Light-Weight Time-Packing Detection Schemes for Optical Feeder Link Adaptation in High Throughput Satellite Systems

This paper shows low complex decoding algorithms for time-packed optical feeder links when they are used in High Throughput Satellite (HTS) system with fully regenerative payloads. Time-packed M-ary Pulse Amplitude Modulation (M-PAM) is used to modulate the intensity of the laser diode beam by means of an external Mach-Zehnder modulator. At the receiver, the symbols are detected by resorting to a photodetector, encapsulated into the 5G radio frame of the access link, and demodulated using the Viterbi Algorithm (VA). However, if the modulation order and/or the overlapping factor are highs and/or the roll-off factor of the pulse-shape is low, then the number of Viterbi states can be too high. Towards this regard, we have studied the mitigation capability of Minimm Mean Square Error (MMSE) equalizer and transversal filter adapted by Least-Mean Squares (LMS) algorithm. As expected, both techniques, although sub-optimal, permit to mitigate in a large extent the Inter-Symbol Interference (ISI) and so, provide a finer granularity on the link adaptation of the optical feeder link.