Comparison of homodyne and intradyne detection for high-order modulation schemes in optical intersatellite communication systems

In order to increase the data rate and lower the power consumption in satellite communication systems, optical laser terminals are an attractive alternative to the conventional RF systems. By using optical coherent detection, high receiver sensitivity as well as full signal recovery is achieved. However, the local oscillator at the receiver requires a carrier recovery system. In order to achieve homodyne detection, an optical phase-locked loop can be used. Each optical PLL structure is fixed to a specific modulation format and its complexity increases with modulation order. Therefore, applying an intradyne detection scheme, where the local laser runs un-synchronized and frequency offset and phase noise compensation is done by digital signal processing after the optical front end, seems to be a possible alternative. We present numerical results for both coherent detection schemes and compare them in terms of receiver sensitivity.