4-Level Optical Modulation Formats for LISLs in a Satellite Broadband Constellation Network

This paper presents three 4-level optical modulation formats; two of which are intensity modulation formats - the 4-pulse amplitude modulation (4-PAM) and the absolute added correlative coding (AACC); and one coherent modulation format - the quadrature phase shift keying (QPSK); in a laser inter-satellite link (LISL), respectively. Each modulated link is modelled to operate in a low Earth orbit (LEO) satellite broadband constellation network and simulated for various performance parameters. These parameters include the power-efficiency, link-extendibility, receiver-sensitivity and spectral-efficiency of the modelled links. As all three modulated LISLs share a spectral-efficiency, the 4-PAM is observed to need a minimum transmitter laser power of 32 dBm to support a bit rate of 20 Gbps at the maximum LEO LISL distance of 6000 km. The AACC and QPSK required 28 dBm. Keeping to a bit-error rate (BER) of 10
⁻⁹
and a constant transmitter power of 30 dBm, the AACC and QPSK sustains the maximum LEO LISL distance whereas the 4-PAM supports a link distance of 4000 km. The AACC modulated LISL also observed an improvement of ~ 7 dBm in receiver-sensitivity over the 4-PAM. All three modulated LISLs are then simulated for a bit rate of 40 Gbps. The 4-PAM and QPSK were found to support a link distance of 3000 km and 5000 km, respectively, whilst the AACC sustains up to a distance of 6000 km.