By Rob Thompson, Ph.D., Sercomm; Donald Jones, Sercomm
Adjacent Channel Interference (ACI) and its mitigation strategies are well understood for mid-split and high-split deployments as low likelihood interference to legacy services. ACI can be an in-Premises interference problem, mostly affecting tuner-sensitive legacy video set-top boxes (STBs). Increased spectral overlap associated with high-split can overcome port-to-port isolation in taps causing ACI to neighbor equipment. Low tap port return loss can also be troublesome for customers with both a higher speed tier modem and one or more STBs. The newly defined Data Over Cable System Interface Specifications 4.0 (DOCSIS® 4.0) band splits, with added upstream capability, will have even more spectral overlap, compounding the ACI problem further by impacting legacy and newer generation equipment. This paper’s first goal is to summarize standards-based features necessary for minimizing the increasing impact of ACI for future 10G networks.
Successful Full Duplex DOCSIS (FDX) operation was based on the expectation that interference conditions would be more challenging and diversified, so mechanisms including interference group (IG) and transmission group (TG) management were included to minimize their impact and maintain DOCSIS fidelity. FDX’s echo cancellation (EC) also plays a role in interference minimization. CCI and ALI are FDX interferences that must be managed to enable coexistence between upstream and downstream signaling in either the same or directly adjacent spectrum.
ACI impacts for both mid-split and high-split systems is becoming well understood, but more needs to be learned as overlapping bandwidths increase for both FDX and Frequency Division Duplex (FDD) networks. This paper’s second goal will be to summarize and review the current ACI research, adding new data, where necessary to provide a comprehensive overview of ACI as it applies to both FDD and FDX networks. Finally, this paper will conclude with recommendations for the minimization of ACI in future 10G networks.