4.7　Transmission-related Ancillary Technologies

4.7.1　The dispersion compensation design of a WDM digital transmission system shall be in accordance with the following requirements:

1　An incoherent detection repeaterless WDM digital transmission system may perform pre-dispersion compensation at the transmitter and post-dispersion compensation at the receiver；dispersion compensation may be fixed dispersion compensation and/or self-adaptive dispersion compensation；and the two may be combined to achieve precise single-channel dispersion compensation.

2　An incoherent detection repeatered WDM digital transmission system may perform its dispersion compensation through a combination of evenly distributed dispersion-compensation spans along the cable line and the compensation mechanism of terminal equipment described in Item 1of this clause.

4.7.2　The design of an incoherent detection WDM digital transmission system shall take into consideration the impact of PMD，and the DGD penalty shall be within the tolerance of the performance budget.

4.7.3　The application of power equalization technologies shall comply with the following principles:

1　For a reperterless WDM digital transmission system，the SLTE shall have the function of optical power equalization，and single-channel power equalization may be performed automatically without personal involvement；

2　For a repeatered WDM digital transmission system，power equalization may be achieved by combining the installation of gain equalizers along the cable line and the optical power equalization of the terminal equipment.

4.7.4　Based on the cost of submerged equipment，submarine digital transmission systems should adopt the state-of-the-art FEC，coding modulation，and receiver technologies.

4.7.5　According to the distance between landing stations and design capacity，repeaterless digital transmission systems may adopt pre-amplifiers，post-amplifiers，pre-remote EDF amplifiers，post-remote EDF amplifiers，or Raman amplifiers.