MATLAB: 5G Downlink Waveform

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I'm using the demo here: https://www.mathworks.com/help/5g/gs/downlink-carrier-waveform-generation.html to generate the waveform. Here is a picture of the magnitude of the waveform.

My question is why is there a spike in the last few samples? According to the resource grids, no symbol is allocated in that part.

Best Answer

Hi Bryan,

Windowing and overlapping are automatically applied to the modulated waveform. In order to keep the waveform length independent of the window length and make it easy to concatenate with itself without additional processing, the first N samples (window size) of the waveform are overlapped with the last N. For alignment purposes, the waveform is circularly shifted so that these overlapped samples are moved to the end of the resulting waveform.

This effect will only be visible for channels/signals allocated in the first OFDM symbol. You can undo the circular shift operation as:

info = [bwpset.Info];
w = max([info.Windowing]);
wave = circshift(waveform(:,:),w);

If windowing is not a requirement, you can also disable it by setting:

waveconfig.Windowing = 0;

in NRDownlinkWaveformGenerationExample.m before the call to hNRDownlinkWaveformGenerator function.

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MATLAB: 5G NR Downlink Carrier Waveform Generation

Hi Javier,

You can provide any values. But the best guide to run different simulations is the Transmission bandwidth configurations provided in the standard spec of TS 38.104 Section 5.3.2.

For example to configure a value of Channel Bandwidth of 30 MHz of 15 kHz SCS and 50 MHz bandwidth of 60 kHz SCS, make the following updates to carrier structure and bwp structure:

% Carriers Configuration
carriers = [];
carriers(1).SubcarrierSpacing = 15; % 15 kHz
carriers(1).NRB = 160;  % 160 resource blocks comprise 30 MHz bandwidth
carriers(1).RBStart = 0;
carriers(2).SubcarrierSpacing = 60; % 60 kHz
carriers(2).NRB = 65;    % 65 resource blocks comprise to 50 MHz bandwidth
carriers(2).RBStart = 0;
% Bandwidth parts configuration (Occupying complete carrier for both numerologies)
bwp = [];
bwp(1).SubcarrierSpacing = carriers(1).SubcarrierSpacing;          % BWP Subcarrier Spacing same as carrier subcarrier spacing 1
bwp(1).CyclicPrefix = 'Normal';         % BWP Cyclic prefix for 15 kHz
bwp(1).NRB = carriers(1).NRB;                        % Size of BWP

bwp(1).RBOffset = 0;                   % Position of BWP in SCS carrier

bwp(2).SubcarrierSpacing = carriers(2).SubcarrierSpacing;          % BWP Subcarrier Spacing
bwp(2).CyclicPrefix = 'Normal';         % BWP Cyclic prefix for 60 kHz
bwp(2).NRB = carriers(2).NRB;                        % Size of BWP
bwp(2).RBOffset = 0;                   % Position of BWP in SCS carrier

This will generate the output waveform for both the numerologies.

Hope this helps.

Regards,

Sriram

MATLAB: 5G carrier aggregation parameters

Take a look at 5G NR spec documents, TS 38.101-x.

Graham

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MATLAB: 5G NR Downlink Carrier Waveform Generation

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