|
To allow the Radiocommunication Bureau to
treat submissions under Article 4 of Appendices 30 and 30A of the Radio
Regulations that have parameters different from those described in
Annexes 5 and 3 of those Appendices, the “Worst Case Approach” has
been developed. It is applied to interference calculations when one
or both signals employ a “non-standard” frequency or bandwidth and the
interfering signal uses analogue modulation.
The “Worst Case
Approach” has been approved by the Radio
Regulations Board (RRB) and has provisional status until relevant ITU-R
Recommendations are available.
A description of the “Worst Case
Approach” is provided below. This methodology is integrated into MSPACEg
software and has been applied by the Bureau in its
technical analyses since 1998.
1.
The “Worst Case Approach”
The “Worst Case Approach” is applied
for calculation of interference from assignments using analogue modulation
involving “non-standard” wanted or interfering assignments.
It is based on the
variation of the relative protection ratio in dB as a linear function of the
overlapping bandwidth. This relative protection ratio is the difference between
the co-channel protection ratio and a protection ratio at a given frequency
offset. It has a purpose similar to the adjustment factor described in ITU-R
Rec. BO.1293-1, but with the opposite sign.
The
following existing technical characteristics/models have been used for the
development of the “Worst Case Approach”:
·
existing protection ratio values for different interfering categories;
·
protection mask provided in Figure 1 of Annex 6 of Appendix 30;
·
protection mask provided in Figure 6 of Annex 5 of Appendix 30;
·
ratios between bandwidth, channel spacing and protection masks’
elements (plateau part[1]
and other parts of the masks);
·
adjustment factor notion as described in ITU-R Recommendation BO.1293-1
2.
The "Worst Case Approach" for the Regions 1 and 3 Plans/Lists
Definitions:
Assuming that:
Fi,
and Fw are the centre frequency values in MHz of the interfering and
wanted channels respectively;
Bi,
and Bw are the frequency bandwidths in MHz of the interfering and wanted
channels respectively;
Ov is the overlapping
bandwidth in MHz between the wanted and interfering channels;
fo
is the frequency
offset/difference in MHz between the wanted and interfering channels;
RelPR
is the relative protection ratio in dB used to protect the wanted channel
against the interfering channel.
2.1 For
WRC-97 Regions 1 and 3 Plan assignments having status “P” and “A”[2] and modifications to
WRC-97 Regions 1 and 3 Plans:
The
overlapping bandwidth Ov (between
wanted and interfering assignments) is defined by the formula:
Ov
= (Bi + Bw) / 2 - | Fi
- Fw |
The
frequency offset/difference limit fol1
corresponding to the limit of the flat part of the protection mask can be
expressed as follows, in the case of the Regions 1 and 3 Plan:
fol1
= 7 * (Bi + Bw) / 27
assuming that the flat part of the
protection mask provided in Figure 1 of Annex 6 of Appendix 30 is based on two
identical interfering and wanted analogue signals using 27 MHz and having a
plateau part of 10 MHz in the case of the relative protection ratio of 0 dB and
of about 14 MHz in the case of the relative protection ratio of -7 dB.
E.g.
in the standard analogue case where Bi=Bw=27 MHz, fol1 = 14 MHz.
The
overlapping bandwidth limit Ovl
corresponding to this frequency offset limit fol1
can be expressed as follows:
Ovl
= 13 * (Bi + Bw) / (2 * 27) in the case of a wanted analogue signal
E.g.
in the standard analogue case where Bi=Bw=27 MHz, Ovl = 13 MHz.
The
above formula defines the width of the flat part of the protection mask and
results in a wider plateau than that of the WARC-77 mask. This formula has been
chosen because it is in accordance with the interference effect produced in this
part of the mask by the increase of the peak-to-peak frequency deviation of both
the wanted and interfering signals which is an implicit consequence of the
adoption of reduced co-channel protection ratios by WRC-97 (i.e. 30/24 dB
instead of 40/31 dB respectively for the feeder-link and downlink Regions 1 and
3 Plans).
However,
although it might not be necessary to have such a wide plateau, for simplicity
and to be consistent with the worst case approach, the width of the plateau was
derived from the WARC-77 protection mask at the -7 dB relative protection ratio
level.
The
width of the plateau resulting from the above definition in the case of signals
with different bandwidths, either wider or narrower, varies in the same
direction as that indicated by the results of the available measurements: i.e.
the plateau is wider in the case of wider bandwidth signals and narrower in the
case of narrower bandwidth signals.
