Research On Subcarrier Multiplexing Technology Inelastic Optical Network

Due to the rapid growth of business demand,the development of optical networks is facing with the dual pressures of improving transmission capacity and bandwidth flexibility.Meanwhile,due to the fixed grid limiting of conventional WDM(Wavelength Division Multiplexing)system,it is difficult to solve the dynamic bandwidth requirements and efficient spectrum allocation.In order to overcome the above problems,the next generation of ultra-100Gb/s flex-grid EON(Elastic Optical Network)becomes research hot spot.Flexible grid optical networks break the constraint of fixed grids by splitting the 50 GHz fixed channel spacing into finer granularity(such as 12.5GHz channel spacing).In finer granularity subcarrier system,the spectrum efficiency has significant improvement because bandwidths can be adaptively allocated as needed.On the other hand,the subcarriers with configurable number,location and modulation format can realize variable rate and flexible transmission.Besides,this system will provide improved tolerance to the nonlinear characteristics of fibersFor applications in EON's,this paper proposes a sub-wavelength granularity optical signal transmission technique based on sub-carrier multiplexing in electrical domain with high flexibility,fine granularity and high efficiency.The digital signal processing in electrical domain can help to support flexible configurability on different sub-wavelength signals with different modulation formats and transmission rates.To meet the flexibility requirements from sub-wavelength signal transmission in EON's,this paper also proposes a linearly frequency chirped pilot signal-based channel estimation and frequency-domain equalization(FDE)method.Detailed studies are pursued with focuses on performance comparisons between pilot signal-based FDE and training sequence-based time-domain equalization plus FDE's with different equalization algorithms.Simulation results show that the pilot signal-based zero-forcing FDE algorithm can obtain effective dispersion compensation and improve the transmission performance with low computation complexity.Meanwhile,taking into account the flexibility requirements from frequency slot and routing configuration in sub-wavelength granularity EON's,this paper uses numerical simulations to study in detail the transmission performance with different subwavelength signal numbers,transmission lengths or modulation formats.It is verified that the linearly frequency chirped pilot signal-based channel estimation and FDE method can achieve good adaptability under different EON configurations and is one of the key technologies to be used in reconfigurable optical transceivers and sub-wavelength signal transmissions in EON's.In practice,considering the variation of environmental temperature and other factors,the lasers of an optical network node will inevitably appear wavelength or frequency drift.As a result,the frequency spacing two adjacent subcarrier optical signals from different optical nodes changes with time in a random way.According to ITU.T-WDM standard,the traditional 50 GHz channel spacing of WDM system requires the laser center wavelength drift to be in a range of ±2.5GHz.The random wavelength drift has little effect on conventional WDM systems on account of the large channel spacing.However,since the channel spacing of flex-grid subcarrier system becomes smaller,the ICI(Inter Carrier Interference)of the subcarriers frequency drift may lead to serious degradation to the system performance.Then,the influence of random laser wavelength drift on the subcarrier system with different granularity is analyzed.Meanwhile,the solution of decreasing the random frequency is proposed in this paper.Based on the theoretical model,the simulation and comparative analysis were carried out.