BPR-10 — Application Procedures and Rules for Digital Television (DTV) Undertakings (sf10158)

Annex G - Interference Analysis between DTV Assignments or Allotments and National Television Systems Committee (NTSC) Assignments

This Annex describes the interference analysis between NTSC and DTV assignments.

G1. NTSC Parameters (For Information Only)

G1.1 NTSC Assignments

The following table provides standard operating parameters of NTSC stations for the three frequency bands.

Table G1: Standard Operating Parameters of NTSC Stations
NTSC Class UHF UPPER VHF LOWER VHF
ERP EHAAT ERP EHAAT ERP EHAAT
R 325 kW 150 m 100 kW 150 m
C 1 MW 300 m
B 100 kW 150 m
A 10 kW 100 m
LP 5 kW 30 m 400 W 30 m 100 W 30 m

G1.2 Antenna Height and Power Equivalence

Where the antenna height exceeds the values shown in the above table, the effective radiated power (ERP) shall be reduced to provide equivalence with the maximum or other permissible parameters. Equivalence requires that the contours as defined by the field strengths in Table G2 of Section G2.1 remain at the same location.

G2. Interference Analysis

G2.1 Protected Contour

In predicting the distance to the protected service contour of NTSC assignments, the field strengths listed in the second column of Table G2 and the F(50,50) curves should be used. The F(50,50) curves represent the field strength at 9.1 m above ground, which is exceeded at 50% of the locations and 50% of the time as measured in decibels above one microvolt per metre. The curves are based on an effective power of one kilowatt radiated from a half-wave dipole in free space and can be found in Annex F.

The protected area of an NTSC assignment is the geographic area inside the protected service contour where the (50,50) field strength, as predicted using the appropriate effective radiated power (ERP) and a terrain-sensitive propagation model, equals or exceeds the NTSC field strength values as specified in Table G2. Protection is provided within a distance of 89 km for a low VHF regular (R) station, 82 km for a high VHF regular (R) station, 70 km for a Class C UHF station, 45 km for a Class B UHF station, 25 km for a Class A UHF station and 12 km for a low-power (LP) station.

The following table gives the various field strengths of the protected contour for NTSC and DTV assignments or allotments.

Table G2: Contours of DTV and NTSC Assignments
Band (Channels) DTV Field Strength (dBµV/m) NTSC Field Strength (dBµV/m)
Low VHF (2-6) 28 47
High VHF (7-13) 36 56
UHF (14-69) 41 – 20 log(615/F)* 64
* Where F is the channel mid-frequency in MHz.

G2.2 Separation Distances

The separation distances between various services and channel relationships are to be based on the protection ratios of Section G2.3 of this Annex. The interfering field strength at the protected contour shall be based on the F(50,10) propagation statistics in all cases.

The F(50,10) propagation statistics curves can be found in Annex F.

Assignments and allotments that may be a source of interference are identified as a function of distance and channel relationships. Only those assignments or allotments whose distance from the protected station is less than the value given in Table G3 are considered as potential sources of interference.

Table G3: Culling of Undesired Assignments or Allotments
Interfering Channel Offset Relative to Desired Channel Maximum Distance from Protected Station to Interfering Station (km)
–1 200
0 450
+1 200
±2, ±3, ±4, ±7, ±8, +14, +15 135

G2.3 DTV/NTSC System Protection Ratios

The system protection ratios are given as input voltage ratios (D/Uiv) in the following tables.

Table G4: Co-channels
Interference D/Uiv Ratio (dB)
DTV into NTSC 34
NTSC into DTV 2*
*  The D/U ratio for co-channel interference in Table G4 is only valid at locations where the signal-to- noise (S/N) ratio is 25 dB or greater. At the noise-limited bounding contour, where the S/N ratio is 16 dB, the co-channel D/U ratio is 21 dB. At locations where the S/N ratio is greater than 16 dB, but less than 25 dB, D/U values for co-channel interference can be found in Table G5. Use linear interpolation for S/N values between those given in the table.

Table G5: Co-channel D/U Ratios at Various S/N
S/N Ratio (dB) D/Uiv Ratio (dB)
16.00 21.00
16.35 19.94
17.35 17.69
18.35 16.44
19.35 7.19
20.35 4.69
21.35 3.69
22.35 2.94
23.35 2.44
25.00 2.00

This adjustment is made to the co-channel D/U ratios to account for degradation due to increased noise when the S/N ratio is near the limiting value for reception.

Table G6a: Adjacent Channels
Interference D/U iv Ratio (dB)
Lower DTV into NTSC* –14
Upper DTV into NTSC* –17
Lower NTSC into DTV –48
Upper NTSC into DTV –49

* Table G6b: For LPDTV into NTSC, the following D/U ratio applies
Interfering Channel Offset Relative to Protected Channel D/U Ratio (dB)
–1 (Lower Adjacent)
+1 (Upper Adjacent)
for Simple Mask
10
–1 (Lower Adjacent)
+1 (Upper Adjacent)
for Stringent Mask
0
–1 (Lower Adjacent)
+1 (Upper Adjacent)
for Full Mask
−14
−17

Table G7: Other Channel Relationships (UHF Only)
DTV into NTSC (Channel N)
DTV Channel D/Uiv Ratio (dB)
N–2 –24
N+2 –28
N–3 –30
N+3 –34
N–4 –34
N+4 –25
N–7 –35
N+7 –43
N–8 –32
N+8 –43
N+14 –33
N+15 –31

