SDM for Cable Overview

Our SDM application in downstream cable modulates up to an 18MHz baseband multi-sub-band signal. One sub-band of guardband is needed between this SDM channel and legacy modulation (analog or digital). Recall from the technology overview section:

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SDM in the Downstream

The downstream signal of the plant will be converted to IF and the upconverted into the RF passband of the cable plant.

The expected downstream data capacity of the channel will be 179.8Mbps @ 18MHz, running with an effective baud rate of 10 bits per second per Hz, equivalent to 1024QAM. The modulator will be capable of performing up to the equivalient of 4096QAM where channel noise conditions permit. The downstream modulator will be provisionable for 6MHz, 8MHz, 12MHz, 16MHz, and 18MHz wide channel operation to suit a wide variety of deployment scenarios.

SDM is a lowest level Physical Layer modulation technology that provides a bit stream to higher level services, such as MPEG2 Transport Stream (MPEG2-TS) packets. SDM provides a significant increase in MPEG channel (port) digital capacity that is transparent to and completely supportive of current MPEG2-TS based channels, including video, conditional access, and DOCSIS downstream data. SDM fits completely underneath these services without requiring a change of architecture.

SDM in the Upstream

The upstream data capacity of the channel will be dictated by the CNR experienced by each sub-band; e.g., each sub-band will operate at the best baud rate allowed by the noise in the sub-band channel. The upstream will allow a data capacity peak rate approaching 150Mbps, conditions permitting.

The upstream system will provide baseband coverage over 5MHz to 65MHz allowing the same chip to meet the European 5Mhz to 65MHz split plan, the Japanese 5MHz to 50MHz split plan, as well as the North American sub-split (low-split) system of 5MHz-42MHz. In all cases, only those sub-bands will be turned-on where there is available RF spectrum to modulate. The steep stopbands allow Wavelet modulation to run up to, adjacent, and around existing services without disruption or known stable noise sources (e.g. 27MHz to 30MHz) as well as up close to passband edges. It is expected that one demodulator will cover the entire upstream spectrum for all configurations.