Complementary signal structure proposals for future airborne SBAS L5 signal and other non-airborne applications

This paper studies complementary signal structures to the SBAS L5 SIS ICD definition which increases its original bit rate without degrading or even improving the SBAS L5 SIS ICD signal key performances. The proposition of this paper is based on modifying only certain characteristics of the current SBAS L5 SIS ICD signal structure and on keeping the signal characteristics which allow a perfect compatibility with SBAS L5 SIS ICD message content: symbol rate, bit information rate (250 bps), basic information units of 250 bits and capability of interrupting the nominal message at each second in order to transmit alarm messages. The main signal design modifications are first the introduction of linear block channel codes, instead of a convolutional code, in order to reduce header and CRC bits and in order to decrease the signal demodulation threshold. Second, new signal components, such as the synchronization component or a second data component, are introduced allowing an easier synchronization and increasing the effective bit rate. Smart combinations of the two data components are suggested to not degrade the final demodulation threshold. Finally, the selective introduction of a Code Shift Keying (CSK) modulation is also proposed to further increase the bit rate. Demodulation, carrier phase tracking and secondary PRN code acquisition performances are explained and analyzed for the complementary proposed signal structures.