# SECTION 6 Analysis of Interference Potential to Various Services {#section-6-analysis-of-interference-potential-to-various-services .unnumbered}

## INTRODUCTION

The potential impact of a single access BPL device to representative
ground-based federal receivers is examined in this section, as is the
impact of multiple co-frequency BPL devices on in-flight aeronautical
receivers. Because of the wide range of federal systems that are of
concern, representative systems in the fixed, land-mobile, maritime and
aeronautical services were chosen for analysis.[^1] The criteria for
evaluating the risk of interference are defined in terms equivalent to
moderate and high potential risk levels.

## 6.2 METHODOLOGY {#methodology .unnumbered}

It was assumed that the BPL systems conform to Part 15 field strength
limits using existing BPL compliance measurement practices. Analyses of
potential interference to fixed, land-mobile and maritime mobile
services used the same methodology. For distances less than one
kilometer, a NEC-4.1 model of a three-phase power line driven with a
single source was used to estimate electric field strengths, from which
received BPL interfering signal power was derived. Analyses of potential
interference to aeronautical systems followed a somewhat different
approach. An analytical model was developed using a Matlab software
shell. In this time simulation, an aircraft operating an aeronautical
mobile receiver was flown over and near a BPL deployment area. BPL
signal levels were calculated with the aircraft either approaching or
directly above the service area.

For all services, the calculated received BPL signal power was used with
median background noise values to determine expected (I+N)/N
characteristics at the potential radio receiver sites. This parameter
was used to illustrate the effective increases in the radio receiver
noise power level due to the combination of BPL interfering signals and
noise. Calculations were performed at 4 MHz, 15 MHz, 25 MHz and 40 MHz
using the same type of BPL system and power line configuration, but in
the case of potential interference to aircraft radios, the power lines
were randomly oriented.

In these interference calculations, it was recognized that the Part 15
field strength limits are defined in terms of quasi-peak and, as used in
interference analyses, the power levels for noise are root mean square
(rms) values. Consequently, to compute a valid ratio of the two, or more
specifically the power ratio (interference-plus-noise)-to-noise,

(I + N)/N, a quasi-peak-to-rms conversion factor should be applied to
the interfering signal power levels so that I and N both are specified
as rms values. From a theoretical standpoint, the conversion factor for
a pure sinusoidal signal is zero dB, whereas for a non-frequency-agile
pulse-like signal having a uniform pulse repetition rate, quasi‑peak
levels can exceed rms by about 10 dB. BPL signals are expected to fall
between these two extremes depending on their duty cycle. Limited
measurements documented in Appendix D (See Section D.3.4) for a system
employing OFDM modulation, show the conversion factor from quasi‑peak to
rms to be in the range of 0 to 5 dB. For this preliminary study,
quasi-peak values were assumed to exceed rms values by 5 dB. Further
study of this factor is needed.

## RISK EVALUATION CRITERIA

### **Interfering Signal Thresholds**

A given level of unwanted (interfering) signal power may cause
interference ranging from barely perceptible to harmful levels depending
on the magnitude of environmental and equipment noise, the desired
signal level, as well as the temporal variability of each of these
parameters.[^2] Because these and several underlying parameters may vary
substantially among locations and over time, the level of interference
caused by BPL systems is both temporally and spatially stochastic. Other
important considerations are whether the radio system is operating
continuously or only occasionally (*e.g.*, as a back-up means of
communications) and the speed with which harmful interference can be
eliminated should it occur. These considerations relate to risk
tolerance.

If the received desired signal is consistently very much more powerful
than the noise and unwanted BPL signals, interference will not occur and
receiver performance is dictated by the ratio of desired signal to noise
power. Likewise, if the received unwanted BPL signal is very weak in
relation to environmental noise power, it is unlikely to cause
interference and receiver performance is dictated by desired signal and
noise power levels. It is instructive to consider both permutations of
variables for evaluation of BPL interference risks, namely, the ratio of
received BPL signal power to noise power under conditions of strong and
weak desired signal levels. As shown in Equations 6-1 through 6-3,
below, this interference-to-noise power ratio (I/N) relates directly to
an increase in the receiver noise floor or a reduction in the ratio of
desired signal-to-total noise (*i.e.*, the ratio (N+I)/N or -S/N).

  ---------------------------------- ------- ------------------ -----------------
  S/N = -(N+I)/N =                   (6-1)                      
  -10log(10^0.1(I/N)^ + 1)                                      

  S/N -(I/N), for I/N \> 6 dB                (6-2)              

  I/N F~u~ - F­­~am~, F­­~am~ \>\>                                  (6-3)
  receiver system noise figure                                  
  ---------------------------------- ------- ------------------ -----------------

where:

> *S/N* is the change in signal-to-noise power ratio (dB) caused by the
> unwanted\
> signal (always a negative number corresponding to a reduction of S/N);
>
> *I/N* is the ratio of unwanted signal power to total receiver system
> noise power\
> (dB), with power levels measured in the same reference bandwidth;
>
> *F~u~* is the field strength of the BPL signal (dB(V/m)); and
>
> *F­­~am~* is the total field strength of all environment radio noise
> (dB(V/m)).