The
linear variation of the relative protection ratio as a function of the
overlapping bandwidth is defined considering that this function f(x)
= a*x + b must pass through the following two points:
(Ovl
MHz, 0 dB) and (7.82 MHz, -8 dB)
0
= a * Ovl + b, and
-8
= a * 7.82 + b
The
resulting relative protection ration RelPR
can be expressed as a function of the overlapping bandwidth Ov as follows:
RelPR
= 0
(dB) for Ovl < Ov
RelPR
= - 8 * (Ov - Ovl) / (7.82 - Ovl)
(dB) for 0 < Ov <= Ovl
The linear function described above can
also be expressed as a linear function of the frequency offset fo
as follows:
RelPR
= - [8 * (14 * (Bi + Bw) / (2 * 27) - |fo|)] /
(7.82 - Ovl) (dB)
The
above formula defines the slope of a protection mask which has a less steep
slope than that of the WARC-77 mask. It has been chosen because it is in
accordance with the effect produced on this part of the mask by the increase of
the peak-to-peak frequency deviation of both the wanted and interfering signals
which is an implicit consequence of the adoption of a reduced co-channel
protection ratio by WRC-97.
The “analogue” approach defined above in the case of the WRC-97 Regions 1 and 3 Plans is applied to deal
with both analogue to analogue and analogue to digital interference situations.
2.2 For
the Plan Assignments Notified, Which Are in Conformity with Appendices 30 and 30A, Brought into Use, and for Which the Date of Bringing into Use Has Been
Confirmed to the Bureau before 27 October 1997 (having status “PE” and
“AE”[3];
so called “existing” systems):
The same definitions
as described in Section 2 above are used.
The formula for the
overlapping bandwidth described in Section 2.1 above is also employed.
The
frequency offset/difference limit fol1
corresponding to the limit of the flat part of the protection masks can be
expressed as follows, in the case existing systems in the Regions 1 and 3
feeder-link or downlink Plans:
fol1
= 5 * (Bi + Bw) / 27
assuming
that the flat part[4] of the protection mask
provided in Figure 1 of Annex 6 of Appendix 30 is based on two identical
interfering and wanted analogue signals using 27 MHz and having a plateau part2
of 10 MHz in the case of the relative protection ratio of 0 dB.
e.g.
in the standard analogue case where Bi=Bw=27 MHz, fol1 = 10 MHz.
The
overlapping bandwidth limit Ovl
corresponding to this frequency offset limit fol1
can be expressed as follows:
Ovl
= 17 * (Bi + Bw) / (2 * 27) in the case of a wanted analogue signal
e.g.
in the standard analogue case where Bi=Bw=27 MHz, Ovl = 17 MHz.
As
with other non-standard cases, the width of the plateau resulting from the above
definition in the case of signals with different bandwidths, either wider or
narrower, varies in the same direction as that indicated by the results of the
available measurements: i.e. the plateau is wider in the case of wider bandwidth
signals and narrower in the case of narrower bandwidth signals.
The
linear variation of the relative protection ratio as a function of the
overlapping bandwidth is defined considering that this function f(x) = a*x + b must pass through the following two points:
(Ovl
MHz, 0 dB) and (7.82 MHz, -19 dB), in the case of existing systems in the
feeder-link Plan; and
(Ovl
MHz, 0 dB) and (7.82 MHz, -16 dB), in the case of existing systems in the downlink
Plan
In
the case of existing systems in the feeder-link Plan, the resulting function is
thus defined as follows:
0
= a * Ovl + b, and
-19
= a * 7.82 + b
In
the case of existing systems in the downlink Plan, the resulting function is
thus defined as follows:
0
= a * Ovl + b, and
-16
= a * 7.82 + b
The
resulting relative protection ration RelPR
can be expressed as a function of the overlapping bandwidth Ov as follows:
In
the case of existing systems in the feeder-link Plan:
RelPR
= 0
(dB) for Ovl < Ov
RelPR
= - 19 * (Ov - Ovl) / (7.82 - Ovl) (dB) for 0 < Ov
<= Ovl
The
slope of the protection mask defined by the second formula above, is steeper
than that of the WARC-77 mask. It has been chosen because it is in accordance
with the decision taken at the WARC-ORB-88 Conference to have a higher
difference between the co-channel and the first adjacent-channel protection
ratios in the case of the feeder-link Plan (40-21 = 19 dB) than in the case of
the downlink Plan (31-15 = 16dB).
The
feeder-link co-channel protection ratio of 40 dB was justified by the limitation
of the effect of the feeder-link path into the downlink path, which should
produce a reduction of 0.5 dB into the downlink co-channel protection ratio of
31 dB, as mentioned in Section 3.2 of Annex 3 of Appendix 30A.
Nevertheless,
the WARC-ORB-88 Conference decided not to apply the same reduction for the first
adjacent channel, which means that a relaxed protection against interference
from this first adjacent channel was assumed.
In
the case of existing systems in the downlink
Plan:
RelPR
= 0
(dB) for Ovl < Ov
RelPR
= - 16 * (Ov - Ovl) / (7.82 - Ovl) (dB) for 0 < Ov
<= Ovl
The
linear function described above can also be expressed as a linear function of
the frequency offset fo as follows:
In
the case of existing systems in the feeder-link Plan:
RelPR
= - [19 * (10 * (Bi + Bw)
/ (2 * 27) - |fo|)] / (7.82 - Ovl) (dB)
In
the case of existing systems in the downlink Plan:
RelPR
= - [16 * (10 * (Bi + Bw)
/ (2 * 27) - |fo|)] / (7.82 - Ovl) (dB)
The
“analogue” approach defined above in
the case of existing systems in the Regions 1 and 3 feeder-link or downlink
Plans is applied to deal with both analogue to analogue and analogue to
digital interference situations.
