|How to use Radiosim|
Click the " Start " button in the bottom left corner of your Desktop, point " Run " and type C:\Radiosim\Rs.exe (supposing you installed the software in C:\Radiosim). You can also run Radiosim from Windows explorer, simply double-clicking Rs.exe.
Menu of the "First" windowJust after the software is run (First window), if the user clicks the "Edit" menu, the "Canal" window is displayed. In this window, the user is proposed a list of library modules, among them he drags with the mouse or selects with the keyboard the modules he wants to be included in his canal. A canal is a sequence of modules. A module generally represents an electric circuit (quadripole). The following image shows a typical canal simulating a digitally modulated transmission link.
The "Canal" window
Then, the user clicks a module to select it, clicks the "Parameters" button, and fix the various parameters values. The following figure shows the editing window of the "Digital modulator" module, a rather complex one.
The "Parameters" window
In order to help beginning users, 50 pre-registered canals can be loaded, representing typical transmission scenarios such as :
Several examples of digital links with different modulation, including modulator, non-linear amplifier (with or without a predistorter or a Butler matrix), transmit and receive filters, autoadaptive equalizer, demodulator.
Two frequencies FSK, quadratic detection.
IRF (Interference reduction factor).
Minimax optimisation : to equalize the group delay of a filter, minimize a BER, minimize intermodulation products.
Filters without intersymbol interference at the impulse response zero crossings (clock recovery).
Bit error rate and phase hops due to carrier recovery.
Differential gain and differential phase in FM modulation.
Envelope variation of a frequency modulated signal crossing a filter.
Carrier suppression in phase modulation with a 2.41 index (very simple canal).
"Load" window and "Comments" window
The above figure shows the "Load" window in which the user can select a pre-registered canal and read a corresponding comment.
The canal being loaded or built from scratch, the user gives a numerical value to each parameter of each module ("Parameters" window), reads Help screens, runs the program, watches results on graphs and tables, and runs again the program after modifying some parameter values. A good idea for a beginner is to start from a pre-registered canal, modify some parameters and watch the results.
A " Loop " module allows to write a table giving one or several results, as a function of one, two or three parameters, incremented in fixed steps.
A " Minimax " module allows to adjust several parameters to optimise one or several results.
Without stopping the program, the user can read the on-line contextual Help, save the canal and a comment on disk in order to avoid a long entry at a further session, modify the presentation of graphics (margins, graduations, titles) and print them on paper or save them in a file for importation in a word processor (remember that, under Windows, you can switch instantaneously from any program such as Radiosim to any other one, hitting Alt + Tab or clicking the programs in the task bar).
Utility programs are included to write user-specific files, needed by some modules ( Filter defined point per point, non-linear quadripole (amplitude / amplitude and phase / amplitude characteristics), specification templates (filters, spectral density, rise time, etc.), interferers, coefficients of a transversal filter, etc.
The computing time of a typical canal (Dummy.can) with N = 4096 samples, including a digital modem, transmit and receive raised cosine filters, a non-linear amplifier and two " Graphics " modules, is near 5 seconds for a typical Pentium PC.
The computing time is almost proportional to the number of samples N.Unlike former DOS versions of Radiosim, N is practically unlimited. With modern PC, a very high value such as 220 = 1,048,576 can be used with a reasonable computation time.
A high number of samples N is needed in three cases :
1) when the filters roll-off is very steep, as in modern high spectrum efficiency radiolinks. Then, the impulse response has long trails, and a long pseudo-random sequence is needed to test the worst case of the influence of the symbol sequence on the inter-symbol interference,
2) for non-coherent demodulation schemes, in which the thermal receiver noise is directly simulated, instead of using the Erfc( ) function as in the Coherent demodulation module,
3) when several carriers with different bit rates share a same transmission medium. In such a case, even if a relative low number (f.i. 256) of symbols is needed for the lower bit rate carrier, Ns must be higher in a ratio larger bit rate/lower bit rate (and N must be at least eight times higher than Ns if a non-linearity is present).