In order to minimize potential interference and promote efficient reuse
of assigned and adjacent frequencies, by treaty, radio transmission
systems should not radiate substantially more power than what is needed
to fulfill communications requirements.[^3] For most frequency sharing
situations, it is well established in international and domestic
spectrum management practices to generally limit interfering signal
levels in a manner that preserves good control over radio system
performance by designers and operators (*e.g.*, (I+N)/N = 0.5 or 1 dB).
However, for the interference risk evaluation herein, the focus is on
risks under the most typical situations (*i.e.*, the statistical mode of
possible scenarios). Less favorable situations are not considered,
*e.g.*, where desired signals are near the minimum levels needed to
fulfill performance objectives. Thus, in general, it is assumed herein
that substantial and perhaps harmful interference will occur in a high
percentage of cases if the (I+N)/N ratio exceeds 10 dB (a factor of 10).
It is assumed that substantial interference will occur in a smaller but
still significant percentage of cases if (I+N)/N is 3 dB (a factor of 2,
or a doubling of the \"noise floor\" of the receiver). There is still a
small probability that interference will occur with (I+N)/I of 1 dB or
less (I/N of -6 dB or less) and, at the least, unwanted signals at these
levels manifest interference during signal fading (*i.e.*, reductions in
communications availability). In this phase of study, the extent of
geographic areas associated with various levels of (I+N)/N are
determined. Levels of (I+N)/N of 3 dB and 10 dB are considered as
important interference risk thresholds because these levels relate to
moderate and high likelihood of interference, respectively, for unknown
levels of desired signal power.

To put the 3 dB and 10 dB (I+N)/N levels (S/N reductions) in
perspective, Figure 6-1 illustrates the S/N reduction caused by an
unwanted signal at the Part 15 limit level. Figure 6-1 shows that in an
environment having the typical median noise power level of a residential
environment (Kansas City, MO), field strength at the Part 15 limit would
reduce the S/N by over 15 dB.

![](media/image1.wmf){width="5.991666666666666in"
height="2.4972222222222222in"}

**Figure 6-1: Change in Receiver Signal-to-Noise Power Ratio Caused By
Unintentional Emissions at the Part 15 Limit**[^4]

To illustrate the extent of area in which (I+N)/N is greater than or
equal to 3 dB, Figure 6-2 depicts the range of separation distances
generally needed between a receiving antenna and one Part 15 device
acting as a single-point source and radiating power toward the antenna
at a level that exactly complies with the Part 15 field strength limit.
As noted above, actual BPL system radiating characteristics will be
considered in the interference risk analysis, and so, radiation at the
level of the present Part 15 limits would occur only in the direction(s)
of peak radiation.

![](media/image2.wmf){width="5.991666666666666in" height="2.5in"}

**Figure 6-2: Distance at which external noise levels equal FCC Part
15**

**radiated emission limits (Class B)**[^5]

### **Noise Calculations**

For the purposes of this study, ambient background noise was calculated
using the Institute for Telecommunication Science's NOISEDAT computer
program.[^6] This program implements the data contained in the ITU-R
Rec. P.372-8 discussed in section 5.4.4. Noise was calculated for a
centrally-located geographic point (Kansas City, Kansas.) for all times
of the day and seasons of the year under residential conditions. From
this data, the median noise levels at each frequency of interest were
used as background noise for (I+N)/N calculations. The one exception to
this regime for the noise power levels used for off-shore ship station
calculations, for which noise data at a location off the Atlantic coast
near Wallops Flight Facility in Virginia under "quiet rural" conditions
was used.

After adjusting for a single-sideband (SSB) receiver noise bandwidth of
2.8 kHz for frequencies less than 30 MHz and a bandwidth of 16 kHz for
frequencies greater than 30 MHz, the noise power levels listed in Table
6-1 were used.

Table 6-1: Noise power values for (I+N)/N calculations.

+---------------+------------+---------+---------+---------+---------+
| **Service**   | **Location | **Noise |         |         |         |
|               | and        | Power,  |         |         |         |
|               | Co         | dBW     |         |         |         |
|               | nditions** | (N~     |         |         |         |
|               |            | dBW~)** |         |         |         |
+---------------+------------+---------+---------+---------+---------+
|               |            | **4     | **15    | **25    | **40    |
|               |            | MHz**   | MHz**   | MHz**   | MHz**   |
+---------------+------------+---------+---------+---------+---------+
| Land          | 39.12 N,   | -111.3  | -128.8  | -135.6  | -134.3  |
| Stations[^7]  |            |         |         |         |         |
|               | 94.62 W,   |         |         |         |         |
|               |            |         |         |         |         |
|               | R          |         |         |         |         |
|               | esidential |         |         |         |         |
+---------------+------------+---------+---------+---------+---------+
| Ship Stations | 37.69 N,   | -119.3  | -136.9  | -150.0  | -147.5  |
|               |            |         |         |         |         |
|               | 75.25 W,   |         |         |         |         |
|               |            |         |         |         |         |
|               | Quiet      |         |         |         |         |
|               | Rural      |         |         |         |         |
+---------------+------------+---------+---------+---------+---------+

## INTERFERENCE MODELS

NEC modeling for this report was used to derive electric field strength
and far-field radiation patterns due to a power line energized by a
single BPL device. Electric field strength levels generated by the
simulated BPL system in areas where the representative ground-based
receivers typically operate were evaluated statistically.

### **Receiving Systems**

Representative systems from the land-mobile, fixed, maritime and
aeronautical services were chosen, and system characteristics were
subsequently used in interference calculations. Various parameters from
all the chosen systems are listed in Table 6-2.

Table 6-2: Receive system characteristics used in interference study.

