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From: Bob on 28 Jun 2010 12:06
12 Conclusions and recommendations
This study has examined the likelihood and extent of RF interference
from in-home PLT devices over the next 5 to 10 years via two main
routes; radiated emissions directly from the PLT user's home and
interference from indirect PLT powerline radiation via a shared mains
connection. In the case of both of these routes we have concluded that,
provided uptake increases in line with our market forecasts, there will
be a high probability of interference to HF users by 2020 if PLT device
features do not change from those currently implemented. However, our
results also indicate that interference mitigation techniques currently
being developed by PLT device vendors and being discussed in
international standards bodies will be sufficient to reduce this
interference to negligible levels for most HF users. The exception to
this is the safety critical aeronautical bands which will require
notching by default.
In addition our study has considered the potential for interference from
emerging PLT devices at VHF. While this is less of a concern than at HF
due to reduced power levels, we have still found that action does need
to be taken to protect VHF users including safety critical aeronautical
systems.
Our conclusions across each of the interference mechanisms investigated
can be summarised as follows:
� Cumulative effect of ground wave over very large areas - The
likelihood of interference from PLT devices via this route is low.
Instead the observed interference signal at the victim receiver is
dominated by the closest PLT devices.
� Cumulative effect of sky wave over very large areas - Based on results
from NATO, the likelihood of interference from PLT via the cumulative
effect of sky wave is low. The exception to this is in quiet rural areas
where interference is more noticeable.
� Cumulative effect of line of sight interference to airborne HF users -
Based on results from the ITU, there is a significant chance of
interference to these HF users. Both power control and notching combined
with a maximum transmit power level of -63dBm/Hz are required to bring
PLT signals below the interference threshold.
� Cumulative effect of radiated emissions to ground based HF users - The
likelihood of interference via this route is similar across the three HF
victim receiver types. The probability of interference is high with
notching or power control alone but can be reduced to negligible if both
techniques are used together. IARU bands are already notched by default
in most PLT devices on sale today, but it is worth noting that earlier
PLT devices did not include IARU notches and mayneed to be updated.
� Cumulative effect of line of sight interference to airborne VHF users
- Based on our modelling of aeronautical instrument landing systems we
have found that a small variability in PLT transmit power level or
antenna gain of household wiring could dramatically change the
probability of interference. This probability is borderline if VHF PLT
devices are widely adopted in the near future, rising to high in the
longer term. We therefore recommend that these bands are notched by
default.
� Cumulative effect of radiated emissions to ground based VHF users - Of
the VHF victim receivers examined sensitive narrowband FM receivers and,
to a lesser extent, FM broadcast receivers give most cause for concern
and some bands may require notching. Nonetheless such
receivers operating near the limit of their sensitivity may still have a
low but measurable probability of interference.
� Interference from indirect PLT powerline radiation via a shared
overhead cable - The likelihood of interference via this route is low to
medium from now up to 2020 if PLT devices do not change. However, the
introduction of power control is likely to reduce interference via this
route to negligible levels. It should be noted that there is uncertainty
over the filtering effects of UK consumer units which could affect this
conclusion.
� Interference from indirect PLT powerline radiation via a shared mains
connection close to the victim receiver - The likelihood of interference
via this route is medium to high from now up to 2020 if PLT devices do
not change. However, the introduction of power control is likely to
reduce interference via this route to negligible levels. It should be
noted that there is uncertainty over the filtering effects of UK
consumer units which could affect this conclusion.
Based on these conclusions we recommend the following:
� The maximum transmit power of PLT devices should be harmonised. Our
conclusions are based on a quasi peak transmit power level of -50dBm/Hz
which is the maximum transmit power level for UPA devices. However,
currently PLT product manufacturers can vary the transmit power of PLT
chipsets and the Homeplug AV standard operates at the lower level of
-55dBm/Hz. This ambiguity makes future interference levels difficult to
predict and levels will vary depending which devices become dominant.
From our extension of ITU results for airborne HF users we note that a
maximum PLT power level of -63dBm/Hz (in addition to notching and power
control) is desirable to protect these safety critical services.
� Power control and smart notching should be implemented. Power control
and smart notching are anticipated to be available in Q2 and Q3 of 2010
respectively. Our results show that these features need to be introduced
in these timescales to keep interference at manageable levels and
recommend that these features are implemented in PLT devices in a timely
manner.
� Notches in the IARU bands should be implemented. Most PLT vendors
already notch the HF IARU bands by default and our results show that
this is an essential interference mitigation approach. However, we have
not yet seen notching of amateur radio bands at VHF. We therefore
recommend that notching of amateur radio and other similar sensitive
narrowband receiver bands are implemented both at HF and VHF.
� Notches in the HF aeronautical bands should be implemented. Our
results show that notching and power control will be required to protect
the HF aeronautical bands from PLT interference over the next 5-10
years. As the incoming signals are likely to be at low levels and of
short duration we recommend that permanent notching rather than smart
notching is applied. We have also assumed a protection radius of 100m in
our analysis and this should be discussed with the operators of
aeronautical ground stations.
� Notches in the VHF aeronautical radionavigation bands should be
mandated. Our results for ILS localiser receivers indicate that the
probability of interference is likely to become high during the next
5-10 years. We therefore recommend that these safety critical bands are
notched bydefault.
Additional options include:
� Interference between PLT and VDSL should be monitored. There have been
suggestions of interference between VDSL and PLT devices where the
cables are installed next to each other. Our assessment is that this
could lead to interference only in very specific installation
situations, but we recommend that Ofcom monitor this situation with BT
as VDSL is deployed in the UK.
� The filtering effects of UK consumer units should be measured. Our
results in relation to conducted interference are based on measurements
that exist of PLT signal loss through consumer units, and lead us to
recommend action on power control and notching. It would beprudent to
test the filtering effects of a range of typical consumer units in the
UK to ensure that consumer units with a lesser filtering effect are not
present in large numbers.
� Measurements of radiated emissions from in-home PLT devices deployed
in the UK. We found a lack of measurements of radiated emissions
specifically from in-home PLT devices. One such study has been carried
out recently in Canada measuring emissions outside a single PLT
home. However, it would be useful to repeat this in the UK at distances
covering the near field, far field and ground wave propagation to
understand any dependency on UK-specific wiring practicesand to examine
the effect as the number of PLT homes increases.
<http://www.ofcom.org.uk/research/technology/research/emer_tech/PLT/pltreport.pdf>
From: Jeff Liebermann on 28 Jun 2010 12:59
On Mon, 28 Jun 2010 17:06:57 +0100, Bob <bob(a)invalid.invalid> wrote:

