Robust optical FFH-CDMA communications: coding in place of frequency and temperature controls

Abstract

In wavelength division multiplexing (WDM), transmitters require stringent and complex frequency control loops to avoid wavelength drifts due to temperature fluctuations. This makes the transmitters heavy, bulky, and inappropriate for local- and short-haul communications networks, as well as for manufacturing locales and other open areas where temperature control is not feasible. We propose and analyze a technique we call robust fast frequency hopping code division multiple access (FFH-CDMA), particularly suitable for severe, hostile, noncontrollable environments. This approach avoids all conditioning and frequency stabilization loops in the transmission end. We develop a modified version of extended hyperbolic congruence codes to achieve environment-resistant codes. We present expressions for the auto- and cross-correlation functions for optical implementation of the codes. We simulate the encoding/decoding operations with parameters from real Bragg gratings. We evaluate probability of error for a single user and as an average over all users versus capacity (the number of simultaneous users). Robust FFH-CDMA is an efficient access technique for hostile environments. It avoids the frequency and temperature control problems of WDM and nonrobust FFH-CDMA at the cost of lower overall capacity in terms of number of simultaneous users.