\$ If it is just a PHY-layer demo, then there's no coding. In any case: these demos are all relatively well-documented, I've been told. \$\endgroup\$ Commented Mar 31, 2017 at 16:32
  • \$\begingroup\$ Continuing this discussion, I have another query. I'm trying to measure the spectral efficiency (this is my own doing, there's no documentation online) by calculating the data rate at the transmit end and measuring the bandwidth of the main lobe of the spectrum at the receiving end. I then find the spectral efficiency as the ratio of data rate to bandwidth. This value is far lesser than the theoretical spectral efficiency (I get around 2.53 bits/s/Hz, although the theoretical maximum is 4 bits/s/Hz). What do you think causes such a drastic reduction? \$\endgroup\$
    – V-Red
    Commented Mar 31, 2017 at 16:39
  • \$\begingroup\$ Don't ask new questions in the comments, ask them as separate questions, please. \$\endgroup\$ Commented Mar 31, 2017 at 17:02
  • \$\begingroup\$ Also, many real-world systems have pilot symbols to aid in clock recovery, so some symbol slots do not transport information. \$\endgroup\$ Commented Nov 16, 2023 at 4:24

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