3.
The "Worst Case Approach" for the Region 2 Plan
The
same definitions as described in Section 2 above are used.
The
formula for the overlapping bandwidth as described in Section 2.1
above is also employed.
The
frequency offset/difference limit fol1
corresponding to the limit of the flat part of the protection mask can be
expressed as follows, in the case of the Region 2 Plan:
fol1
= 8.36/2 * (Bi + Bw) / 24 = 4.18 * (Bi + Bw)
/ 24
assuming
that flat part[5]
of the protection mask provided in Figure 6 of Annex 5 of Appendix 30 is based
on two identical interfering and wanted analogue signals using 24 MHz and having
a plateau part2 of 8.36 MHz in the
case of the relative protection ratio of 0 dB.
E.g.
in the standard analogue case where Bi=Bw=24 MHz, fol1 = 8.36 MHz.
The
overlapping bandwidth limit Ovl1
corresponding to this frequency offset limit fol1
can be expressed as follows:
Ovl1
= (24-8.36) * (Bi + Bw) / (2 * 24) in the case of a wanted analogue signal
E.g.
in the standard analogue case where Bi=Bw=24MHz, Ovl = 15.64 MHz.
The
width of the plateau resulting from the above definition in the case of signals
with different bandwidths, either wider or narrower, varies in the same
direction as that indicated by the results of the available measurements: i.e.
the plateau is wider in the case of wider bandwidth signals and narrower in the
case of narrower bandwidth signals.
The
first linear variation of the relative protection ratio as a function of the
overlapping bandwidth is defined considering that this first function f1(x)
= a1*x + b1 must pass through the following two points from the formulae
associated to Figure 6 of Annex 5 of Appendix 30:
(Ovl1
MHz, 0 dB) and (Ovl2 MHz, -12.45694 dB),
where: Ovl2 = (24-12.87)
* (Bi + Bw) / (2 * 24)
0
= a1 * Ovl1 + b1
and
-12.45694
= a1 * Ovl2 + b1
Similarly,
the second linear function f2(x) = a2*x +
b2 must pass through the following two points:
(Ovl2’
MHz, -12.45198 dB) and (Ovl3 MHz, -22.1225 dB)
where: Ovl3 = (24-21.25)
* (Bi + Bw) / (2 * 24)
-12.45198
= a2 * Ovl2 + b2
-22.1225
= a2 * Ovl3 + b2
Similarly,
the third linear function f3(x) = a3*x +
b3 must pass through the following two points:
(Ovl3’ MHz, -22.12 dB) and (Ovl4
MHz, -37.94 dB)
where: Ovl4 = (24-29.16)
* (Bi + Bw) / (2 * 24)
-22.12
= a3 * Ovl3 + b3
-37.94
= a3 * Ovl4 + b3
The resulting
relative protection ration RelPR can
be expressed as a function of the overlapping bandwidth Ov
as follows:
RelPR
= 0
(dB)
for Ovl1 < Ov
RelPR
= - 12.45694 * (Ov - Ovl1) / (Ovl2 - Ovl1) (dB)
for Ovl2 < Ov <= Ovl1
RelPR
= - (22.1225-12.45198) * (Ov - Ovl2) / (Ovl3 - Ovl2)-12.45198 (dB) for Ovl3 <
Ov <= Ovl2
RelPR
= - (37.94-22.12) * (Ov - Ovl3) / (Ovl4 - Ovl3)-22.12 (dB)
for Ovl4 <= Ov <= Ovl3
The
slope of the mask resulting from the above definition in the case of signals
with different bandwidths varies in the same direction as that indicated by
available measurements: i.e. the slope is less steep for wider bandwidth signals
and is more steep for narrower bandwidth signals.
The
“analogue” approach defined above in the case of the Region 2 Plan will be
applied to deal with both analogue to analogue and analogue to digital
interference situations.
The
relative protection ratio, described above, has to be associated with the Region
2 Protection Ratios defined in Section 3.4 of Annex 5 of Appendix 30 and
derived from the template in Figure 6. However, in order to maintain the level
of accuracy provided by the formulae, which describes the template in Figure 6
of Annex 5 of Appendix 30, it is required to calculate the Region 2 Protection
Ratio values with a higher precision. MSPACEg software (since version 1.90)
applies the following protection ratio values, derived from this Figure:
28
dB for co-channel signals;
13.57468
dB for adjacent-channel signals;
-9.94
dB for second adjacent-channel signals.
[1]
Corresponds
to the part of the signal where the spectral power density has an almost
constant maximum value.
[2]
See Articles 11 and 9A of Appendices 30 and 30A respectively.
[3]
See Articles 11 and 9A of Appendices 30 and 30A respectively.
[4]
Corresponds to the part
of the signal where the spectral power density has an almost constant
maximum value
[5]
Corresponds to the part
of the signal where the spectral power density has an almost constant
maximum value.
|
