By Mark E. Laubach, Yi Ling, William J. Miller, Tracy R. Hall
Bandwidth needs of customers on cable plants have increased dramatically over recent years and will continue to rise in the near future. Increasing the order of QAM modulation has been the most popular way to satisfying the bandwidth needs until recently when nonlinear distortions and limited dynamic range in HFC systems have proved to be an obstacle for reliable 256 QAM service. Hence, it is of both practically necessary and theoretically interesting to investigate approaches other than QAM to increase bandwidth efficiency and to provide higher tolerance of composite distortions all at the same time. Sub-band Division Multiplexing (SDM) is one of these new approaches. In this paper, we give an introduction of the Sub-band Division Multiplexing (SDM) technique based on filter bank scheme and wavelet mathematics. SDM represents a philosophical change comparing to standard QAM in terms of baseband signal formulation and alphabets selection. To show this change, the fundamentals of SDM will be overviewed. Unique characteristics resulting from the SDM fundamentals will also be presented. It will be shown that these characteristics implying multiple advantages of SDM over equivalent QAM on cable applications, especially the tolerance of composite distortions. Simulation results and measurements on the Broadband Physics prototype system from the lab and field trials also will be presented in the paper to verify the theoretical results.