This section describes the characteristics of a cable television plant, assumed to be for the purpose of operating a data-over-cable system. It is not a description of CMTS or CM parameters. The data-over-cable system MUST be interoperable within the environment described in this section.
Whenever a reference in this section to frequency plans or to compatibility with other services conflicts with any legal requirement for the area of operation, the latter shall take precedence. Any reference to analog TV signals in a particular frequency band does not imply that such signals are physically present.
B.5.1 Equipment Assumptions
Frequency Plan
B.5.1.1
In the downstream direction, the cable system is assumed to have a pass band with a lower edge of down to 47 MHz. Typically, the lower edge of the downstream pass band is at 87.5 MHz. The upper edge is implementation-dependent but is typically in the range of 300 to 862 MHz. Within that pass band, PAL/SECAM analog television signals in 7/8 MHz channels and FM radio signals are assumed to be present, as well as other narrowband and wideband digital signals. 8 MHz channels are used for data communication.
In the upstream direction, the cable system is assumed to have a pass band of 5-65 MHz. PAL/SECAM analog television signals in 7/8 MHz channels may be present, as well as other signals.
Compatibility with Other Services
B.5.1.2
Fault Isolation Impact on Other Users
B.5.1.3
See Section 5.1.3.
Cable System Terminal Devices
B.5.1.4
Compliance with EMC requirements is not covered by this specification. The protection requirements with respect to electromagnetic compatibility are contained in harmonized standards published in the Official Journal of the
European Union.
Any reference in the present document to the transmission of television in the forward channel that is not consistent with [EN 300 429] is outside the normative scope as only [EN 300 429] is used for digital multi-program TV distribution by cable in European applications.
Requirements for safety are outside the scope of the present document. Safety standards for European applications are published by CENELEC. Examples of such CENELEC product safety standards are [EN 60950-1] and [EN 50083-1]. For CENELEC safety categories of interfaces, see [EG 201 212].
B.5.2 RF Channel Assumptions See Section 5.2.
Transmission Downstream
B.5.2.1
The RF channel transmission characteristics of the cable network in the downstream direction assumed for the purposes of minimal operating capability are described in Table B–2. These numbers assume total average power of a digital signal in an 8 MHz channel bandwidth for carrier levels unless indicated otherwise. For impairment levels, the numbers in Table B–2 assume average power in a bandwidth in which the impairment levels are measured in a standard manner for cable TV systems. For analog signal levels, the numbers in Table B–2 assume nominal analog video carrier level (peak envelope power) in a 7/8 MHz channel bandwidth. Transmission is from head-end combiner to the CM input at the customer location. All conditions are present concurrently.
Table B–2 - Assumed Downstream RF Channel Transmission Characteristics
Parameter Value
Frequency range Cable system downstream operating range is from 47 MHz to 862 MHz. However, the operating range for data communication is from 108 to 862 MHz and the values in this table only apply to this frequency range. The use of frequencies between 108 and 136 MHz may be forbidden due to national regulation with regard to interference with aeronautical navigation frequencies.
RF channel spacing (design bandwidth) 7/8 MHz, 8 MHz channels are used for data communication Transit delay from head-end to most distant customer ≤ 0.800 ms (typically much less)
Carrier-to-noise ratio in an 8 MHz band (analog video level)
Not less than 44 dB1
Carrier-to-interference ratio for total power (discrete and broadband ingress signals)
Not less than 52 dB within the design bandwidth
Composite triple beat distortion for analog modulated carriers
Parameter Value
Composite second-order distortion for analog modulated carriers
Not greater than -57 dBc within the design bandwidth2
Cross-modulation level Under consideration
Amplitude ripple 2.5 dB in 8 MHz
Group delay ripple in the spectrum occupied by the CMTS
100 ns over frequency range 0.5 – 4.43 MHz
Micro-reflections bound for dominant echo -10 dBc @ ≤ 0.5 µs -15 dBc @ ≤ 1.0 µs -20 dBc @ ≤ 1.5 µs -31.5 dBc @ > 1.5 µs
Carrier hum modulation Not greater than -46 dBc (0.5%)
Burst noise Not longer than 25 µs at a 10 Hz average rate
Seasonal and diurnal signal level variation 8 dB
Signal level slope, 85 – 862 MHz Maximum slope of 12 dB in either the positive or negative direction
Maximum analog video carrier level at the system outlet, inclusive of above signal level variation
17 dBmV3
Lowest analog video carrier level at the system outlet, inclusive of above signal level variation
0 dBmV4
Table Notes:
Note 1 This presumes that the average digital carrier is operated at analog peak carrier level. When the digital carrier is operated below the analog peak carrier level, this C/N may be less.
Note 2 For SECAM systems the value is no greater than -52 dBc within the design bandwidth. Note 3 For SECAM systems the value is 14 dBmV.
Note 4 For SECAM systems the value is -3 dBmV.
Transmission Upstream
B.5.2.2
The RF channel transmission characteristics of the cable network in the upstream direction assumed for the purposes of minimal operating capability are described in Table B–3. Transmission is from the CM output at the customer location to the head-end. All conditions are present concurrently.53
Table B–3 - Assumed Upstream RF Channel Transmission Characteristics
Parameter Value
Frequency range. 5 to 65 MHz edge to edge
Transit delay from head-end to most distant customer ≤ 0.800 ms (typically much less) Carrier-to-noise ratio in active channel Not less than 22 dB
Carrier-to-ingress power (the sum of discrete and broadband ingress signals) ratio in active channel
Not less than 22 dB1
Carrier-to-interference (the sum of noise, distortion, common-path distortion and cross-modulation) ratio in active channel
Not less than 22 dB1
Carrier hum modulation Not greater than -23 dBc (7.0%)
Burst noise Not longer than 10 µs at a 1 KHz average rate for most cases2,3
Amplitude ripple across upstream operating frequency range (maximum)
2.5 dB in 2 MHz
Group delay ripple across upstream operating frequency range (maximum)
300 ns in 2 MHz
Micro-reflections (maximum) – single echo -10 dBc @ ≤ 0.5 µs -20 dBc @ ≤ 1.0 µs -31.5 dBc @ > 1.0 µs
Seasonal and diurnal signal level variation Not greater than 12 dB min to max Table Notes:
Note 1 Ingress avoidance or tolerance techniques may be used to ensure operation in the presence of time- varying discrete ingress signals that could be as high as 0 dBc.
Note 2 Amplitude and frequency characteristics sufficiently strong to partially or wholly mask the data carrier. Note 3 Impulse noise levels more prevalent at lower frequencies (<15 MHz).
B.5.2.2.1 Availability See Section 5.2.2.1. B.5.3 Transmission Levels See Section 5.3. B.5.4 Frequency Inversion See Section 5.4.