Wireless Waffle - A whole spectrum of radio related rubbish
We're Jammin' (Part II)signal strength
Monday 31 December, 2007, 11:01 - Spectrum Management
Posted by Administrator
In a little known, sleepy backwater of the European Commission, moves are afoot to introduce a relatively obscure piece of legislation to allow mobile phones to be used on aircraft. There's nothing newsworthy in this you might think, Ryanair have already announced that they intend to install the equipment to allow their passengers to do just that and Air France have already begun trialling the service.

airborne base stationThe equipment concerned is basically a GSM base-station (working only in the GSM 1800 frequency band) installed inside the aircraft and connected back to the rest of the world via an external satellite link. However, the function of the equipment goes beyond just the role of making a connection between the mobiles on the plane - it must also stop the mobiles on the aircraft from connnecting with any terrestrial, ground based networks. Why is this important? It's argued that in order to allow mobile communication on aircraft, the power of the mobile transmitters must be kept to an absolute minimum to avoid interference to the avionics on the plane, which is a fairly sensible caveat to put in place. By forcing the phones on the plane to only connect with the on-board base-station their output power can be controlled and minimised, thereby minimising the risks concerned. The power needed for them to connect to a terrestrial network could be relatively high and could thus cause interfere with the avionics (there is some evidence to suggest this can happen) and this is why phones should normally be switched off during the flight (and especially during take-off and landing when pilots rely more heavily on the sensitive equipment in the cockpit).

jammingSo how are the on-board base-stations going to stop switched on phones from connecting to terrestrial networks? They are going to emit a jamming signal on all mobile frequency bands to stop terrestrial networks from being received whilst subscribers are sat on the plane. Yes, that's right, a jamming signal. And not just jamming of GSM 1800 but, in order to meet the legislation, they will have to jam all possible mobile bands including 450 MHz (occasionally used in Europe for CDMA-1x), 900 MHz (used for GSM 900) and 2100 MHz (used for WCDMA/3G). As the systems described in the European Commission legislation are for use in European airspace, the jammers will not have to cover 800 MHz or 1900 MHz (used widely in the Americas for CDMA-1x and GSM) or 1500 MHz (used in Japan).

It's interesting that most mobile operators have raised violent objections to the use of GSM or 3G jammers where these have been used to block mobile communications (in prisons, mosques and theatres for example). It's true that the transmitter power levels at which the jammers will operate are designed such that they will should not, under normal circumstances, affect ground-based users. However it will be interesting to see what happens if:

phone on plane
  • the on-board base-stations are left on at lower altitudes, or even on the ground, when they will have the potential to cause widespread wipe-outs of nearby mobile phone communications;
  • the base-stations enter a fault condition and jam critical aeronautical communications (such as the radars which occupy the frequencies immediately adjacent to the GSM 900 band above 960 MHz);
  • European planes leave the equipment switched on whilst traversing Asia or the Americas where the frequencies they are jamming are used for other purposes and thus could cause interference to many other services (such as point-to-point links or emergency communications);
  • non-European mobiles (such as those designed for CDMA 1900, CDMA 1700 or one of the Japanese PDC or PHS standards), their users thinking it's now OK to leave their mobiles switched on whilst in flight but which are not blocked by the jammer, log on to terrestrial networks and transmit at higher powers causing interruptions in the functioning of the on-board avionics.
Whilst there is no doubt that there will be big demand from air passengers to be able to send text message and make calls from the air (if the price is right - and that's a completely different issue), whether or not the equipment involved proves an unnecessary risk to air safety is something that is to be hoped will never be tested.
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Essentials of Modern Spectrum Managementsignal strength
Wednesday 31 October, 2007, 05:35 - Spectrum Management
Posted by Administrator
Spectrum management has traditionally been about the use of technical criteria developed through long-winded compatibility studies to determine what can (and can not) be allowed access without causing harmful interference to other users. essentialsofmodernspectrummIncreasingly, however, regulators are using forward looking market-based spectrum management techniques such as administrative incentive pricing, auctions and comparative selection (beauty parades), trading and property rights in order to be able to adapt to the rapidly changing and liberalised markets which use the radio spectrum.

