Design of 400 Gbps Dual-Polarisation QPSK Backhauling for Current and Future Mobile Networks: Practical Conditions, Applications, Challenges, and Research Directions

This study describes the design and analysis of a 400 Gbps dual-polarisation quadrature phase shift keying (DP-QPSK) backhaul system optimized for existing and future high-capacity mobile networks, such as 5G and 6G. To meet the growing demand for bandwidth-intensive applications such as AR, VR, and ultra-high-definition streaming, the system utilizes advanced optical transmission technologies, digital signal processing (DSP), and spectral efficiency techniques. The design uses Maxwell's equations and the nonlinear Schrödinger equation (NLSE) to simulate electromagnetic wave propagation and nonlinear impairments, including self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM). Novel real-time, dynamic environmental modeling of fiber impairments, including temperature-dependent attenuation, dispersion, and polarisation mode dispersion (PMD), enables precise impairment mitigation, thereby enhancing signal integrity over extended distances. To achieve extremely low bit error rates, the system uses neural network-based equalizers, adaptive DSP, and unique impairment tracking. The challenges of nonlinear effects, fiber impairments, and integration with existing networks are examined, as well as potential solutions to improve resilience, scalability, and efficiency. The report also discusses future research topics, such as weather-resilient free-space optical communication, quantum-resistant security, and cost-effective deployment methods. Extensive simulation findings support the usefulness of the suggested technique, demonstrating near-error-free transmission capabilities, excellent spectrum efficiency, and durability under practical situations, thereby providing a potential foundation for next-generation high-capacity backhaul networks.