Estimation of the Throughput Capacity of a Coherent Fiber-Optic Transmission System for QPSK-OFDM Signals

The study examines a multi-span coherent fiber-optic transmission system for signals with Orthogonal Frequency Division Multiplexing (OFDM), designed for long-distance communication. Channels are formed using the spectrally efficient modulation format - Quadrature Phase-Shift Keying (QPSK). The bandwidth of the channel signals does not exceed $2.5 \mathrm{~Gb} / \mathrm{s}$, allowing for the avoidance of technologies to compensate for accumulated dispersion in the line. The upper limit of transmission system performance is investigated, taking into account nonlinear phase noise originating from optical fiber and noise from Erbium Doped Fiber Amplifiers (EDFA) amplifiers. It is demonstrated that utilizing 64-channel QPSKOFDM signals can achieve transmission distances of approximately $6400 \mathrm{~km}$ at a fiber bit rate of $320 \mathrm{~Gb} / \mathrm{s}$.