PERFORMANCE ANALYSIS OF CDMA OPTICAL COMMUNICATION-SYSTEMS WITH AVALANCHE PHOTODIODES

The performance of optical code-division multiple-access (CDMA) commun ication systems with avalanche photodiodes (APD) is analyzed. The bit error rate (BER) can be accurately computed by using the saddlepoint m ethod. The effects of the multiple-user interference (MUI), signal-dep endent shot noise, and receiver thermal noise are investigated. Result s of the numerical integration illustrate the non-Gaussian property of the receiver output distribution. Exact means and variances are deriv ed for the Gaussian approximation. It is found that when the MUI incre ases, the saddlepoint approximation yields satisfactory results, but t he Gaussian approximation yields higher BER floors. Prime codes and on -off keying (OOK) are considered. Examples illustrate the effects of t he system parameters such as the APD gain, threshold, prime code lengt h, and the number of simultaneous users.