Modified Hierarchical Modulation for Hybrid RF-FSO Satellite Communication

This paper proposes a Modified Hierarchical Modulation (MHM) technique implemented over a Hybrid Radio Frequency-Free-Space Optical (RF-FSO) satellite system. At the transmitter, a data block with a fixed length N is divided into two streams—the high-priority (HP) stream and the low-priority (LP) stream. The HP stream contains n bits and is transmitted over the RF link, while the LP stream contains m bits and is transmitted over the FSO link. At the receiver, the HP stream is demodulated and used as an a priori information to demodulate the LP stream. We show that this system performs better in terms of Bit-Error Rate (BER) over different levels of Signal-to-Noise Ratio (SNR) and elevation angles compared to classical combining schemes such as Maximal Ratio Combining (MRC). The reported Monte Carlo simulations show that for an operational range of SNR, the proposed technique increases the 0.01 data rate percentile a 14.9%.