Performance Analysis of CO-OFDM System Using 4-QAM Modulation on Inter Satellite–Optical Wireless Communication (Is-OWC)

Inter-satellite optical communication (Is-OWC) stands out among OWC technologies due to its ability to facilitate high data rates, operate in unlicensed spectrum, achieve high bandwidth increase, maintain immunity to interference, ensure high data transmission security, and operate at low transmission power.However, the performance of the Is-OWC system can be significantly degraded by multipath fading interference, which occurs when the signal has more than one propagation path.To address this, the study proposes a coherent optical (CO)-OFDM system model using 4-quadrature amplitude modulation (QAM) modulation with an optical external modulation method and optical direct detection power of 0 dBm.The test parameters focus on the OFDM modulator power ranging from 10 dBm to 20 dBm for a transmission distance of 500 km low earth orbit (LEO) to 5000 km medium earth orbit (MEO).Based on the results of the system model test, the validation of the 4-QAM CO-OFDM system model on Is-OWC technology has a special suitability based on theoretical calculations of optical reception power with simulation results as a depiction of light propagation conditions in outer space.The proposed system model uses optical external modulation and optical coherent detection, which can increase receiver sensitivity.Based on the results of BER, SER, and EVM obtained for the use of a bit rate of 10 Gbps, the system model is very suitable for application up to 2000 km (LEO-MEO) with a minimum OFDM modulator power of 10 dBm.While for the bit rate of 20 Gbps, this CO-OFDM system model is still very reliable for the use of inter-satellite data communication up to 1500 km with a minimum OFDM modulator power of 12 dBm.The increase in BER and SER is quite large and relatively constant for the use of bit rates of 30 Gbps and 40 Gbps, where the EVM obtained is almost more than 30% for all distance variations.However, the EVM value using a bit rate of 30 Gbps, which is still less than 30% up to 1000 km, provides an opportunity to develop the proposed model system.