Abstract:
Four wave mixing (FWM) nonlinear crosstalk degrades the performance of Wavelength Division Multiplexing (WDM) transmission system significantly. Characteristics of FWM are closely related to frequency allocations of channels. Equally spaced channels have a lot of FWM lights whose frequencies are coincident with those of signal lights. As a result, a signal-to-noise ratio for equally spaced channels is heavily degraded by FWM. On the other hand, unequally spaced channels do not have any FWM lights whose frequencies agree with those of the signal lights. In unequal spaced channels, however, a total bandwidth which is occupied by all the signals expands drastically with an increase in the number of channels. Thus, it is difficult to accommodate a lot of channels in unequal scheme. It is important to achieve a total bandwidth of all the signals as narrow as possible. Many methods have been developed to solve the problem. However, to overcome the problems, Repeated Unequally Spaced Channel Allocation (RUSCA) is proposed here as a new frequency allocation. RUSCA method is formed by repeating an Unequal Spaced Channel Allocation (USCA). It is observed that RUSCA has a narrower total bandwidth than USCA when the number of channels and the minimum channel spacing are common in both channels. But the bandwidth for the RUSCA method is large when the channel number is large. To reduce the bandwidth of RUSCA method, the method is modified which is named as Equally Repeated Unequal Spaced Channel Allocation (ERUSCA) and Unequally Repeated Unequal Spaced Channel Allocation (URUSCA). Both methods are same as RUSCA. The proposed method provides a fast and simple alternative to solve the channel allocation problem by reducing the FWM effect significantly and also overcomes the limitations of earlier methods. This method finds an appropriate solution for any value of channel number and their spacing, reducing the time complexity, minimizes the total optical bandwidth requirement and able to find the new channel locations directly without changing old channel locations if the channel number is need to be increased.