+--------------------+----------+------------+-----------+------------+
| **Receiver         | *        |            |           |            |
| Characteristics**  | *STATION |            |           |            |
|                    | TYPE**   |            |           |            |
| **(2-30 MHz)**     |          |            |           |            |
+====================+==========+============+===========+============+
|                    | **Fixed  | **Land     | *         | **Aero     |
|                    | and      | Mobile**   | *Maritime | nautical** |
|                    | Land**   |            | Mobile**  |            |
+--------------------+----------+------------+-----------+------------+
| Bandwidth (kHz)    | 2.8      | 2.8        | 2.8       | 2.8        |
+--------------------+----------+------------+-----------+------------+
| Modulation         | J3E      | J3E        | J3E       | J3E        |
+--------------------+----------+------------+-----------+------------+
| Antenna Type       | Ho       | Vertical   | Vertical  | Vertical   |
|                    | rizontal | whip       | whip      | whip       |
|                    | dipole   |            |           |            |
+--------------------+----------+------------+-----------+------------+
| Antenna Height (m) | 42.7     | 2          | 9         | 6, 9, & 12 |
|                    |          |            |           | km         |
+--------------------+----------+------------+-----------+------------+
| Antenna Length (m) | 24.4     | 3          | 4         | 3          |
+--------------------+----------+------------+-----------+------------+
| Polarization       | Ho       | Vertical   | Vertical  | Vertical   |
|                    | rizontal |            |           | or         |
|                    |          |            |           | horizontal |
+--------------------+----------+------------+-----------+------------+
| Noise Environment  | Res      | R          | Quiet     | R          |
|                    | idential | esidential | Rural     | esidential |
+--------------------+----------+------------+-----------+------------+
| Antenna Gain       | 0        | -4.8 @ 4   | 0         | 0          |
| (towards horizon)  |          | MHz        |           |            |
| dBi                |          |            |           |            |
|                    |          | -0.9 @ 15  |           |            |
|                    |          | MHz        |           |            |
|                    |          |            |           |            |
|                    |          | 0.3 @ 25   |           |            |
|                    |          | MHz        |           |            |
+--------------------+----------+------------+-----------+------------+
| Horizontal         | 0-4 km   | 0-4 km     | 0-4 km    | 0-50 km    |
| distance from BPL  | from     | from       | from      | from       |
|                    | single   | single BPL | single    | center of  |
|                    | BPL      | emitter    | BPL       | BPL        |
|                    | emitter  |            | emitter   | service    |
|                    |          |            |           | area       |
+--------------------+----------+------------+-----------+------------+
| Interference       | 3 & 10   | 3 & 10 dB  | 3 & 10 dB | 3 & 10 dB  |
| Criteria (I+N)/N   | dB       |            |           |            |
+--------------------+----------+------------+-----------+------------+
| **Receiver         |          |            |           |            |
| Characteristics**  |          |            |           |            |
|                    |          |            |           |            |
| **(30-50 MHz)**    |          |            |           |            |
+--------------------+----------+------------+-----------+------------+
| Bandwidth (kHz)    | 16       | 16         | 16        | 16         |
+--------------------+----------+------------+-----------+------------+
| Modulation         | F3E      | J3E        | J3E       | J3E        |
+--------------------+----------+------------+-----------+------------+
| Antenna Type       | Vertical | Vertical   | Vertical  | Vertical   |
|                    | whip     | whip       | whip      | blade      |
+--------------------+----------+------------+-----------+------------+
| Antenna Height (m) | 42.7     | 2          | 9         | 6, 9, & 12 |
|                    |          |            |           | km         |
+--------------------+----------+------------+-----------+------------+
| Antenna Length (m) | 6        | 2          | 2         | 2          |
+--------------------+----------+------------+-----------+------------+
| Polarization       | Vertical | Vertical   | Vertical  | Vertical   |
+--------------------+----------+------------+-----------+------------+
| Noise Environment  | Res      | R          | Quiet     | R          |
|                    | idential | esidential | Rural     | esidential |
+--------------------+----------+------------+-----------+------------+
| Antenna Gain       | 3        | 2          | 2         | 0          |
| (towards horizon)  |          |            |           |            |
| dBi                |          |            |           |            |
+--------------------+----------+------------+-----------+------------+
| Horizontal         | 0-4 km   | 0-4 km     | 0-4 km    | 0-50 km    |
| distance from BPL  | from     | from       | from      | from       |
|                    | single   | single BPL | single    | center of  |
|                    | BPL      | emitter    | BPL       | BPL        |
|                    | emitter  |            | emitter   | service    |
|                    |          |            |           | area       |
+--------------------+----------+------------+-----------+------------+
| Interference       | 3 & 10   | 3 & 10 dB  | 3 & 10 dB | 3 & 10 dB  |
| Criteria (I+N)/N   | dB       |            |           |            |
+--------------------+----------+------------+-----------+------------+

### **Power Line Model**

The NEC power line model used in these analyses consisted of three
parallel straight wires, each 340 meters long, spaced in a horizontally
parallel configuration 0.6 meters apart. The three wires were given
conductivity characteristics equal to copper wire and AWG 4/0 diameter.
They were placed 8.5 meters above a "Sommerfeld" ground with average
characteristics (relative permittivity ~r~ = 15, conductivity = .005
Siemens/meter) to simulate land-mobile and fixed service conditions, and
above a Sommerfeld ground with saltwater characteristics (relative
permittivity ~r~ = 81, conductivity = 5 Siemens/meter) to simulate power
lines along a coast line for maritime conditions. One of the outer power
lines was center-fed using a voltage source to simulate the BPL coupler.
The source was set to provide 1 volt. The source impedance (modeled by
serially loading the segment upon which the source was placed) was given
a real impedance of 150 Ω.

The ends of the long wires were connected together at each end by
inter-phase loads of 50 Ω each (wires 1 and 2 and wires 2 and 3 were
connected in this manner) to simulate a degree of system loading and
discontinuity.

The wires used for this model were segmented following recommendations
from Lawrence Livermore National Laboratories NEC documentation.
Specifically, segment length was set to provide 20 segments per
wavelength at the desired frequency, rounded up to an odd number of
segments. This resulted in 340-meter-long wires consisting of 91, 341,
567 and 907 segments each for 4 MHz, 15 MHz, 25 MHz and 40 MHz,
respectively. Convergence testing (by increasing the number of segments
for each frequency) and average gain testing indicated good model
stability and behavior.

