lte downlink test model (e-凯发k8网页登录

overview

the lte specifications define conformance test models for transmitter tests. these include transmit signal quality, output power dynamics, error vector magnitude (evm) for various modulation schemes, base station (bs) output power, reference symbol (rs) absolute accuracy, etc. this example demonstrates how these different test model waveforms can be generated using lte toolbox functions.

the following general parameters are used by all e-utra test models as defined in ts 36.141, section 6.1.2 [ 1 ] :

the following physical channels and signals will be generated:

test models are selected according to required test cases. in our example, the considered test model, e-tm1.1, should be used for tests on:

test model selection

a number of test models are defined in ts 36.141 section 6.1 [ 1 ]. this example will generate test model 1.1 as shown below.

tm = '1.1';     % test model number

allowed test model values in the toolbox are ('1.1', '1.2', '2', '2a', '3.1', '3.1a', '3.2', '3.3').

bandwidth selection

the test model generation function in the toolbox requires the bandwidth to be specified as shown below:

bw = '1.4mhz';     % bandwidth

test model generation

the channel model number and the bandwidth determine the physical channel and signal parameters as specified in ts 36.141. the generated waveform timedomainsig is a time domain signal after performing ofdm modulation, cyclic prefix insertion and windowing. txgrid is a 2-dimensional array representing the resource grid spanning 10 subframes.

[timedomainsig, txgrid, txinfo] = ltetestmodeltool(tm,bw);

plot transmitted resource grid

plot the resource grid txgrid, with a legend describing which resource elements are allocated to which physical channels and signals.

hplotdlresourcegrid(txinfo,txgrid);

plot spectrogram

plot a spectrogram of the time domain signal.

% compute spectrogram
[y,f,t,p] = spectrogram(timedomainsig, 512, 0, 512, txinfo.samplingrate);
% re-arrange frequency axis and spectrogram to put zero frequency in the
% middle of the axis i.e. represent as a complex baseband waveform
f = (f-txinfo.samplingrate/2)/1e6;
p = fftshift(10*log10(abs(p)));
% plot spectrogram
figure;
surf(t*1000,f,p,'edgecolor','none');
xlabel('time (ms)');
ylabel('frequency (mhz)');
zlabel('power (db)');
title(sprintf('spectrogram of test model e-tm%s, %s',tm, bw));

further exploration

for over-the-air transmission and analysis of the test model waveform, refer to the following example: .

appendix

this example uses the following helper function:

selected bibliography