LTE user documentation(if there are inappropriate places, please correct me!) )7 using Fading TraceThis section describes how to use the fading traces in LTE emulation.
(1) Generate Fading traces generate fading traces by using the code provided by the dedicated MATLAB script (/lte/model/fading-traces/fading-trace-generator.m). The script contains a typical taps configuration for 3 3GPP scenes (for example, pedestrians, vehicles, and cities, defined in Annex B.2 of [TS36104]); However, users can also introduce their specific configurations. The configurable parameters are as follows:
- FC : Frequency of Use (calculations that affect Doppler speed)
- v_km_h : User's speed;
- traceduration : Duration of trace total length (s);
- numrbs : The number of resource blocks to estimate;
- Tag: The tag applied to the generated file;
The resulting file contains the actual value in ASCII format, in matrix form: Each row is related to a different RB, and each column is related to a different temporary fading trace sample. Note that the Ns-3 LTE module is capable of working with any fading trace file, in accordance with the ASCII format described above. As a result, other external tools can also be used to generate custom fading traces, such as other emulators or experimental devices.
(2) using fading traces when using the fading trace file, it is important to specify the appropriate trace parameters in the simulation, so the fading model can be loaded and used correctly. The configuration parameters are as follows:
- tracefilename : The file name (absolute path or relative path) of the trace file to be loaded;
- tracelength : Trace duration (s);
- samplesnum : number of samples;
- windowsize : The size of the fading sample window;
Note that the sample interval for the fading trace must be at least 1 ms and an integer multiple of 1 ms in order to properly handle the fading module. The MATLAB script default configuration provides trace duration of ten s, consisting of 10,000 sample numbers (for example, one sample per tti=1ms), using a window size of 0.5 second amplitude. These are also the default values for the above parameters, so when fading trace involves them, you can avoid their settage (? ). In order to activate the fading module (which is not activated by default), the following code is included in the emulator:
ptr<ltehelper> ltehelper = createobject<ltehelper> (); Ltehelper->setfadingmodel (" Ns3::tracefadinglossmodel ");
Set parameters:
Ltehelper->setfadingmodelattribute ("TraceFileName", StringValue ("Src/lte/model/fading-traces/fading_trace_epa_3kmph.fad")); Ltehelper->setfadingmodelattribute ("Tracelength", TimeValue (Seconds (10.0)) ; Ltehelper->setfadingmodelattribute ("Samplesnum", Uintegervalue (10000)); Ltehelper->setfadingmodelattribute ("windowsize", TimeValue (Seconds (0.5)) ; Ltehelper->setfadingmodelattribute ("Rbnum", Uintegervalue ( -));
It is important to note that TraceFileName does not have a default value, so it must always be set explicitly. based on the configuration defined in Annex B.2 of [TS36104], the emulator comes with 3 kinds of fading traces. These traces files are in the folder src/lte/model/fading-traces/ . A excerpt for these traces.
Excerpt of the fading trace included in the simulator for a pedestrian scenario (speed of 3 kmph).
Excerpt of the fading trace included in the simulator for a vehicular scenario (speed of kmph).
Excerpt of the fading trace included in the simulator for a urban scenario (speed of 3 kmph).
Reference documents
Https://www.nsnam.org/docs/models/html/lte-user.html
LTE Module User Documentation (translator 4)--Using fading Trace
