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Re: Ofdm transceiver with more than 16QAM

From: Marcus Müller
Subject: Re: Ofdm transceiver with more than 16QAM
Date: Thu, 12 Nov 2020 18:25:45 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1

You don't need to measure it. You need to ask yourself *why* a
constellation with many points might not work well with a low SNR.

Then you have your answer.

On 11.11.20 14:03, pv@koalatech.pt wrote:
> I don know how can I measure the SNR with QAM modulation. There is only
> a MPSK SNR probe.
> Can you tell me how to measure SNR with MQAM?
> Thanks for your help,
> Pedro Viegas
> Citando Marcus Müller <mmueller@gnuradio.org>:
>> Hi. this is a typical question like I'd ask it when talking a student
>> through a test for a digital comms computer lab. So here's a hint:
>> "Constellations with very many points" don't always work. It has to do
>> with SNR. Can you explain what the problem is with low SNR?
>> Best regards,
>> Marcus
>> On 10.11.20 12:56, pv@koalatech.pt wrote:
>>> Hi, I'm trying to make an OFDM transmission of a png file (9.3 kB) with
>>> 256QAM with the gnuradio
>>> example of OFDM transmitter / receiver. The USRP I'm using is the ettus
>>> n210 with the cbx daughter board. With the QPSK and 16QAM modulations it
>>> works, but with 64QAM or 256QAM I can´t receive the file, sometimes it
>>> receives some packets but most of the time it doesn't receive any byte.
>>> Can anyone help me with with this problem?
>>> Thanks in advance.
>>> Pedro Viegas

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