IMD compensation for CDMA through FEC coding and nonlinearity recovery technique for optical fiber feeder system

Optical feeding between base stations (BS) and radio network control (RNC), proposed in this paper, is an efficient technique for third generation wideband CDMA mobile communication systems. The proposed technique provides the compensation to the intermodulation distortion (IMD) instituted by both the power amplifier (an electrical component) and the laser diode (an optical component). This IMD can impose strong limitations on CDMA and deteriorate system performance. In this paper IMD compensation is proposed through unification of FEC codes and a post nonlinearity recovery block (PNRB). System performance is evaluated through calculating the transfer functions of FEC codes, laser diode and PNRB. The transfer functions of the FEC codes are calculated by using the flow graph rules, and of the laser diode and PNRB through Volterra kernels. Performance of the PNRB alone for narrowband CDMA signals was sought in our previous work (Pervez and Nakagawa, 1996), whereas performance of PNRB combined with digital coding protection to compensate for the nonlinearities of the laser diode (LD) and power amplifier (PA) for wideband CDMA is pursued here.