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In this paper, a new coding architecture is proposed for fiber-optic synchronous code division multiple access (S/CDMA) network by using parallel cancellation scheme and bit-stuffed unipolar m-sequence. The wellknown maximal length code (m-sequence) with one bit stuffing which is called bit-stuffed unipolar m-sequence in this paper can achieve unique cross-correlation value . Due to the uniqueness of cross-correlation value of unipolar m-sequence, the proposed parallel cancellation scheme can completely suppress the interuser interference in the negligible effects of noise. In the proposed architecture, the correlator employs avalanche photodiode (APD) for photodetection, and the correlator output can be modeled as a Gaussian random process [7][8]. In addition to the suppression of interuser interference, the inevitable effects of APD noise and thermal noise in the process of photodetection are also investigated in this paper.

This study investigates how to adjust the transmit power of femto base station (FBS) to mitigate interference problems between the FBSs and mobile users (MUs) in the 2-tier heterogeneous femtocell networks. A common baseline of deploying the FBS to increase the indoor access bandwidth requires that the FBS operation will not affect outdoor MUs operation with their quality-of-service (QoS) requirements. To tackle this technical problem, an FBS transmit power adjustment (FTPA) algorithm is proposed to adjust the FBS transmit power (FTP) to avoid unwanted cochannel interference (CCI) with the neighboring MUs in downlink transmission. FTPA reduces the FTP to serve its femto users (FUs) according to the QoS requirements of the nearest neighboring MUs to the FBS so that the MU QoS requirement is guaranteed. Simulation results demonstrate that FTPA can achieve a low MU outage probability as well as serve FUs without violating the MU QoS requirements. Simulation results also reveal that FTPA has better performance on voice and video services which are the major trend of future multimedia communication in the NGN.

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