Evaluation of the required EbN0¶

We choose a coding technique based on LDPC codes as introduced in DVB-S2 standard. This is a powerful coding scheme allowing higher spectral efficiencies for a given Eb/N0 compared to basic modulations.

Here is a table extracted from DVB-S2 standard (ETSI EN 302 307 V1.2.1, table 13), corresponding to quasi-error free performance:

Given the MODCOD previously determined, we can read in this table the required value of Es/N0. Then, Eb/N0 can be computed thanks to the relation:

$(\frac{E_{b}}{N0})_{dB}=(\frac{E_{S}}{N0})_{dB}-10*log_{10}(\frac{\eta}{1+\alpha})$

With $\eta$ the value of the spectral efficiency corresponding to the given MODCOD (second row of the table above). In fact, this value of spectral efficiency does not take into account the roll-off of the shaping filter, so we correct it in order to get the real spectral efficiency of the system.

Remarks:

• The table specifies the ideal Es/N0. Margin for non-ideal demodulator will be taken into account in the computation of the link budget.
• We can notice that lower MODCODs sometimes require higher Eb/N0 (at transition between modulations). In fact, lower modulation are preferred if possible even if it requires higher Eb/N0. In fact, there are more robust to perturbations such as multipath or phase noise for instance. This has to be kept in mind in order to explain some curves plotted in the result part.