Lossless real-time signal acquisition from USRP 2955

Hi,

I am trying to receive contiguous real-time signal from USRP-2955 (X310) device. But i observe losses in acquisition. For an example, in the following code i try to receive a signal with a sampling rate of 200kHz for 10 seconds. 200e3 samples is fetched by the code for each time. 200e3 samples corresponds 1 second of signal. So I expect to to fetch 200e3 samples of signal in 1 second to accomplish real-time acquisition. As seen at the output of the code, transfer duration (from USRP to computer) of a frame is about 0.007sn (which is very good), but on the other hand, fetch duration is about 1.6sn (which eventually causes signal loss in reception). And 10 seconds of signal is retrieved in 26 seconds.

Even if i change the value of 'SamplesPerFrame', fetch duration never equals to frameDuration (= rcvr.SamplesPerFrame / Fs).

Am i wrong to think that "X seconds of signal must be fetched in X seconds for real-time acquisition", or is there any other mechanism to achieve real-time acquisition?

Thanks in advance.

rcvr = comm.SDRuReceiver(...
                'Platform',             'X310', ...
                'IPAddress',            '192.168.40.2', ...
                'CenterFrequency',      105e6, ...
                'Gain',                 15, ...
                'MasterClockRate',      200.0e6, ...
                'DecimationFactor',     1000, ...
                'ChannelMapping',       2, ...
                'SamplesPerFrame',      200000);            
info(rcvr)
Fs = rcvr.MasterClockRate / rcvr.DecimationFactor;
rcvdSignal = complex(zeros(rcvr.SamplesPerFrame,1));
secondsToAcquire = 0;
frameDuration = rcvr.SamplesPerFrame / Fs
len = uint32(0);
tstart = tic;

while secondsToAcquire < 10  
    
    tstartFetch = tic; % start time of fetching signal
    while len <= 0
        tstartTransfer = tic; % start time of transfering signal to computer
        [rcvdSignal, len] = step(rcvr); % ask for signal
        TransferDuration = toc(tstartTransfer);  % stop time of transfering signal to computer     
    end
    FetchDuration = toc(tstartFetch); % stop time of fetching signal
    
    if len > 0 
        sprintf('Transfer duration: %f sn \n Fetch Duration : %f sn', TransferDuration, FetchDuration)
        secondsToAcquire = secondsToAcquire + frameDuration;
        len = uint32(0);
    end  

end
telapsed = toc(tstart)

release(rcvr);

ans =

struct with fields:

Mboard: 'X310'

RXSubdev: 'UBX RX'

TXSubdev: 'UBX TX'

MinimumCenterFrequency: -70000000

MaximumCenterFrequency: 6.0800e+09

MinimumGain: 0

MaximumGain: 37.5000

GainStep: 0.5000

CenterFrequency: 105e+06

LocalOscillatorOffset: -1.1050e+03

Gain: 15

MasterClockRate: 200000000

DecimationFactor: 1000

BasebandSampleRate: 200000

frameDuration =

1

ans =

'Transfer duration: 0.007381 sn

Fetch Duration : 11.182971 sn'

ans =

'Transfer duration: 0.007092 sn

Fetch Duration : 1.630546 sn'

ans =

'Transfer duration: 0.006913 sn

Fetch Duration : 1.637092 sn'

ans =

'Transfer duration: 0.006939 sn

Fetch Duration : 1.636543 sn'

ans =

'Transfer duration: 0.006733 sn

Fetch Duration : 1.685166 sn'

ans =

'Transfer duration: 0.006724 sn

Fetch Duration : 1.668035 sn'

ans =

'Transfer duration: 0.006891 sn

Fetch Duration : 1.657259 sn'

ans =

'Transfer duration: 0.006692 sn

Fetch Duration : 1.663458 sn'

ans =

'Transfer duration: 0.006837 sn

Fetch Duration : 1.675342 sn'

ans =

'Transfer duration: 0.006869 sn

Fetch Duration : 1.678966 sn'

telapsed =

26.1198

Answer 1

[Karunya Choppara]

Hi,

The increase in time doesn't indicate data loss during acquisition.

The losses in acquisition will be indicated using the overflow output from the SDRuReceiver System Object.

https://in.mathworks.com/help/supportpkg/usrpradio/ug/comm.sdrureceiver-system-object.html#mw_7a92be3e-9bde-4fcd-9fa4-5418cad12089

In R2021b, performance enhancement to USRP System Objects are available, with which data acquisition time will be equal to the frame duration in a step call

See the section - "Improved performance for SDRu receiver System object with data reception time and number of overruns" in the release notes for R2021b https://in.mathworks.com/help/supportpkg/usrpradio/release-notes.html

[ömer]

Thanks for your answer Karunya.