A novel satellite on-board processing scheme based on photon frequency conversion is proposed for the purpose of realizing frequency conversion. For the received intermediate frequency signal, a Mach-Zehnder modulator is used to convert it into an optical signal. The modulated optical signal and an optical signal generated by a tunable laser enter the photodiode through a coupler to perform heterodyne beat frequency and generate an intermediate frequency signal of the target carrier frequency, thereby reducing the cost and power consumption of on-board processing. Simulation results show the spectrograms and constellation diagrams of frequency conversion from Q-band to V-band in 8PSK modulation format. The bit error rate(BER) obtained by simulation shows that in a satellite communication system, when the OSNR is higher than 5dB, the BER performance can meet the 2×10-2 threshold when using 8PSK modulation format, which indicates that error-free transmission can be achieved when using 20% soft-decision FEC. The Q factor obtained by simulation shows that when the OSNR is higher than 5dB, the Q factor can reach more than 6.5 when using QPSK modulation format, which indicates that reliable transmission can be achieved. Compared with existing solutions, this scheme has the advantages of lower cost, lower power consumption and more flexible frequency selection, it can also solve the inflexibility and improve the performance of radio frequency conversion in traditional scheme.
On the basis of multi-layer satellite network, this paper presents a GEO/LEO double-layer satellite optical network structure that can meet the global all-weather coverage. Due to the limited number of antennas on the satellite, the LEO satellites are divided into two categories according to the function. One of the categories, as cluster-head satellites, should both establish link with LEO satellites and GEO satellites. The cluster head satellites will also be grouped with the link distance as the index. Each group has the same number of satellites which communicate with the same GEO. A reasonable grouping method is used to avoid the problem of too many links being set up simultaneously with the same GEO satellite, which will affect the transmission delay and communication efficiency. In terms of route selection, the hop cost factor is introduced to improve the traditional KSP algorithm. Compared to the KSP algorithm at the cost of link distance, the designed algorithm limits the number of jumps during service transmission, so as to balance the link length and the number of hops well. Through MATLAB simulation, the proposed algorithm improves the efficiency of the utilization of interorbit link, reduces blocking rate, and makes the resource allocation more reasonable.
A Probabilistic Shaping (PS) 12-QAM scheme based on Set-Partitioned (SP) Two-Polarization (TP) is proposed to improve the effectiveness and reliability of Probabilistic Shaping 12-QAM (PS-12QAM). In this scheme, the Uniform 12- QAM constellation points are divided into two set partitions, and two polarization states are used to broaden the dimension between two set partitions. Moreover, the system capacity is further approached to Shannon limit by Probabilistic Shaping. The simulations on PS-8QAM, PS-12QAM, PS-16QAM and Probabilistic Shaping Set-Partitioned Two-Polarization 12- QAM (PS-SP-TP-12QAM) have been completed. The results show that, compared with PS-12QAM, the Euclidean distance between adjacent constellation points in PS-SP-TP-12QAM scheme is significantly optimized, and the bit error rate (BER) of this scheme is greatly improved up to 0.5dB. Compared with PS-8QAM and PS-16QAM, it brings a better balance between effectiveness and reliability performance.
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