## INTERFERENCE CALCULATIONS

### **Scaling Output Power to Meet FCC Part 15 Limits**

FCC Part 15 measurement procedures generally follow American National
Standards Institute (ANSI) publication C63.4-1992, which specifies
measurements with both vertical and horizontal polarization. To ensure
the modeled radiation from the wires met FCC Part 15 limits consistent
with existing BPL measurement practices, initial NEC runs were executed
to find the expected electric field in the x-, y- and z-vector
directions at a height of one meter above the ground, 30 meters away
from the wire on which the voltage source was placed, for 4 MHz, 15 MHz
and 25 MHz, and at a distance of 3 meters away at 40 MHz. The rms values
of the NEC-calculated electric field x, y and z-vectors would be found
in a straightforward manner, assuming a sinusoidal BPL test signal, as
shown in the following equation.

  ------------------------------------------------------------------------------------------------------------------ -------------------------
  $E_{x} = \frac{E_{\circ x}}{\sqrt{2}},E_{y} = \frac{E_{\circ y}}{\sqrt{2},}E_{z} = \frac{E_{\circ z}}{\sqrt{2}}$   (6-4)

  ------------------------------------------------------------------------------------------------------------------ -------------------------

> *where*
>
> *E~ox~*, *E~oy~*, *E~oz~* are the magnitudes of the NEC-calculated x-,
> y- and z-vector\
> electric-fields

The calculated electric field values were then divided by the FCC Part
15 limits (30 V for frequencies less than 30 MHz, 100 V for frequencies
greater than 30 MHz), and the maximum such value found along the line in
any vector was used to scale all subsequent electric field calculations.
Because measured quasi-peak values of field strength are expected to be
near or slightly exceed the above rms values (see Appendix D, Section
D.3.4), this scaling process may yield adjusted field strength values
slightly in excess of values needed for compliance using a quasi-peak
detector. The purpose of this exercise was to ensure the radiated signal
complied with FCC Part 15 limits for each frequency.

### **Analysis Methodology for Land-Mobile, Fixed and Maritime Services**

After the initial "scaling" runs, NEC simulations were performed to find
the spatial distribution of electric field strength values. The
calculations were made for a geographic grid of points with 5 meter
spacing along and away from the line to a distance of 1 km, at heights
of 2 meters, 42.7 meters and 9 meters to simulate land mobile vehicle,
mobile-base/fixed and ship antennas, respectively. This grid included
points lateral to the power lines and excluded points off the end of the
modeled power line, as it was felt that the arbitrary ending of the
power line at both ends of the power line layout would yield unrealistic
radiation properties in nearby areas. The NEC simulations indicated
substantial radiation off the ends of the line, and real-world power
lines do indeed terminate at many points.

Electric field values were calculated using NEC's ground wave capability
for distances greater than one kilometer from the line. These values
were calculated in cylindrical coordinates, meaning values were found
for a given distance and height in a circle around the power line model.
Values were calculated in 5-degree increments at distance increments of
100 meters from 1 km to 4 km, at the same antenna heights used for
near-field calculations.

In addition to the above NEC runs, a "close-in" simulation was completed
to gather fine detail along the line at land-mobile antenna height (two
meters). This was done to determine the degree of potential interference
expected to be found on streets next to power line runs. This "close-in"
run was done using NEC's near-field facility on a grid with 0.5 meter
spacing out to a distance of 15 meters from the line.

Once calculated, the electric field values were scaled and the relevant
real field value (E~x~ for the vertical land mobile antenna, E~y~ and
E~z~ for horizontal fixed and maritime antennas) was translated into
received interfering signal power as follows:

  -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ------------------------
  $\begin{array}{r}                                                                                                                                                                                        (6-5)
  P_{\left( \text{dBW} \right)} = \text{20} \cdot \text{Log}_{\text{10}}\left( E_{V/m} \right) - \text{20} \cdot \text{Log}_{\text{10}}\left( F_{\text{MHz}} \right) + G_{r\left( \text{dBi} \right)} \\   
   + \text{10} \cdot \text{Log}_{\text{10}}\left( \text{BW} \right) + \text{10} \cdot \text{Log}_{\text{10}}(\varphi) + \delta + \text{12}\text{.}8                                                        
  \end{array}$                                                                                                                                                                                             

  -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ------------------------

> *where*
>
> *E~V/m\ ~*is the received signal strength in V/m
>
> *F~MHz\ ~*is the measurement frequency in MHz
>
> *G* is the gain of the receiving antenna
>
> *BW* is the ratio of receiver to measurement bandwidth
>
> is the average duty cycle
>
> is a quasi-peak to rms measurement factor

For the purposes of this study, the *average duty cycle* () was taken to
be 55%, which was midway between an always-on (100%) downstream signal
and an intermittent (10%) upstream customer-to-internet signal.
Additionally, to compensate for differences between ambient noise levels
expressed in rms values and BPL signal radiation measured using
quasi-peak detection, a *measurement factor* () adjustment of -2 dB was
applied to the calculated received BPL signal power.

From the received signal power and the background noise, the (I+N)/N
ratio was calculated at each point in the assumed receiver operating
areas:

  ------------------------------------------------------------------------------------------------------------------------------------------------------- --------------------------
  $(I + N)N = \text{10} \cdot \text{Log}_{\text{10}}\left\lbrack 1 + \text{10}^{\left( P_{\text{dBW}} - N_{\text{dBW}} \right)\text{10}} \right\rbrack$   (6-6)

  ------------------------------------------------------------------------------------------------------------------------------------------------------- --------------------------

Once these calculations were complete, the percentages of locations for
each distance value (near field and ground wave calculations) or in
areas around the BPL-energized line (for close-in land-mobile
situations) exceeding given (I+N)/N values were determined.

