Amplitude Modulation for Constant Envelope OFDM Using Relay in Satellite Communications

Constant envelope orthogonal frequency division multiplexing (CE-OFDM) has emerged as a compelling solution to the high peak-to-average power ratio (PAPR) challenge inherent in conventional OFDM, particularly suited for energy-limited scenarios such as satellite downlink communications. By leveraging phase modulation on conjugate symmetric signals, CE-OFDM significantly mitigates PAPR, leading to enhanced bit error rate (BER) performance, albeit with the trade-off of reduced spectral efficiency. To overcome this limitation, a novel scheme utilizing a relay node to apply amplitude modulation (AM) to the CE-OFDM signals, namely AM-CE-OFDM is introduced, where the satellite employs constant envelope modulation to maximize amplifier efficiency and extend communication range, while the relay’s AM substantially boosts spectral efficiency. Simulation results indicate that the proposed scheme yield significant spectrum efficiency enhancement over traditional CE-OFDM systems, presenting a robust solution for next-generation satellite communication systems.