[Contents] [Prev] [Next] [Index] [Report an Error]


Radio Frequency (RF) Specifications

For reference purposes, Table 47 through Table 51 are reproduced from the CableLabs DOCSIS Radio Frequency Interface Specification, SP-RFI-I05-991105. For the complete DOCSIS specifications, see the appropriate CableLabs document.

This appendix contains the following tables:


Table 47: Downstream RF Channel Transmission Characteristics

Parameter
Value
Frequency range
Cable system normal downstream operating range is from 50 MHz to as high as 860 MHz. However, the values in this table apply only at frequencies >= 88 MHz.
RF channel spacing (design bandwidth)
6 MHz
Transit delay from headend to most distant customer
<= 0.800 msec (typically much less)
Carrier-to-noise ratio in a 6-MHz band (analog video level)
Not less than 35 dB4
Carrier-to-interference ratio for total power (discrete and broadband ingress signals)
Not less than 35 dB within the design bandwidth
Composite triple beat distortion for analog modulated carriers
Not greater than -50 dBc within the design bandwidth
Composite second order distortion for analog odulated carriers
Not greater than -50 dBc within the design bandwidth
Cross-modulation level
Not greater than -40 dBc within the design bandwidth
Amplitude ripple
0.5 dB within the design bandwidth
Group delay ripple in the spectrum occupied by the CMTS
75 ns within the design bandwidth
Micro-reflections bound for dominant echo
-10 dBc @ <= 0.5 m sec, -15 dBc @ <= 1.0 m sec
-20 dBc @ <= 1.5 m sec, -30 dBc @ > 1.5 m sec
Carrier hum modulation
Not greater than -26 dBc (5%)
Burst noise
Not longer than 25 m sec at a 10 Hz average rate
Seasonal and diurnal signal level variation
8 dB
Signal level slope, 50-750 MHz
16 dB
Maximum analog video carrier level at the CM input, inclusive of above signal level variation
17 dBmV
Lowest analog video carrier level at the CM input, inclusive of above signal level variation
-5 dBmV

1.    Transmission is from the headend combiner to the CM input at the customer location.

2.    For measurements above the normal downstream operating frequency band (except hum), impairments are referenced to the highest-frequency NTSC carrier level.

3.    For hum measurements above the normal downstream operating frequency band, a continuous-wave carrier is sent at the test frequency at the same level as the highest-frequency NTSC carrier.

4.    This presumes that the 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.

5.    Measurement methods defined in [NCTA] or [CableLabs2].



Table 48: Upstream RF Channel Transmission Characteristics

Parameter
Value
Frequency range
5 to 42 MHz edge to edge
Transit delay from the most distant CM to the nearest
CM or CMTS
<= 0.800 msec (typically much less)
Carrier-to-noise ratio
Not less than 25 dB
Carrier-to-ingress power (the sum of discrete and
broadband ingress signals) ratio
Not less than 25 dB2
Carrier- to-interference (the sum of noise, distortion, common-path distortion and cross-modulation) ratio
Not less than 25 dB
Carrier hum modulation
Not greater than -23 dBc (7.0%)
Burst noise
Not longer than 10 msec at a 1 kHz average rate for most cases3,4,5
Amplitude ripple
5-42 MHz: 0.5 dB/MHz
Group delay ripple
5-42 MHz: 200 ns/MHz
Micro-reflections -- single echo
-10 dBc @ <= 0.5 m sec
-20 dBc @ <= 1.0 m sec
-30 dBc @ > 1.0 m sec
Seasonal and diurnal signal level variation
Not greater than 8 dB min to max

1.    Transmission is from the CM output at the customer location to the headend.

2.    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 [CableLabs1].

3.    Amplitude and frequency characteristics sufficiently strong to partially or wholly mask the data carrier.

4.    CableLabs report containing distribution of return-path burst noise measurements and measurement method is forthcoming.

5.    Impulse noise levels more prevalent at lower frequencies (< 15 MHz).



Table 49: Downstream RF Signal Output Characteristics

Parameter
Value
Center Frequency (fc)
91 to 857 MHz 1
Level
Adjustable over the range 50 to 61 dBmV
Symbol Rate (nominal)
64QAM
256QAM

5.056941 Msym/sec
5.360537 Msym/sec
Nominal Channel Spacing
6 MHz
Frequency response
64QAM
256QAM

~18% Square Root Raised Cosine shaping
~12% Square Root Raised Cosine shaping
Total Discrete Spurious Inband (fc
Inband Spurious and Noise (fc
Adjacent channel (fc
Adjacent channel (fc

Next adjacent channel (fc


Other channels (47 MHz to 1,000 MHz)
< -57dBc
< -48dBc; where channel spurious and noise includes all discrete spurious, noise, carrier leakage, clock lines, synthesizer products, and other undesired transmitter products. Noise within +/- 50kHz of the carrier is excluded.
< -58 dBc in 750 kHz
< -62 dBc, in 5.25 MHz, excluding up to 3 spurs, each of which must be <-60 dBc when measured in a 10 kHz band
Less than the greater of -65 dBc or -12dBmV in 6MHz, excluding up to three discrete spurs. The total power in the spurs must be < -60dBc when each is measured with 10 kHz bandwidth.
< -12dBmV in each 6 MHz channel, excluding up to three discrete spurs. The total power in the spurs must be < -60dBc when each is measured with 10kHz bandwidth.
Phase Noise
1 kHz - 10 kHz: -33dBc double sided noise power
10 kHz - 50 kHz: -51dBc double sided noise power
50 kHz - 3 MHz: -51dBc double sided noise power
Output Impedance
75 ohms
Output Return Loss
> 14 dB within an output channel up to 750 MHz;
> 13 dB in an output channel above 750 MHz
Connector
F connector per [IPS-SP-406]

1.    



Table 50: DOCSIS Downstream Channel Rates and Spacing

Nominal Symbol Rate
(Msym/sec)
Nominal Channel Spacing
(kHz)
Bit Rate (bps)
5.056941 (64QAM)
6000
30,341,646
5.360537 (256QAM)
6000
42,884,296


Table 51: DOCSIS Maximum Upstream Channel Rates and Widths

Symbol Rate
(ksym/sec)
Channel Width
(kHz)1
Bit-rate/sec
(QPSK)
Bit-rate/sec
(16QAM)
160
200
320,000
640,000
320
400
640,000
1,280,000
640
800
1,280,000
2,560,000
1,280
1,600
2,560,000
5,120,000
2,560
3,200
5,120,000
10,240,000

1.    Channel width is the -30 dB bandwidth.



[Contents] [Prev] [Next] [Index] [Report an Error]