High performance gain demodulate system for hybrid fiber-coaxial

Gigabit capable of Hybrid Fiber-Coaxial (HFC) represented an increase. The goals of the next generation HFC system are to efficiently utilize the precious last 100 m of the coaxial cable and to achieve a Gigabit transmission rate. This target demands higher requirements regarding the physical layer (PHY) throughput. Firstly, the PHY architecture of next generation HFC system is given in detail. Secondly, in order to meet challenging high PHY throughput, a class of Low Density Parity Check (LDPC) code is selected as the Forward Error Correction (FEC) scheme, the ultimate choice is made on the basis of system with a better bit error rate performance. Finally, this paper combines the characteristics of Gray code symbol mapping for Quadrature Amplitude Modulation (QAM) constellation to design a soft decision algorithm based on signal diversity. Especially in terms of power efficiency, this algorithm can beyond the performance of log-MAP algorithm.