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The effective capacity and the immunity to noise and impairments of upstream transmissions in a DOCSIS system can be enhanced through the use of an advanced physical layer. Such improvements are valuable for deployment of advanced services. In addition, these improvements serve to increase the number of cable systems around the world that provide a transmission environment ready to sustain successful operation of DOCSIS communications channels. This paper indicates how a specific spread-spectrum technology, called synchronous code division multiple access (S-CDMA), can be incorporated into DOCSIS-based systems. The potential inclusion of S-CDMA as an evolutionary enhancement to DOCSIS provides backward compatibility with existing DOCSIS systems and equipment. The paper shows how this requirement can be met using the same physical channel. The theory of operation of S-CDMA is provided, along with analysis and simulation results showing the improvements that can be obtained. S-CDMA is also compared with other technologies that may also play a role in extending the capabilities of the DOCSIS upstream physical layer.