Re: How to remove channel noise?

[Johannes Demel]

Hi,

besides the hint to work through textbooks, I'd like to point out that 
you will probably have more success if you start with nearly perfect 
"Channel Model" coefficients and then observe changes in the following 
order:
1. Noise Voltage: 0 (and raise it slowly e.g. in 1e-2 increments.
2. Taps: 1 + 0j (play around with more values, change it to a vector 
e.g. [1., .3+.3j])
3. Frequency Offset: 0 (Increase this value slowly observe the 
constellation sink)
4. Epsilon: 1.0, supposed to simulate sample rate mismatch between 
transmitter and receiver.

Further, it'd be a good idea to start with e.g. QPSK as an initial 
constellation. It is sufficiently simple and easy to observe channel 
influences.

Cheers
Johannes


On 18.06.21 08:50, Kyeong Su Shin wrote:
> Hello 能书能言,
>
> You can take multiple samples and average out the noise (if the 
> transmitted signal is not varying quickly), but you need to obtain 
> channel estimates in order to recover the original phase and amplitude. 
> You will have to transmit additional signals (known by the receiver) and 
> use them as the reference signals to recover the channel state.
>
> Please note that long-term averaging may not work as expected on 
> real-world environments, due to the non-stationary channel and various 
> hardware imperfections, like CFO.
>
> You are probably better off if you just use off-the-shelf digital 
> transceivers to transmit data in digital manner (if you are not required 
> to implement things in this way.. by some weird reason).  If you have to 
> implement this by yourself (in real-world, especially), I recommend 
> going through information theory and communication theory textbooks 
> before jumping into the implementation.
>
> (Also, 2V noise in the channel noise block is somewhat... high. Pretty 
> low SINR it is. )
>
> Regards,
> Kyeong Su Shin
> ------------------------------------------------------------------------
> *보낸 사람:* 能书能言 <2127629883@qq.com> 대신 Discuss-gnuradio 
> <discuss-gnuradio-bounces+ksshin=postech.ac.kr@gnu.org>
> *보낸 날짜:* 2021년 6월 18일 금요일 오후 12:46
> *받는 사람:* discuss-gnuradio <discuss-gnuradio@gnu.org>
> *제목:* How to remove channel noise?
> Hi,guys.
> My flowchart is attached in the attachment, this is just a test case. I 
> sent a constant complex number directly to pass it through a channel 
> module, and the received result was also expected, and it was seriously 
> disturbed. The real situation is like this. I have several such complex 
> constant data (there may be hundreds or thousands). If I send it 
> directly like this, I will definitely suffer similar interference, so is 
> there any good way to make it? Can I send and receive these data 
> accurately? In other words, there may still be interference, but at 
> least it is within a controllable range.
> Remarks: These data are plural data, not file dataThanks in advance!
> Sincerely