### **Analysis Methodology for Aeronautical Service**

In order to calculate interference to an aircraft receiver, several
parameters were defined:

-   BPL service area: circular area of 10 km radius (6.2 miles)

-   Number and density of co-channel BPL transmitters: 1200, 300, and 75
    deployed over an area of 314 km^2^, with approximately 0.5, 1, and 2
    km separation between units, respectively

-   BPL unit radiated power:

```{=html}
<!-- -->
```
-   For 4 MHz: -69.8dBW/2.8 kHz

-   For 15 MHz: -67.3dBW/2.8 kHz

-   For 25 MHz: -64.9dBW/2.8 kHz

    -   For 40 MHz: -81.1dBW/16.0 kHz

BPL device output power was derived from the NEC scaling runs.
NEC-calculated power line input power was scaled by the square of the
scaling factor for each frequency, as well as by the ratio between the
receiver and measurement bandwidths.

Additionally, NEC was used to find the far-field directional gain
pattern from the modeled power lines for all frequencies of interest.
Simulations were run using the directional gain pattern in azimuthal
directions both parallel and perpendicular to the main radiation lobe of
the power line. The average directional gain levels for each elevation
were found for the two patterns (Figure 6-3) used in the analysis.

![](media/image3.wmf){width="5.998611111111111in"
height="3.4993055555555554in"}

Figure 6-3: Average far field directional gain antenna patterns used for
aeronautical interference calculations.

As mentioned previously, a Matlab model was used to simulate an aircraft
at various heights and horizontal distances from the centroid of a BPL
deployment area. This model simulated the signal effects of multiple BPL
devices in different deployment cells at the aircraft location.

As with interference calculations for the other services, several
additional factors were taken into account. Two of these, duty cycle ()
and quasi-peak to rms measurement factor () were discussed in subsection
6.3.2, and the same values were used here (55% and -2 dB, respectively).
An additional adjustment factor, *polarization mismatch*, was used with
aeronautical service calculations. This factor was designed to
compensate for the fact that the aeronautical service antenna used in
this simulation was vertically polarized, whereas the BPL structure was
horizontally polarized. Both structures interacted with radiation of the
opposite polarization in NEC simulations. For example, the BPL structure
produced significant (or even primary) radiation that was vertically
polarized in most azimuthal directions. Further, over a significant
number of azimuthal directions, the short aeronautical antenna could be
expected to respond well to both horizontally- and vertically-polarized
radiation. Nonetheless, for a small number of orientations a
cross-polarization effect would likely reduce coupling between the BPL
structure and the receiving antenna. In order to account for this
effect, an overall decrease of 1 dB in the received BPL signal was
assumed.

## RESULTS OF INTERFERENCE CALCULATIONS

### **Land-Mobile Service**

Calculations of close-to-the-line interference potential for vehicular
land-mobile receivers due to a BPL transmitter operating at FCC Part 15
limits show that there would be significant increases in the noise floor
due to interference. As can be seen in

Table 6-3, for frequencies less than 30 MHz, virtually all points close
to the line would experience (I+N)/N levels greater than 10 dB. In other
words, there would be at least a ten-fold increase in total receiver
noise power on the street adjacent to the BPL device and power lines. At
40 MHz, a majority of the areas in a road along the power line would see
this level of interference.

Table 6-3: Percent of points exceeding specified interference level, by
frequency, for land-mobile receiver system within 15 meters of a
BPL-energized power line. Radiated power and noise are into a 2.8 kHz
bandwidth for 4 MHz, 15 MHz and 25 MHz, and a 16 kHz bandwidth at 40
MHz.

  ------------- ------------ --------- ----------- ----------- ----------- ----------- ----------- -----------
  **Frequency   **Radiated   **Noise   **3 dB      **10 dB     **20 dB     **30 dB     **40 dB     **50 dB
  (MHz)**       Power        (dBW)**   (I+N)/N**   (I+N)/N**   (I+N)/N**   (I+N)/N**   (I+N)/N**   (I+N)/N**
                (dBW)**                                                                            

  4             -69.8        -111.3    99.3%       93.2%       54.7%       6.2%        0.0%        0.0%

  15            -67.3        -128.8    99.8%       99.7%       95.7%       59.5%       4.3%        0.0%

  25            -64.9        -135.6    99.8%       99.0%       92.1%       58.5%       18.5%       0.0%

  40            -81.1        -134.3    87.9%       49.2%       10.0%       0.0%        0.0%        0.0%
  ------------- ------------ --------- ----------- ----------- ----------- ----------- ----------- -----------

The increases in the noise floor a land-mobile system might encounter
along a BPL-energized power line are further illustrated in Figure 6-4.
In this figure, (I+N)/N values are depicted using colors from red to
blue, with dark red representing 50 dB and dark blue representing zero.

It can be inferred from these calculations that a vehicle-mounted HF
receiver operating in a residential environment on a roadway adjacent to
a BPL-energized power line may experience harmful interference,
depending upon the frequency, the distance along the line away from the
BPL transmitter, the BPL transmitter duty cycle and the number of BPL
devices on the line.

![](media/image4.png){width="6.0in" height="0.53125in"}

![](media/image5.png){width="6.0in" height="0.53125in"}

![](media/image6.png){width="6.0in" height="0.53125in"}

![](media/image7.png){width="6.0in" height="0.53125in"}

Figure 6-4: (I+N)/N values around the modeled power line, to a distance
of 15 meters. Colors

represent a range from zero dB (dark blue) to 50 dB (dark red). a) 4
MHz. b) 15 MHz. c) 25 MHz. d) 40 MHz. The BPL structure is denoted with
a dark horizontal line in the center of each plot.

Near-field calculations of interference levels stemming from a single
BPL device, out to a distance of one kilometer from the power line,
indicated a sharp falloff in the level of interference with distance. As
shown in Figure 6-5, out to distances on the order of 120 meters from
the power line, a land-mobile receiver operating in the modeled noise
environment could experience interference.

