White Space Coexistence Workshop 10th October 2013 REPORT

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On behalf of the Radio Telemetry interest group of the LPRA I visited the White Space Coexistence Workshop hosted by Ofcom in London on the 10th October 2013.  

From an LPRA perspective the concept of White Space usage at first would appear to be a good idea, in particular as ultimately licence free operation would be permitted by circa 2015/16. 

 The media spin on White Space portrays it as the holy grail for delivering rural broadband which we would agree is a fantastic idea. However, other ideas tabled such as remote telemetry and the monitoring of key infrastructure assets is something  I personally would not advocate in particular when you consider the risks, complexity and concerns raised by myself and others, in particular those from the PMSE community, which  includes professional broadcast companies like the BBC, theatres and entertainment sectors.  For those not familiar with the White Space [WS] concept, the plan is to dynamically permit the use of the un-used channels in the digital terrestrial TV bands DTT and PMSE “white spaces”  between 470MHz and 800MHz for nondescript licence free services.

 White Space operates on a Master Slave basis where the Master has to access an official database via the internet that allocates its operating frequency and transmission power level based upon its geographical location with respect to DTT transmitters, repeaters, PMSE users and other WS devices.  The first concern I raised during the Workshop was that of changes in atmospheric conditions that lead to enhanced propagation of signals. Without doubt under the right conditions this could lead to interference to DTT and/or between WS devices.   The reply was much as expected. In the case of interference to WS devices from DTT, this is something that has to be accepted and service interruption or deterioration assumed. However, when the interference is coming from the WS device and it is impacting on DTT the database will be dynamically re-adjusted and the WS device will be instructed to switch off, lower power or to alter its operating frequency all within a matter of minutes.  Ofcom further acknowledged that the trials and current databases did not take into account atmospheric extremes such as “lift” and the concern was indeed a real possibility that required further investigation. 

 The second and more significant concern was that of resilience of WS services when you consider that everything hinges on the access to the database. I raised the question as to what guards are there to protect WS services in the event of the database crashing, being corrupted or subject to a cyber attack. The answer rather disconcerting, in particular if you were contemplating running mission critical monitoring or data gathering services – simply if the WS system looses connection with the internet for longer than 15-minutes it has to automatically shutdown!

 The final concern that I feel is worth documenting is the future plans to re-allocate the 700MHz band (694-790MHz) of the DTT allocation to mobile services. This would necessitate the squashing of the existing DTT and PMSE into 470-694MHz with the possible untold consequences on any WS services.

Full details of meeting proceedings and papers on white space are available from the Ofcom website http://stakeholders.ofcom.org.uk/spectrum/tv-white-spaces/consultations-statements/

In summary, I personally believe there is merit in White Space technology, however, there is a big risk that it could be over hyped by media and those looking for investment. I share the sentiments of the PSME community when they request guard bands and believe that White Space as the backbone for the “internet of things” is over ambitious. Rural broadband and fixed links however yes a fantastic idea providing the power levels are set to allow margins for atmospheric “lift”, etc.

Brian M Back BEng(Hons) CEng FIET MIoD.