<http://www.ofcom.org.uk/research/technology/research/emer_tech/PLT/pltreport.pdf>

One problem is that the report assumes that interference to ham radio
HF operation will be cured by installing notch filters for the ham
bands. They are used on larger industrial systems:
<http://motorola.wirelessbroadbandsupport.com/solutions/bpl/>
I have yet to see a unit with such a filter on a HomePlug device.

The UK opposition:
<http://www.ukqrm.org>

Incidentally, some users are finding that PLT/BPL devices tend to rip
on DSL signals when the power and phone wires are loosly coupled.
<http://www.mikeandsniffy.co.uk/UKQRM/badforall.html>
I have several slow DSL 1500/384 kbit/sec installs, where the HomePlug
device is in the same cabinet and same power plug as the DSL modem. No
effect that I can see. However, on one 6000/512 Kbits/sec DSL, there
seemed to be some interaction, so I removed the HomePlug device.

--
Jeff Liebermann jeffl(a)cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
From: Bob on 28 Jun 2010 13:32
On 28/06/2010 17:59, Jeff Liebermann wrote:
> On Mon, 28 Jun 2010 17:06:57 +0100, Bob<bob(a)invalid.invalid> wrote:
>
> <http://www.ofcom.org.uk/research/technology/research/emer_tech/PLT/pltreport.pdf>
>
> One problem is that the report assumes that interference to ham radio
> HF operation will be cured by installing notch filters for the ham
> bands.
Not quite "Cumulative effect of radiated emissions to ground based HF
users - The likelihood of interference via this route is similar across
the three HF victim receiver types. The probability of interference is
high with notching or power control alone but can be reduced to
negligible if both techniques are used together." "can" and "negligible"
to me means that there will be will still be some people who will get
interference especially since some amateurs still like to experiment
with equipment.

"Smart Notching has been investigated within ETSI with guidelines for
signal detection and notch depth published in 2008 [8]. Plugtests,
carried out in 2007 by ETSI using Sony and DS2 smart notching
demonstrators, have shown the feasibility of smart notching and have
given the encouraging results that shortwave radio stations were
received as well when smart notching was activated as when there were no
PLT devices active [9]. It is worth noting that the IP for smart
notching via this route is owned by Sony and so there could be an
additional cost to PLT vendors if this feature was required."

"It should be noted that Smart Notching does not necessarily operate
effectively down to ambient noise level, but it has been demonstrated to
the �minimum planned signal level� of other systems such as short wave
radio."
>They are used on larger industrial systems:
> <http://motorola.wirelessbroadbandsupport.com/solutions/bpl/>
> I have yet to see a unit with such a filter on a HomePlug device.