Ground wave calculations of interference levels at a distance from one
to four kilometers were in good agreement with those for the near field.
Results at a nominal one kilometer near-field/ground-wave juncture were
well-matched. In no areas adjacent to, and more than 120 meters from the
power lines would the modeled land-mobile system be likely to experience
significant interference from a single BPL transmitter operating at FCC
Part 15 limits.

![](media/image8.wmf){width="5.991666666666666in"
height="3.4305555555555554in"}

![](media/image9.wmf){width="5.991666666666666in"
height="3.410416666666667in"}

Figure 6-5: Percent of near-field points, by distance, where a
land-mobile receiver would see the specified (I+N)/N levels due to a BPL
transmitter operating at Part 15 limits. a) 4 MHz. b) 15 MHz.

![](media/image10.wmf){width="5.991666666666666in"
height="3.410416666666667in"}

![](media/image11.wmf){width="5.991666666666666in"
height="3.4166666666666665in"}

Figure 6-5 continued: c) 25 MHz. d) 40 MHz.

### **Fixed Service**

NEC interference calculations for an assumed fixed service or mobile
base station receiving antenna found substantial (I+N)/N values at
greater distances from the line than those found for land mobile
receivers. This was especially true at 15 and 25 MHz.

The near field results are depicted in Figure 6.6. As can be seen, at 15
MHz the potential for a 3dB (I+N)/N level exists beyond 500 meters away,
and at 25 MHz some locations more than 700 meters away could see this
level of interference. Additionally, locations past 300 and 400 meters
from the BPL-energized line on 15 MHz and 25 MHz, respectively, could
experience (I+N)/N levels in excess of 10 dB.

The differences in potential interference found with different
frequencies are partly due to the ambient noise floor decreases as the
frequency is increased. However, the increased gain of the modeled
antenna with frequency also plays a part, which means that higher gain
antennas and lower-noise areas could face greater risks of interference
at lower frequencies. Likewise, receivers with lower-gain antennas and
high-noise environments would likely experience less degradation in the
noise floor, but would likely also see a reduced S/N. This is true for
all of the services modeled.

### **Maritime Service**

As noted previously, the calculations for a ship receiver differed from
the fixed and land-mobile services in two important respects: the use of
lower ambient noise levels and the use of salt-water ground
characteristics. This model assumed a power line running along the
shoreline, and the ship receiver possibly in a bay or harbor.

Results for the simulated maritime receiver were similar to those for
the fixed service receiver. Substantial areas near the shore (near
field) would likely see greater than 3 dB increases in the noise floor.
As with the other services, this effect would be most pronounced at 25
MHz with the assumed power lines. According to the calculations, a
single BPL device could S/N at 25 MHz by 3 dB for more than 50% of
points within 100 meters of the shore (Figure 6-7).

Despite the lower noise levels seen by the simulated system at distances
greater than one kilometer from shore, calculations indicated that at no
point would the simulated system experience (I+N)/N levels greater than
3 dB.

![](media/image12.wmf){width="5.998611111111111in"
height="3.410416666666667in"}

![](media/image13.wmf){width="5.995833333333334in"
height="3.3916666666666666in"}

Figure 6-6: Percent of near-field points, by distance, where a fixed
receiver would see the specified (I+N)/N levels due to a BPL transmitter
operating at FCC Part 15 limits. a) 4 MHz. b) 15 MHz.

![](media/image14.wmf){width="5.998611111111111in"
height="3.4034722222222222in"}

![](media/image15.wmf){width="5.995833333333334in"
height="3.4118055555555555in"}

Figure 6.6 continued: c) 25 MHz. d) 40 MHz.

![](media/image16.wmf){width="5.991666666666666in"
height="3.4305555555555554in"}

![](media/image17.wmf){width="5.991666666666666in"
height="3.410416666666667in"}

Figure 6-7: Percent of near-field points, by distance, where a maritime
receiver would see the specified (I+N)/N levels due to a BPL transmitter
operating at FCC Part 15 limits. a) 4 MHz. b) 15 MHz.

![](media/image18.wmf){width="5.991666666666666in"
height="3.410416666666667in"}

![](media/image19.wmf){width="5.991666666666666in"
height="3.4166666666666665in"}

Figure 6-7 continued: c) 25 MHz. d) 40 MHz.

### **Aeronautical Service**

The analysis of potential interference to aeronautical transceivers
covered modeled deployments of 1200, 300, and 75 co-frequency BPL
devices in an area of 10 km radius. Results indicated that multiplying
the number of BPL devices by a factor of four produced a straightforward
6 dB increase in aggregate interfering BPL signal power; therefore only
the analysis with 300 units is presented. The calculated data is listed
in Table 6-4 and shown graphically in Figure 6-8.

Table 6-4: Calculated (I+N)/N values, in dB, for aircraft receiver at
listed distance, frequency and height, with 300 BPL units visible to the
receiver in a 314 km^2^ area.

