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Over comparable RF bandwidth, SDM has
significant performance and cost advantages over
combined QAM logical ports

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SDM Compared to Combining of QAM Channels into Logical Channels

There has been much discussion in the industry about the notion of combining QAM channels into a larger, logical channel. This is called inverse multiplexing in other networking disciplines. The motivation for using a larger logical channel is to increase the advantages of using statistical multiplexing techniques to increase the number of active program streams in the channel. The shared wisdom in the industry is that the larger the digital capacity of a channel, the better the statistical multiplexing gains. Logical QAM channels, while increasing the size of the channel, do not increase the spectral efficiency of the channel. SDM has significant advantages over combined QAM logical ports:

1. SDM's single contiguous RF channel is more spectrally efficient than 2 or 3 combined discontiguous RF channels
2. SDM silicon size is likely to be 1/2 to 1/3 that of 2- or 3-combined QAM silicon, therefore likely to be 1/2 to 1/3 the cost of QAM silicon
3. SDM ports are less complex as they do not require inverse multiplexing decision logic for switching MPEG packets amongst different physical QAM channels.

The following table shows the digital capacities for 2 QAM and 3 QAM logical channels for both United States and European configurations.