>
> The UK opposition:
> <http://www.ukqrm.org>
>
> Incidentally, some users are finding that PLT/BPL devices tend to rip
> on DSL signals when the power and phone wires are loosly coupled.
> <http://www.mikeandsniffy.co.uk/UKQRM/badforall.html>
> I have several slow DSL 1500/384 kbit/sec installs, where the HomePlug
> device is in the same cabinet and same power plug as the DSL modem. No
> effect that I can see. However, on one 6000/512 Kbits/sec DSL, there
> seemed to be some interaction, so I removed the HomePlug device.
>
They noted that some form of monitoring with BT systems should take
place as this seems to be an installation specific problem and perhaps
some form of "advice" on installation issued.
I am in the process of moving house and all the phone sockets in the
new house are next to mains sockets so when I have time I will experiment.
From: Jeff Liebermann on 28 Jun 2010 17:55
On Mon, 28 Jun 2010 18:32:50 +0100, Bob <bob(a)invalid.invalid> wrote:

>On 28/06/2010 17:59, Jeff Liebermann wrote:
>> On Mon, 28 Jun 2010 17:06:57 +0100, Bob<bob(a)invalid.invalid> wrote:
>>
>> <http://www.ofcom.org.uk/research/technology/research/emer_tech/PLT/pltreport.pdf>

>"Smart Notching has been investigated within ETSI with guidelines for
>signal detection and notch depth published in 2008 [8]. Plugtests,
>carried out in 2007 by ETSI using Sony and DS2 smart notching
>demonstrators, have shown the feasibility of smart notching and have
>given the encouraging results that shortwave radio stations were
>received as well when smart notching was activated as when there were no
>PLT devices active [9].

Please note that Smart Notching requires a *TRANSMITTER* to determine
what frequencies to notch. The full name is Adaptive Smart Notch,
which installs a notch in the broadband noise transmitted by the
device if it detects a qualifying transmitted signal. That's
tolerable for some ham operation, which usually transmits at or near
the same frequency as reception. It's useless for receive only HF
signals, such as DRM stereo, SWL, packet radio monitoring, HF APRS
gateways, and others, where there's no transmitter available to
convince the device to shut up.

From 5.3.4 in the Ofcom report.
Smart notching is estimated to be available from Q3 2010.
This provides a monitoring function in the chipset which
will detect the presence of transmissions to which PLT devices
may cause interference and apply a frequency notch as appropriate.

>They noted that some form of monitoring with BT systems should take
>place as this seems to be an installation specific problem and perhaps
>some form of "advice" on installation issued.

The stuff radiates well beyond your house. I pickup junk from BPL
systems that are about 500 meters away. Probably farther if I had a
decent antenna.

> I am in the process of moving house and all the phone sockets in the
>new house are next to mains sockets so when I have time I will experiment.

There's no interfernce between BPL/PLT and POTS phone service.

--
Jeff Liebermann jeffl(a)cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
From: Bob on 29 Jun 2010 03:50
On 28/06/2010 22:55, Jeff Liebermann wrote:
> On Mon, 28 Jun 2010 18:32:50 +0100, Bob<bob(a)invalid.invalid> wrote:
>
>> On 28/06/2010 17:59, Jeff Liebermann wrote:
>>> On Mon, 28 Jun 2010 17:06:57 +0100, Bob<bob(a)invalid.invalid> wrote:
>>>
>>> <http://www.ofcom.org.uk/research/technology/research/emer_tech/PLT/pltreport.pdf>
>
>> "Smart Notching has been investigated within ETSI with guidelines for
>> signal detection and notch depth published in 2008 [8]. Plugtests,
>> carried out in 2007 by ETSI using Sony and DS2 smart notching
>> demonstrators, have shown the feasibility of smart notching and have
>> given the encouraging results that shortwave radio stations were
>> received as well when smart notching was activated as when there were no
>> PLT devices active [9].
>
> Please note that Smart Notching requires a *TRANSMITTER* to determine
> what frequencies to notch. The full name is Adaptive Smart Notch,
> which installs a notch in the broadband noise transmitted by the
> device if it detects a qualifying transmitted signal. That's
> tolerable for some ham operation, which usually transmits at or near
> the same frequency as reception. It's useless for receive only HF
> signals, such as DRM stereo, SWL, packet radio monitoring, HF APRS
> gateways, and others, where there's no transmitter available to
> convince the device to shut up.
If there is no "Transmission" then what do receivers detect?
I haven't seen any specs regarding the Rx sensitivity for these "smart
notch" filters but they did say "encouraging results that shortwave
radio stations were received" so they must have agreed some form of
"threshold" level.
>
> From 5.3.4 in the Ofcom report.
> Smart notching is estimated to be available from Q3 2010.
> This provides a monitoring function in the chipset which
> will detect the presence of transmissions to which PLT devices
> may cause interference and apply a frequency notch as appropriate.
>
>> They noted that some form of monitoring with BT systems should take
>> place as this seems to be an installation specific problem and perhaps
>> some form of "advice" on installation issued.
>
> The stuff radiates well beyond your house. I pickup junk from BPL
> systems that are about 500 meters away. Probably farther if I had a
> decent antenna.
>
>> I am in the process of moving house and all the phone sockets in the
>> new house are next to mains sockets so when I have time I will experiment.
>
> There's no interfernce between BPL/PLT and POTS phone service.
>
My broadband is on the POTS line and the "mains sockets" refer to the
electric supply in the UK. My broadband/phone at the moment interferes
with my newly installed burglar alarm causing it to give a line fault
indication every time I use the phone and the installer is going to have
to reset the noise threshold level on the line so that I don't get
plagued by text messages. I will be interested to see if there is a
similar effect using "Homeplug" devices.
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