<table style="width:100%;">
<colgroup>
<col style="width: 14%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
</colgroup>
<tbody>
<tr class="odd">
<td></td>
<td colspan="3"><p><strong>(I+N)/N (dB)</strong></p>
<p><strong>4 MHz</strong></p></td>
<td colspan="3"><p><strong>(I+N)/N (dB)</strong></p>
<p><strong>15 MHz</strong></p></td>
<td colspan="3"><p><strong>(I+N)/N (dB)</strong></p>
<p><strong>25 MHz</strong></p></td>
<td colspan="3"><p><strong>(I+N)/N (dB)</strong></p>
<p><strong>40 MHz</strong></p></td>
</tr>
<tr class="even">
<td><p><strong>Height</strong></p>
<p><strong>Distance</strong></p></td>
<td><strong>6 km</strong></td>
<td><strong>9 km</strong></td>
<td><strong>12 km</strong></td>
<td><strong>6 km</strong></td>
<td><strong>9 km</strong></td>
<td><strong>12 km</strong></td>
<td><strong>6 km</strong></td>
<td><strong>9 km</strong></td>
<td><strong>12 km</strong></td>
<td><strong>6 km</strong></td>
<td><strong>9 km</strong></td>
<td><strong>12 km</strong></td>
</tr>
<tr class="odd">
<td>0 km</td>
<td>0.8</td>
<td>0.5</td>
<td>0.4</td>
<td>12.2</td>
<td>8.9</td>
<td>6.4</td>
<td>8.9</td>
<td>6.3</td>
<td>5.7</td>
<td>0.3</td>
<td>0.1</td>
<td>0.0</td>
</tr>
<tr class="even">
<td>5 km</td>
<td>0.7</td>
<td>0.5</td>
<td>0.3</td>
<td>11.3</td>
<td>8.9</td>
<td>6.6</td>
<td>9.2</td>
<td>6.5</td>
<td>5.5</td>
<td>0.2</td>
<td>0.1</td>
<td>0.1</td>
</tr>
<tr class="odd">
<td>10 km</td>
<td>0.5</td>
<td>0.4</td>
<td>0.2</td>
<td>10.7</td>
<td>8.6</td>
<td>6.7</td>
<td>9.6</td>
<td>6.2</td>
<td>4.5</td>
<td>0.2</td>
<td>0.1</td>
<td>0.1</td>
</tr>
<tr class="even">
<td>15 km</td>
<td>0.3</td>
<td>0.3</td>
<td>0.2</td>
<td>9.3</td>
<td>7.8</td>
<td>6.6</td>
<td>9.0</td>
<td>6.1</td>
<td>3.8</td>
<td>0.1</td>
<td>0.1</td>
<td>0.1</td>
</tr>
<tr class="odd">
<td>20 km</td>
<td>0.2</td>
<td>0.2</td>
<td>0.1</td>
<td>7.8</td>
<td>6.9</td>
<td>5.9</td>
<td>8.4</td>
<td>6.7</td>
<td>4.3</td>
<td>0.1</td>
<td>0.0</td>
<td>0.0</td>
</tr>
<tr class="even">
<td>25 km</td>
<td>0.1</td>
<td>0.1</td>
<td>0.1</td>
<td>6.0</td>
<td>6.1</td>
<td>5.3</td>
<td>7.4</td>
<td>6.3</td>
<td>5.0</td>
<td>0.1</td>
<td>0.1</td>
<td>0.0</td>
</tr>
<tr class="odd">
<td>30 km</td>
<td>0.1</td>
<td>0.1</td>
<td>0.1</td>
<td>4.1</td>
<td>5.4</td>
<td>4.6</td>
<td>6.4</td>
<td>5.6</td>
<td>5.0</td>
<td>0.1</td>
<td>0.1</td>
<td>0.0</td>
</tr>
<tr class="even">
<td>35 km</td>
<td>0.0</td>
<td>0.1</td>
<td>0.1</td>
<td>2.6</td>
<td>4.3</td>
<td>4.4</td>
<td>5.5</td>
<td>4.8</td>
<td>4.6</td>
<td>0.1</td>
<td>0.1</td>
<td>0.0</td>
</tr>
<tr class="odd">
<td>40 km</td>
<td>0.0</td>
<td>0.0</td>
<td>0.0</td>
<td>1.7</td>
<td>3.1</td>
<td>3.8</td>
<td>4.6</td>
<td>4.4</td>
<td>3.9</td>
<td>0.1</td>
<td>0.1</td>
<td>0.0</td>
</tr>
<tr class="even">
<td>45 km</td>
<td>0.0</td>
<td>0.0</td>
<td>0.0</td>
<td>1.1</td>
<td>2.2</td>
<td>3.1</td>
<td>3.6</td>
<td>4.1</td>
<td>3.3</td>
<td>0.0</td>
<td>0.0</td>
<td>0.0</td>
</tr>
<tr class="odd">
<td>50 km</td>
<td>0.0</td>
<td>0.0</td>
<td>0.0</td>
<td>0.7</td>
<td>1.6</td>
<td>2.4</td>
<td>2.8</td>
<td>3.6</td>
<td>3.1</td>
<td>0.0</td>
<td>0.0</td>
<td>0.0</td>
</tr>
</tbody>
</table>

As the figures indicate, an aircraft traveling above or near the modeled
BPL deployment area could see substantial S/N degradation. These
calculations include parts of the far-field radiation pattern (off the
ends of the power lines, or on-axis) that exhibited potentially elevated
power gain levels. Further study is needed of representative power line
gain levels in skyward directions.

![](media/image20.wmf){width="5.998611111111111in"
height="3.4993055555555554in"}

![](media/image21.wmf){width="5.998611111111111in"
height="4.095138888888889in"}

Figure 6-8: Calculated (I+N)/N level for an aeronautical receiver at the
specified distance and height from a BPL deployment, with 300 BPL
devices visible to the receiver. (a) 4 MHz. (b) 15 MHz.

