Hi Ifly,
yes, I understood that you wanted to make the LTE-typical OFDM
configuration, but again, you can't measure anything useful with
only that! So, what *exactly* do you want to measure with your
setup? I promise you, you'll get better results if you try to
explain your overall application to us! The first thing I (and
anyone else) would do if I were to take up the job to do
consulting with you is to sit down and figure out what you're
actually trying to do *in the bigger picture*, and then help you
understand your own requirements, and only after that, help you
implement these. In case you ever happen to write a paper, thesis
or any other publication about this: [1] is a must-read.
Best regards,
Marcus
I want to create a spread of 15khz sub carriers ( like LTE ) that fills up bandwidth of 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz ( like LTE bandwidths ). In the 1.4 MHz block there are 72 15 khz subcarriers, 180 in a 3 MHz block, 300 in a 5 MHz, 600 in a 10 MHz, 900 in a 15 MHz, and 1200 in a 20 MHz bandwidth.
The subcarriers are to be modulated with a constant QPSK, or 16 QAM or 64 QAM. A BladeRF or HackRF One will be used to measure and generate these signals. Preferably the HackRF because the BladeRF seems to be more unstable (locks up) in my experience. May be bad code or hardware, not sure which one.
The goal is to test RF components to see if they are causing signal distortion. In the past I had access to a LTE signal generator that would key up all sub-carriers with 64 quam and a LTE signal analyser that would measure EVM and that was a great way to see if a system could transmit 64 QAM without issue. If the EVM was over a certain X for 64 QAM, 16 QAM or QPSK then the components needed to be addressed.
Below is the chart that shows Bandwidth and Subcarriers in an LTE signal.
Thanks,
Andrew
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-------- Original Message --------
Subject: Re: [Discuss-gnuradio] Pay You $$$ to Mentor Me - Tx OFDM 64 QAM and Rx Measure Error Vector Magnitude
Local Time: September 24, 2017 3:54 PM
UTC Time: September 24, 2017 8:54 PM
From: address@hidden
To: address@hidden
HI IFly88,
I don't fully understand your requirements – on one hand, you just say "I just want OFDM with 15 kHz subcarrier spacing and QAM/QPSK inside", on the other hand you mention LTE: an arbitrary OFDM signal with the right subcarrier spacing and constellation mapping does not constitute a validly measurable LTE signal. Your LTE receiver needs a lot of specific structure in the frames to be able to synchronize, and equalize, to an LTE transmission.
So, what exactly are you using to measure EVM? What is the higher level goal of this? Your transmit hardware will always also play a part in the signal quality you receive, so it's usually better to first sit down and contemplate what you want to measure, then design a system.
Best regards,
Marcus
On 09/23/2017 10:30 PM, Ifly88 wrote:
Name your price to give me pointers and help me kick start this project. I want to emulate a 64qam, 16qam, and qpsk LTEs signal to test for signal impairments. Basically take 15khz sub carriers over channel bandwidths of 1.4mhz to 20 mhz and modulate them with 64qam, 16qam, and qpsk. I want to use another receiver to Rx the signal and calculate error vector magnitude for each of those three modulations. I'll be using HackRF One radios or will use BladeRF if necessary.
I'be been spinning my wheels for a few days trying to get this to work on GRC and need some guidance.
Please help.
ifly88 at protonmail dot com
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