- 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.