![](media/image22.wmf){width="5.998611111111111in"
height="3.9006944444444445in"}

![](media/image23.wmf){width="5.998611111111111in"
height="3.9006944444444445in"}

Figure 6-8 continued: c) 25 MHz d) 40 MHz

## CONCLUSION

Interference risks were estimated using NEC models for four
representative types of federal radio stations operating in the fixed
and mobile services: a land vehicular radio; shipborne radio; a fixed or
mobile-base station with roof top antenna; and an aircraft radio in
flight. These risks were gauged from the extent of geographic areas in
which BPL emissions would reduce the ratio of desired radio signal power
to ambient noise power by amounts associated with moderate and high
probabilities of interference (*i.e.*, 3 dB and 10 dB reductions in
(S/N), respectively). Along with the four representative radio stations,
a three-phase power line structure was modeled using NEC. Predicted
nationwide, Springtime, median ambient noise power levels were assumed
and analyses were performed at four frequencies between 1.7 -- 80 MHz.
The BPL device output was adjusted to produce emissions at the limits of
Part 15 for unintentional radiators (Class B above 30 MHz), as generally
determined by compliance measurement practices extant with the exception
that measurement distances were applied with respect to the BPL device
and power lines rather than only the BPL device. This exception
generally results in compliance at BPL output power levels lower than
output levels that yield compliance when distances are measured from the
BPL device. For all of these analyses, the frequencies at which the
lowest and highest reductions in S/N occur may change for different
power line configurations.

The results for the vehicular mobile receiver predict that the received
BPL signal power near the Earth surface falls off rapidly with distance
from the lines. For the two frequencies at which the highest BPL signal
power levels were received (15 MHz and 25 MHz), signal power from one
co-frequency BPL system (one device) equaled noise power (3 dB reduction
in S/N) at fifty percent of the locations within seventy and seventy
five meters of the power lines. At these same frequencies, BPL signals
reduced S/N by 10 dB at fifty percent of locations within twenty-five
and thirty meters of the power lines. The distances within which these
thresholds were exceeded at fifty percent of locations were modestly
smaller at a third frequency (4 MHz) and much smaller at the fourth
frequency (40 MHz). In all land vehicular cases considered, reductions
in S/N were less than 3 dB and 10 dB beyond one-hundred-and-twenty-five
meters and fifty-five meters, respectively.

The results for the fixed service (or mobile base station) receiver
predict that the received BPL signal power falls off less rapidly with
distance from the power lines than occurred for the land vehicle case.
For the two frequencies at which the highest BPL signal power levels
were received, signal power from one co-frequency BPL system (one
device) equaled noise power (3 dB reduction in S/N) at fifty percent of
the locations within three-hundred-and-ten and four-hundred meters of
the power lines. At these same frequencies, BPL signals reduced S/N by
10 dB at fifty percent of locations within one-hundred-and-seventy-five
and two-hundred-and-thirty meters of the power lines. In all cases,
reductions in S/N were less than 3 dB and 10 dB beyond
seven-hundred-and-seventy meters and four-hundred-and-fifty meters,
respectively.

The results for the shipborne receiver predict that the received BPL
signal power falls off rapidly with distance from the power lines, but
less rapidly than for the land vehicle case. For the two frequencies at
which the highest BPL signal power levels were received, signal power
from one co-frequency BPL system (one device) equaled noise power (3 dB
reduction in S/N) at fifty percent of the locations within one-hundred
meters of the power lines. At these same frequencies, BPL signals
reduced S/N by 10 dB at fifty percent of locations within fifty-five
meters of the power lines. In all cases, reductions in S/N were less
than 3 dB and 10 dB beyond one-hundred-and-thirty-five meters and
eighty-five meters, respectively.

For the aircraft receiver, aggregate interference effects were
considered for simultaneously active, co-frequency BPL systems deployed
at a density of one per square kilometer over an area having ten (10)
kilometers radius. The power lines were assumed to be randomly oriented
and an average of the power line far-field gain levels were used in each
direction under consideration. Aircraft were assumed to be operating at
altitudes of 6 to 12 km at locations ranging from zero to fifty (50)
kilometers from the center of the BPL deployment area. Results showed
that aggregate interference levels to the aircraft could exceed average
ambient RF noise levels at two frequencies (15 MHz and 25 MHz), at
distances ranging from thirty-three kilometers (six kilometers altitude)
to over fifty kilometers (altitudes between six and twelve kilometers).
The S/N reduction exceeded 10 dB at only one frequency, at six
kilometers altitude within twelve kilometers of the center of the BPL
deployment area. At the two frequencies where the assumed BPL systems
produced the lowest interfering signal power levels (*i.e.*, 4 MHz and
40 MHz), S/N reductions peaked at about 0.8 dB and 0.3 dB directly over
the center of the BPL deployment area. Higher or lower densities of
active co-frequency BPL units would raise or lower the predicted
interference levels in direct proportion to the unit density.

[^1]: Maritime and aeronautical services also have ground-based
    receivers. Although not specifically addressed in NTIA's modeling,
    these stations are expected to be impacted similarly to the fixed
    service case modeled by NTIA.

[^2]: \"Interference\" is defined in 47 C.F.R., §2.1. "Parties
    responsible for equipment compliance should note that the limits
    specified in this part will not prevent harmful interference under
    all circumstances." 47 C.F.R. §15.15(c).

[^3]: *See e.g.*, ITU Radio regulation Nos. 3.3, 4.3, 4.11, and
    especially 15.2 (\"Transmitting stations shall radiate only as much
    power as is necessary to ensure a satisfactory service.\")

[^4]: Above 30 MHz, the limit and bandwidth for Class B devices is
    assumed in Figure 6-1. Noise levels used are median for Kansas City,
    MO.

[^5]: Figure 6 assumes that Fam = Fu (see equation 6-3). The "40 Log..."
    curve is representative for a point source radiating toward a radio
    antenna located at most a few meters above the ground. The "20
    Log..." curve pertains to a radio antenna located well above ground
    level (*e.g.*, \>10 meters).

[^6]: NOISEDAT is available from the ITU Website, URL:
    http://www.itu.int/ITU-R/software/study-groups/rsg3/databanks/ionosph/index.html.

[^7]: Land stations include land mobile, fixed, maritime coast and
    aeronautical stations.