Analysis of a DPSK link with on board processing and diversity for medium data rate EHF frequency hopping systems: compromise between the SATCOM system operating and jamming performances

We analyse a DPSK link with on-board-processing and diversity combining features for medium data rate frequency hopping systems. In a system approach, we address the following questions. (1) What is the optimum diversity combining solution that can both multiplex the data rates and protect the system against jammers? (2) What is the best compromise between satellite transmitted power, ground terminal transmitted power and protection against jammers? The results we present show that, contrary to the conventional OBP point of view, up-and-down links are not independent without on board decoding. That's why a small margin on the satellite transmitted power enable our system to work with smaller ground terminals and improves the protection on the uplink in terms of Eb/Nj. We prove that the use of diversity in order to multiplex the data rates degrade the performance in terms of Eb/N0 and so oversizes the terminals. Multiplexing data rates with diversity is not compulsorily the best strategy under strong jamming. Finally, we analyse the interest of diversity versus the jammer strategy and the hopping bandwidth. For SHF systems where the available band is small (about 100 MHz), a diversity of 2 may be sufficient because the jammer can easily spread over this band and does not need to optimize its strategy. As for EHF systems where the hopping band is greater (2 GHz), a diversity level of 4 is interesting in order to constrain the jammer to spread over the whole band. The lower the diversity is, the more intelligent the jammer needs to be in order to reduce the system performance and so the less likely it is.