Analysis of Receiver Sensitivity Performance for DPSK Optical Communication using Enhanced Saddle Point Approximation

Abstract

An optical communication system can be designed with minimum transmission errors and maximum data rate. This can be achieved by an optimal modulation format with proper receiver design. The primary source of additive noise in optically amplified systems is due to the amplified spontaneous emission (ASE) noise produced by the optical amplifiers used as intermediate repeaters and as preamplifiers at the receiver ends. The interaction between the linear effect and signal-ASE beat noise is assumed generally as Gaussian distribution and for the first time it is assumed that the noise interaction has chi square distribution, this statistical distribution of signal-ASE noise is assumed to be non Gaussian and its behavior is analyzed using the enhanced saddle point approximation method. We have employed two new techniques in determining the saddle points in this enhanced method. A performance comparison has been done with the parameters like time consumption, accuracy and finally complexity between these two techniques. Receiver sensitivity performance has been analyzed for various phase shift keying modulation formats like non return to zero (NRZ -DPSK)differential phase shift keying, return to zero (RZ-DPSK) and carrier suppressed return to zero(CSRZ-DPSK) using this technique for the same bit error rate with Gaussian and chi square noise distributions . It is found that chi square distribution of CSRZ-DPSK shows better signal to noise ratio performance for the given Bit error rate(BER) than the Gaussian approximation and finally the simulated results agree with the analytical results.