ANSI/SCTE 133:2007 pdf download.Downstream RF Interface for Cable Modem Termination
Systems.
5.2.1 Frequency Plan
In the downstream direction. the cable system is assumed to have a pass band with a lower edge between 50 and 54 MHz and an upper edge that is implemenLation-dependent hut is typically in the range of 300 to 870 MIk Within that pass band. NTSC analog tclevision signals in six-MHz channels are assumed present on the Standard (STD1, l-IRU or IRU frequency pbns of (CEA.542.HJ. as well as other narrowband and widehand digital signals.
5.2.2 Cornpallbili( sslth Other Sersices
The CM and EQAM or CMTS MUST coexist with the other services on the cable network, for example:
a They MUST be intcropcrablc in the cable spectrum assigned for EQAM or CMTS-C’M interoperation. while the balance of the cabk spectrum is occupied by any combination of television and other signals and
b. Thcy MUST NOT cause harmful intcrkiencc to any other scrviccs that are assigned to the cable network in speciruin outside of that allocated to the EQAM or CMTS. The latter is undetsiond as:
I. No measurable degradation (highest level of compatibility)
2. No degradation bclow the perceptible level of impairments for all services (standard or medium level of compatibility) or
3. No degradation below the minimal standards accepted by the industry (for exmnple. FCC for analog video services) or other service provider (minimal level of compatibility)
5.2.3 Fault Isolation Impact on Other Users
As downstream transmissions are on a shared-media. point-lo-multipoint system, fault-isolation procedures should take into account the potential harmful impact ol faults and fault-isolation procedures on numerous users ot’ the data-over-cable. video, and other services.
For the interpretation of harmful impact, see Section 52.2 above.
5.3 Downstream Plant Assumptions
Thc DRFI specifications have been developed with the downstream pLant assumptions of this section
5.3.1 Transmission Levels
The nominal power level of the downstream RF signal(s) within a six-MHz channel (average power) is targeted to be in the range: -10 dUe 10-6 dlle. reLative to analog video carrier level (peak power) and will normally nut exceed analog video carrier level.
5.3.2 Frequency Ins ersion
There will be no frequency inversion in the transmission patti in either the downstream or the upstream directions. (i.e.. a positive change in frequency at the input to the cable network will result in a positive change in frequency at the output).
Several new features are supported in this Standard. The DOCSIS l.z and 2,0 Standards do not reflect thc ability of vendon to support multiple RF channels per physical RF port. This document presents the requirements and optional functions that enable an EQAM. or a CMTS, with multiple channels per RF port to be tested, measured and. if auceesaful, qualified.
For an M-CMTS, module aynehroniaation is no( as easy as with an integrated CMTS. A DRFI-compliant EQAM has a timing port on ii that enables a high precision (DTltto be used to distribute a common clock .ind ünuing signals. This permits the FOAM to be used in all modes, including S-(.DMA mode, because of the high stability and low jitter of the external clock and distribution system. The DOCS(S Timing Interface is defined in the (DTIJ Standard.
6,3 I)ossnstrearn
6.3.1 flow nstreani Protocol
The downstream PMD sublayer MUST conform to l’fl.-T Recommendation J.83 Anne,t B IITU-T i.83.BI. except for Clause B.6.2. lnterlcavcr depths are defined in Section 6.3.3 of this document. The applicability of a particular intcrlcavcr depth depends on the data service provided on a particular QAM RF channel, Applicability of interleaver depths for service deliv en, other than LXKSIS high-speed data, is beyond the scope of this document.
6.3.2 Spectrum Format
The downstream modulator for each QAM channel of the FOAM, or CMTS. MUST provide operation with the RF signal format of 5(t) — l(t)-coa4ua) + Q(t)’sin(wt), whcrei denotes time. w dcnutes RF angular frequency, and where 1(t) and Q(t) are the respective Roo.Nyquist filtered bascband quadrature components of’ the constellation, as specified in ITLJ.T Recommendation J,83. Annes 13 IITL-T J.S3-13]
6.3.3 Scaleablc Interleaving to Support Video and high-Speed Data Services
The CMTS or EQAM downstream PMI) sublayer MUST support a variable-depth interleaver. IITU-T i.83.B) defines the variable interleaver depths in “Table B,2.’J.83 Level 2 interleaving.”
A CMTS or EQAM MUST support the set of intericaver depths described in Table 6-I and Table 6-2. Requirements for operational availability of inicilcaver depths are given in Section 6.3.52, sub-section 1.