G2.4 Evaluation of Separation Distances

Depending on the relative strength of the two stations involved, separation distances may be based on the protection of the contour on the near side or the far side. The required distance between adjacent channels is based on the near-side value, whereas the required distance between co-channels is based on the maximum of the near side and far side, whichever gives the largest distance. Both cases are calculated at the edge of a circle with a radius distP around the desired station, which corresponds to the existing assignment to be protected. The distP can be computed using the appropriate propagation statistics from Annex F using the Desired (D) field strength as specified in Table G2 of Section G2.1, the overall EHAAT and the maximum ERP of the desired station. If the desired station is an NTSC, one should use the F(50,50) statistics and if it is a DTV, the F(50,90) statistics should be used. The undesired (UNS and UFS) maximum acceptable field strengths for the proposed assignment or allotment are computed with the following formulas:

\[ U_{NS} = D -D/U_{iv} + FB \mbox{ in the near-side case}\]

and

\[ U_{FS} = D - D/U_{iv} \mbox{ in the far-side case}\]
where:
FB is the front-to-back ratio of the receive antenna in dB, given in Table G8;
 
D/Uiv in dB is the system input voltage protection ratio as given in the tables in Section G2.3;
 
D is the desired field strength in dB;
 
UNS is the undesired field strength in dB for the near side; and
 
UFS is the undesired field strength in dB for the far side.

The front-to-back ratios for different bands are given in the table below:

Table G8: Front-to-Back Ratio (dB)
Channels NTSC Station DTV Station
2-6 6 10
7-13 6 12
14-69 6 14

Once the undesired field strength values are computed (UNS and UFS), one can then use the undesired station’s maximum ERP and overall EHAAT, together with the F(50,10) propagation statistics given in Annex F to calculate the minimum required distances between the undesired station and the edges of the circle (distUNS and distUFS).

In order to compute the total required distance to protect the desired station, the radius of the previously defined circle (distP) is then added to distUNS in the near-side case or subtracted from distUFS in the far- side case:

\[ dist_{REQns} = 1.12 \times (dist_{UNS} + dist_{p}) \mbox{   in the near-side case}\] \[ dist_{REQfs} = 1.12 \times(dist_{UFS} - dist_{p}) \mbox{  in the far-side case}\]
where:
distP:
is the radius of the circle computed with the appropriate propagation statistics using the desired (D) field strength (Table G2, Section G2.1 of this Annex), the maximum ERP and the overall EHAAT of the desired station;
 
distUNS:
is the minimum required distance between the undesired station and the near-side edge of the circle, computed with the F(50,10) propagation statistics; and
 
distUFS:
is the minimum required distance between the undesired station and the far-side edge of the circle, computed with the F(50,10) propagation statistics.

Once the far side and the near side distance values are computed using the equations in this Section, one should retain the maximum of the two as the required distance to protect the existing assignment.

As it is also necessary to identify the possibility of interference from the existing assignment to the proposed assignment, the procedure shall be repeated, using the existing assignment (former desired station) as the current undesired station and the proposed assignment as the desired one.

Once both procedures have been repeated, the required distance between the two assignments is the greater of the two calculated distances.

G2.5 Short-Spacing and Interference Analysis

This Section describes the procedure to be followed when the distance between two stations/allotments is less than the required separation distance calculated as described in Section G2.4 of this Annex.

For the interference calculations, the receiving antenna is assumed to have a directional gain pattern, which tends to discriminate against off-axis undesired stations. The receiving antenna pattern for DTV stations is given in Section E3.1 of Annex E. The receiving antenna pattern for NTSC stations has an attenuation, in dB, of MAX(-6, 20log(cos4(θ))), where θ is the angle between the lines joining the desired and undesired stations to the reception point. The transmitting antenna is assumed to have a vertical gain pattern as indicated in Section E3.2 of Annex E.

G2.5.1 Interference Calculations

The interference analysis should be based on a terrain-sensitive method, such as the Longley-Rice model or PREDICT 2.08r2 software, using the appropriate time and location statistics. The area within a station’s protected service contour is normally divided into square cells. The coordinates of the census blocks inside each cell are retrieved along with the population of each block. The census blocks should be based on the 2001 Statistics Canada census data. From this information, the total population and the coordinates of the cell centroid are determined for each cell. It is suggested that a square cell size of 2 km or less on a side be used.

First, the desired field strength is evaluated for each cell within the protected service contour. A radio path between the desired TV transmitter and the population centroid of each cell is examined using a terrain-sensitive propagation model applied for the median situations for 50% of locations, 50% of the time at a receiver antenna height of 10 m above ground. The interference analysis retains only those population cells that have been determined to have desired field strength above the threshold for reception given in Table G2 of this Annex. Radio paths between undesired DTV transmitters and the point representing protected population are examined. For each such radio path, a terrain-sensitive propagation model is applied for median situations for 50% of locations, 10% of the time at a receiver antenna height of 10 m above ground. The terrain elevations data used in the analysis should be based on 3 arc second data from the most recent Canadian Digital Elevation Data (CDED) or United States Geological Survey (USGS). A protected population cell being examined is counted as having interference if the ratio of desired-to-undesired input voltage from each interference source is less than the D/U ratios given in Section G2.3 of this Annex. It should be noted that the comparison is made after applying the discrimination effect of the receiving antenna.

G2.5.2 Calculation of Population Service Loss

The population service loss caused by the new proposal is calculated as:

% Population Service Loss \(= \frac{A}{B} × 100\% \)

Where:
A = the population within the protected area predicted to receive interference from only the new DTV proposal, and
 
B = the population within the protected area