Mssrs. Cave, Webb and Doyle have documented the current state of play in these forward looking techniques (often lumped together under the banner of 'Spectrum Pricing') in their new publication Essentials of Modern Spectrum Management. They describe developments in both the technical and economic tools used to manage the radio spectrum as well as looking at other related issues such as the need for and benefits of spectrum commons. There's also a good discussion of why Ultra Wide Band (UWB) has made many regulators reflect on whether existing spectrum management techniques are appropriate or have sufficient longevity and flexibility to cope with such new approaches to spectrum use.http   www assoc amazon co uk e ir t sheffieldrock 21 amp l ur2 amp o 2

cave webb doyle

The book uses a number of international case studies together with the practical experience of the authors to illustrate many of the concepts involved. Whilst the book would not be suitable for someone wishing to gain an overall understanding of spectrum management, it provides a useful and inciteful reference on these more advanced techniques and would suit anyone who has experience of spectrum regulation and who wanted to understand better how such regulation is being transformed to encourage more efficient spectrum use. Certainly a book that should be on the shelves of any self-respecting modern spectrum manager!
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Trains, Boats, Planes, God, Kylie Minogue, and more Planessignal strength
Saturday 22 September, 2007, 07:08 - Spectrum Management
Posted by Administrator
Years ago I used to know the frequency¹ for the downlink of Capital Radio in London's 'Flying Eye', the aircraft used to scout about for travel blackspots. It was a useful frequency to have as there was no better place to get the latest travel news. I also remembered that there was an uplink from the studio on around 455 MHz too.

minaret antennaOne quiet afternoon I thought I'd have a tune around to see whether or not the old up and downlink frequencies were still active. Listening around 467 MHz, there seemed to be no sign of the downlink (though being around 25 miles outside of central London and with a downlink power of less than a Watt, this wasn't perhaps, that surprising). The uplink, however, is still active on 455.075 MHz.

What was rather odd, however, was to hear dozens of Imam's calling their congregation to prayer on frequencies just below this at around 454.5 MHz. Was this some freak long-distance propagation carrying signals from arabic speaking countries in North Africa or the Middle East? Was it a freak spurious response on my receiver, allowing reception of, perhaps, satellite radio? Were these the link frequencies to the numerous 'Radio Ramadan' stations that appear on the FM band during the festival?

No. It was none of these. Instead it seems that there is a radio service, established in around 2000, called 'On-Site Religious Observation' or OSRO. This a a licensed radio service which allows any religious body to use the old Wide Area Paging (WAP) channels to deliver voice communications to pagers. What a good use for these otherwise quiet channels: to allow Muslim's their right to hear the Imam's call without the need to build noisy minarets, just build unsightly radio towers instead!

A bit more digging revealed that there are all sorts of interesting frequencies in the range 454 to 458 MHz as listed below:

lego kylie454.0125 to 454.8375 MHz OSRO/WAP
454.84375 to 454.98125 MHz Cab Secure Radio (CSR)²
454.9875 to 455.475 MHz Programme Making and Special Events (PMSE)³
455.475 to 455.850 MHz Airport Security and Operations (455.5125, 455.5375, 455.5875, 455.625, 455.6625, 455.675 and 455.6875 MHz also used for CSR)
455.850 to 456.000 MHz Fire Service
456.000 to 456.9875 MHz Private Mobile Radio (PMR) Simplex and Duplex use
457.000 to 457.250 MHz Fire Service
457.250 to 457.475 MHz PMSE
457.475 to 457.500 MHz Fire Service
457.500 to 458.500 MHz Scanning Telemetry (457.525, 455.5375, 457.550, 455.5625 and 457.575 MHz also used for On-Board Ship Communications)

With Ofcom considering reconsidering its previously aborted plans to re-align the band it will be interesting to see where these services end up. And in the meantime if anyone has the frequency used for the Flying Eye's downlink, do share it with us!

¹467.6625 MHz if I remember correctly.
²Radio system used by Network Rail in areas where rail services have no conductor and thus the driver can not leave the cab to commnunicate with the signaller.
³Links and talkback for radio stations, TV studios, film sets, theatres and so on. Could be used by production team at a Kylie Minogue concert for example...
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ITU Frequency Allocation Tablessignal strength
Thursday 5 October, 2006, 11:39 - Spectrum Management
itulogoSomething that's always been a nuisance is that the International Telecommunications Union (ITU) has made it's frequency allocation tables (i.e. the table which shows which frequencies are allocated to which services in which countries) something that has to be paid for if you want a full copy. The 'ITU Radio Regulations' is a large set of documents that describe radio usage and the heart of it is a set of 3 regional tables that allocate frequencies to specific uses and currently costs 252 Swiss Francs (about GBP107 at today's exchange rate). radiodialIf you just want to know whether fixed links have an allocation at 8 GHz in France, that's rather a lot to pay.

I was delighted, therefore, to discover that the Region 1 (Europe, Africa, the Middle East and Asiatic Russia) and Region 3 (Asia and Australasia) information can now be access for free on the web-site of telecommunications consultants 'InterConnect Communications'. Their Electronic Frequency Allocation Table (E-FAT) service allows you to query the ITU tables viewing either the whole table or just the allocations to specific services.

A similar service, but only for specific European countries (well certain CEPT members) is provided by the European Communications Office (ECO) in the form of their European Frequency Information Services (EFIS).

Dead handy!
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